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Scatterplot
12-09-2005, 01:48 PM
This made for some interesting debate on another forum I'm on, hopefully we can get some good discussion going on here.

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

Evan
12-09-2005, 01:54 PM
Forget the wheels and think about teflon coated skis on a teflon belt.

Teflon has a lower coefficient of friction than wet ice. Teflon skis on a teflon belt would have about the same friction as wheels. The coefficient of friction for teflon on teflon is 0.04, the lowest known for a solid substance. The coefficient of friction for rubber tires rolling on concrete is about 0.035 (side note: The friction coefficient for tapered roller wheel bearings is 0.0018, rubber sliding on pavement is .75)

Planes take off with skis all the time, at least around here this time of year.

By eliminating the wheels from the idea we eliminate a source of confusion. The skis have the same friction characteristics as the wheels but obviously cannot be used to propel the aircraft (also no brakes).

With skis on the plane the teflon belt could be turned on in the backward direction with the plane engine off and the plane would just sit there at first. The inertia of the plane would prevent it from accelerating backward with the belt immediately. Only a very small force would be required in the forward direction to hold it in place, even with the belt at full speed backward.

This force could be provided by the aircraft engine at idle which is enough to cause a plane to taxi.

With the belt running at full speed under the skis and the engine idling the plane remains at rest on the moving conveyor since the small amount of thrust from the idling engine is enough to overcome the very small friction of the skis on the belt. In effect, the plane is still parked as if the belt were motionless. We have no bearings to consider and no wheel rpms to think about, just the skis slip-sliding on the moving belt.

So, here we have a plane sitting on a moving belt. The plane remains in the same place even if the belt is moving because there isn't enough friction between the teflon skis and the teflon belt to drag it backward against the thrust of the idling engine.

Now we apply full power to the airplane engine.

What happens?

JRouche
12-09-2005, 01:56 PM
Get enough air over the wing and the plane will lift, not enough and it will not. Simple aerodynamics http://bbs.homeshopmachinist.net//wink.gif JRouche

Scatterplot
12-09-2005, 01:57 PM
Heh, you guys are good. Better than the ones on the last forum. I was all like no, of course not, then someone said yeah it will, and then I was like duh, I'm an idiot. http://bbs.homeshopmachinist.net//smile.gif

ZINOM
12-09-2005, 02:04 PM
No

John

Guido
12-09-2005, 02:36 PM
The way I sees it------

IF------- 100% of the jet engines' energy were mechanically driving the aircraft wheels against the conveyor (Zero exhaust forces to rear of craft) the whole mess would sit still, providing the thrust of the driven wheels against the conveyor always equalled the thrust of energy provided by the conveyors' power supply.

BUT--------the jet engines thrust is against the surrounding air and not the conveyor, so the plane will proceed to lift off.

HOWEVER-----With a robust conveyor system which will keep a speed equal to the plane, them wheels on the plane are probably gonna explode somewhere before liftoff. http://bbs.homeshopmachinist.net//eek.gif

G

Allan Waterfall
12-09-2005, 02:41 PM
Airspeed not ground speed enables a plane to fly,if I read the post correctly the plane would be standing still.

Allan

sauer38h
12-09-2005, 02:42 PM
You haven't defined the problem adequately. "The plane is sitting on a runway", then suddenly "the plane moves in one direction" - by what agency?

If it's being moved by its engines, what the runway does is of little consequence. Lift is a function of, among other things, air speed, not ground speed. The plane will take off normally. There are boundary layer effects but in this case they're negligible.

So where's the "interesting" part?

Evan
12-09-2005, 02:49 PM
Also, the jet engines do not "act on the surrounding air", they pump it through the engine producing thrust.

dp
12-09-2005, 02:51 PM
The only consequence of this configuration is that the wheels will be spinning at twice the normal speed when the plane lifts off.

If it were a train it would never leave the station but planes are not driven-wheel machines.

Pat Miles
12-09-2005, 02:53 PM
If I read the original question correctly the plane starts moving because of thrust from the engines. The conveyer belt runway starts moving in the OPPOSITE direction matching the speed of the plane so the plane actually is not moving forward thus no lift. Kind of like running on a treadmill. You run forward on a belt moving in the opposite direction. You are running in place.

nheng
12-09-2005, 02:58 PM
My first thought was yes, of course it will take off, and quicker BUT ...

It could also become sort of an engine test stand because while the engines are pulling forward, due to zero body velocity the wings may never get enough volume and velocity of "incoming" air.

Den

debequem
12-09-2005, 03:00 PM
I am not sure you worded the question correctly. I assume that you realize that there is a difference between groundspeed and airspeed? Airspeed is what is critical for takeoff. You can have a groundspeed of 100 knots and a tailwind of 50 knots and a net airspeed of 50 knots. If a plane needs an airspeed of 135 knots to get airborne, then the preceding example requires the groundspeed to increase to 185 knots. That is why aircraft take off into the wind.

Regardless, the aircraft is a jet and the propulsion system is not through the aircraft’s wheels, but the hot expansion of gases that produce thrust for the engines. The thrust will still propel the aircraft forward regardless of what speed the wheels are spinning. In the real world I would doubt that the friction induced by the wheel bearings would be enough to prevent takeoff. This assumes that the question you cited claims that the conveyer will match the groundspeed of the aircraft relative to the Earth and not the conveyer belt. Takeoff speed for a normal 747 is about 140 knots, so the wheels would be rotating at about 280 knots at takeoff, which is not outside the realm of reality for that aircraft.

Incidentally, the aircraft will leave the ground at about the same point it would down a normal runway minus any effects from wheel bearing friction.

Jim Caudill
12-09-2005, 03:00 PM
Pat Miles has stated it correctly. The aircraft develops lift by air flowing over the wings. In this scenario there is no airflow, the aircraft is motionless as it sits on the "treadmill". If you had a stepladder. you could climb right up on the wing as it is sitting there (just don't get near the engine intake). What is taking place at the landing gear level is irrelevant, only the airflow over the wing produces lift - not the rotation of the wheels.

Boomer
12-09-2005, 03:05 PM
What if there were no hypothetical questions?

Evan
12-09-2005, 03:07 PM
This is a no brainer. The motion of the treadmill has no impact on the plane except to spin the wheels. So what? Read my post on skis.

The plane takes off as usual. Sheesh.

Scatterplot
12-09-2005, 03:07 PM
You guys saying "no" must remember that the plane Will move. The conveyor belt will not impede the motion of the plane.

(BTW, the question was worded that way to make it more confusing and to add some debate http://bbs.homeshopmachinist.net//smile.gif)
(it was copied and pasted from somewhere else)

debequem
12-09-2005, 03:12 PM
No, that will not happen. The thrust of the aircraft is not against the conveyer belt, it is against the aircraft.

There will be a net force exerted by the conveyer belt on the aircraft. However, the aircraft is on free rolling wheels. It is like trying to pull the rug out from under a roller skater versus someone standing with sneakers on the same rug. The skater will not move in the direction of the rug much at all. The only force that will be exerted against the aircraft is equivalent to the friction (at first static, then dynamic) that is inherent in the wheels’ wheel bearings.

The force exerted by the conveyer belt will be much, much less than the huge force generated by the 747 engines in the opposite direction. The aircraft will experience increased wheel bearing friction since the wheels will be rotating faster than normal, but it will not be significant and probably will not even be noticed at takeoff.

<font face="Verdana, Arial" size="2">Originally posted by Pat Miles:
If I read the original question correctly the plane starts moving because of thrust from the engines. The conveyer belt runway starts moving in the OPPOSITE direction matching the speed of the plane so the plane actually is not moving forward thus no lift. Kind of like running on a treadmill. You run forward on a belt moving in the opposite direction. You are running in place.</font>

[This message has been edited by debequem (edited 12-09-2005).]

nheng
12-09-2005, 03:13 PM
-- deleted, never mind --

Debequem summed it up nicely. Massive engines, massive thrust, takes off "in place".

[This message has been edited by nheng (edited 12-09-2005).]

Evan
12-09-2005, 03:16 PM
"Yeah but Evan, the engines develop thrust over the wings but there is no volume of surrounding air at "typical" take off velocities and volumes."

What???? All aircraft begin at a standing start. So what is different in this case?

nheng
12-09-2005, 03:21 PM
Evan, See my "deleted - never mind" post ... I get it now http://bbs.homeshopmachinist.net//biggrin.gif

It's not going to stay on the belt for long.

[This message has been edited by nheng (edited 12-09-2005).]

12-09-2005, 03:23 PM
yes

no

[This message has been edited by Your Old Dog (edited 12-09-2005).]

Maybe

[This message has been edited by Your Old Dog (edited 12-09-2005).]

debequem
12-09-2005, 03:26 PM
That also assumes you get clearence from the tower. ;-)

Pat Miles
12-09-2005, 03:29 PM
Massive thrust yes,but the original post said the conveyer belt could match the speed of the plane. Massive conveyer belt. The plane is standing still thus no air over the wing and no lift for takeoff.

sauer38h
12-09-2005, 03:29 PM
In fact, the craft need not be a 747. There is NO aircraft which will fail to take off in this scenario, except a glider which is launched by towing behind a wheeled tow vehicle. Even a balloon will take off. And even a human-pedalled aircraft like Gossamer Condor, which depends on ground effect to get into, and stay in, the air. Ground effect depends on ground proximity, not ground speed.

Move on to the next question.

12-09-2005, 03:29 PM
<font face="Verdana, Arial" size="2">Originally posted by Your Old Dog:
yes

no

[This message has been edited by Your Old Dog (edited 12-09-2005).]

Maybe

[This message has been edited by Your Old Dog (edited 12-09-2005).]</font>

Are we taling daytime or night

[This message has been edited by Your Old Dog (edited 12-09-2005).]

Sure, why not?

[This message has been edited by Your Old Dog (edited 12-09-2005).]

The pilots a male right?

[This message has been edited by Your Old Dog (edited 12-09-2005).]

Anyone know if there's a fly in the cockpit?

[This message has been edited by Your Old Dog (edited 12-09-2005).]

no. http://bbs.homeshopmachinist.net//biggrin.gif

[This message has been edited by Your Old Dog (edited 12-09-2005).]

Evan
12-09-2005, 03:31 PM
"Massive thrust yes,but the original post said the conveyer belt could match the speed of the plane. Massive conveyer belt. The plane is standing still thus no air over the wing and no lift for takeoff."

So what if the conveyor moves? It isn't connected to the plane by cables or something.

lynnl
12-09-2005, 03:34 PM
OK guys, let's chip in and charter a 747 and run our own test. Anybody got an 8000ft conveyor belt they're not using right now?

That will prove that aside from slightly increased wheel bearing and tire deflection that the doubled spin rate of the wheels will have on the frictional effect, it will lift off as normal.

Come to think of it, we probably need to get two 747's on parallel runways. ...but we'll only need one conveyor of course.

PTSideshow
12-09-2005, 03:36 PM
But where is the mill/drill or tig welder? Lol

------------------
Glen
Been there, probally broke it doing that

Pat Miles
12-09-2005, 03:42 PM
OK, I might really be stepping in it but if the equal and opposite movement of the conveyer belt matches the speed of the planes movement why does said plane have to accelerate down a runway(without said conveyer belt under it)to cause air to flow over the wing for lift and takeoff? What I am saying is why can't the airplane takeoff while standing still as what it would be doing on the conveyer belt?

debequem
12-09-2005, 03:45 PM
Pat,

The misnomer is that the thrust is acting against the conveyer belt, but it is really acting against the aircraft, which is a free rolling entity.

Your point would be valid if the aircraft was replaced with a car. The car's thrust would be via the drive wheels, which are in direct contact with the moving conveyer belt.

Since the jet engines' thrust acts against the aircraft, the net effect would be to push the aircraft forward. Even though the conveyer begins to roll backward at the same speed that the aircraft moves forward, the opposing force of the conveyer through the wheels' bearings are swamped by the jet engines's thrust.

In this case the wheels isolate the aircraft from the conveyer belt much like putting jet engines on a hover craft. You can spin the Earth as fast as you want under the hover craft, but the moment you light up the engines that baby (hover craft) is going to be propelled forward.

<font face="Verdana, Arial" size="2">Originally posted by Pat Miles:
Massive thrust yes,but the original post said the conveyer belt could match the speed of the plane. Massive conveyer belt. The plane is standing still thus no air over the wing and no lift for takeoff.</font>

Pat Miles
12-09-2005, 04:01 PM
OK,Uncle

.RC.
12-09-2005, 04:02 PM
OK now we put an aircraft carrier on the treadmill and when a plane gets catapulted off the carrier the treadmill goes backwards in the opposite direction but when the plane goes to take off the earth starts spinning in the opposite direction to the treadmill also the galaxy starts spinning the the opposite direction to the earth does the plane take off or is there no plane at all?????????

nheng
12-09-2005, 04:04 PM
The plane is not going to stay on the belt for long. The engines will pull it forward regardless of what the belt is doing.

It will not take off while on the belt but it WILL take off http://bbs.homeshopmachinist.net//biggrin.gif

Norman Atkinson
12-09-2005, 04:13 PM
As I am just a stupid old ninny, can someone Google, the Angel of The North and put in the post.

That's the way that we did it!

Norm

freddycougar
12-09-2005, 04:16 PM
the plane the plane the plane boss...will take off
freddy

mochinist
12-09-2005, 04:48 PM
<font face="Verdana, Arial" size="2">Originally posted by Evan:
This is a no brainer. The motion of the treadmill has no impact on the plane except to spin the wheels. So what? Read my post on skis.

The plane takes off as usual. Sheesh. </font>I cant believe people are actually thinking it wont take off. These must be the same guys that think a pound of gold is heavier than a pound of feathers.

Kdahm
12-09-2005, 04:56 PM
<font face="Verdana, Arial" size="2">Originally posted by Pat Miles:
Massive thrust yes,but the original post said the conveyer belt could match the speed of the plane. Massive conveyer belt. The plane is standing still thus no air over the wing and no lift for takeoff.</font>

It's a frame of reference question.

Convert the plane to a black box. Assume for the moment that there is no wind or other convection currents.

The plane produces a force T (thrust) by accelerating a stream of air to the rear. This is independent of the movement of the ground or conveyer underneath the plane. and is usually of the magnitude w/4 where w is the weight of the plane. The second force acting on the plane is gravity, which is expressed as w since I don't want to get into the math.

The final force on the plane is F, the friction caused by the moving conveyor(or ground). This will be approximately equal to 0.035*w, based on the coefficient of friction from the thread. Since this is a rolling resistance, it is independent of the speed of the conveyor (or the ground) from the point of view of the plane.

Since T(=w/4) is much greater than F(=0.035w), the plane will accelerate down the runway until it takes off.
********************************
From the viewpoint of the wheel, the situation changes a bit. The axle is motionless. The outside edge of the wheel moves at the speed of what it is in contact with. The rotation of the wheel in rpm is G/(d*pi) where G is the ground speed and d is diameter in the same units.

Since the plane is on a conveyor moving equal and opposite to the plane (referenced to the control tower), G will simply be twice what it would otherwise be. The only problem is if the wheel or the bearings fail at 2G.

Karl

LastOldDog
12-09-2005, 04:59 PM
Well, I just got off the treadmill, trying to launch a kite. No matter my efforts, that stupid kite just lay there. . . LOD

graymatter
12-09-2005, 05:00 PM
You all have clearly missed the most important point. The plane will stay on the conveyor until it falls off the edge of the earth. Then it will glide. But to where?

Arcane
12-09-2005, 05:23 PM
The plane takes off of course.

bolmas
12-09-2005, 05:48 PM
&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;These must be the same guys that think a pound of gold is heavier than a pound of feathers.&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;

the pound of gold is lighter than the pound of feathers, in fact its 3/4 the weight.

plastikosmd
12-09-2005, 06:08 PM
1) plane in the air flying...under normal thrust from engines...still moves foreward
2)plane on ground ...under normal thrust from engines still moves foreward
3)plane on ground...on treadmill not moving in any direction ..still moves foreward
3) plane on ground ..on treadmill that is driving backwards, matching speed.. against wheels ..plane moves foreward but wheels are now doing about 2x normal speed, minus losses.

scott

mochinist
12-09-2005, 06:16 PM
<font face="Verdana, Arial" size="2">Originally posted by bolmas:
&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;These must be the same guys that think a pound of gold is heavier than a pound of feathers.&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;

the pound of gold is lighter than the pound of feathers, in fact its 3/4 the weight.</font>

IOWOLF
12-09-2005, 06:17 PM
Someone said it best, the wings make lift, no forward movement, no lift. if the engines were pointed downward it would hover. the answer is NO.Unless the jet engines made enough thrust to make enough air move over the wings, I doubt this will happen.

------------------
The tame Wolf !

Evan
12-09-2005, 06:23 PM

It's a little known effect that isn't well appreciated. It's called the eider-pinion effect. Because feathers are so much less dense than gold they obviously occupy a greater volume. This results in a significant portion of the feather mass being at a greater distance from the center of the earth than the mass of gold resulting in increased tidal forces. It's like the tidal forces produced by the moon that causes the earth to bulge away from the moon on the far side even though the moon is pulling in the opposite direction. Incidentally, tidal forces don't follow inverse square but instead they follow inverse cube law which greatly magnifies the effect.

[This message has been edited by Evan (edited 12-09-2005).]

mochinist
12-09-2005, 06:34 PM
<font face="Verdana, Arial" size="2">Originally posted by Evan:

It's a little known effect that isn't well appreciated. It's called the eider-pinion effect. Because feathers are so much less dense than gold they obviously occupy a greater volume. This results in a significant portion of the feather mass being at a greater distance from the center of the earth than the mass of gold resulting in increased tidal forces. It's like the tidal forces produced by the moon that causes the earth to bulge away from the moon on the far side even though the moon is pulling in the opposite direction. Incidentally, tidal forces don't follow inverse square but instead they follow inverse cube law which greatly magnifies the effect.

[This message has been edited by Evan (edited 12-09-2005).]</font>
Okay I can live with that, but the plane will still take off.

IOWOLF
12-09-2005, 06:35 PM
How? There is no lift.

------------------
The tame Wolf !

.RC.
12-09-2005, 06:37 PM
<font face="Verdana, Arial" size="2">Originally posted by mochinist:
These must be the same guys that think a pound of gold is heavier than a pound of feathers.

</font>

It's a bit of a difficult question to answer....The gold will depend on what the gold market is trading at at the time and I don't know how many feathers 1 pound will buy... http://bbs.homeshopmachinist.net//wink.gif

splicer
12-09-2005, 06:38 PM
The key here is that the conveyor can never match the forward speed of the aircraft. All it can attempt to do is increase the rotational speed of the aircraft's wheels but that wheel speed is independent of the thrust being generated. The engines are producing a positive thrust against the aircraft's structure regardless of the wheel rpm in any direction. The only limiting factor will be the wheel bearing drag up to the point that they overheat and sieze. If tires and bearings remain intact over the conveyor and survive the shock load if/when they hit stationary pavement the plane will take off.

ex-pilot
Splicer

mochinist
12-09-2005, 06:39 PM
<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
Someone said it best, the wings make lift, no forward movement, no lift. if the engines were pointed downward it would hover. the answer is NO.Unless the jet engines made enough thrust to make enough air move over the wings, I doubt this will happen.

</font>
Yes but this is not car we are talking about here, the wheels are not under power, have you ever seen a jet do a burnout? The tires are not producing the force to move forward and move air over the wings, the jet engines are doing that, the only reason the tires are there is to carry the jet on the ground.

Jim Hubbell
12-09-2005, 06:41 PM
A pound is a pound is a pound. Gold, feathers whatever. 1lb troy (gold) is 0.822lbs advp (feathers). As was stated the 747 will fly as usual as the wheels mearly support it on the ground.

.RC.
12-09-2005, 06:41 PM
What happens if we put a singularity 200ft behind the plane will it escape the event horizon??????? http://bbs.homeshopmachinist.net//wink.gif

Evan
12-09-2005, 06:42 PM
What wheels? It has skis.

Paul Alciatore
12-09-2005, 06:44 PM
The question is poorly stated. "the plane moves in one direction". There is no reference to the airplane's engines so it can not be assumed that they are the motive force.

All motion is relative. You must state what you are moving with respect to. If the plane is moving at x miles per hour WITH RESPECT TO THE RUNWAY which is moving at -X miles per hour with respect to the earth and air, then the plane is at rest with respect to the air (X-X=0) and it will not fly.

On the other hand, if the plane is moving at a speed of X with respect to the earth and air and the runway is moving under it at a speed of -X with respect to the earth and air, then the plane will fly because it is the AIR speed which determines lift. That is why aircraft carriers are turned into the wind for air operations. Or an airplane sitting still on a runway and facing into a hurricane force wind can "take off" with no engine power at all. That's why they have tie downs on the tarmac.

So please restate your problem so we can determine what the air speed is and then the question can be answered.

Paul A.

IOWOLF
12-09-2005, 06:51 PM
WHAT wheels? If the plane isnt moving forward it will not fly.

The plane may as well be held by a strong cable tied to the tail,Right?

------------------
The tame Wolf !

Mike Burdick
12-09-2005, 06:54 PM
....................

mochinist
12-09-2005, 06:58 PM
<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
WHAT wheels? If the plane isnt moving forward it will not fly.

The plane may as well be held by a strong cable tied to the tail,Right?

</font>

why wouldnt the plane move forward?

bobbybeef
12-09-2005, 07:02 PM
I think Iowolf has it right. If in doubt hand it all to the Padre as he reckons prayer can move anything.
Bobby.

bobbybeef
12-09-2005, 07:03 PM
I think Iowolf has it right. If in doubt hand it all to the Padre as he reckons prayer can move anything.
Bobby.

splicer
12-09-2005, 07:05 PM
Try it this way..... Instead of a conveyor, you have a set of engine driven rollers under the aircraft's wheels. No matter how fast you drive those rollers, the aircraft will still pull forward and away from them as soon as it's engine power is applied.

Wirecutter
12-09-2005, 07:42 PM
Wow. This really is an easy one. The plane will take off, but the wheels will spin at twice their normal speed. Are these speed-rated tires by any chance? I suppose the tires might be damaged...

Show me a plane that takes off by powering it's wheels (like a car) and we can both watch it come right back down just after it leaves the ground.

hoffman
12-09-2005, 07:59 PM
The thing works by air having to travel farther over the top of the wing than the bottom. Bernelli principle I think? If air isn't flowing over the airfoil of the wing it won't fly.

Put it on jackstands, power the wheels to spin at the rpm they would spin at take off speed and see if it flies.

I jacked my truck up with it in gear and revved it up to 75 mph. My dog didn't stick his head out the window...

If it flew you wouldn't have catapults on aircraft carriers...

[This message has been edited by hoffman (edited 12-09-2005).]

IOWOLF
12-09-2005, 08:12 PM
OK, Mo, let me make this easy for you,take the wheels and conveyor out of the equation, Becouse they cancel each other out.
If there is no air(wind) over and under the wings it will NOT fly.This is a law of physics.

------------------
The tame Wolf !

sauer38h
12-09-2005, 08:13 PM
<font face="Verdana, Arial" size="2">Originally posted by mochinist:
I cant believe people are actually thinking it wont take off. These must be the same guys that think a pound of gold is heavier than a pound of feathers.</font>

Much better to put it in terms of feathers and lead. Once you mention gold somebody will chime in with the annoying fact that precious metals are too often weighted in troy pounds (with 12 troy ounces per troy pound), and a troy pound is a piddling 373 grams. A real ("avoirdupois") pound, the type sensible people use for feathers and lead, is 453.6 grams. In these terms, a pound of feathers weighs the same as a pound of lead, but both are heaver (by 21.4 percent) than a pound of gold.

Like I said, annoying.

torker
12-09-2005, 08:15 PM
When you take your first "stress test"...you are going to show the treadmill who is the boss. The nurse smiles and keeps turning the damn speed up....your legs(= jet engines) are trying to push you ahead as fast as you can go. You are NOT moving ahead but you are going as fast as you can.
An airfoil needs forward motion to create lift....it doesn't matter if it is a jet engine or a tow line.
The wheels are not powered on the jet but do provide a means for the plane to move forward.
If the conveyor counteracts any forward motion....how do you get lift?
There is a terminal velocity with the jet engines anyway. If the belt can go fast enough it can equal the terminal velocity and it is a stalemate.
You could fly a plane that is tied to a big rock or tree or whatever...providing the wind blows hard enough to create the required lift. You just won't go anywhere....bring a lunch http://bbs.homeshopmachinist.net//biggrin.gif
Russ

Evan
12-09-2005, 08:19 PM
Since when are the jet engine in contact or somehow working against the conveyor? The conveyor is irrelevant.

Jet engines aren't like legs. Legs are like powered wheels.

Replace the jet aircraft with a missile on wheels. What happens? What is the difference?

[This message has been edited by Evan (edited 12-09-2005).]

torker
12-09-2005, 08:20 PM
Oh ya...a pound of feathers always weighs more than a pound of gold....you forgot about the bag the feathers are in http://bbs.homeshopmachinist.net//biggrin.gif

12-09-2005, 08:23 PM
Russ,
Nope. In a treadmill test, your legs are providing the forward thrust. In the case of the plane (and it could be prop-driven, too), the wheels are merely 'idlers' if you will.
The earlier analogy to skis was a good one; doesn't matter what the wheels are doing, unless they were to somehow limit the speed of the plane (yeah, worn bearings, etc; phooey).
So long as the plane reaches X speed (compared to the surrounding air), it will lift. The wheels/conveyor, regardless of the speed of those parts, can have only a negligible effect on that.
Thanks,

IOWOLF
12-09-2005, 08:26 PM
AHHHH, but a prop plane will blow wind over the wings, Jet engines will not,will they?

------------------
The tame Wolf !

Fasttrack
12-09-2005, 08:44 PM
Although i am not a fan of free-body diagrams, a free-body diagram (or force diagram) would best exemplify the effects of the situation. The plane will indeed take off, no doubt about it. The forward movement is generated in relation (read relative to) the air or atmosphere, not the ground. The thrust acts against the plane (not against the air, a common misconception...if it did act against the air, a rocket in space would never work)and the speed in the forward direction is independent of the speed of the ground or wheels. The wheels will just spin twice as fast.
Secondly, a pound is not always a pound. Don't forget about gravitational anomolies in the earth, plus its not perfectly uniform. The force of gravity via Earth is in no way constant (on very small levels at least http://bbs.homeshopmachinist.net//smile.gif ) Better to say a "kilogram" of gold is equall to "kilogram" of feathers as this refers to ammount of matter present, no force of gravity taken into account. i.e. a gram is a gram no matter where you are, space or earth.
thirdly..."debequem" is that German for something? seems like bequem meant comfortable in german

12-09-2005, 08:53 PM
Wolf,
Well, a puller prop will, but that's more of a pain than a help.
It sure doesn't provide enough 'coverage' to lift a plane and what it does cover is the wing roots where the lift is negligible.
Mostly just loads one side up and one side down.
Thanks,

mochinist
12-09-2005, 08:54 PM
<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
OK, Mo, let me make this easy for you,take the wheels and conveyor out of the equation, Becouse they cancel each other out.
If there is no air(wind) over and under the wings it will NOT fly.This is a law of physics.

</font>

You need to make it easy for yourself, your letting your brain fool you. Its been explained and Evan probably did the best job explaining it, so I guess if you dont get it you never will.

JRouche
12-09-2005, 08:55 PM
Ok, back to shop terms yall can grasp at.

Take your belt sander, the portable or the six inch wide one.

Start the sander (upside down for the portable) to simulate the conveyor.

Now take your kids small car and hold it still ontop of the moving sand paper.

Your hand holding the car is the planes engine (jet or prop).

You can move the car forward, against the motion of the conveyor (sandpaper) but that would be the same as the conveyor moving slower than forward motion of the plane.

The key to the scenario is motion.

The conveyor is directly tied to the motion of the planes wheels. No rotation of the wheels no movement of the wheels.

As you increase thrust on the engines the wheels will start to rotate and the conveyor will match the speed.

So, as long as the conveyor can match the speed of the rotating wheels you will get no forward motion and not air over the wing.

Again, simple aerodynamics....JRouche

motorworks
12-09-2005, 09:12 PM
Yes the plane will take off and Sir John
will make it to Morocco!!
e

black powder
12-09-2005, 09:28 PM
what about the harrier vertical take off ,then move nozzle for forward flight

johnhurd
12-09-2005, 09:35 PM
be the same thing as George Jetsons car, of course it will take off

BillH
12-09-2005, 09:36 PM
Its been said already many times. I dont care what the wheels are doing, as long as the airspeed over the wing is enough that is all that matters.

Yankee1
12-09-2005, 09:36 PM
The air flow over the wing causes lift. without sufficient air flow over the wing there will be no lift.

debequem
12-09-2005, 10:02 PM
That is a common misconception as far as the airfoil is concerned. You do not even need an airfoil or Bernoulli's principle to get an aircraft to fly. Case in point, look at an aerobatic aircraft's wing. It does not have an airfoil at all. Both top and bottom of the wing are the same with respect to curvature! Aerobatic planes fly upside down just fine. Why?

So, you ask, what lifts the aircraft upward? Simple, it is called angle of attack (AOA). AOA is the angle the wing makes with the air-stream that it is passing through.

Here is a real brain teaser:

Here is a simple thing to try. Take your faucet and turn it on so a steady stream of water flows from it.

Now, take a spoon and lightly suspend it from the handle so that the spoon section hangs straight down from your fingers. The spoon, if touched, should swing freely in your fingers, but not fall out of your grip.

Now, slowly back the convex section of the spoon into the water flow so that the water just strikes the curved back of the spoon. What do you observe?

What do you predict will happen? Will the spoon not be pushed away from the water as the force of the water strikes the spoon's back?

Go ahead, try it yourself and then try to explain to me what you see.

This is an interesting experiment that is more intellectually stimulating than launching a plane off of a conveyer belt. ;-)

Marv

<font face="Verdana, Arial" size="2">Originally posted by hoffman:
The thing works by air having to travel farther over the top of the wing than the bottom. Bernelli principle I think? If air isn't flowing over the airfoil of the wing it won't fly.

Put it on jackstands, power the wheels to spin at the rpm they would spin at take off speed and see if it flies.

I jacked my truck up with it in gear and revved it up to 75 mph. My dog didn't stick his head out the window...

If it flew you wouldn't have catapults on aircraft carriers...

[This message has been edited by hoffman (edited 12-09-2005).]</font>

debequem
12-09-2005, 10:06 PM
De Beque is the French spelling, but it appears that my ancestry is actually German. There was a dispute about a 100 or so years ago where one of my ancestors claimed we were French, so he changed the spelling from De Beck to De Beque.

<font face="Verdana, Arial" size="2">Originally posted by Fasttrack:
Although i am not a fan of free-body diagrams, a free-body diagram (or force diagram) would best exemplify the effects of the situation. The plane will indeed take off, no doubt about it. The forward movement is generated in relation (read relative to) the air or atmosphere, not the ground. The thrust acts against the plane (not against the air, a common misconception...if it did act against the air, a rocket in space would never work)and the speed in the forward direction is independent of the speed of the ground or wheels. The wheels will just spin twice as fast.
Secondly, a pound is not always a pound. Don't forget about gravitational anomolies in the earth, plus its not perfectly uniform. The force of gravity via Earth is in no way constant (on very small levels at least http://bbs.homeshopmachinist.net//smile.gif ) Better to say a "kilogram" of gold is equall to "kilogram" of feathers as this refers to ammount of matter present, no force of gravity taken into account. i.e. a gram is a gram no matter where you are, space or earth.
thirdly..."debequem" is that German for something? seems like bequem meant comfortable in german</font>

rsr911
12-09-2005, 10:16 PM
Beating a dead horse some more....

The plane with take off and fly no problem. The others are correct in stating that airflow over the wings causes lift and thus take off. This airflow is caused by forward movement. Forward movement is caused by the engines sucking in air, compressing it, adding fuel and creating combustion which leads to heat and pressure out the rear of the engine. Since the engines are attached to the airframe that rearward force (thrust) pushes the plane forward until such time that enough air velocity is achieved and the plane lifts off the ground. I think many of you are confusing the planes wheels on a conveyor with driven wheels like a car would have. The conveyor in this case is irrelevant.

Look at it like this:

We have two dragsters, the first is powered by a jet turbine and uses thrust for forward motion, it's wheels are not driven. The second is a typical V8 powered Top Fuel car and it's engine is coupled to the rear wheels which provide forward motion through traction with the pavement. If both of these where put on side by side conveyors only the jet car would accelerate forward because it does not rely on traction for forward momentum.

Heres a simple one, if two cars start from the same point and one car drives 100 miles east and the other 100 miles west which car traveled farther. Let's assume both cars are going 60mph and both travel a flat straight road in the direction they travel.

------------------
-Christian D. Sokolowski

debequem
12-09-2005, 10:23 PM
I don't think your last question works when you use cars. You have to use two trains traveling in opposite directions. Every physics book uses trains because it is mathematically impossible using cars. http://bbs.homeshopmachinist.net//biggrin.gif

<font face="Verdana, Arial" size="2">Originally posted by rsr911:
Beating a dead horse some more....

The plane with take off and fly no problem. The others are correct in stating that airflow over the wings causes lift and thus take off. This airflow is caused by forward movement. Forward movement is caused by the engines sucking in air, compressing it, adding fuel and creating combustion which leads to heat and pressure out the rear of the engine. Since the engines are attached to the airframe that rearward force (thrust) pushes the plane forward until such time that enough air velocity is achieved and the plane lifts off the ground. I think many of you are confusing the planes wheels on a conveyor with driven wheels like a car would have. The conveyor in this case is irrelevant.

Look at it like this:

We have two dragsters, the first is powered by a jet turbine and uses thrust for forward motion, it's wheels are not driven. The second is a typical V8 powered Top Fuel car and it's engine is coupled to the rear wheels which provide forward motion through traction with the pavement. If both of these where put on side by side conveyors only the jet car would accelerate forward because it does not rely on traction for forward momentum.

Heres a simple one, if two cars start from the same point and one car drives 100 miles east and the other 100 miles west which car traveled farther. Let's assume both cars are going 60mph and both travel a flat straight road in the direction they travel.

</font>

Jim Caudill
12-09-2005, 10:29 PM
Any pilot can understand and answer this easily. I have over 6,000 hrs and instructed in the USAF. Aircraft have pitot tubes to measure the impact effect of air molecules moving over the aircraft. Angle of attack is the angle formed between the airfoil and the moving stream of air. The pilot sitting in the aircraft waits until the pitot tube tells him he has sufficient airflow over the wings to generate the required lift, at that point he will rotate the nose of the aircraft by using the aerodynamic force developed by the tail section of the aircraft so as to place the wing at a desired Angle-of-Attack, thus allowing the wing to produce the desired lift and bring the aircraft into flight.

Since there is no relative airflow, the pilot will see zero airspeed on his indicator (see dog not sticking his head out the window as referenced earlier), there is no aerodynamic force developed by the tail to allow the pilot to raise the nose and no lift generated by the wing. The thrust developed by the engines is purely keeping the aircraft from being propelled backwards by the force of the conveyor system. In the example, if the engines were shutdown while on the conveyor, the effects of the belt would no longer be balanced and the aircraft would be subject to frictional and inertial forces.

The engines would only have to exert enough force to ovecome the friction forces involved in rotating the wheels. If there were zero friction devices on the landing gear, a child could hold the airplane in place with a dog leash attached to the nose gear.

My interpetation of the question said that the engines would only be used to counter the effects of the conveyor (keeping the aircraft from moving backwards) and dictating the zero air velocity over the wings. If the engines will be brought up to full power regardless of relative motion, then the aircraft will move forward and flight could occur with the wheels spinning twice as fast as normal at liftoff.

Lew Hartswick
12-09-2005, 10:30 PM
&gt;AHHHH, but a prop plane will blow wind over &gt;the wings, Jet engines will not,will they?

&gt;------------------
&gt;The tame Wolf !

Mr Wolf you forgot the smiley. :-)
...lew...

mochinist
12-09-2005, 10:38 PM
<font face="Verdana, Arial" size="2">Originally posted by Jim Caudill:
Any pilot can understand and answer this easily. I have over 6,000 hrs and instructed in the USAF. Aircraft have pitot tubes to measure the impact effect of air molecules moving over the aircraft. Angle of attack is the angle formed between the airfoil and the moving stream of air. The pilot sitting in the aircraft waits until the pitot tube tells him he has sufficient airflow over the wings to generate the required lift, at that point he will rotate the nose of the aircraft by using the aerodynamic force developed by the tail section of the aircraft so as to place the wing at a desired Angle-of-Attack, thus allowing the wing to produce the desired lift and bring the aircraft into flight.

Since there is no relative airflow, the pilot will see zero airspeed on his indicator (see dog not sticking his head out the window as referenced earlier), there is no aerodynamic force developed by the tail to allow the pilot to raise the nose and no lift generated by the wing. The thrust developed by the engines is purely keeping the aircraft from being propelled backwards by the force of the conveyor system. In the example, if the engines were shutdown while on the conveyor, the effects of the belt would no longer be balanced and the aircraft would be subject to frictional and inertial forces.

The engines would only have to exert enough force to ovecome the friction forces involved in rotating the wheels. If there were zero friction devices on the landing gear, a child could hold the airplane in place with a dog leash attached to the nose gear.

My interpetation of the question said that the engines would only be used to counter the effects of the conveyor (keeping the aircraft from moving backwards) and dictating the zero air velocity over the wings. If the engines will be brought up to full power regardless of relative motion, then the aircraft will move forward and flight could occur with the wheels spinning twice as fast as normal at liftoff.</font>

Just because you fly a plane doesn't mean you know the first thing about physics, it just means you passed a flying test.

For the plane to move, it doesn't "push down" on its wheels, it SUCKS IN and PUSHES BACK AGAINST THE AIR to propel it forward, IRRESPECTIVE of what the wheels are doing. Remember, they just roll passively forward, while continuing to hold up the plane.

OK, here's another analogy, that is less simple than the rollerskate/treadmill analogy, but perhaps it will help you guys understand this very simple concept.

Let say that the runway is at an ANGLE. Say a 45 degree angle. The plane has wheel brakes (they all do) and it can hold itself on the angled runway so it doesn't move. When the plane releases its brakes, gravity will accelerated the plane "down" the runway, even as the conveyor runway attempts to keep the plane where it started. Also gravity doesn't act exactly like the plane's thrust (the rope/treadmill does EXACTLY, though), it is still an force external to the runway/wheels that will accelerate the plane.

There is a very basic law in newtonian physics called F=MA where F=force, M=Mass, and A=acceleration. The plane's thrust represents a force vector towards the nose of the plane. Unless a force counteracts this force, there WILL BE ACCELERATION. The conveyor runway tries to counteract act this, but it CANNOT because the wheels cannot translate a horizontal foce in the direction of wheel travel to the plane because of very little rotational friction in the wheel/axle. If the runway cannot act on the plane (with a force other than the normal force), then it cannot stop the acceleration of the plane down the runway.

For the love of god, try to understand this. THINK REALLY HARD WITH THE LAST BRAIN CELLS THAT YOU HAVE...

mochinist
12-09-2005, 10:49 PM
While were on treadmills, this just makes me laugh

Jim Caudill
12-09-2005, 10:56 PM
As originally stated:
"A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction)."

Well, after reading thru so many posts, you sometimes forget what the original premise was. What I stated in my post is absolutely correct, I tried to cover myself by what I assumed was originally stated. Going back and re-reading the original statement reveals that I had lost track of what was actually written. It states that the conveyor belt will only move at an opposite velocity to the aircrafts speed (re-read as airspeed). So, as the aircraft begins to move forward the conveyor begins to go backward causing the wheels to travel at twice the forward velcoity of the aircraft - the aircraft will still be moving forward relative to the air, but the wheels will be behaving as if they were only half their diameter.

I had misinterpeted the problem as stating the engines would only be used to counter the backwards rolling effect of the conveyor. Essentially like a vehcile on a dynamometer.

Yes, the aircraft will takeoff based on relative airspeed - nothing to do with the rotational speed of the landing gear.

3 Phase Lightbulb
12-09-2005, 10:58 PM
I can understand why IOWOLF would think the plane would not take off, but I'm shocked to see there are others too.. http://bbs.homeshopmachinist.net//eek.gif

Jim Caudill
12-09-2005, 11:11 PM
By the way Mochinist, I do have a degree in Physical Science (albeit almost 30 years ago) with probably over 30 hrs in Physics. My failing was in assuming that I correctly understood the stated problem. Pat Miles first post about zero relative motion (treadmill analogy) got me going in the wrong direction. We used to have an acronym for my problem - RTFQ (read the fxcking question).

mochinist
12-09-2005, 11:15 PM
<font face="Verdana, Arial" size="2">Originally posted by Jim Caudill:
By the way Mochinist, I do have a degree in Physical Science (albeit almost 30 years ago) with probably over 30 hrs in Physics. My failing was in assuming that I correctly understood the stated problem. Pat Miles first post about zero relative motion (treadmill analogy) got me going in the wrong direction. We used to have an acronym for my problem - RTFQ (read the fxcking question).</font>Well I am a college drop out if that makes you feel any better, and really I didn't mean that post to be insulting to you, but I didn't want to edit it. I hope the funny treadmill gif would made you smile

plastikosmd
12-09-2005, 11:31 PM
maybe we can put this in simpler terms...so everyone has walked on a treadmill or ran...generally you dont make much progress getting across the room right? now try this...turn on your treadmill, run it as fast or as slow as you want just make sure you match your walking speed so you dont go anywhere...grab a large gas turbine engine, hold it over your head, point the thrust aft...now holding on tight give it a whole bunch of fuel...do you not think you will "take off?"
scott

BillH
12-09-2005, 11:39 PM
the airplanes wheels are free spinning, The whole treadmill thing wouldnt add up to jack, the friction from the wheels rolling would be insignificant to the thrust of the engines. Now on the other hand if the wheel brakes were ON...

lugnut
12-09-2005, 11:48 PM
So, would you recomend a HSS or a Carbide bit to get this thing in the air?

http://bbs.homeshopmachinist.net//smile.gif
Mel

lugnut
12-09-2005, 11:50 PM
So, would you recomend a HSS or a Carbide bit to get this thing in the air?

http://bbs.homeshopmachinist.net//smile.gif
Mel

.RC.
12-10-2005, 12:07 AM
What happens if you replace the jet engines with Impulse Engines as used on the Enterpise..

BillH
12-10-2005, 12:22 AM
<font face="Verdana, Arial" size="2">Originally posted by Ringer:
What happens if you replace the jet engines with Impulse Engines as used on the Enterpise..</font>

You mean the Photon Torpedo drive?(Non Star Trek speak) The total conversion of matter into energy with the use of anti matter which there is only 2 known methods to contain. 1. Some kind of energy field, and 2, J-lo's Box, since the cells in her uterus can regenerate at a faster rate than the anti matter can destroy and her vagina is known to be nuclear proof.
Ok, I was wanting to say that on my Astronomy test but the question was never asked http://bbs.homeshopmachinist.net//frown.gif jokingly of course.

SJorgensen
12-10-2005, 12:22 AM
There isn't enough information to answer the question. At the start the aircraft has all of its weight on the gear. There is no momentum and no aerodynamic drag and no drag from the gear.

Yet as soon as it starts to move, the aerodynamic drag starts to rise to the square of the increase in airspeed. Drag from the gear would increase as well, but no to the square of the forward speed. And if everything goes as planned the weight on the gear would decrease and drag would normally reduce. In this scenario the drag from the gear is arbitrarily increased to 200% of the normal increase in ground speed.

Jet aircraft used to be known for accellerating slowly. Of course now-a-days they have very powerful engines. Still they don't produce maximum thrust at the beginning because they can't get the engine airflow that they do in flight.

This scenario would be like taking off on a snow covered runway and with the snow getting deeper all the time. If the snow gets too deep, too soon, you won't make it. Yet if the weight comes off the gear quicker than you are mushing through it, everything will be fine.

It is a great question, because no matter how sure you are that you know the answer, it becomes an entirely different scenario when 300 people are riding in the back.

The only way to know the answer is to solve it mathmatically and there isn't enough information to answer the question.

Why not ask how much fuel could be saved if the belt were running the other direction?

Why not ask, if steam catapults were used to launch airliners, how much fuel would be saved? The fuel savings would probably be substancial.

Spence

mochinist
12-10-2005, 12:32 AM
Have another bong hit spence.

Carl
12-10-2005, 12:34 AM
The plane will take off at normal air speed and normal ground speed. The speed of the conveyor will be equal to ground speed in the opposite direction.

[This message has been edited by Carl (edited 12-10-2005).]

SJorgensen
12-10-2005, 12:42 AM
It is a different question to those of us who are pilots.

Every take-off is like a motorcycle jump. It has to be right.

It has been many years since I ever did a bong. I don't regret it, but I sure am glad that I never tried any of the meth and coke and heroin that is going around today. Much of my computer consulting work is with drug rehabs and so I see the results of that on a daily basis.

Maybe you should try a bong. It might do you some good and take the mean edge off of you.

Kdahm
12-10-2005, 12:45 AM
<font face="Verdana, Arial" size="2">Originally posted by JRouche:
Ok, back to shop terms yall can grasp at.

Take your belt sander, the portable or the six inch wide one.

Start the sander (upside down for the portable) to simulate the conveyor.

Now take your kids small car and hold it still ontop of the moving sand paper.

Your hand holding the car is the planes engine (jet or prop).

You can move the car forward, against the motion of the conveyor (sandpaper) but that would be the same as the conveyor moving slower than forward motion of the plane.

The key to the scenario is motion.

The conveyor is directly tied to the motion of the planes wheels. No rotation of the wheels no movement of the wheels.

As you increase thrust on the engines the wheels will start to rotate and the conveyor will match the speed.

So, as long as the conveyor can match the speed of the rotating wheels you will get no forward motion and not air over the wing.

Again, simple aerodynamics....JRouche</font>

Close, but not quite. Your hand is the jet engine. If you push forward with your hand (throttle the engines up), the car will move forward. It doesn't matter whether the belt is moving at the forward speed of the car, twice that speed, or ten times the speed.

mochinist
12-10-2005, 12:48 AM
<font face="Verdana, Arial" size="2">Originally posted by SJorgensen:
It is a different question to those of us who are pilots.</font>
It is the same question regardless of whether or not you fly or not.

<font face="Verdana, Arial" size="2">Originally posted by SJorgensen:
Maybe you should try a bong. It might do you some good and take the mean edge off of you.

</font>I gave mine away 6 years ago and never looked back, I had a 2' tall double bubble Jerome Baker glass bong that would rock your world. It was fun while it lasted and it should definately be legal but I don't need it or want to smoke it anymore.

[This message has been edited by mochinist (edited 12-09-2005).]

SJorgensen
12-10-2005, 12:55 AM
Carl,

There will be a measurable effect, so you are wrong in dismissing it. The effect will be greatest at the beginning when the craft is all on the ground.

It isn't a simple question really. Oh, just a little pinch of sinsemilla in the bong and I'll cogitate on it awhile.

tenfingers
12-10-2005, 01:41 AM
This is a close call. The fastest speed rating for any 747 tire is 245 mph. Can a 747 take off with an airspeed around 122.5 mph? Maybe.

10F

darryl
12-10-2005, 03:07 AM
If I can get over the treadmill video, I'll take a stab at the question.

Yes, the plane will take off. The action of the tires is twofold. One, they hold the attitude of the plane so it's basically poised for takeoff. Second, they reduce the friction of forward motion enough so the thrust from the engines is able to accelerate the weight of the loaded aircraft to the takeoff speed within the length of the runway. The conveyor belt matches the forward speed of the plane while moving in the opposite direction. If the plane takes off at 200 mph, the conveyor is moving at 200 mph as well. Theoretically, the tires will spool up to 400 mph just at the point where the plane lifts off.

As the plane accelerates, the wings generate lift. The faster it goes, the less load the tires have to bear. The bearing friction will not increase to anywhere near the point where it will impede the progress of the plane down the moving carpet. If the tires overheat but don't yet blow, they don't give any mechanism that would impede the forward motion of the plane. For the length of the takeoff roll, they cannot heat up to the point where the melting rubber would stick to the conveyor belt. They will blow from the rotational forces, coupled with any weakening that might happen due to the increased heating. Because of the safety factor, the plane will have reached at least 75 percent of take-off speed before the tires blow. At this point, they are mostly unloaded from the weight of the plane. Now let's assume that they all blow out.

If a ruptured fuel tank doesn't ignite and make everyone lift off at this very moment, the worst that will happen is that everyone behind first class will soil themselves, then try to regroup and come up with a plan. But it doesn't matter about them, they're just dead weight, and that weight hasn't changed, except maybe it has shifted a little downwards. The balance of the plane is not affected much at all. All the fumage detectors would be going off my now, though.

It's safe to assume that the tires now have a higher rolling friction than they did a few moments ago. But at the moment they all blew at once, they were 3/4 unloaded, and the increased friction from the blown tires isn't as much as the their friction earlier when the plane was rolling down the red carpet for takeoff, with all of the planes weight on them. The wheels are still intact, and there is a round rolling surface left, so it's not like the plane is suddenly skidding on a rubber sheet. Cars seem to roll along quite well on just the rims. Just check out some of those cop shows. The plane is still accelerating, and will continue to do so because the pilot has just seen the need to push the throttles up to 100 percent from 80 percent. There is enough runway left because of the safety factor built in to the whole process of lofting a fully overloaded human dunnage tubule into the air. So up they go.

Interestingly, the second from last factor in all this is that the conveyor belt having been moving all along, and at speeds approaching 200 mph, has been drawing wind along with it. This wind has lessened the speed which the plane has had to accelerate to in order to achieve lift-off. In all likelyhood, the tires will survive this torture and the plane will take off normally, without anyone having had to scream at a stewardess about anything.

There would be some increased effects from the gyroscopic forces of those overspeeding tires as the mechanisms operate to raise the landing gear. They probably don't rip off, but even if they do, so what? The plane is in the air.

Now the last possible factor would be something hotter than those possibly exploding melting chinese rubber tires. That's if a fuel tank did rupture and ignite. I think it's safe to assume that a lot of the plane would lift off, even if the tires never left the ground. On the plus side, the conveyor would be taking much of the wreckage back towards the airport, so the fire trucks would be able to reach it more quickly.

[This message has been edited by darryl (edited 12-10-2005).]

Evan
12-10-2005, 04:25 AM
I'm really disappointed that nobody called me on the eider-pinion effect....

Ernest Kerr
12-10-2005, 05:40 AM
An aircraft will fly when thrust exceeds drag and lift exceed weight. The wing angle of incidence will create lift at designed airflow. The ground run of an aircraft creates the required airflow for lift and since the 747 is not experiencing a ground run with airflow over the wings it will not fly. Even though the undercarriage experiences a very high rotation it will not create lift.
Kerr

12-10-2005, 06:54 AM
Scatterplot, congratulations on this thread going "Platinum". Maybe Neil should send you a little something extra in your email, maybe a couple lines of "kudos" http://bbs.homeshopmachinist.net//biggrin.gif

IOWOLF
12-10-2005, 07:32 AM
" I gave mine away 6 years ago and never looked back, I had a 2' tall double bubble Jerome Baker glass bong that would rock your world. It was fun while it lasted and it should definately be legal but I don't need it or want to smoke it anymore."

[This message has been edited by mochinist (edited 12-09-2005).]

This explanes alot,But why do you keep wanting to thrust your problem on others?

As I said the wheels/conveyor cancel each other out.
Would we be haveing this conversation if it were a F15 which we all know has more thrust than weight of the plane?

------------------
The tame Wolf !

mattc
12-10-2005, 08:55 AM
my question is the tower on the convayor with the plain so they can both take off in different directions?

IOWOLF
12-10-2005, 09:08 AM
I think you hit on it now.

Too many questions not enough answers!

------------------
The tame Wolf !

Tinkerer
12-10-2005, 09:33 AM
Humm... I think it will crash. A conveyor as large as a runway rotating at 190+ knots is going to create a hellofa down draft and turbulence in front of and around the wings. Without clean air over them the wings lift will not be efficient enough to lift the plane. Or the lower pressure caused by the air moving from the belt will.... oh hell get the Myth Busters on this one they can do a scale mock up of it and prove or disprove this in thirty minutes or less. http://bbs.homeshopmachinist.net//wink.gif

Evan
12-10-2005, 09:54 AM
Heh. It is over 50 pages with over 1000 replies on the Mythbusters forum.

Mcgyver
12-10-2005, 10:12 AM
Evan, as usual we took what you had to say as gospel and moved.

the 3/4 is BS, but thought it was to make the point. as weight is a measure gravitational pull, not mass, the premise seemed reasonable. It also seemed reasonable to assume they'd be sitting in on a plane, it would be hard for them to float in space and have the same centre of gravity, with indeed the feathers making a higher pile. Whether the difference in gravitation pull over such a short difference is measurable I don’t know, but it will be there nonetheless.

tenfingers
12-10-2005, 10:24 AM
I doubt the aircraft has enough thrust to accelerate and take off with blown tires. It's not necessarily true that the tires will unload a lot with speed -- the lift coefficient might not be that high at static attitude. The real unloading of the tires happens at rotation.

The tires might overheat or develop standing waves but when they blow, the friction goes from about 0.015 to around 0.2. With all the weight on a 0.2 friction coefficient, and all the aero drag it's really unlikely that you'd be doing any more accelerating.

10F

mochinist
12-10-2005, 10:29 AM
<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
This explanes alot,But why do you keep wanting to thrust your problem on others?</font>What problem am I thrusting on others?

<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
As I said the wheels/conveyor cancel each other out.
Would we be haveing this conversation if it were a F15 which we all know has more thrust than weight of the plane?

</font>If you don't get it I guess you never will.

debequem
12-10-2005, 10:58 AM
That has to be some carpet burn. Ouch!

<font face="Verdana, Arial" size="2">Originally posted by mochinist:
While were on treadmills, this just makes me laugh

Michael Az
12-10-2005, 11:30 AM
Just yesterday I had to spin these up in my lathe. Even though the lathe weighs 3,000 lb., it moved forward several inches at 300 rpm. At 400 rpm liftoff was attempted. Still trying to figure it out.
Michael
http://myweb.cableone.net/michaelaz/prop2.jpg

Wirecutter
12-10-2005, 12:32 PM
Scatterplot - another congrats on going platinum.

FWIW. Some years ago, when I first started setting up a shop in my basement, I built an RC plane from "scratch". (Stamped balsa wood to flyable) The plane I chose was called the Senior Telemaster, from Hobby Lobby, IIRC. Ugly as hell plane, really, and not based on any real aircraft. It was developed in Germany, I'm told, to assist in stringing wires across rivers. The interesting part is that it's the size of a "giant scale" RC, but it's a "60-size" plane. It's light and has a 95" wingspan (almost 8 feet) It can carry 10 lbs of payload with a .060 engine. Finally, it can take off with a "negative ground speed", that is, rolling backwards.

A guy at a local hobby shop had seen this - it was a "normal" Senior Telemaster in a steady breeze of about 7 kt. The pilot brought the plane into the wind and down to about shoulder-level and backed off the throttle. Eventually, the plane hung still in the air and began drifting backwards. It's wind over the wings that makes the plane fly, not spinning the wheels.

<font face="Verdana, Arial" size="2">Originally posted by mochinist:
have you ever seen a jet do a burnout?
[/B]</font>

http://bbs.homeshopmachinist.net//biggrin.gif

<font face="Verdana, Arial" size="2">Originally posted by hoffman:
The thing works by air having to travel farther over the top of the wing than the bottom. Bernelli principle I think? </font>

That's just one way a wing can create lift, and it's generally the best way. But as someone said, aerobatic planes have essentially flat wings, and they still fly. Half of the time, they fly upside down, hence the flat wings. They do it with angle of attack. With the same principle, a sheet of plywood can fly, at least theoretically. (I wouldn't buy a ticket on one... http://bbs.homeshopmachinist.net//biggrin.gif )

<font face="Verdana, Arial" size="2">Originally posted by hoffman:
If it flew you wouldn't have catapults on aircraft carriers...
</font>

Cats on carriers are there for the same reason that, during flight operations, the carrier wants to be going full-speed-ahead into the wind. Get more wind over the wings so the aircraft can take of with an insanely short takeoff roll. The catapult gets the plane from 0-100 kt in something like a second and a half. Steaming into the wind also helps to keep the groundspeed low when landing. Of course, for landing, they have the tailhook and the arrestor cable, too.

I wonder if this thread will go double-platinum?

-M

Carl
12-10-2005, 02:07 PM
Here's another scenario for ya...747 sitting on runway, brakes locked. A hurricane force headwind, equal to the take off speed of the plane comes up and is sustained. The pilot advances the throttles just enough to create enough thrust to overcome the aerodynamic drag of the plane in take off trim. He pulls the yoke and rotates the aircraft to take off angle of attack. The 747 lifts off and hovers like a helicopter. The pilot decreases the throttles very slightly and the 747 flies very slowly backward in relation to the ground. Didn't think a 747 could fly backward...did you? Then the headwind abruptly stops, and the definition of wind shear becomes clear to all http://bbs.homeshopmachinist.net//biggrin.gif

debequem
12-10-2005, 02:25 PM
That would not be wind shear. Wind shear, in the sense that most people understand it, is a vertical component to the wind.

Actually, shear is caused by two opposing wind components where the result produces a turbulence or rolling action in the wind. So you have rising air on one side and descending air on the other side of the roll.

What you described is simply a stall condition of the aircraft.

The good news is, for every takeoff there is guaranteed a landing!

<font face="Verdana, Arial" size="2">Originally posted by Carl:
Here's another scenario for ya...747 sitting on runway, brakes locked. A hurricane force headwind, equal to the take off speed of the plane comes up and is sustained. The pilot advances the throttles just enough to create enough thrust to overcome the aerodynamic drag of the plane in take off trim. He pulls the yoke and rotates the aircraft to take off angle of attack. The 747 lifts off and hovers like a helicopter. The pilot decreases the throttles very slightly and the 747 flies very slowly backward in relation to the ground. Didn't think a 747 could fly backward...did you? Then the headwind abruptly stops, and the definition of wind shear becomes clear to all http://bbs.homeshopmachinist.net//biggrin.gif</font>

lynnl
12-10-2005, 02:51 PM
<font face="Verdana, Arial" size="2">Originally posted by debequem:
That would not be wind shear. Wind shear, in the sense that most people understand it, is a vertical component to the wind.

Actually, shear is caused by two opposing wind components where the result produces a turbulence or rolling action in the wind. So you have rising air on one side and descending air on the other side of the roll.

</font>

It certainly is wind shear!
The problem is that "most people" don't understand wind shear.

It is simply the change in wind velocity (vector, comprising both speed and direction). Can be either vertical or horizontal components, but MUCH MORE commonly is in the horizontal, e.g. CAT (clear air turbulence) in the vicinity of the jet streams, or frontal boundary zones.

darryl
12-10-2005, 04:17 PM
Of course, the real answer has to be no, because nobody who's rated to fly a 747 would attempt such a thing.

Has just occured to me that the plane would have to track absolutely straight down the path of the conveyor belt, otherwise the tires would quickly veer to one side or the other. If the wings weren't so long, the plane would be doing a roll in no time. Instead it will be doing a combination flat spin and roll. Because this is not part of it's envelope of operation, it will snap all the non-certified bolts holding it together and become a huge mass of burning debris and human carnage.

So I've changed my mind. No pilot alive could track that takeoff run so accurately that this wouldn't happen. I'm cancelling my ticket.

darryl
12-10-2005, 04:32 PM
Forget about the plane. Everyone on it is doomed anyway. What I want to know now is where is gold weighed? At sea level, or at the top floor of a highrise in Denver? What happens to a weigh scale when operated at different altitudes?

IOWOLF
12-10-2005, 04:40 PM
<font face="Verdana, Arial" size="2">Originally posted by darryl:
Forget about the plane. Everyone on it is doomed anyway. What I want to know now is where is gold weighed? At sea level, or at the top floor of a highrise in Denver? What happens to a weigh scale when operated at different altitudes?</font>

Now there is a dunb question.IMHO

------------------
The tame Wolf !

sauer38h
12-10-2005, 05:08 PM
<font face="Verdana, Arial" size="2">Originally posted by darryl:
What happens to a weigh scale when operated at different altitudes?</font>

A spring or strain-gauge scale would show weight decreasing with altitude, if it happened to be sensitive enough to show any change at all. A balance scale wouldn't measure any change.

[This message has been edited by sauer38h (edited 12-10-2005).]

Fasttrack
12-10-2005, 05:19 PM
Why's it a dumb question? Gravity is a inverse-square force; he brings up a good point. If it was measured on a spring scale, i.e. measuring weight based on gravity, altitude could impact the values. On a balance scale you are measuring quantity, i.e. kilograms, by comparing the effect of gravity on the unkown amount of gold to the effect of gravity on a known amount of some substance. Since both components are at the same altitude, they both feel the same pull from gravity and the gravity component drops out of the equation. Now you have substance a equalls amount of gold (once the scales are balanced)

ricksplace
12-10-2005, 05:32 PM
Bernoulli's Principle
http://www.mca.k12.nf.ca/bernoulli/bernoulliprinciple.htm

Wirecutter
12-10-2005, 06:41 PM
<font face="Verdana, Arial" size="2">Originally posted by Carl:
Here's another scenario for ya...747 sitting on runway, brakes locked. A hurricane force headwind, equal to the take off speed of the plane comes up and is sustained. The pilot advances the throttles just enough to create enough thrust to overcome the aerodynamic drag of the plane in take off trim. He pulls the yoke and rotates the aircraft to take off angle of attack. The 747 lifts off and hovers like a helicopter. The pilot decreases the throttles very slightly and the 747 flies very slowly backward in relation to the ground. Didn't think a 747 could fly backward...did you? Then the headwind abruptly stops, and the definition of wind shear becomes clear to all http://bbs.homeshopmachinist.net//biggrin.gif</font>

Well, that certainly would be interesting to watch, from many thousand feet away. Here's another one for you... (veering even further off-topic)

In the "old days", many attempts at flying involved some kind of human-powered thing wherein someone straps on a pair of wings. It just can't work that way, we now know, because humans are just not strong enough relative to their weight. Birds have such optimizations as hollow bones, lungs that work more like our heart (pumping through, rather than in-and-out), and incredible food throughput for their weight. Even the most phyisically fit human can't flap their arms hard enough to power a set of wings like a bird. But...

On the moon, gravity is much weaker. If you could enclose an Earth-like atmosphere in some large structure, a human could fly like a bird. Wouldn't that be a worthwhile application for a multi-billion dollar space program? http://bbs.homeshopmachinist.net//biggrin.gif

<font face="Verdana, Arial" size="2">Originally posted by debequem:
That would not be wind shear. Wind shear, in the sense that most people understand it, is a vertical component to the wind. </font>

I have to agree with lynnl here. I don't know how many different varieties of wind shear there are, but I have also heard it described that way - I believe it was a rather detailed article in "Flying" magazine. It was probably after a famous crash attributed to wind shear.

The point Carl was making was that, if the plane is in a strong wind which is keeping it aloft, and the wind suddenly dies, there is no way that the 747 can accelerate its many, many tons of mass fast enough to keep from dropping like a stone.

I would hazard a guess that there are a few pilots here who may have experienced rapid wind shifts and felt themselves drop. Either the sudden loss of a headwind, or the sudden appearance of a tailwind will do it. If you're close to the ground when this happens, it could be a very bad day.

C'mon double platinum!

-Mark

Jim Hubbell
12-10-2005, 06:53 PM
The foregoing posts have been and seem to go on providing a lot of fun for the imagination. It also provides a good insight into why a problem must be stated fully and concisely before it is put up for discussion. Much was left to the readers imagination. Assumptions were made according to the readers experience and knowledge. This produced quite a few conflicting answers. IMO the exercise was purposely set up this way to illustrate how willing we are to “solve” a problem that has no clear parameters and therefore solutions as per assumptions.
Accordingly, with my assumptions, of course it will fly.

Evan
12-10-2005, 07:57 PM
Bernoulli's Principle isn't wrong but it isn't the main reason a wing works. It only contributes a minor portion of the lift. The main lift component is produced in a much more intuitive and simple way and is why a fully symmetrical airfoil or flat plate can produce lift. The angle of attack simply deflects air downwards. Action produces reaction.

All the books and science texts that credit Bernoulli's Principle as the explanation for how a plane flies are wrong. NASA pointed this out quite a few years ago but nobody listened. Even NASA has some web pages online that still give the same tired old (wrong) explanation.

A good example is a helicopter. It doesn't suck itself into the sky, it blows vast amounts of air downwards which anyone can plainly see when it hovers over water.

Jim Hubbell
12-10-2005, 08:49 PM
I wonder why the vortex forms at the wing tip as the denser air makes its way around from under the wing? Why does a wing stall, even at high speed, when the angle of attack is in creased beyond a certain point? Are all propellars made incorrectly and a couple of slats out in front would do just as well? Including chopper blades. Oh well!

Evan
12-10-2005, 09:03 PM
Bernoulli's Principle does provide some of the lift, just not the majority. The air attaches to the upper surface of the wing because of the Coanda effect. Beyond a certain angle of attack the momentum of the airflow exceeds that attaching boundary layer effect and the airflow detaches causing a stall. A flat plate is actually the most efficient airfoil until it stalls. That however occurs at a very low angle of attack, only a few degrees. It is also an impossible engineering structure to build with any strength.

sauer38h
12-10-2005, 09:05 PM
<font face="Verdana, Arial" size="2">Originally posted by Jim Hubbell:
I wonder why the vortex forms at the wing tip as the denser air makes its way around from under the wing? Why does a wing stall, even at high speed, when the angle of attack is in creased beyond a certain point? Are all propellars made incorrectly and a couple of slats out in front would do just as well? Including chopper blades. Oh well!</font>

The pressure on the bottom of the wing is higher than the pressure on the top of the wing. This is what generates lift. Whether that pressure arises because of the camber of the wing (a la "Bernoulli effect"), or if it's the stagnation pressure caused by the angle of attack (which is ALSO "Bernoulli effect" - look at the full form of the Bernoulli equation!), doesn't matter. High pressure air will do what it does best, which is try to flow to where the low pressure is - and that's on top of the wing. Hence the flow around the wing tip, and the resulting vortex.

Just about all airfoils (or "wing sections", as the textbooks tend to call them) stall when the angle of attack is around 14 degrees. Some sections stall more gracefully (that is, less suddenly) than others. Flaps with slats and little tabs to add turbulence to the boundry layers can push that up a bit, but not enough to get exited about - the stall angle will still be around 14 degrees no matter what you do.

A propeller pretty much IS a couple of slats out front (a tractor propeller is, at least). The twist is there because the outer parts of the blade are moving faster. For all of the blade to contribute its share of the thrust, the parts at smaller radii need greater slopes.

Jim Hubbell
12-10-2005, 09:50 PM
In order to keep this topic going, I might note that the P-36 Apache dive bomber of WW2 had a nearly symetrcal airfoil. It was later renamed P-51 Mustang and went on to become one of the top WW2 fighters. I don't remember them taking off on conveyer belts, but I bet they could have.

wierdscience
12-10-2005, 09:50 PM
<font face="Verdana, Arial" size="2">Originally posted by Scatterplot:
This made for some interesting debate on another forum I'm on, hopefully we can get some good discussion going on here.

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?</font>
Of course the plane takes off,for it to move at all it must use the thrust from it's engines to push against the air behind it.The belt has no effect since the wheels aren't pushing the plane foward.

The real question is,if that plane is a Delta airlines plane then how much of the passenger's luggage will be lost? http://bbs.homeshopmachinist.net//biggrin.gif

Jim Hubbell
12-10-2005, 10:03 PM
It was noted above that a wing stalls as the air pulls away and becomes turbulant over the top of the wing. It was also proposed that most of the lift is generated by the angle of attack forcing the air mass down. Why does a little turbulance over the wing negate all that lift below the wing?

Evan
12-11-2005, 01:23 AM
If you look at a wing in cross section while flying at a positive angle of attack you find the trailing edge of the wing is in effect angled downward towards the ground. The air flow under the wing is deflected downward and the flow over the top of the wing while attached is also directed downward. That's why a wing produces a downwash behind it.

When the flow over the top detaches in a stall it is no longer directed down off the upper trailing edge and a major amount of lift is lost while all the drag remains.

The majority of the lift is produced by accelerating air downward. A flat plate at zero angle of attack produces no lift. At a low positive angle of attack it produces lift.

The F104 fighter was the closest to having a flat plate airfoil which accounts for it's very high landing speed since it was extremely stall sensitive. It also had very unforgiving handling, also because of the wing loading and nearly flat airfoil. The wing was only 4.2 inches thick at the root and 2 inches thick at the tip with a knife leading edge. The thickness ratio was only 3.4%.

CompositeEngr
12-11-2005, 02:41 AM
Evan is correct.
Most lift is produced by accelerating x lbs of air down per unit of airspeed.
There is also a circulation effect, where the air swirls from the lower surface to the top. I'd have to look that mechanism up again to explain further.

There are two reasons curved airfoils are used instead of flat plates:
- Efficiency. A big enough motor will make anything fly. Maybe not very well.
- Flow separation (where the airflow doesn't follow the airfoil anymore) occurs less suddenly over a curved surface.

And the problem is complete exactly as stated. The plane will take off, and the wheels will be spinning 2x as fast.

Jim Hubbell
12-11-2005, 03:26 AM
So it might be safe to say that a major amount of lift is lost when the air above the wing is "messed up". And therefore a major amount of lift must be generated above the wing. Seems to hint of the old theory.

Evan
12-11-2005, 07:46 AM
Once again Jim, the airflow above the wing, when still "attached", follows the shape of the wing to the trailing edge. What was previously still air (ideal conditions) is now moving air (accelerated) and is moving down off the trailing edge. Air is actually quite massive, at STP about one kilo per cubic meter IIRC. It's simple Newtonian physics.

Stand behind a plane doing a run up. That blast of accelerated air is producing an opposite and equal reaction that we call thrust. A plane does not suck itself forward, it blows. Same for a helicopter as well as the wing.

The pressure differential as per Bernoulli does play a minor part but is not the main component.

<font face="Verdana, Arial" size="2">
From before powered flight actually occurred until about twenty years ago, the actual lift of an aircraft was generally attributed to Bernoulli lift. Within the past twenty years, most descriptions now entirely discard Bernoulli lift and instead credit Reaction lift. The reality is that both are acting. Very large modern aircraft generally are designed to create about 4/5 Reaction Lift and 1/5 Bernoulli Lift, in order to carry the heaviest possible loads. Smaller aircraft generally have a more even proportion, say 2/3 Reaction Lift and 1/3 Bernoulli Lift. </font>

http://mb-soft.com/public2/lift.html

Toolmaker Extrodinair
12-11-2005, 10:01 AM
Read the post carefully, the conveyor is controlled to move as fast as the plane speed. At some point the plane will run out of runway and onto a busy street and another scenario as in Chicago. Good Day.

Evan
12-11-2005, 11:28 AM
"the conveyor is controlled to move as fast as the plane speed."

So?

3 Phase Lightbulb
12-11-2005, 11:41 AM
Hey IOWOLF, You should learn how to use your computer. You left your webcam on:

www.bbssystem.com/iowolf.wmv (http://www.bbssystem.com/iowolf.wmv)

mochinist
12-11-2005, 11:49 AM
Thats too funny. LMAO

lynnl
12-11-2005, 11:53 AM
<font face="Verdana, Arial" size="2">Originally posted by Toolmaker Extrodinair:
Read the post carefully, the conveyor is controlled to move as fast as the plane speed. At some point the plane will run out of runway and onto a busy street and another scenario as in Chicago. Good Day.</font>

Nah, the plane will rotate at essentially the same point as it would on a fixed/rigid runway surface. (with wheels spinning twice as fast)

Re the Bernouli effect: Its importance is evident in the disastrious effects that just a thin coating of ice or even frost on the wings can have, especially on takeoff.

Wirecutter
12-11-2005, 12:41 PM
<font face="Verdana, Arial" size="2">Originally posted by 3 Phase Lightbulb:

Hey IOWOLF, You should learn how to use your computer. You left your webcam on:
</font>

ROFLMAO. That's cold. http://bbs.homeshopmachinist.net//biggrin.gif

sauer38h
12-11-2005, 12:43 PM
<font face="Verdana, Arial" size="2">Originally posted by CompositeEngr:
Evan is correct.
Most lift is produced by accelerating x lbs of air down per unit of airspeed.
</font>

No, ALL of the lift is from momentum transfer to the surrounding air, not just "most of it". You have no lift at all unless some air is accelerated downward. To get more lift, you have to accelerate more air.

Guido
12-11-2005, 02:25 PM
Keep 'em flying-----check out www.petroleummuseum.org/index.html (http://www.petroleummuseum.org/index.html)

If/when you're in West Texas, the sporty cars of Jim Hall are on display at Midlands' Petroleum Museum.

Hall shares first credits in using upside down wings and stalled wings to win races. A result is the use of front and rear wings on todays Indy and F1 racers. His legacy includes how air is hanled as it passes underside of racecars.

G

Sandy H
12-11-2005, 03:12 PM
"A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor)."

The premise is set, the plane is a 747 passenger jet. This means it is a real plane with real conditions (such as finite friction in the wheels etc).

"The plane moves in one direction, while the conveyor moves in the opposite direction."

'The plane moves' says to me that the plane is moving with reference to a stationary observer who is presumably not on the conveyor. I have yet to see an observer who can run at speed over, I'll say 30mph, but regardless of the rare chance someone could do that for some small amount of time, my opinion of the stated question is that the plane moves with reference to a fixed point with reference to the Earth.

"This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction)."

Some sort of conveyor is moving the plane's wheels twice as fast as the plane's global positional velocity.

I would say that, since the plane is moving with a fixed reference to position (from the second premise) if the plane reaches the correct velocity with reference to the air in the local vicinity, the plane will indeed lift off. I guess the belt speed would therefore mean that the plane's tires are moving at twice the normal rate for a typical takeoff.

If tires blowing, the cosmic speed of the reference plane (Earth) or other arguments are put into play, then there could be some variation.

My theory, from the facts as I interpret them in the postulated question, says that the plane is moving with reference to ambient air conditions and therefore the pilot's pitot tube would say the plane has forward velocity. If the plane's forward velocity is high enough for the pilot to choose to provide the control changes to allow the plane to become airborne, the I believe the plane will indeed leave the ground.

My opinion from how I read the posted question.

Sandy.

Carl
12-11-2005, 04:39 PM
<font face="Verdana, Arial" size="2">The F104 fighter was the closest to having a flat plate airfoil which accounts for it's very high landing speed since it was extremely stall sensitive. It also had very unforgiving handling, also because of the wing loading and nearly flat airfoil. The wing was only 4.2 inches thick at the root and 2 inches thick at the tip with a knife leading edge. The thickness ratio was only 3.4%.</font>

Evan, when you mentioned flat plate wing, I too thought of the F-104. What A beautiful, hot rod aircraft that was!

http://img.photobucket.com/albums/v35/lathefan/5333ee5b.jpg

[This message has been edited by Carl (edited 12-11-2005).]

Duct Taper
12-11-2005, 05:14 PM
http://img.photobucket.com/albums/1003/dvonborn/Sailingships.jpg

Jim Hubbell
12-11-2005, 05:47 PM
Evan, I agree that to achieve lift a wing must accelerate a suitable volume of air so that the reaction ( lift ) is in the desired direction. I was working toward the fact, as others have pointed out, that no small part of the lift is generated by the airflow over the wing. When a wing stalls, it drops. I will be happy to follow as you address this point.

The “ hot-rod “ aircraft you made mention of were fly-by-wire as no pilot could handle them for long.

Another interesting experiment during the ‘30s was a disc shaped wing. Attached by cabane struts to the fuselage it was said to be able to slow-fly quite slowly and simply settle to the ground under reduced power.

As I mentioned before, there is a lot of interpreting of the original poser going on.

Arcane
12-11-2005, 06:06 PM
Here`s a little vid clip of an airplane landing....
http://www.bordergatewayprotocol.net/~jon/humor/video/Airplanelanding.asf

sauer38h
12-11-2005, 06:08 PM
<font face="Verdana, Arial" size="2">Originally posted by Jim Hubbell:
Another interesting experiment during the ‘30s was a disc shaped wing. Attached by cabane struts to the fuselage it was said to be able to slow-fly quite slowly and simply settle to the ground under reduced power.
</font>

A regular wing does that just fine if it's large enough and/or has a section which provides gobs of lift at low speeds. The penalty for either is high drag. Hence the introduction of variable-geometry wings - high lift and high drag in one configuration, low lift and low drag at the other extreme.

IOWOLF
12-11-2005, 06:14 PM
I am surprised Mr Thomas hasn't chimed in here.
Oh wait ,I know why, becouse there is no correct answer and if he said one way or the other he May be wrong.

------------------
The tame Wolf !

sauer38h
12-11-2005, 06:15 PM
I don't know that I'd call the F-104 a flat plate airfoil. It's a stretched diamond shape, closer to a laminar-flow wing section than a plate.

In the faster jets - even something less extreme like the F-4 - the body provides enough lift to keep the thing up. The wings are just there for something to hang the control surfaces onto, and to make it possible to fly at semi-realistic landing speeds.

12-11-2005, 06:16 PM
You guys sound bored maybe too much time on your hands, Go make something in your shops and post some pictures for us to view.

Arcane
12-11-2005, 06:23 PM
Let`s not forget the most advanced flying machine of all time...
http://www.bordergatewayprotocol.net/~jon/humor/video/skycutter.wmv

Wirecutter
12-11-2005, 07:04 PM
<font face="Verdana, Arial" size="2">Originally posted by Arcane:
Let`s not forget the most advanced flying machine of all time...
http://www.bordergatewayprotocol.net/~jon/humor/video/skycutter.wmv</font>

Arcane -
I've really got to thank you for that - I knew it existed, and I even saw the plans for it in a magazine. Thanks.

-Mark

wierdscience
12-11-2005, 09:17 PM
<font face="Verdana, Arial" size="2">Originally posted by wierdscience:

Originally posted by Scatterplot:
This made for some interesting debate on another forum I'm on, hopefully we can get some good discussion going on here.

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?</font>
Of course the plane takes off,for it to move at all it must use the thrust from it's engines to push against the air behind it.The belt has no effect since the wheels aren't pushing the plane foward.

The real question is,if that plane is a Delta airlines plane then how much of the passenger's luggage will be lost? http://bbs.homeshopmachinist.net//biggrin.gif

Better question,with 160+ posts in this thread is the plane also loaded with HSM copies on Cd-rom? http://bbs.homeshopmachinist.net//biggrin.gif

andy_b
12-11-2005, 11:15 PM
<font face="Verdana, Arial" size="2">Originally posted by Wirecutter:
Arcane -
I've really got to thank you for that - I knew it existed, and I even saw the plans for it in a magazine. Thanks.

-Mark</font>

i was at the local hobby shop last night and one of these is hanging from the ceiling and for sale. didn't someone make a model of a witch on a broomstick one time that flew?

oh, as to the 747, i was thinking about it some more today. the original statement was that the conveyor speed exactly matches the 747 speed only in the opposite direction. so of course the plane can reach take-off velocity. in fact, the statement leaves open the possibility that the 747 is just flying over the conveyor, and the conveyor is moving the same speed in the opposite direction without the plane's wheels even touching it. the original statement never specifies that the plane's wheels must remain in contact.

andy b.

darryl
12-12-2005, 12:14 AM
Hmm. I'm surprised no one has picked up on my idea of the tracking problem, that is, the tires not wanting to stay on the conveyor belt. Thinking about this more, I came up with another possibility. Let's assume that the plane has attained a speed of 100 mph so far. The tires are seeing 200 mph. That's about 17,000 ft per minute. If you were to chuck a round bar or tube in a lathe, say the tube is 4 inches diameter- that's about one foot circumference, so to equal the 17000 ft/minute, this tube would have to be rotating at about 17000rpm so it's surface speed would match the 200 mph.

So here we have a 4 inch diameter pipe spinning at 17000 rpm. So far we've managed to duplicate the speed the tires see against the conveyor belt. Now we take a rubber tired idler wheel and press it against that spinning pipe. As long as it's tracking perfectly straight, it doesn't veer sideways, but the moment it goes off axis by even the smallest amount, it veers to one side. Look at this two ways- if it's castoring, it will track absolutely true. But if you run a castor in reverse, it very quickly spins around and castors the other way. If it isn't free to castor, it will veer sideways and try to carry it's load along with it. In this case, the load is the heavy 747. Because the plane is massive, it's inertia resists following the tires as quickly as the tires would want to go. The end result is that the plane would try to roll, as I suggested earlier, but before it could, the tires would have been ripped off the rims and/or erased into nubbins. The wheels would be next. It's entirely possible that the landing gear would collapse.

Check this out on your lathe. Chuck up some round stock and touch a rubber surfaced idler wheel down onto it. Start with a low rpm. See how fast it goes sideways as you vary the angle. Now imagine gearing up for 17000 surface feet/minute. For very small off tracking angles, the speed at which it veers is slower, but the more it veers, the more it mistracks, and the more it veers. Before you can compensate, it's gone.

In this case, the 747 gets to experience an exponentially increasing sideways motion. For this example, I've used 200 mph, and the plane is only going 100 mph. Increase that speed to near takeoff speed, and see if you can imagine the antics of the guy trying to steer the nosewheel.

Now somebody is going to come along and tell me that the nosewheel castors, and there will be no such problem happen.

sauer38h
12-12-2005, 12:25 AM
<font face="Verdana, Arial" size="2">Originally posted by darryl:
Now somebody is going to come along and tell me that the nosewheel castors, and there will be no such problem happen. </font>

Worse than that, all the wheels are steerable. That makes crosswind landings much less exciting - the wheels can be aligned with the runway and the plane's path, not necessarily with the plane's axis.

CompositeEngr
12-12-2005, 01:04 AM
No, there is an answer. Just not one that you believe.
You can't make the world flat just by believing it is flat.

<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
I am surprised Mr Thomas hasn't chimed in here.
Oh wait ,I know why, becouse there is no correct answer and if he said one way or the other he May be wrong.

</font>

Evan
12-12-2005, 03:35 AM
Jim said,

"I was working toward the fact, as others have pointed out, that no small part of the lift is generated by the airflow over the wing. When a wing stalls, it drops. I will be happy to follow as you address this point."

I haven't claimed that all the lift is provided by reaction to downwash, just the majority of it. When a plane is flying straight and level the forces of lift, drag and thrust are balanced. Change any one of these even a little and the flight attitude changes.

People think the elevator on a plane is used to control ascent and decent. It isn't. It is used to control the attitude of the aircraft. Whether it ascends, decends or flys level is determined by the balance of forces.

If anything happens to cause the wing to stall then some lift is lost. When the airflow over the top of the wing becomes detached some of the Bernoulli lift is lost as well as reaction lift. It doesn't matter if that is only 10 percent of the total lift, if it is lost the forces are not in balance and the attitude of the aircraft changes.

Stall is determined by angle of attack which is not directly related to aircraft velocity. I have nearly stalled a Grumman Yankee at 110 knots while pulling over three gees in a steep turn.

When the aircraft stalls it will assume a new attitude until the forces are again balanced.

The Bernoulli effect is real but is not the sole or even the main reason that an aircraft is able to fly. The majority of lift is provided by accelerating air down.

What I take issue with is that it is still claimed and explained by most supposedly authoritative sources that the Bernoulli effect is THE reason that an aircraft is able to fly. That's hogwash.

Allan Waterfall
12-12-2005, 03:43 AM
I might be wrong on this but....

If the conveyor was replaced with a rolling road type set up you would have the same result.

When a car's on a rolling road it doesn't move forward,therefore there is no forward movement through the surrounding air.
To me it follows that there would therefore be no airflow over a wing so no lift would be generated.

Allan

Evan
12-12-2005, 03:46 AM
Think skis.

SJorgensen
12-12-2005, 04:44 AM
Evan,

Your theory cuts against the grain of nearly 100 years of aeronautical knowledge.

Everyone knows that it isn't the Bernouli effect or the low pressure above the wing that keeps a craft aloft.

Only one thing is powerful enough to get any craft aloft. Nothing gets off the ground without it.

Money.

IOWOLF
12-12-2005, 06:25 AM
There is an old saying amongst R/C fliers...

"you can get a barn door to fly with enough power"

We are not talking a barn door,we are talking a 747 with no forward motion.

------------------
The tame Wolf !

12-12-2005, 06:55 AM
Haven't read the entire post but maybe the question should be, will it fly as a rocket or fly as a plane in the absence of substantial airflow over the wings? (Gawd I hope no body else said that http://bbs.homeshopmachinist.net//biggrin.gif )

Evan
12-12-2005, 09:40 AM
[This message has been edited by Evan (edited 12-12-2005).]

Jim Hubbell
12-12-2005, 01:42 PM
I am amazed at the range of assumptions this exorcise has generated. Let us think of the originally proposed setup. Then change only one stipulation. The conveyor will move in the direction of the aircraft as it starts its takeoff roll. The craft moves, the conveyor moves. As the plane reaches takeoff velocity it might be noted that the wheels have not made a single revolution. The plane will lift off. Midway between these two assumptions is, the conveyor does not run. Not much different than a regular runway and again the plane lifts off. The wheels though, are rotating at takeoff RPM. Now back to the original conveyor which moves counter to the movement of the plane. For the conveyor to move at all the plane must move. There is nothing on board the craft to indicate anything unusual as the only unusual occurrence is the wheels turning at twice normal speed. Barring any mechanical failures the plane will lift off. It really makes no difference what way or if the wheels turn. Chew on that for a while.

phil burman
12-12-2005, 02:47 PM
I can’t believe I’m being sucked into this.

Wrong, If nothing fails the aircraft will not take off. Providing the co-efficient of friction of the aircraft tires on the runway (conveyor) is above a certain value.

You have to think about forces not velocities.

The jet engine lights up and produces a certain force trying to accelerate the mass of the aircraft. This acceleration produces a change in velocity. The conveyor senses this change in velocity and starts to move in the other direction. This transfers a force to the tires on the aircraft in the direction the conveyor is moving. The conveyor increases in speed until this force equals the force generated by the jet engine, unless the tires slip on the conveyor. The sum of these forces is zero (because you have told the conveyor to increase in speed to make it is so) therefore no acceleration therefore no velocity therefore no lift. The aircraft can’t take of it has zero air speed.

If you resolve the forces you will see where the issue is. Of course you have to resolve the force related to the revolving wheel but the same force on the tire acts on the wheel axle, in the same direction. The rotating wheel is just an added complication.

I’ll bet the contents of my workshop against yours that this is correct. Any takers. Are yu feeling lucky punk.

Regards http://bbs.homeshopmachinist.net//cool.gif
Phil (Clint) Burman

<font face="Verdana, Arial" size="2">Originally posted by Jim Hubbell:
I am amazed at the range of assumptions this exorcise has generated. Let us think of the originally proposed setup. Then change only one stipulation. The conveyor will move in the direction of the aircraft as it starts its takeoff roll. The craft moves, the conveyor moves. As the plane reaches takeoff velocity it might be noted that the wheels have not made a single revolution. The plane will lift off. Midway between these two assumptions is, the conveyor does not run. Not much different than a regular runway and again the plane lifts off. The wheels though, are rotating at takeoff RPM. Now back to the original conveyor which moves counter to the movement of the plane. For the conveyor to move at all the plane must move. There is nothing on board the craft to indicate anything unusual as the only unusual occurrence is the wheels turning at twice normal speed. Barring any mechanical failures the plane will lift off. It really makes no difference what way or if the wheels turn. Chew on that for a while.</font>

[This message has been edited by phil burman (edited 12-12-2005).]

[This message has been edited by phil burman (edited 12-12-2005).]

Evan
12-12-2005, 03:00 PM
"The conveyor increases in speed until this force equals the force generated by the jet engine"

Impossible. If that were remotely the case the aircraft wouldn't take off on a regular runway. Wheels are very low friction devices, that's why they use them.

Kdahm
12-12-2005, 03:06 PM
<font face="Verdana, Arial" size="2">Originally posted by phil burman:
I can’t believe I’m being sucked into this.

Wrong, If nothing fails the aircraft will not take off. Providing the co-efficient of friction of the aircraft tires on the runway (conveyor) is above a certain value.

You have to think about forces not velocities.

The conveyor increases in speed until this force equals the force generated by the jet engine, unless the tires slip on the conveyor. The sum of these forces is zero (because you have told the conveyor to increase in speed to make it is so) </font>

Wrong. The problem states that the conveyor moves in the opposite direction AT THE SAME SPEED, not to produce the same force. As I have said, take a force balance around the plane and see what happens.

I’ll bet the contents of my workshop against yours that this is correct. Any takers. Are yu feeling lucky punk.

Regards http://bbs.homeshopmachinist.net//cool.gif
Phil (Clint) Burman

Sure, I'd be willing to bet the contents of my workshop, as long as it's the one at my house rather than the one where all of the goodies are. I don't like taking advantage, though, so no bet.

Kdahm, P.E.

[This message has been edited by Kdahm (edited 12-12-2005).]

3 Phase Lightbulb
12-12-2005, 03:08 PM
I can't stop laughing as some of these replys http://bbs.homeshopmachinist.net//smile.gif

747 moves forward 150 mph, conveyer moves backwards 150 mph, and wheels spin at 300 mph. The pilot will need a little extra throttle to overcome the wheel friction at 300 mph vs 150 mph. The 747 lifts off if there is enough elevator trim, or when the pilot pulls back on the yoke enough to create negative lift on the tail changing the relative wind angle of atack over the front wings, blah, blah, blah...

The inflight movie starts shortly after, in flight food service also starts, etc, etc. Nothing is out of the norm except a little more power needed at take off....

P.S: I have a skycutter kit (unopened) in my basement along with a Toro colored monokote kit for it. I was going to build it but never got around to it.. If anyone wants to make an offer, let me know.

plastikosmd
12-12-2005, 03:11 PM
Phil, "conveyor increases in speed until this force equals the force generated by the jet engine, unless the tires slip on the conveyor. The sum of these forces is zero (because you have told the conveyor to increase in speed to make it is so) therefore no acceleration therefore no velocity therefore no lift. The aircraft can’t take of it has zero air speed."

I dont believe you have correctly summed up your forces in your diagram. The only force that the conveyor exerts other than than the "normal force" that supports the wheel is through friction of the wheel assembly. In fact if were frictionless the jet would sit there, no matter the speed of the conveyor. Add a jet engine and you will move foreward, eg Evans frictionless skis) Try my experiment of running on a treadmill (or if you prefer sit on a creeper or something) while holding a jet engine over your head then accelerating it.. http://bbs.homeshopmachinist.net//wink.gif PS make sure to remove the wall in front of you.
scott

3 Phase Lightbulb
12-12-2005, 03:31 PM
<font face="Verdana, Arial" size="2">Originally posted by plastikosmd:
Try my experiment of running on a treadmill (or if you prefer sit on a creeper or something) while holding a jet engine over your head then accelerating it.. http://bbs.homeshopmachinist.net//wink.gif PS make sure to remove the wall in front of you.
scott</font>

IOWOLF tried running on his tredmill yesturday and forgot to turn off his webcam: http://bbssystem.com/images/smiles/newsmile_BangHead.gif

http://www.bbssystem.com/iowolf.wmv

http://bbssystem.com/images/smiles/newsmile_laughing4.gif

phil burman
12-12-2005, 03:32 PM
Ok so I've just moved my workshop contents to my neighbors garage. But in my defense I miss read the original question. Tried to make it more complicated than it was.

Maybe I should just shut up. Ye, perhaps that's best. Norman have you got any space there with matron, maybe I need a lay down.

Regards
Phil (dumb arse) Burman http://bbs.homeshopmachinist.net//redface.gif

<font face="Verdana, Arial" size="2">Originally posted by 3 Phase Lightbulb:
I can't stop laughing as some of these replys http://bbs.homeshopmachinist.net//smile.gif

747 moves forward 150 mph, conveyer moves backwards 150 mph, and wheels spin at 300 mph. The pilot will need a little extra throttle to overcome the wheel friction at 300 mph vs 150 mph. The 747 lifts off if there is enough elevator trim, or when the pilot pulls back on the yoke enough to create negative lift on the tail changing the relative wind angle of atack over the front wings, blah, blah, blah...

The inflight movie starts shortly after, in flight food service also starts, etc, etc. Nothing is out of the norm except a little more power needed at take off....

P.S: I have a skycutter kit (unopened) in my basement along with a Toro colored monokote kit for it. I was going to build it but never got around to it.. If anyone wants to make an offer, let me know.

</font>

lynnl
12-12-2005, 03:53 PM
...and the mental masturbation goes on. ..and on. http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

Hey, just for giggles let's try this scenario: It's a calm day. It's an infinitely long conveyor, that's already moving backward at the liftoff speed of the 747 (we'll say 140Kt), even before the pilot throttles up. So that in effect we have a 140 knot tailwind, and the plane moving backwards with the wheels not turning.

Now what happens when he opens the throttles?

Evan
12-12-2005, 03:59 PM
Bah. When a fly hits the windshield of your car what's the last thing that goes through it's mind?

phil burman
12-12-2005, 04:05 PM
I was just playing with my computer, onist guv. Do't know what you're doing in front of yours but it doesn't sound healthy.

Depends on whether a 747 is designed to fly backwards at 140 knots, the McD.D engines might not like it either. RR would probably be OK though.

Maybe 5 pages of unhealthy metal practices is enough.

Phil

<font face="Verdana, Arial" size="2">Originally posted by lynnl:
...and the mental masturbation goes on. ..and on. http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

</font>

3 Phase Lightbulb
12-12-2005, 04:06 PM
<font face="Verdana, Arial" size="2">Originally posted by lynnl:
...and the mental masturbation goes on. ..and on. http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

Hey, just for giggles let's try this scenario: It's a calm day. It's an infinitely long conveyor, that's already moving backward at the liftoff speed of the 747 (we'll say 140Kt), even before the pilot throttles up. So that in effect we have a 140 knot tailwind, and the plane moving backwards with the wheels not turning.

Now what happens when he opens the throttles?

</font>

A tail wind will require a longer run way and a faster ground speed. In a 140 knot tailwind, you get zero air resistance at 140 knots so the airplane doesn't need a lot of power to get to 140 knots (zero air resistance). Once the airplane starts going faster than 140 knots, it will be the same as taking off (except engine throttle/speed is higher, and wheel resistance is higher).

BillH
12-12-2005, 05:14 PM
The wheels are not providing forward motion, they are free wheeling. The Conveyor matches the airplanes speed, so the conveyor is not moving at first, apply thrust, the airplane moves forward, the conveyor starts to move, all it does is make the wheels spin faster, the airplane itself is gaining forward momentum as long as the drag on th wheels is not too great.
Now if the conveyor is moving at a great speed, perhaps its providing some wind over the wings as well? The drag of the conveyor and the wheels for the life of me can not equal more than the say... 200,000 lbs of thrust those 4 engines are generating? The airplane will take off.
As for what generates lift, I was taught in school that 75% of the lift is from the low pressure zone above the wing and the remaining 25% was from wind deflection. Take that as AOA if you want. Oh and a fully symetrical wing, apply a tiny bit of positive AOA, guess what? You created a Low Pressure zone above the wing, you get lift. Lot of you seam to get confused on the application of the basics. For instance, "A fully symetrical wing provides just as much lift if the airplane is flying upsdie down as is right side up, therefore AOA creates all the lift" Ehhhh no.

Evan
12-12-2005, 05:59 PM
Bill,

I recommend this page which is partially funded by NASA. It describes clearly how a wing provides lift and what is wrong with the common explanation that relies on the Bernoulli Principle.

http://www.allstar.fiu.edu/aero/airflylvl3.htm

Scatterplot
12-12-2005, 07:56 PM
Wow, this thread is doing well. http://bbs.homeshopmachinist.net//smile.gif.

Could someone define "platinum" and "double platinum" for me though?

And you know, I actually haven't quite gotten around to signing up for the magazine yet... http://bbs.homeshopmachinist.net//wink.gif

hsmike
12-12-2005, 09:16 PM
I don't get it. If your running on a treadmill and hold your hand out, I really dont think your going to feel a breeze. I can't seem to get over 50 mph though.
No way is that plane going to take off...

snowman
12-12-2005, 09:27 PM
I think I'll have to go down and find my dowsing rod so I can find some water while I wait this thread out.

-Jacob

mochinist
12-12-2005, 09:33 PM
<font face="Verdana, Arial" size="2">Originally posted by Evan:
Bah. When a fly hits the windshield of your car what's the last thing that goes through it's mind?</font>Its asshole of course.

Jim Hubbell
12-12-2005, 09:36 PM
Evan, thank you for the link to Dave Anderson’s article on dynamics of lift. He makes very clear that which you and I agree on regarding lift in flight. I do note he states the top of the wing has more to do in diverting the air than the bottom does. This is mostly due to the Coanda effect and is lost when said effect breaks down. The Coanda effect is pulling ( sucking ) at the boundary layer which when stressed past a certain point no longer holds. The immediate result of this breakdown is a dramatic loss of lift ( stall ). I still think Bernoulli can be worked in there somehow though not with the same old tired diagrams.

Scatterplot
12-12-2005, 09:54 PM
<font face="Verdana, Arial" size="2">Originally posted by hsmike:
I don't get it. If your running on a treadmill and hold your hand out, I really dont think your going to feel a breeze. I can't seem to get over 50 mph though.
No way is that plane going to take off...</font>
The conveyor will not impede the jet's motion... your legs push against the conveyor to move, while the jet pushes against air (which it will do with or without the ground moving in under it)

mochinist
12-12-2005, 09:57 PM
<font face="Verdana, Arial" size="2">Originally posted by snowman:
I think I'll have to go down and find my dowsing rod so I can find some water while I wait this thread out.

-Jacob

</font>

Ha ha now that was a classic thread at the PM site

snowman
12-12-2005, 10:01 PM
Just be careful that the plane isn't made by ford and has firestone wheels. One of those wheels is gonna blow and cause the plane to flip over...boy would that be a mess!

Jim Hubbell
12-12-2005, 10:13 PM
Hsmike,
Ya got to hold both hands out a little farther!

hsmike
12-12-2005, 10:24 PM
Jim-- Did you see MOCHINIST's video? on page three I think. I ain't lettin go, besides if it does work I only have 8 Ft ceilings.

sauer38h
12-12-2005, 11:26 PM
<font face="Verdana, Arial" size="2">Originally posted by Jim Hubbell:
Evan, thank you for the link to Dave Anderson’s article on dynamics of lift. He makes very clear that which you and I agree on regarding lift in flight. I do note he states the top of the wing has more to do in diverting the air than the bottom does. This is mostly due to the Coanda effect and is lost when said effect breaks down. The Coanda effect is pulling ( sucking ) at the boundary layer which when stressed past a certain point no longer holds.</font>

That page is a mix of confused thinking and hand-waving - not unusual when NASA money is being sloshed around. These guys have other views of lift vs. Coanda effect, and are more entertaining -

http://www.av8n.com/how/htm/spins.html#sec-coanda-fallacy

though I don't believe either of them has it quite right, either.

Rustybolt
12-12-2005, 11:41 PM
Still doesnt explain how a sailboat can sail into the wind.

phil burman
12-12-2005, 11:46 PM
Does this mean even NASA doesn't have the technology to explain why a 747 can fly. God help us all. No wonder I drink when I fly. But then again I don't need to fly to drink. Nar... it's much easier to blame NASA.

By the way if we keep this crap going for a few more posts it's going to be a record. The meaning of life would have been more commendable but then NASA probably doesn't have a clue in that direction either.

Phil

<font face="Verdana, Arial" size="2">Originally posted by sauer38h:
That page is a mix of confused thinking and hand-waving - not unusual when NASA money is being sloshed around. These guys have other views of lift vs. Coanda effect, and are more entertaining -

http://www.av8n.com/how/htm/spins.html#sec-coanda-fallacy

though I don't believe either of them has it quite right, either.

</font>

3 Phase Lightbulb
12-12-2005, 11:54 PM
<font face="Verdana, Arial" size="2">Originally posted by Rustybolt:
Still doesnt explain how a sailboat can sail into the wind.</font>

Sailing up wind is possible because lift off the sail is pulling you to the side and sligly angled forward. The more you angle yourself directly out of the wind line, the more the lift off the sails starts pulling you in the direction your moving.

If you're on a pair of roller skates holding onto a rope and someone directly to your side starts pulling on the rope, you're going to fall over. If they are to your side but just a little bit ahead or behind you, it will both try to pull you over, and a little forward, or backward.

Same with sailing.. If you're sailing directly into the wind at zero degres relative to the lift angle off the sail, then the lift your getting is not going to move you, but once you angle a little bit you will get side lift and a little forward lift. With a keil, some of that side lift is transfered into forward movement (Like jumping on a skateboard and having it slip out from under you).

[This message has been edited by 3 Phase Lightbulb (edited 12-12-2005).]

sauer38h
12-13-2005, 12:12 AM
<font face="Verdana, Arial" size="2">Originally posted by phil burman:
Does this mean even NASA doesn't have the technology to explain why a 747 can fly. God help us all.</font>

No, it means that the fact that NASA chipped in doesn't by itself mean it's any good.

And, of course, NASA doesn't have to know why it flies. Boeing has to know why it flies. NASA doesn't design anything, NASA just farms out money, not all of which goes to anything worthwhile....much like any other government program.

Evan
12-13-2005, 12:34 AM
"That page is a mix of confused thinking and hand-waving - not unusual when NASA money is being sloshed around. "

Well, that same confused handwaving is how new aircraft are designed by way of computer simulation. They (aircraft) usually work these days, unlike in earlier times.

As for sailing into the wind what Adrian failed to mention is that the forward speed of the sailboat changes the direction of the apparent wind. When sailing on any point into or across the wind this both changes the apparent wind direction and increases the apparent wind speed. The lift of the sail is a function of wind speed by the square of the velocity so this has a big impact on the force the sail produces.

On a close hauled reach (into the wind) the sail is pulled in tight to the long axis of the boat and the force generated is nearly at right angles to the keel. The keel is also an airfoil and produces lift in the water in the exact same manner as a wing in air. The fluid dynamics are the same in water as in air at subsonic velocities. At velocities less than about mach .6 air is treated as an incompressible fluid for the purpose of calculation. That is exactly how I generated the symmetrical airfoil on a computer to design the leeboard for my canoe. I used the same math as for a wing in air.

The sail produces force in the direction away from the wind and the keel translates that to force toward the wind.

The force vector generated is a combination of the force of the sail and the keel with the resultant being the direction the boat actually moves toward the wind.

sauer38h
12-13-2005, 12:59 AM
<font face="Verdana, Arial" size="2">Originally posted by Evan:
The keel is also an airfoil and produces lift in the water in the exact same manner as a wing in air.</font>

Only if the boat's turned turtle. When wet it's a hydrofoil.

Norman Atkinson
12-13-2005, 01:39 AM
A quicky to Phil!

And I thought that I was the village idiot!
I have never ever read so much about so little. What is left of a great mind simply boggles.

At the present moment I have not really entered into this. All my efforts are being concentrated on trying to get Matron to take off. She's a big woman, Big, BIG.
I usually like em big but there is a critical mass. Matron, Phil, is a critical mass.

A million years ago when Matron was just a slip of a girl- or something like that, I gazed at a fiendish contraption which had come of the USS Missouri. 1949, I would guess. What was left of the Battle of Britain aces and the sheer might of the Bomber Harris's crews gathered around to pass considered judgement. The hallowed turf of one of aviation's most famous airfields contained this Thing. Being only small fry, I kept jumping up and down to see this heap of scrap iron over the wise old heads assembled.

With a clatter and a bang, this monster started to vibrate- and whir about. The throng was ushered back further and further and the noise increased. Suddenly, it began to lift- and it took off. All the wind of its rotor things was sucked into gaping heroes.

The first helicopter had taken off! Off course, it would crash before it left the edge of the airfield. The crash tender was already ringing its bell. The guys were in their asbestos suits egging it to fail.

Now, it or its successors, can be still seen in ever increasing numbers.

So, gentlemen, you will forgive me for not participating. Apart from the excitement with Matron, I have seen it all before!

Norm.

12-13-2005, 11:09 AM
Anybody worried about this thread hitting 300? If a topic about going nowhere is the single most popular topic do we all have to change our login names to save face or just hang it all out there for all of cyber space to see? http://bbs.homeshopmachinist.net//biggrin.gif

"This car climbed Pikes Peak"
"I survived the Blizzard of 77"
"I'm a member of the Fly United Mile High Club"
"I participated in a cyber thread going nowhere"

We might have a problem on our hands http://bbs.homeshopmachinist.net//biggrin.gif

Evan
12-13-2005, 11:20 AM
"Only if the boat's turned turtle. When wet it's a hydrofoil."

The leeboard on my canoe swings out of the water. Then it's an airfoil. http://bbs.homeshopmachinist.net//biggrin.gif

Rustybolt
12-13-2005, 11:34 AM
The more you angle yourself directly out of the wind line, the more the lift off the sails starts pulling you in the direction your moving.

If such were the case, the best sailing position would be when the wind is off the beam.(side)

The best sailing position for most cat rigged(Schooner)sailboats is a few points off the wind.(wind from directly ahead) They are least efficient when the wind is from the stern.(directly behind)

Norman Atkinson
12-13-2005, 11:59 AM
YOD!
I am a member of the Rockall Golf Club and a founder member of the Romney, Hythe and Dymchurch Mountain Rescue Team.
It's a forerunner to having sex standing up in a hammock!

Open the cage

Norm

Beware of Spurious Imitations!

Jim Hubbell
12-13-2005, 12:24 PM
Even at its strangest this bbs is many magnitudes more interesting and entertaining than most that I have looked in on. Everyone is free to pass by an odd topic. Sometimes truth arrives amid chaos. But then again the naysayer and ornery cuss will add to the length and possibly uncover an interesting point. So I say it’s a great bunch that post here and I am humbled by but gladly partake of the knowledge so freely given out.

Norman Atkinson
12-13-2005, 12:49 PM
Who said it was free?

This is the stuff that Doctors of Philosop- how do you spell it?- Phil(well, something) get all those fancy hats and things trimmed with vermin!

This me, old son, is the Sink Tank of the Western Union-er World! we have people here with all sorts of shades- sunglasses- and that, who are prepared to make spectacles- of themselves.All in the cores of sci- well something like that!

Have you any idea just how much this is costing us in ti- er, Alcohol? It's all got to carefully, carefully??? Bugger, lost me thread- and me trousers keep falling down.

Norm.

Carl
12-13-2005, 02:38 PM
If you think we are good at this sort of internet nonsense, click on the logo below:

http://www.urinal.net/urinal_logo.jpg (http://www.urinal.net/)

Norman Atkinson
12-13-2005, 03:51 PM
I still that we should all stand up to the challenge.Face our destiny and take our courage in both hands. Let us shake defiance as liberal peers in this, the greatest debating chamber. Let us not stall in our efforts and closet ourselves from our true destiny. Even that great humourist, W C Fields took part in the Bank Dick. It may be stretching things a bit but he never took part in Chevallier's Clochemerle. Of course, we have read the book in the original French. A bit old, 1934 but it deals with the erection- and I use the word advisedly- of an edifice in the village of Clochemerle. There are problems- as all French f-arses have and M.Le Maire is none other than Pie-chut. Pronounce it as you will. Finally, the edifice raised to the three cardinal virtues of all things Gallic- Gallic-Non, non. ( The P is silent as in Bath) Liberte, Egalite and Maternite. Ironically- as French pissoirs are- M.Le Maire has to don his red, white and bleu sash, Frock( no, no, he was far from queer) coat and inaugerate the thing. Despite, the off stage cavorting, he has prostate problems and finally, he released back from Mayoral to more common affairs.

I did want to write about one of my long departed mentors who had a Masonic meeting in the gentlemen's toilets in Kings Cross Station in London. As he was sitting with his Brothers, on and around the Throne of Solomon attired in his best dinner suit he spied up the makers name on th jacket. The trousers were somewhat further away but the name tab said "London, New York and British Museum" I missed the rest of the story as
the actual architect of Kings Cross and its attendent facilities was non other than my wife's great uncle, John Dobson.
Happily, Queen Victoria was present at the opening. In fact, she did it, never missing an opportunity.

What happened at Water-loo, we must ask Napoleon who had his balls pickled in St Helena.

Then the story of Queen Victoria's grand daughter at a certain Royal Air Force Station. The lady may well have passed away but the memory of her is still preserved.
Sort of the anals of Royal Air Force history.

A bit for the Internet?

Norm

Jim Hubbell
12-13-2005, 04:09 PM
HEAR HEAR ! !

glenj
12-13-2005, 04:17 PM
If it's not too late to join the silliness, consider the following...

Picture the 747 on the magic conveyor belt runway and a cable tied to the front landing gear strut. This cable is 3km long and tied to a very large tree in front of the 747 at the far end of the magic conveyor belt and it is pulled tight. Lets say someone turned on the conveyor belt and it was soon up and running with a surface speed of 100km/h. There would be some additional tension on the cable but only due to the friction caused by the tires and bearings. So we have a 747 being held in place by a lightly tensioned cable and a conveyor belt running at 100km/h turning the 747's tires at 100km/h. The 747 is not moving relative to the tree at the end of the runway nor the air surrounding it. Now, lets say the conveyor belt was set to 200km/h or even 300km/h. Other than a small (relative) increase in cable tension we still have a 747 at rest and some furiously spinning tires.

Now, lets say the pilot fires up all 4 engines and they spool up, generating a good deal of thrust. What will happen to the previously force balanced situation? If the thrust of the engines is great enough to just overcome the tension in the fixed cable the 747 will roll slowly forward (relative to the tree and the air) and the cable will go slack. If the engines are capable of generating thrust far exceeding the tension in the cable (which I imagine they are) then the 747 can and will accelerate down the runway (relative to the tree and air) and once it reaches take-off (air) speed it will become airborne...although not for long unless they get rid of that pesky cable and assuming they clear the tree that is.

3 Phase Lightbulb
12-13-2005, 04:31 PM
<font face="Verdana, Arial" size="2">Originally posted by Your Old Dog:
Anybody worried about this thread hitting 300? If a topic about going nowhere is the single most popular topic do we all have to change our login names to save face or just hang it all out there for all of cyber space to see? http://bbs.homeshopmachinist.net//biggrin.gif

"This car climbed Pikes Peak"
"I survived the Blizzard of 77"
"I'm a member of the Fly United Mile High Club"
"I participated in a cyber thread going nowhere"

We might have a problem on our hands http://bbs.homeshopmachinist.net//biggrin.gif</font>

Hey, I almost built an entire plow last weekend from scratch.. I can afford to participate in a "cyber thread going nowhere" and not feel useless http://bbs.homeshopmachinist.net//smile.gif

Also, IOWOLF has set the bar so low, it's almost impossible for anyone to feel useless around here http://bbs.homeshopmachinist.net//smile.gif

Norman Atkinson
12-13-2005, 04:51 PM
Making a plough? Are you going to try to stop this Immaculate Deception- or something- from taking off?

Bloody Luddite- what are you. Here are these wonderful people planting trees at the ends of runways and miles and miles of wire- and you want to have a Harvest Festival and sing "We plough the fields and scatter". Give the- shush- idiots a chance!
Ta!

Norm.

IOWOLF
12-13-2005, 04:54 PM
Adrian, You are a dick ,and a punk,You have more money than brains,and if anyone has doubt, think about this.... Who would put a manual pump jack on a lightweight snowplow when you can drill 3 holes and move it manually lock it with a pin quicker,easier and alot less effort.And you want to put 2 on this thing.What a moron.

But if you want to further attack me watch your self, you may get a package from an admirer.

BillH
12-13-2005, 05:00 PM
<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
...Who would put a manual pump jack on a lightweight snowplow when you can drill 3 holes and move it manually lock it with a pin quicker,easier and alot less effort.And you want to put 2 on this thing... </font>

Thats how the plow on our john deere was. Wish it was hydralic powered from where I sat though, some 140's had that.

IOWOLF
12-13-2005, 05:08 PM
And that makes it right? NO

3 Phase Lightbulb
12-13-2005, 05:14 PM
<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
Adrian, You are a dick ,and a punk,You have more money than brains,and if anyone has doubt, think about this.... Who would put a manual pump jack on a lightweight snowplow when you can drill 3 holes and move it manually lock it with a pin quicker,easier and alot less effort.And you want to put 2 on this thing.What a moron.
</font>

The \$20 3-TON long-ram jacks provide many functions:

#1 They are there just to piss you off.
#2 They provide upper support for the snow blade (long rams will be angled upwards above the A-frame)
#3 They are there just to piss you off.
#4 They provide easy Horizontal angle adjustment
#5 They are there just to piss you off.
#6 They can also provide limited Vertical angle adjustment.
#7 They are there just to piss you off.
#8 The Long rams are easily removable and useable for other tasks when I don't need the plow.
#9 They are there just to piss you off.

<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
But if you want to further attack me watch your self, you may get a package from an admirer. </font>

Thanks in advance for the package. I hope it will contain something useful, but I'm sure it will be a dud knowing the source...

IOWOLF
12-13-2005, 06:23 PM
But you wasted your money as usual, this makes me happy. http://bbs.homeshopmachinist.net//smile.gif

3 Phase Lightbulb
12-13-2005, 06:35 PM
<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
But you wasted your money as usual, this makes me happy. http://bbs.homeshopmachinist.net//smile.gif</font>

You're right.. For \$15 more I think I could have gotten the 6 TON rams.

Joel
12-13-2005, 07:14 PM
Ok, you don't like each other. We get it already.

3 Phase Lightbulb
12-13-2005, 07:25 PM
<font face="Verdana, Arial" size="2">Originally posted by Joel:
Ok, you don't like each other. We get it already.</font>

The only thing I don't like about IOWOLF is he's the Omega. He whimpers and whines with his tail between the legs.

IOWOLF
12-13-2005, 07:28 PM
At least I have something there,A Penis, not a *****, like you Adrian.

wierdscience
12-13-2005, 07:58 PM
Ooh oooh...let me try!

Lets say you have a conveyor belt a block long.Adrian is on one end with his plow and Iowolf is on the other.Now lets say the belt is moving 100 mph towards Adrian,how long will it take Iowolf to get p--ed off at Adrian? http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

Wirecutter
12-13-2005, 08:18 PM
<font face="Verdana, Arial" size="2">Originally posted by Evan:
Bah. When a fly hits the windshield of your car what's the last thing that goes through it's mind?</font>

His butthole. C'mon Evan. More jigawatts. http://bbs.homeshopmachinist.net//biggrin.gif

Wirecutter
12-13-2005, 08:36 PM
Wow. Double platinum. I think we just got there before the Matron got up off of Norman so he could amuse and confuse us here. Now 3 Phase and IOWOLF are at it. It just feels like home.

Scatterplot: Platinum = 100 replies

You know the rest.

It's great to see that the gang's all here. I think we've heard from most of the regulars, with the exception of the poster-formerly-known-as-ibewgypsie.

I'd just like to thank the members of the academy, and wish everyone a happy retail season. Cheers!

-M

mochinist
12-13-2005, 08:49 PM
<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
At least I have something there,A Penis, not a *****, like you Adrian.</font>
Are you talking about what you ate last night IOPUPPY?

12-13-2005, 09:27 PM
<font face="Verdana, Arial" size="2">Originally posted by Jim Hubbell:
Even at its strangest this bbs is many magnitudes more interesting and entertaining than most that I have looked in on. Everyone is free to pass by an odd topic. Sometimes truth arrives amid chaos. But then again the naysayer and ornery cuss will add to the length and possibly uncover an interesting point. So I say it’s a great bunch that post here and I am humbled by but gladly partake of the knowledge so freely given out.</font>

Read your post three times Jim. Very well put and my sentiments exactly. It's what keeps this forum head and shoulders above the rest in my book.

BillH
12-13-2005, 09:37 PM
<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
And that makes it right? NO</font>

IOWOLF, The plow on our tractor was how you described, a few holes for the angle adjustment and a pin that locks it in place.

spope14
12-13-2005, 09:38 PM
Yes, the plane will take off. Automobiles are dependent upon the wheels for propulsion, thus the power drive is direct to the treadmill. Aircraft however, are not at all dependent upon the wheels for propulsion. Ther actual item being propelled is one step in the chain removed from the treadmill. The plane moves forward irregardless of the treadmill moving, the wheels just move faster in relation to the speed of the treadmill, and the wheels only act as a spacer between the aircraft and the ground to in effect keep it up off the ground.

Now, if the plane was landing, brakes are involved in the wheels, and a treadmill working in the opposite direction or the same direction of landing would then have effect.

Hey, am I a regular?

BillH
12-13-2005, 09:40 PM
As for the banter and romper room antics on this forum, I enjoy watching it. Just shows there are many personalities on this forum and when some clash it can be quite humorous, as long as it stays humorous and doesnt spill outside of this forum.

darryl
12-14-2005, 01:51 AM
'plane is not dependent on the tires for propulsion'- true. 'tires act only as a spacer to keep the plane off the ground' basically true, but add in here that they reduce the impedance to forward motion. They still do that even if the conveyor belt is moving backwards. But the tires will do one more thing- they will act like keels. Consider a canoe on a river. Head upstream. As long as you keep your heading dead on to the current, you can track straight up the current. The moment you skew sideways a bit, you begin to have to fight to keep your heading. If you don't fight, the canoe will start to swing around unless or until it is going downstream with the current. At that point you can more easily swing the canoe around in circles. If you were on a motionless lake, you can gain speed but nothing except your own paddling will skew the canoe around. I'm leaving wind out of the picture because it's a needless complication in my analogy.

The moving conveyor belt is the flowing current, and the plane's tires are the keels. The plane will not track in a stable manner without the tires being steered. Bear in mind that the tires are heading into a nearly 400 mph oncoming 'current'. The poor saps on the plane are dead meat. Maybe they have a chance if Mario Andretti is steering- I still won't be getting on that plane.

Here's another way that many of us could check out this action. Line up your bicycle with the treadmill, and put just the front wheel on the belt. Crank up a bit of speed, now play with the steering. What happens?

[This message has been edited by darryl (edited 12-14-2005).]

Norman Atkinson
12-14-2005, 02:48 AM
Darryl,

I'm a bit concerned about you being out there in a canoe. You really haven't much of a clue about canoes and how they work. It's no good insisting upon Maritime law, sitting out in the middle of the pond with two black balls stuck on a paddle- one above the other. These crazy lot will kill you in what is left of your prime.

And-yes- putting your black balls, one above the other is a sign of distress.
Just bringing up an element of safety- nothing more. One of us has a problem- haven't you- I*****?

Norm

Jim Hubbell
12-14-2005, 03:17 AM
Darrel, As to steering the plane at 400mph or even 200mph , yes it would be tricky chore. But it is my understanding that the steering is a steer-by-wire arrangement which does away with human error to a great extent.

The front wheel of a bicycle on a tread mill, operated at about 5mph, would be easily “ridden” in place. Staying within a normal speed range it should be no problem to keep it on track.

darryl
12-14-2005, 03:30 AM
Well, Norm, the last time I was out in a canoe I had a merree-ol-time and I do thinks me balls were black. It was midnight after all.

Thanks for the safety warning. I'll be keepin me eyes open just in case there's a paddle looking for me nuggets. Who'll be swingin it, I dinna nae, but black balls in the daylight, now that'll be a killin. Me. And one above the other, now that'll be a distressin to take a dishankerin ta. Doffin me boffin to ya.
ergo de brut, vin en gestoad, vlat den shend bit seissen en mesqean. OUszzen blot weden shep ooneierware es shetten. diharreaan dan verb espeken nonunden shtanded. Behyonden mon comphereenshen. Vot ee say? Alotten de ghreeckenschpechen.

John@JCDLESales
12-14-2005, 03:50 AM
AC is going nowhere except off the end of treadmill until you get 160 KIAS worth of air flowing over the wings and you could run 115%N1 until the cows come home.

Norman Atkinson
12-14-2005, 04:05 AM
Absolutely splendid rendition which would give credit to Billy Connolly. My compliments but what Alistair would say is questionable. After all, I'm a Geordie which is a Scotsman with his brains kicked in.

The German is a singular delight. I am sort of missing my trips across and down into Austria. There is a little Austrian Church nestling at the head of a quiet valley. Have a look. Google into- I think- Musicholiday.com in Berwang.Have a look at the 2002 course. Next to Cynthia Gee, extreme left with clarinet is an old gent in blue. Cynthia was Princess Anne's housemistress at Benendon. My better half is there- keeping well away- appears in shades elsewhere- with clarinet.

No canoeing now. Too old. The mountains are still there and over is home. Look up- webcam Les Arcs 1800- Oh, Yes!

Have fun

Norman

darryl
12-14-2005, 04:54 AM
Yet another possibility? Suppose the plane does take off. Nobody said the conveyor belt would stop or anything else, just that it would match the plane's speed, albeit in the opposite direction. Well, once the plane gets up to 30,000 ft, the conveyor belt has reached supersonic speed, and sends a supersonic standing wave across the airfield. Amid broken glass, the flight controllers have ordered the plane to return to the airport, in order to slow the conveyor belt and save the town.

The astonished onlookers see the conveyor belt rip up the runway as it twists around to match the direction the plane is turning. After all, it has to match the speed of the plane, but in the opposite direction. It keeps skewing around, tearing up more and more real estate, demolishing about ten square miles of land including the airport buildings. It comes to rest in the same position that it started from. Those who survive the destruction see the plane on it's approach. It comes in, touching down on the conveyor belt, which is of course moving pretty quickly to match the landing speed of the 747. As the tires touch down, they screech and howl wildly, then they all explode. (don't tell me they can take that kind of punishment without throwing a tantrum) The plane has come in heavy with fuel since their trip had been cut short, and that fuel now ignites (Hmm, am I obsessed with fire or what) and blows the livin fecal matter out of everything that still has some in it.

After one heck of a day so far, the conveyor belt finally comes to a stop, it's task completed. There will be no more flights that day.

Norman Atkinson
12-14-2005, 05:24 AM
Darryl!

On second thoughts- Stick to canoeing!

Cheers from someone else who is up the Creek without a paddle.

Norm

darryl
12-14-2005, 05:32 PM
At least if I'm canoeing, there's plenty of water about to put out a fire.

Kansas_Farmer
12-14-2005, 06:57 PM
Darryl, you owe me a new keyboard!!!! For some reason it didn't appreciate the mouthful of adult beverage your post applied to it.

LOL

darryl
12-14-2005, 08:17 PM
Sorry about the jeyboard, KF. I guess it's all just physics, in this case it's sudden acceleration and decceleration of rye and coke. Did any of it overshoot the keyboard? In comes the fire trucks with the handywipes http://bbs.homeshopmachinist.net//smile.gif

[This message has been edited by darryl (edited 12-14-2005).]

Daminer
12-14-2005, 08:43 PM
The 747 will accelerate normaly relative to the air and the non-moving portion of the surface.....
however, since the conveyer/runway is accelerating opposite to the 747's direction, the maximum tire speed (relative to the "conveyer") will be exceeded before takeoff AIRSPEED is achieved.....
The plane will then collapse onto the moving conveyer and lose airspeed, ergo, no takeoff.....
That's my story and I'm sticking to it.....

Jim

spope14
12-15-2005, 10:18 PM
It is all the same theory as a car hydroplaning on a road. The plane takes off, the wheels are like the water on the road. All the wheels do is hold up the plane off of the runway - creating a space so to speak between one moving objact and another. The water or the space between the moving objects renders the movement of the bottom item - say the treadmill, and the top object - the plane under power - this renders the relative movement between the objects to zero related force vectors, or into relative insignifigance of the problem.

The wheels act much like the water in hydroplaning.

The same idea is found in terms of ice on a road. The ice renders the road surface - or in this case the treadmill insignifigant in terms of stopiong or starting the item into movement. The only thing different in this situation is that ice does have traction, but if this were absolute non-slip ice, then the item above the road - say the wheels of a car, and the road are NOT in contact directly.

The wheels are the ice or water factor. The plane under power is not in direct contact with the treadmill, the wheels theoretically are free moving in any direction all said and done in this example. The plane itself is the directly powered object. The treadmill in itself is the second directly powered object. The wheels act as the "Ice" or the water, thus negating any force vectoring between the moving objects but for the friction that might be otherwise be generated should a third factor such as braking or wheel friction be introduced.

Simple force physics, or from my Mechnics textbook I used to draw this example from.