OT - View inside the A380 office

[PeteF]

As much as I'm not keen on constant OT threads, I know there are a lot of people here who are also interested in aviation, so thought some may be interested in this.

http://www.gillesvidal.com/blogpano/cockpit1.htm

Pete

[Evan]

I'm getting a "Loading failed".

Maybe you can answer a question. The 380 and many others fly directly over us every day. The 380 is LOUD in cruise flight. It's much louder than other aircraft such as the 747-400. Sometimes when it shows up it almost produces a sonic boom. I have heard many sonic booms from high flying aircraft as when I was a teen we lived under the flight path of the test flights of the XB-70. The 380 will announce it self with a sudden loud rumble that sounds like it is just under mach 1.

Have you heard anything about this?

[krutch]

So...it flies with a video joy stick? Must be for these kids that grew up with one in their hands. I like the panic grab handle by the window, is that the emergency exit?
Interesting show though. I know I wouldn't want the responsibility of that job!

[Carld]

Nice :D , so it's a cockpit if men are flying so is it a cuntpit if women are flying it.:eek: :rolleyes:

[PeteF]

I'm getting a "Loading failed".

Maybe you can answer a question. The 380 and many others fly directly over us every day. The 380 is LOUD in cruise flight. It's much louder than other aircraft such as the 747-400. Sometimes when it shows up it almost produces a sonic boom. I have heard many sonic booms from high flying aircraft as when I was a teen we lived under the flight path of the test flights of the XB-70. The 380 will announce it self with a sudden loud rumble that sounds like it is just under mach 1.

Have you heard anything about this?

G'day Evan, how did you tell it's an A380 producing the sound? I didn't think there was too many flying in to North America and I was trying to imagine who would be flying over you and where they'd be going.

I fly the A330 which is reasonably similar on the flight deck (as are all Airbus by design) and we're slower than the 747. I think the A380 cruises around M0.85 which is similar to the 747, so all well below M1.0

On approach the A380 is very quiet, typically each generation of engine becomes both more efficient and quieter. So the bottom line is I haven't heard anything about this and am very surprised.

Krutch, yes it flies with a sidestick, it seems odd but doesn't take long to get used to it. The main thing is it takes minute control inputs so it's easy to over-control at first. The handle by the window is different on the A330, ours it opens the window, it does look like an alternative emergency exit on the A380. I seem to recall it's part of the certification process to have at least 2 exits available, the door is one, and the windows would be another.

Pete

[Your Old Dog]

This is disgusting. I'm still trying to learn ViaCad !!

[Evan]

G'day Evan, how did you tell it's an A380 producing the sound? I didn't think there was too many flying in to North America and I was trying to imagine who would be flying over you and where they'd be going.


We live under the main route to Europe. Williams lake is the navigation point to set up for approach into Vancouver as we have a VORTAC located here as well as a runway that can handle anything that flies in an emergency. Our runway is a little over 7000 feet but with the very well maintained overruns it is nearly 14,000 feet.

Vancouver is fully equipped to handle the 380. The main clue that it is a 380 is the contrails. The 380 leaves 4 distinct contrails that do not merge for a very long distance behind the aircraft. The schedule is two flights per day, one east to west at about 3 to 4 pm with another about 30 minutes later heading east from Vancouver. It would appear that gate 43 has just been cleared for the incoming flight based on the time differences. That will also ensure that the airport doesn't experience an overload of passengers since one 380 full will have just left before the next arrives.

[PeteF]

Ok, I've only flown into Vancouver once, though spent 3 months there, so I'm not familiar with the airspace, but can picture where you are. If it's that close to arrivals/departures you're talking about I can't imagine the noise is any trans-sonic effect. I'll try to grab some charts and work out roughly what speed they'd be doing around where you are, but I'd imagine less than 250 kts if below 10,000 ft. Even though I also hold a Canadian commercial licence I can't recall the restrictions there off the top of my head sorry.

Do you know who regularly flies an A380 into YVR? SQ?

[Evan]

They are still at cruising altitude here. Straight line distance to Vancouver is about 350 kilometres.

Operators could be Air France and Lufthansa.

[PeteF]

Ok, well sorry then no idea what the sound is then. Occasionally I bump into "official" Airbus people and will keep your question in mind for them. I know the aircraft is SUPER quiet inside though!

[Evan]

It almost sounds like the old Tupolev Tu-154 which was very loud and very fast. When I hear it coming it is already overhead. I don't hear the incipient boom every time but it is always loud. Sometimes they throttle down to begin decent into Vancouver so I know that's where they are headed.

This is our airport. It was built in WWII as an alternate for the US Military. The runway is 4 feet thick. It is also an alternate for the Shuttle since when it lands at Edwards it flies not far to the west of us on reentry. If they had to do an abort once around and couldn't make it to Edwards this is on the list in part because this airport is very easy to secure. It's on top of a plateau with only one way up.

Think you could land here in a pinch? :D BTW, it's uncontrolled.


http://ixian.ca/pics7/wlairport.jpg

[A.K. Boomer]

Boy Id like to sit my fat little ass down in those seats - get some ceiling and "wag the tail on that dawg" :p Just kidding....


Unreal "office" Pete, I could barely find the cup holders - What a checklist you guys must have to go through -
People would become a little more patient in understanding slight delays if only they could see a pic of that cockpit...

I was just trying to figure out what those dome like structures were in the middle of the console when I realized the letters above them and concluded they are just a hand rest to keep stability...

[PeteF]

I see what you mean about the clearway Evan!

Trust me the cup holders get well used, they're just behind the tiller and normally contain cups full of bad coffee :p

Regarding the checklists, remarkably enough they're getting smaller with each generation of aircraft. Likewise people are generally so computer literate these days the Flight Management Computers are now produced with QWERTY keyboards instead of the old "seek and destroy" ABCDEF style. How times change 'eh.

Yes if only people had even the remotest idea of what goes on behind the scenes of getting them from point A to point B; from the people who design and built the aircraft right down the chain. Instead it's all about buying a ticket for half the cost of what their taxi ride to the airport costs in a clapped out Ford Falcon with half a million miles on it, and then bitching like they're just had their first-born taken if they don't get their first choice of meal :rolleyes:

[Evan]

So what happens when an aircraft the size and weight of the A-380 is cruising along at maximum cruise heading south west and suddenly encounters the northeast flowing Jet Stream at FL300 or so? Temporarily it can add 100 knots or more to the IAS. We are located where the Jet stream is very frequently overhead.

Talking about times changing the last time I flew on an A320 was in 1997 coming back from Europe. We were flying in the frontmost seats and the captain had left the door open during the flight. I wandered up to the door and asked if I could observe for a while and he invited me in to chat. Saw some beautiful noctilucent clouds on the way over the greenland icecap.

[J Tiers]

Dunno about Evan's noise, but which twin engine widebody (or engine type) is the one that has the very loud "throaty whine" during takeoff and climbout from the airport?

We are near the airport, about 4 or 5 miles, and when one particular type of aircraft passes over after turning south, it is much different sound than most others.

Most have a typical roar, this type has a whine superimposed on that. Not the old time "jet whistle" sound, like some executive jets, it is a much lower tone.

[A.K. Boomer]

Talking about times changing the last time I flew on an A320 was in 1997 coming back from Europe. We were flying in the frontmost seats and the captain had left the door open during the flight. I wandered up to the door and asked if I could observe for a while and he invited me in to chat. Saw some beautiful noctilucent clouds on the way over the greenland icecap.



It makes you realize all the cool stuff that we've lost since 9-11,

all the changes we've had to make and most are in the form of becoming more robotic and less human.

[lakeside53]

We sure have.. In 1991 I sat in the right seat of BA 747 for an hour as we went close to the North Pole flying from Tokyo to London... Nice... Incredible view of the Northern lights all around.

Chance of doing that today is pretty much zero.

[moe1942]

[QUOTE=krutch] I like the panic grab handle by the window, is that the emergency exit?
QUOTE]



That's used to adjust the rear view mirror.:)

[PeteF]

So what happens when an aircraft the size and weight of the A-380 is cruising along at maximum cruise heading south west and suddenly encounters the northeast flowing Jet Stream at FL300 or so? Temporarily it can add 100 knots or more to the IAS. We are located where the Jet stream is very frequently overhead.

Flying into a jetstream like that happens from time to time. When you're flying at very close to the aircraft's maximum altitude for that weight, the maximum speed and stall speed can be quite close to each other. The two limits are represented by a striped red and black line on the airspeed part of the display, colloquially called "the bricks". When you suddenly fly into a strong headwind you'll see the thrust come off, possibly back to idle if the windshear is strong enough. The speed MAY go up into the bricks, but the aircraft won't suddenly go supersonic if that's what you're suggesting. Conversely suddenly flying into a strong tailwind the speed drops suddenly but this is a bit more serious as the thrust is already up close to maximum. This is one of the reasons conservative pilots won't fly up in this area and will stay a couple of thousand feet lower to provide more margin for error.

Pete

[Evan]

I am not suggesting that the aircraft is going supersonic. However, parts of the aircraft may be very close for short time. The shock wave doesn't suddenly appear at Mach 1. As speed approaches Mach 1 the airflow begins to compress closer and closer to the surfaces where it travels the fastest. The incipient shock wave begins to form as a leading region that is ahead of the surface and exhibits a large pressure change over a small distance. The closer the velocity is to Mach 1 the more compressed that region of sudden pressure change becomes and the more it stands away from the surface. At Mach 1 it stands perpendicular to the point of compression as the shock wave is propagated along the sudden pressure drop at the speed of sound.

Well before that happens the sound that is propagating forward is more and more "trapped" in the compression region. This concentrates the acoustic energy which is travelling ahead of the aircraft at a velocity equal to the difference between mach1 and the velocity of the aircraft. If there is a head wind then the velocity of the head wind is also subtracted from the forward velocity of the sound.

If the aircraft is flying 100 knots below Mach 1 in a 100 knot head wind the sound it emanates will be retarded according to the velocity of the aircraft and the velocity of the head wind after it leaves the aircraft. The sound will assume some of the characteristics of a shock wave.

[PeteF]

If there is a head wind then the velocity of the head wind is also subtracted from the forward velocity of the sound.

If the aircraft is flying 100 knots below Mach 1 in a 100 knot head wind the sound it emanates will be retarded according to the velocity of the aircraft and the velocity of the head wind after it leaves the aircraft. The sound will assume some of the characteristics of a shock wave.

Ah, no. The speed of sound is related to the body of air in which it's travelling, not the ground speed. I'd suggest your intermixing the two. The pressure wave will always be travelling away from the aircraft at the same velocity for the same Mach number with respect to the air in which it's flying. Oh course if the aircraft went instantaneously from, say 0 kts headwind to 100 kts headwind, it's inertia may cause an over-speed as it takes a while for it to slow back down to the same relative airspeed. But that's theory only. In a reverse situation I have had ground speeds with tailwinds that would very nearly be "supersonic" with respect to the ground speed, but of course the aircraft was still only doing, say M0.85.

Hope that makes sense.

Pete

[J Tiers]

Hope that makes sense.

Pete

But of course... The aircraft "lives" in the air, and has nothing particular to do with the ground speed.... Or the speed with relation to Alpha Centaurii, either...... With sufficient headwind speed, it might be going BACKWARD as far as ground speed.

I think Evan was referring to your "theory" point.....

[Evan]

I should have included "relative to the aircraft" and "relative to the ground". The ground is relevant because that is where the sound is heard.

If the aircraft is flying 100 knots below Mach 1 in a 100 knot head wind the sound it emanates will be retarded according to the velocity of the airflow relative to the aircraft and the velocity of the head wind after it leaves the aircraft relative to the (listener on the) ground.

[PeteF]

Evan sorry the ground is not a factor to the creation of a shockwave. As Jerry also points out it is immaterial. The aircraft is still travelling across the ground, but the pressure wave is formed between the aircraft and the air in which it is travelling. The pressure wave will move across the ground at the ground speed of the aircraft, in this case the TAS minus 100 kts. Assuming a hypothetical case where the aircraft was flying at just over M1.0 and the headwind was precisely the same speed, the aircraft would appear to hover overhead and you would hear a constant sonic boom. The listener on the ground only becomes part of the equation in terms of the duration they will hear the sound.

Pete

[Evan]

Evan sorry the ground is not a factor to the creation of a shockwave

That isn't what I am saying. What I am trying to explain is that the velocity of sound relative to the observer on the ground will vary according to the movement of the air relative to that observer.

To use your example:

Assuming a hypothetical case where the aircraft was flying at just over M1.0 and the headwind was precisely the same speed, the aircraft would appear to hover overhead and you would hear a constant sonic boom.

The observer would hear nothing if the headwind extends to the ground. From the viewpoint of the observer at A the shockwave would emanate at a 45 degree angle to the rear of the aircraft. Since it is traveling at the speed of sound outward from the aircraft AND the medium that is carrying the compression wave is traveling at the speed of sound relative to the observer for every metre that the shock wave moves away from the aircraft the medium carrying it moves a metre away from the observer.

If the headwind doesn't extend to the ground then the sound will be delayed by the amount of time that it takes for the shock wave to travel the distance required to leave the sonic flow and then at a vector behind the aircraft to reach the observer at A'. The shock wave will appear to emanate from behind the aircraft. In addition, when the shock wave crosses the shear boundary of sonic flow to still air relative to the observer at A' it will be further compressed by the velocity difference of the conducting media.

Einsteinian relativity doesn't apply here, we aren't talking about light. A sound wave follows Newtonian principles and is governed by the Galilean Principle of Relativity.

The observer at A will never hear the shock wave. The observer at A' will hear it after the accumulated travel time of T1 + T2 and it will appear to emanate from someplace along the dotted line.

http://ixian.ca/pics7/mach.gif

[PeteF]

Evan, I agree, it was misleading for me to say "overhead" as that implies directly overhead, what I meant was at the point you correctly showed on your diagram. You have however answered your own question so my reply is somewhat redundant.

The pressure wave is created by the aircraft through the body of air in which it travels, you are introducing Doppler shift into the equation which has nothing to do with it. I understand what you're saying, and agree it sounds plausible in theory [excuse the pun], but it's simply not how it works. It is A (ie singular) pressure wave caused by (each of) the object(s) causing the disturbance, not a sound per se. It just happens to travel at the speed of sound.

I started to type an analogy in another post and deleted it as I thought it may confuse the situation, but here goes anyway. Consider the analogy of a ship steaming up the river at 10 kts. The size and shape of the bow wave is determined by the speed of the ship not by the speed of the river. If the speed of the river is 5 kts and the ship is 10 kts the bow wave will travel up the shore at 5 kts. If you put a cork on the bank representing a listener's ear drum it would bob up and down more or less rapidly depending on how fast the current ran (hence how fast the wave passed the point). That is where I think you're becoming somewhat confused. If the current was 10 kts (and you positioned the cork in the right place as you pointed out), the cork would remain either up or down. If the ship steamed the other way the cork would bob up and down very fast. However in all these scenarios the bow wave from the ship has remained unchanged.

Picture the pressure wave as a single wave the emanates from a surface that disturbs the air mass, because that's basically what it is, not a "sound" or series of waves. Indeed I've been standing about 1000 metres from a Mirage as he went past at about M1.2 and you hear two distinct "booms", one from the pressure wave off the nose of the aircraft, one off the pressure wave from the rear of the aircraft. Yes it's loud. Yes it did a lot of damage. Yes he got in serious doo-doo for doing it :D

I don't know if that explanation helps of hinders. Hopefully it helps as I think it's about the best I've got.

Pete

Edit: Ok, maybe one more example that "may" help?? You're a pilot so you are familiar with ground effect. That is really a similar pressure wave to that we're describing. In the aircraft I fly I enter ground effect at 200 ft (it's quite strong BTW and will easily push me out of the slot if I don't anticipate it). We directly feel the effects of the wing's pressure wave in this scenario, however that pressure wave is emanating from the aircraft at all times, we just don't normally get this feedback. ...ergh ... maybe this isn't helping :(

[Evan]

This is from NASA, emphasis theirs:


There is no upstream influence in a supersonic flow; disturbances are only transmitted downstream.


And, from the same series on the speed of sound:


Air is a gas, and a very important property of any gas is the speed of sound through the gas. Why are we interested in the speed of sound? The speed of "sound" is actually the speed of transmission of a small disturbance through a medium. Sound itself is a sensation created in the human brain in response to sensory inputs from the inner ear. (We won't comment on the old "tree falling in a forest" discussion!)

Disturbances are transmitted through a gas as a result of collisions between the randomly moving molecules in the gas. The transmission of a small disturbance through a gas is an isentropic process. The conditions in the gas are the same before and after the disturbance passes through. Because the speed of transmission depends on molecular collisions, the speed of sound depends on the state of the gas.
http://www.grc.nasa.gov/WWW/K-12/airplane/sound.html

Since the speed of sound depends on the actual collisions between the molecules then if the medium is moving the collisions are also moving along with the medium. Effectively, the speed of sound will vary in a medium transmitting sound if the speed of the medium past the observer varies.

As for your river analogy, it is incorrect. Throw a rock in a fast moving stream and look at how far upstream the ripples travel. The motion of the wave relative to the observer is entirely dependent on the motion of the medium. When you are dealing with very small apparent velocity differences the change isn't obvious but it still exists.

Unlike light the speed of sound is not a constant. However, Like light the speed of sound depends entirely on the characteristics of the medium through which it passes. A wave transmitted through anything moves at a velocity that is determined by the medium. Any motion of the medium relative to the point of measurement changes the measurement. If a taut wire is plucked a sound wave will travel through the wire. If the wire is reeled up faster than the speed of sound in the wire the sound is reeled up along with the wire.

[PeteF]

Evan, I'm not meaning to appear rude, but all of what you say is 100% correct, sadly none of it had any relevance to the question you asked, nor for that matter my explanation.

My river analogy was correct as it relates to the propagation of a pressure wave and I stand by it. I'm sorry, but I'm not interested in that being dissected to the nth degree, that's why they're called analogies and not literal examples. Indeed it is a variation of an explanation from an aerodynamics text I quickly grabbed and blatantly plagiarised for this purpose, as the author had a far better imagination than I in explaining.

One of the greatest misunderstandings in this area comes from the term "sound barrier" as it implies sound (as a series of waves) is involved. Your example of a rock thrown in the river and the ripples implies (together with your previous examples) that you have been similarly misled. As I have said, it is in fact a single pressure wave that extends from each disturbance, not a series of sound waves. Sadly many of the more simplistic diagrams used to describe this process draw the phenomena as a series of circles, which I personally feel only further confuses the issue.

I'd respectfully suggest you are confusing the issue by measuring a wave in moving media with respect to a stationary object. Once again that is looking at Doppler effect and is nothing to do with the shock waves. Your original question asked why the A380 sounded like it was creating a sonic boom. You also said it sounded like it was "just under Mach 1". To create a shock wave an object needs airflow over or around it to be greater than M1.0, less than M1.0 there won't be a shock wave, it won't sound like anything in particular, all you'll get is a strong pressure wave. My understanding of the actual noise we hear is the very rapid pressure change that occurs at the juncture of the shock wave. To achieve this, the object or airflow must be greater than M1.0 at that point. What happens to that pressure or shock wave after that point is largely immaterial; you can't change a shock wave into a pressure wave or visa versa by simply measuring it according to some other reference. It is what it is when it was created and stays that way.

Anyway, with all due respect this has now been 3 pages and I feel I've given it a pretty good shot at explaining it. You asked the question, and thanks for that as it was a good question. High speed aerodynamics used to make my brain hurt in lectures because it's quite different to conventional aerodynamics, and it's probably good to revisit it from time to time; you certainly got me thinking anyway ;) However I'm afraid this seems to be degenerating into an argument and I have no interest in going there. The answer to you question is "no", unless the aircraft itself (or parts of it) go supersonic in the airflow due to over-speeding in a sudden headwind, a shock wave and subsequent "sonic boom" will not be created. If my explanations have not been convincing then I'm sorry as it was the best I could do. Likewise if you choose to believe otherwise that's entirely up to you and I'll leave you with it.

Pete

[PeteF]

Ah, yes, sorry Evan I see the issue here. You even managed to confuse me with your rather convincing diagram. Sorry but I think your diagram is incorrect. Take a look at the schlieren photograph http://www.dfrc.nasa.gov/gallery/Photo/Schlieren/Small/EC94-42528-1.jpg sorry I couldn't find one online at M1.0, but this is close, M1.1. See how the shock waves go out at right angles (well they would be right angles at M1.0), not at a tangent as you've described. In high speed wind tunnels they do indeed create "super-sonic headwinds" and the model is held stationary. If you were an observer directly under the aircraft you would hear it once the sound travelled down to you, it doesn't get "carried back" by the airflow as you suppose.

Hopefully that will clear things up.

Pete

PS Incidentally you can see the 2 strong waves I described at nose and tail

[Evan]

Sorry Pete. Look up Transonic airflow around wings. Also, the doppler effect has everthing to do with the development of a shock wave. The compression of the distance between wave peaks is what produces a shock wave.

See here for a full explanation of how the doppler effect is one and the same effect that produces a shock wave.
http://www.physicsclassroom.com/class/sound/u11l3b.cfm

Also here, excellent animations btw.

http://paws.kettering.edu/~drussell/Demos/doppler/doppler.html

While you haven't been following along on this I have been answering my own question with the research I am doing. Here is perhaps the best explanation of why the A380 may be making an incipient sonic boom.



Shocks actually form before an aircraft reaches the speed of sound (Mach 1), as the air travelling over the top of the wing (and various other parts of the aircraft such as the canopy) is accelerated above the speed of the aircraft. Thus, air travelling over parts of the top of the wings might be travelling at, say, Mach 1.2 when the aircraft itself is only travelling at, say, Mach 0.9. This situation is categorized as transonic flow and is the flow type in which most military and large commercial jets cruise. (In fact, if you're flying on a large commerical jet like a Boeing 747 and the conditions are right, you just might be able to look out the window over the wings and see distortions in the air that are due to shocks.) Transonic flow is much more complicated than supersonic flow (where the flow everywhere over the aircraft is supersonic) and subsonic flow (where the flow everywhere over the aircraft is subsonic) as it consists of behavior found in both of the two extreme categories.

http://www.stanford.edu/~jrdx/shock.html

[PeteF]

Sorry Pete. Look up Transonic airflow around wings. Also, the doppler effect has everthing to do with the development of a shock wave. The compression of the distance between wave peaks is what produces a shock wave.

See here for a full explanation of how the doppler effect is one and the same effect that produces a shock wave.
http://www.physicsclassroom.com/class/sound/u11l3b.cfm

Also here, excellent animations btw.

http://paws.kettering.edu/~drussell/Demos/doppler/doppler.html



Evan, I am reasonably familiar with transonic airflow around wings, unremarkably enough, but thank you for your suggestion. :rolleyes: The Doppler effect I was referring to was NOT at the source, it was in reply to your argument of a listener on the ground, where Doppler effect is immaterial to shock waves. Indeed I think I made it quite clear, on numerous occasions in fact, that the source must be at the aircraft itself.

The explanations you provided in the links are how this is described to school children and 1st year physics majors. Courses in high speed aerodynamics would not describe the phenomena in this way. As I mentioned, I personally feel it creates confusion if it's religiously adhered to at more technical levels.

Yes transonic flow occurs on jet aircraft where air is accelerated, however I'd be surprised if the A380 was particularly remarkable in that regard as it creates a lot of drag, and it's quite an efficient aircraft. It's certainly possible that the A380, maybe accelerates the air around the fuselage transonic as it's pretty fat??? I honestly don't know, but again would be very surprised if it was a significant factor on this particular aircraft due to the drag issues. To give an example, I don't know about the A380, but it's probably similar to the A330 I fly. Most jet aircraft one would calculate the descent point at 3x altitude in still air. Many people may not realise we basically glide from that distance to close to the airfield. The A330 is so efficient we work on 4x altitude, which is a real bummer for me as I was getting pretty good at my 3 times tables ;)

Pete

[Evan]

it doesn't get "carried back" by the airflow as you suppose.


The problem inherent in that statement is that it ignores the time it takes for the wave to propagate. While the wave is propagating the medium is moving in the scenario you proposed and in the diagram I drew. That will indeed "carry back" the wave. In the image of the jet the jet is moving and the medium is stationary in respect of the camera. Once the wave leaves the jet it appears to propagate outward in a straight line. Since the medium isn't moving you are looking at the position of the shock wave as it propagates through the stationary medium at the velocity of the jet. It is propagating forward along with the jet. That is why it appears to be straight.

[Evan]

The explanations you provided in the links are how this is described to school children and 1st year physics majors. If you took courses in high speed aerodynamics you would not find them describing the phenomena in this way. As I mentioned, I personally feel it creates confusion if it's religiously adhered to at more technical levels.


At a higher level it will be described in terms of the mathematics of compressible fluid flow. The net result will look the same.

[Joel R]

Brilliant idea to put a camera overlooking the top of the fuselage in the tail (center of console). Not sure if this is standard on a lot of these planes, but definitely a cool feature.

[PeteF]

The problem inherent in that statement is that it ignores the time it takes for the wave to propagate. While the wave is propagating the medium is moving in the scenario you proposed and in the diagram I drew. That will indeed "carry back" the wave. In the image of the jet the jet is moving and the medium is stationary in respect of the camera. Once the wave leaves the jet it appears to propagate outward in a straight line. Since the medium isn't moving you are looking at the position of the shock wave as it propagates through the stationary medium at the velocity of the jet. It is propagating forward along with the jet. That is why it appears to be straight.

Evan why must you argue constantly? Here's another picture, see the rod up the plane's clacker? It's a model mate, the model is stationary, the media is moving http://en.wikipedia.org/wiki/File:Schlierenfoto_Mach_1-2_gerader_Flügel_-_NASA.jpg again, if it were at M1.0 the waves would be at right angles and you would hear them. The effect is identical. As you would expect.


At a higher level it will be described in terms of the mathematics of compressible fluid flow. The net result will look the same.

Really? That's based on how many courses you've taken in the subject. Because it sure as heck wasn't described that way in any I took! Now please, Evan, please, PLEASE don't argue with absolutely everything that is presented here. You asked a question, I answered the question. I believe my answer was accurate. And that, I'm afraid, really is that.

[Opa]

No, the PC term is box office.;-)

[lakeside53]

Evan why must you argue constantly?.


LOLOLOLOLOL:D :D :D


Because, his name is EVAN;)

[Evan]

Evan why must you argue constantly?

I only argue when I know I am correct.

This is an example of a transonic shock wave. The water vapour in the atmosphere condenses suddenly at the sudden change from high pressure at the shock front to low pressure behind it. It clearly depicts the conical shape of the shock wave. It just as quickly dissipates as the shock wave expands away from the aircraft and the pressure difference is too small to produce the effect. That accounts for the seemingly vertical rear "edge" which is really the base of the cone.

http://ixian.ca/pics7/transonic.jpg


Really? That's based on how many courses you've taken in the subject.

That question directly implies that the only way to learn something is by attending formal classes at an educational institution. I doubt you really believe that.

[dp]

Not to break up a good bicker fest, but at the recent SeaFair airshow with the Blue Angels, they were putting up those halos during solo passes over Lake Washington this year. I'm about 3 miles from there and close enough to hear the jets. This year we got sonic booms. When I brought up the show on the Internet I saw why.

We're under the flight path for several maneuvers and this year we were treated to a look into the cockpits of 6 of them as they did a low knife-edge pass over my deck. My altitude estimating is still pretty good based on all the time spent at airports, and I guesstimate them at around 400' AGL. We heard them long before we saw them.

[jugs]

[quote=PeteF]Evan why must you argue constantly?

To alleviate his feelings of inadequacy & because he's nothing better to do.



Now please, Evan, please, PLEASE don't argue with absolutely everything that is presented here. You asked a question, I answered the question. I believe my answer was accurate. And that, I'm afraid, really is that.


'fraid not, as witnessed he must have the last word, using the might of Google & his little wiki he will smite you down with large amounts of often inappropriate data.

He is the great god EVAN whose wisdom must not be questioned.

Sad really.

john
:)

[PeteF]

I only argue when I know I am correct.

That question directly implies that the only way to learn something is by attending formal classes at an educational institution. I doubt you really believe that.

Holy Cow Evan, you're a smart guy but I have to say I'm very disappointed in you, because now you're just making a fool of yourself. Let me tell you mate, there's a world of difference between displaying your Google prowess and actually learning and understanding a subject. You've consistently demonstrated you have zero understanding of this field, and that's fine, why should you. Each time you've posted I feel I've been more than patient in doing my best to explain how you're mistaken, only to have you zoom in on another pedantic point in the seemingly desperate hope of try to prove me "wrong", and I presume therefore the misguided intrinsic satisfaction that would therefore make you "correct". Since I know you as a smart guy, if you're not "getting" something I'm attempting to explain, I don't see that as your fault, I see that as mine, as clearly my explanation is poor. But having sat up until 2 am local time in a desperate attempt to explain this, one may have hoped that you would come back with something along the lines of "sorry, but I was mistaken" (something, incidentally I have not heard you say in any of your posts, all 30,000+, that I have read anyway!). Heaven forbid, you may have even said "ah, thank you for explaining that, I've also done some more "research" (ie Googled) of my own and between the two am now much wiser". But no. Instead you TELL me how my courses in this area would have been taught!!! Now THAT, I'm afraid, pushes my button.

So no Evan, you don't argue when you know you are correct, you argue because you are a "know-it-all". Frankly I can't imagine what you did before Google came along, but I should imagine you still have the dog-eared set of encyclopaedias sitting in the lounge room book shelf!

No I don't feel good saying the above, but my patience was out, and now it's off my chest. By way of consolation, I will however provide a link to an explanation on the Mach angle, and since you're determined to not believe a word I say, maybe you can email that physics department and tell them they're wrong. Once again I don't like the continued reference to a series of waves, however for this purpose I'll live with it. Where I think you're possibly becoming confused is when you're Googling "transonic", as it is not precisely Mach 1.0, rather a range of speeds from slightly below to slightly above Mach 1.0. The image you provided was very clearly of an aircraft considerably above M1.0, though still arguably transonic. Below is a cut and paste, with my emphasis of the relevant point.


The shock wave from a supersonic object is a cone composed of overlapping spherical wavefronts. As any one of these wavefronts forms, it propagates radially outward at speed c and acquires a radius ct. At the same time the source, traveling at speed v moves forward vt. These two displacements form the leg and hypotenuse, respectively, of a right triangle and can be used to determine the Mach angle at the vertex of the shock cone.

sin θ = c/v

When an object travels slower than sound, the ratio in this equation is greater than one, and the equation does not have a real solution. This makes absolute sense as there is no shock wave to speak of at subsonic speeds. Traveling [sic] at the speed of sound makes the ratio equal one and results in a Mach angle of ninety degrees. At transonic speeds the shock wave is a wall of high pressure moving with the object, perpendicular to its velocity. Above the speed of sound, the ratio is less than one and the Mach angle is less than ninety degrees. The faster the object moves, the narrower the cone of high pressure behind it becomes. Measuring the vertex angle is thus a simple way to determine the speed of a supersonic object.

On that note I'm sorry Evan but I really can't waste any more time with this. Sadly that's precisely what it's become, a waste of time, because it's very clear that no matter what I say you'll argue the opposite. I don't pretend to not make mistakes, but believe my explanations have been accurate and will just have to leave it at that.

Pete

http://physics.info/shock/

[Evan]

Holy Cow Evan, you're a smart guy but I have to say I'm very disappointed in you, because now you're just making a fool of yourself. Let me tell you mate, there's a world of difference between displaying your Google prowess and actually learning and understanding a subject. You've consistently demonstrated you have zero understanding of this field, and that's fine, why should you. Each time you've posted I feel I've been more than patient in doing my best to explain how you're mistaken, only to have you zoom in on another pedantic point in the seemingly desperate hope of try to prove me "wrong", and I presume therefore the misguided intrinsic satisfaction that would therefore make you "correct". Since I know you as a smart guy, if you're not "getting" something I'm attempting to explain, I don't see that as your fault, I see that as mine, as clearly my explanation is poor. But having sat up until 2 am local time in a desperate attempt to explain this, one may have hoped that you would come back with something along the lines of "sorry, but I was mistaken" (something, incidentally I have not heard you say in any of your posts, all 30,000+, that I have read anyway!).

Nothing that I already know supports your explanation. Nothing that I have presented as supporting evidence supports it either. If you think that all I know is what I use to illustrate my points such as images from NASA or REAL LIFE AIRCRAFT doing as I say they will, then you are even more mistaken than you are about the points in question.


I have a question for you to answer.

If a shock wave is to appear to stand vertically out from an aircraft for any significant distance how fast must it travel and in what direction?

Hint. It cannot be instantaneous, therefore it cannot be moving perpendicular to the aircraft.


The attempt to belittle sources of information because they are found "on the Internet" is both sad and ridiculous. I don't rely on sources that are questionable, only those that can be trusted to supply correct information. Yes, there are many sources of correct information online including all the large and small universities including MIT. Many, such as MIT make available their courses for all to study. Please explain how such study is factually inferior to attending lectures in person at the institutions.

I also perform actual experiments to verify what I learn. That happens to include building a wind tunnel in the last ten years. Nothing fancy but it verified the aerodynamic effect that I hypothesized to be true.

I also have on occasion been wrong on a point of fact and have admitted so. I usually do not even post on topics that I don't know well so I am not often wrong when I do post. There is plenty I don't know and that is why I only post statements of fact in a small subset of the threads posted here.

I have no particular interest in proving anybody wrong or even myself right. My interest is always in providing correct explanations of how things work. That is what really matters and that is why I will not leave incorrect information unrebutted.

[dp]

My river analogy was correct as it relates to the propagation of a pressure wave and I stand by it. I'm sorry, but I'm not interested in that being dissected to the nth degree, that's why they're called analogies and not literal examples. Indeed it is a variation of an explanation from an aerodynamics text I quickly grabbed and blatantly plagiarised for this purpose, as the author had a far better imagination than I in explaining.

A vessel on a river moving against the stream but holding it's position over the ground will create a bow wave that is also stationary over the ground, and will arrive at the banks and remain fixed as seen there by a witness. As you say, the speed of the wave is that of the device causing it. If we ignore the shoreline and focus only on the river and the vessel, we will see nothing different than if the vessel were on the open sea.

In the same vein - if a jet is traveling through a stream of air at the speed of sound for that air and, the air itself is traveling across the ground at that same speed of sound, opposite the direction of the jet, the pressure wave from the jet will hit the ground at a fixed point and remain there for as long as the jet remains stationary over the ground. There will be no boom heard by a witness on the ground at the contact point, but instruments will show that the pressure within the wave's contact point will be higher than adjacent areas.

Same scenario but now the jet accelerates to a speed faster than the speed of sound and so appears to move relative to the ground. The pressure wave cannot travel faster than sound so it dissipates from the previous stationary position. However - the jet is still creating a pressure wave and it is still moving at the speed of sound. Clearly, the angle of the wave front has to change - it becomes closer to parallel to the direction of flight and hits the ground at a very shallow angle - think of the intersection angle of scissors as they close.

At lots of mach numbers, the scissors are close to being closed. The wave is being created at the speed of the jet which is very much faster than the speed of sound, but it is a nearly vertical vector going almost straight down as it cannot travel faster than sound. The ground contact point of this very long cone is well behind the jet.

[PeteF]

Dennis, yes that is absolutely correct, thank you, at least somebody got it ;) Of course wind speeds in real life never reach supersonic velocity (well not on earth anyway), however precisely the same situation as occurs in our scenario exists in high speed wind tunnels, where the model is held stationary in supersonic airflow. The results are photographed using schlieren photography which clearly shows the shock waves.


Nothing that I already know supports your explanation.

Well Evan, you said it.

Sorry mate, I won't answer any more questions from you as you clearly have no interest in the answer. If you truly are interested, you have the answer to your question in the link I provided. Incidentally, please don't put words in my mouth, I have never said the internet was a poor source of information. What I SAID was that you cannot simply Google something and declare yourself an expert on it. Any idiot can google a subject and post a link, that does not mean for a moment that they understand the subject. High speed aerodynamics is completely different in many ways to subsonic aerodynamics and it is very clear that you don't understand the former.

If you're truly interested in the subject, and I suspect you would be, there is a readily available text called "Aerodynamics for Naval Aviators". While most of my other notes and texts have long since been packed or given away, I still keep that particular book on my bookshelf. It's not expensive and explains the subject in an easy to understand manner, while still being relatively complete. I'm sure it would be available in your area and you may want to try to track down a copy. If you have any trouble sourcing it PM me and I'll see if I can get my copy to you.

Pete

[A.K. Boomer]

Pete --- don't let it get you down, actually Evan is one of the funnest guys to "debate" with because you never know where the topic is going to go with all the "squirming" around and such.
I got totally frustrated at first too, but if there's one real thing iv learned from the guy its how to cool my jets some and for that im grateful - usually he's been a gentleman to debate with and iv had the hot-head, so it really has been something worth learning - still - there's a road about 3 miles from where i live and its called "Evans road"

Next time I have my camera in the car Iv got to remember to take a pic of it! Your on "Evan's road" fella --- there's no shoulder - no U-turn and its a one way ticket to debating hell and no matter how plain and simple and in his face you put it - it will still be debated - after all one of the first things he told me was to be careful cuz he went to debating school...:p

And your right --- Evan has never ever never ever been wrong - it doesn't matter - i still like the guy (and I can also relate to that kind of stubborness )

Your a good head Pete, Welcome to the club of insanity...

[dp]

Pete --- don't let it get you down, actually Evan is one of the funnest guys to "debate" with because you never know where the topic is going to go with all the "squirming" around and such.

The irony of this is stunning.

[PeteF]

Ha ha, I just wanted to post a cool picture of an A380 flight deck :D

[A.K. Boomer]

The irony of this is stunning.



You know something DP - I see you haven't even lifted a pinky in the flycutter thread in which you inserted your foot in your mouth --- very wise to just take your spanking and let it sink into the horizon --- at least what one can say about the ones that squirm is that they have a little spine left in them...

So sorry for your pain -- don't worry - it will all be over soon...:rolleyes:

[dp]

Hint. It cannot be instantaneous, therefore it cannot be moving perpendicular to the aircraft.

This is exactly right. A perpendicular wave cannot be made except at zero velocity - a speed at which forming a pressure wave is impossible. At speeds near zero, a pressure wave will form that expands nearly perpendicular to the direction through the medium. It is also important to understand that pressure waves can travel at any speed up to the speed of sound. This variable speed is true for waves on the surface of water which is why the waves from throwing a rock into a river will travel up river while a bow wave will travel only as fast as the bow that creates it. Witness the Whammo! Air Blaster. Or this :D http://www.youtube.com/watch?v=hDx-mQqzYNw

If we use the model of a curve being an infinite number of straight lines arranged to form a curve, the pressure wave of a sonic regime airplane is an infinite number of expanding rings forming behind the aircraft. The rings have no horizontal motion - they can only expand. In the time domain they appear as a cone.

The diameter expands at mach 2. That means if they form from a jet flying at mach 1 the "cone" is 45º. As the jet exceeds mach 1 the angle of the cone falls toward 0º though never reaching it as the side opposite is always expanding. This is basic trig and the physical properties of sound in a standard atmosphere.

[dp]

You know something DP - I see you haven't even lifted a pinky in the flycutter thread in which you inserted your foot in your mouth --- very wise to just take your spanking and let it sink into the horizon --- at least what one can say about the ones that squirm is that they have a little spine left in them...

So sorry for your pain -- don't worry - it will all be over soon...:rolleyes:

Why beat it to death? I said I'd toss out the store bought cutter because it forces the tool away from the center line. That mandates a specific tool cross section to prevent this, and that's not something I would wish to be stuck with. End of story. I was right regarding what I said, too. End of story.

The store bought unit had no important characteristics over the shop made unit except it was designed to turn the conventional direction. Not particularly important if your mill is bi-directional and you want a tool to turn that direction. The fundamental design can be used as successfully in the conventional direction, so from a design perspective it is irrelevant.

The notion of balance came up, but that is hardly an issue given the cutter size/length is not defined, and in both cases, the slot that holds the cutter will be full of cutter, putting the shop made unit back in balance. The store bought holder will be out of balance with or without a tool.

And that presumes anyone even cares about balance. It is a fly cutter - it is an ad hoc tool given one will use the cutter of opportunity in it without regard to balance.

The question came up of tool rigidity and the potential the screws won't support rigidity. I claim the tool is not intended to pound the snot out of the work, but if that is the user's intention then they deserve what they get. For example:
http://www.youtube.com/watch?v=Ecs3OpHrfOg
http://www.youtube.com/watch?v=p4ylghZXd90
http://www.youtube.com/watch?v=8m0-ac3sAoY

This is the wrong thread to talk about that thread.

Edit: Correction - I revisited that thread and see I misread the angles (the tools were rotated 180º between pictures) - both tools are intended to turn in the conventional direction. Not that that matters from a design perspective.

[Evan]

And your right --- Evan has never ever never ever been wrong - it doesn't matter -

I have written these words before and will again.

"You are correct. I am wrong."

But, it won't be in this thread.

There are other factors that influence the slope of a shock wave at all Mach numbers including the transonic regime. The only time the shape of the frontmost shock wave will resemble a portion of a circle is if the object producing the shock wave resembles a flat plate, otherwise known as a "bluff body". Real world aircraft are not built that way so another calculation enters the picture. It is the calculation of shock wave obliquity. This effect causes the wave to slope back from the foremost point of the aircraft. The finer the angle of the nose the greater the sweep back of the shock wave at all mach numbers.

[dp]

I have written these words before and will again.

"You are correct. I am wrong."

But, it won't be in this thread.

There are other factors that influence the slope of a shock wave at all Mach numbers including the transonic regime.

This is quite so. The fastest a pressure wave can advance away from the airframe is at the speed of sound, but it can surely leave at slower speeds and there probably exist geometries of airframes that exhibit this even at transonic speeds (air above vs below an airfoil, for example). But when the aircraft is in the sonic regime it is analytically acceptable to consider all pressure waves are at mach 1 for first degree analysis. Surely this is the case in a machinists' forum where putting a very fine point on it does not contribute much except esoterica.

[Evan]

The obliquity angle isn't a fine point Dennis. It applies to all aircraft that fly near the speed of sound including passenger jet transports. Reducing the problem to one where the object under consideration is a flat plate will lead to serious error. You may note that in my simple schematic diagram I used a simplified but realistic representation of the shock forming shape. That wasn't accidental.

[dp]

But with the constraint that the speed of the wave forced away from the airframe cannot exceed the speed of sound for a specific atmosphere, there will be a predictable angle that is a function of airframe speed at and above mach 1. Below the speed of sound that is not the case, but my schpeel was for airframes in the sonic and faster regime. And I'm using an isotropic airframe as that is the only practical airframe we can discuss with any degree of uniformity.

Below the speed of sound there are all manner of structural minutia that come into play. On a normal jet airliner you can watch a pressure wave dance along the top of the wing in the form of light diffraction, for example. That is a shock wave, pure and simple, and it forms because the air traveling over the top of the wing is going much faster than the rest of the airframe. Because it has further to travel.

[A.K. Boomer]

Why beat it to death? I said I'd toss out the store bought cutter because it forces the tool away from the center line. That mandates a specific tool cross section to prevent this, and that's not something I would wish to be stuck with. End of story. I was right regarding what I said, too. End of story.

No - not end of story - you do not and cannot make an incorrect and unsafe statement like this on this site with me "listening" and get away with it - that's the end of story,

Of course you have to use a tool of the proper sizing - that's why they make them in different increments - its that simple, You don't "force the tool away from center", you clamp it down and its stays on center --- period...

You don't throw a 3/8" boring bar into your half inch receptor without a shim do you? Then stop whining about having to use a tooling shank that's a size specifically designed for your cutters head...


The store bought unit had no important characteristics over the shop made unit except it was designed to turn the conventional direction. Not particularly important if your mill is bi-directional and you want a tool to turn that direction. The fundamental design can be used as successfully in the conventional direction, so from a design perspective it is irrelevant.

Totally wrong - the fundamental design between the two is like night and day, I invite you to open any or all of your machining books and look at the flycutters --- they all are like the store bought one that you want to throw away, so according to you any and all the flycutters in these books should be thrown away and the hillbilly cutter that's loading its set screws in the direction of cut should be kept,,,
This IS a BIG issue for the kids reading this and about to build their own cutter, YOU could get somebody SERIOUSLY INJURED!!!
The trouble with building a cutter in the way your talking about that loads the tool bit into the centerline is that it has to use the set screws in this direction to make that possible - What this directly equates to is the set screws will directly take on any and all cutting loads/vibrations/frequencies/harmonics/spike loads from interrupted cuts and on and on -- This is WRONG... they work off of extremely high unit pressures and will either deform into the cutting tool and/or deform their ends and therefor relax their tension...






The question came up of tool rigidity and the potential the screws won't support rigidity. I claim the tool is not intended to pound the snot out of the work,

Dennis - with all due respect - flycutters are used on a variety of interrupted features --- like it or not they get the snot pounded out of them from time to time, Do you really want to be responsible for your post of telling people the incorrect way of building one?




This is the wrong thread to talk about that thread.

Your right - it is - but its safety and it's machining content - If for some reason an OT thread comes back around full circle and not only starts talking about machinery tooling but couples safety to it then I will take whatever heat from that that comes my way and put up a damn good fight about it also....


Now its end of story, keep in mind that there's a ton of newbies out there that could build one of your weapons instead of a proper cutter, there's a reason you don't see the hillbilly's design in any of the catalogs - it's called "Lawsuit":rolleyes:

Now im done...

[A.K. Boomer]

I have written these words before and will again.

"You are correct. I am wrong."

.



I must have skipped that day:rolleyes:


If that's really true then it is I who stand corrected... But if it's one post out of 30 some thou it still drives a point home.

You do realize that you own the word stubborn more than anybody else on the board - I would have to say followed by JT as a close second:p
Sir John is too much of a prankster to hold stubborn for too long - it takes to much energy and he don't like that....

[Evan]

I must have skipped that day

I said it to you.

[A.K. Boomer]

:eek: ,,, you would think I would have remembered that,

by the way - thanks for taking the time way back when to teach me about eddy currents in aluminum:)

[ldn]

PeteF,

Thanks for posting the pic. I enjoyed zooming around and looking at things.

These new glass cockpits are very sleek and efficient. I know they are better in many ways, but I still like the look and feel of the old style, single purpose mechanical gauges.

I learned to fly in a C-152 but never got my license. I still think airplanes are cool though and I enjoy keeping up with the latest.

I also like knowing that if I ever had to steal a small airplane to escape from the island lair of evil bad guys, I probably could. :D

[MichaelP]

Pete,

What's the transparent "magic crystal" hanging on an arm above the left side of the dashboard? Some sort of an LCD screen?

[PeteF]

Pete,

What's the transparent "magic crystal" hanging on an arm above the left side of the dashboard? Some sort of an LCD screen?

That's the crystal ball to tell whether the Captain is going to get laid that night. It almost always says "no!"

Just kidding it's a Head-up Display (HUD), a very cool piece of kit. They present images focussed on infinity on this screen so you can look through it to the world outside but get data on the aircraft's performance etc at the same time. Traditional aircraft used half a dozen or so mechanical instruments to indicate relevant performance, particularly on approach. With the so called "glass" displays, the instruments were combined into 2 screens and included a whole bunch more information also. By combining the information it reduced the physical distance the pilot's eyes needed to move in order to "scan" the instruments. However you still need to look out, refocus your eyes, then look back in, refocus, etc. and that also takes time. The HUD takes it a step further by presenting a smaller amount of relevant data to the approach phase, but up where you really want it. Their main advantage is when landing in poor visibility.

This may explain it better http://www.thalesgroup.com/Press_Releases/Thales_s_Head-Up_Display_certified_for_Airbus_A380/?pid=1569

Pete

[J Tiers]

I

You do realize that you own the word stubborn more than anybody else on the board - I would have to say followed by JT as a close second:p


I'm reforming.... in other words, I got too busy to mess with it that much. Besides, in 6 months less than Evan (since 2004), I have less than 1/3 the number of posts.............


I'd still like to know what that one aircraft type with the loud low frequency whine on takeoff is.......

[Evan]

Besides, in 6 months less than Evan (since 2004), I have less than 1/3 the number of posts.

I probably build at least 3 times as much stuff as you do (and most other people).

[Glenn Wegman]

Boy Id like to sit my fat little ass down in those seats - get some ceiling and "wag the tail on that dawg" :p

Somebody beat you to it...

http://www.youtube.com/watch?v=-yi9C8NE3Ek

[PeteF]

I'm reforming.... in other words, I got too busy to mess with it that much. Besides, in 6 months less than Evan (since 2004), I have less than 1/3 the number of posts.............


I'd still like to know what that one aircraft type with the loud low frequency whine on takeoff is.......

Jerry, is it a twin or 4 engine? Some of the newer high bypass engines do whine like I think you're describing. Does it sound a bit like the Roller at about the 1:55 mark in this video? http://www.youtube.com/watch?v=Ek6adm4iV4Y

...hopefully not like the sound just after that point :D

[A.K. Boomer]

Somebody beat you to it...

http://www.youtube.com/watch?v=-yi9C8NE3Ek


That looks crazy - to much mass to be jacking with...


Iv never really thought about what keeps an airplanes tires on their rims,

is there an extra large rim bead for seating? or are they tube type?

Im thinking those low pressure tires on a small single engine and someone doesn't let go of their crab all the way before TD (weve all felt it) and then there's that abrupt toss you to the other side of your seat feeling, well that "feeling" starts at the tires being misaligned at TD and the side loads on them must be incredible esp. for how small they are - how "gummy" the compound and generally how low pressure they look just in seeming like their half deflated all the time... ?

[MichaelP]

This may explain it better http://www.thalesgroup.com/Press_Releases/Thales_s_Head-Up_Display_certified_for_Airbus_A380/?pid=1569
Pete, thank you. This is very impressive!

[PeteF]

I have written these words before and will again.

"You are correct. I am wrong."

But, it won't be in this thread.



Well why not Evan, I have shown that pretty much every post you've made here in relation to the propagation of shock waves, including your diagram, is wrong. But I'll confess I'm not holding my breath for you to write those magic words :rolleyes:

[dp]

Well why not Evan, I have shown that pretty much every post you've made here in relation to the propagation of shock waves, including your diagram, is wrong. But I'll confess I'm not holding my breath for you to write those magic words :rolleyes:

In my own schpeel I described transonic to supersonic effects of an isotropic airframe (this is an analytic tool and they have no dimension but behave as a perfect object for what ever you are analyzing) but failed to migrate from pressure waves to shock waves, and that changes dramatically in the transonic regime. So far as it went, the pressure wave schpeel is fine, and pressure waves continue to exist when supersonic, but I'll try to describe the emergence of shock waves that form at and beyond transonic speeds later. I'm in another firefight with servers.

H/T to PeteF

[J Tiers]

Jerry, is it a twin or 4 engine? Some of the newer high bypass engines do whine like I think you're describing. Does it sound a bit like the Roller at about the 1:55 mark in this video?

Twin.

not really like that. I have a hard time describing it, or any sound, with words, but there is a lot more low frequency to the whine..... It is most like an air-raid siren slowing down, when it is no longer shrieking, but even that is not quite "it".

I hear it clearly when at the airport by the time they have rotated during takeoff, and I hear it as they go over the house 3 miles or so South of the airport. Most aircraft do not sound like it, just some.

[PeteF]

In my own schpeel I described transonic to supersonic effects of an isotropic airframe (this is an analytic tool and they have no dimension but behave as a perfect object for what ever you are analyzing) but failed to migrate from pressure waves to shock waves, and that changes dramatically in the transonic regime. So far as it went, the pressure wave schpeel is fine, and pressure waves continue to exist when supersonic, but I'll try to describe the emergence of shock waves that form at and beyond transonic speeds later. I'm in another firefight with servers.

H/T to PeteF

Well I'll have to admit I don't know what "H/T" means. :confused:

Yes that's correct Dennis.

[dp]

Well I'll have to admit I don't know what "H/T" means. :confused:

Yes that's correct Dennis.

Hat tip. It's blogger speak.

[PeteF]

Twin.

not really like that. I have a hard time describing it, or any sound, with words, but there is a lot more low frequency to the whine..... It is most like an air-raid siren slowing down, when it is no longer shrieking, but even that is not quite "it".

I hear it clearly when at the airport by the time they have rotated during takeoff, and I hear it as they go over the house 3 miles or so South of the airport. Most aircraft do not sound like it, just some.

Ah yes sorry, I saw that in your original post now. No sorry I can't help then. You've actually seen it? It's not a turbo-prop is it? The SAAB 340 makes a weird arse sound when it's taxiing around because of the pitch of the propellors. They're just flapping around like huge paddles until just before takeoff when you put the lever basically into flight mode. They make a real "growl" sound otherwise, quite distinct. But that's certainly not in flight or takeoff.

[PeteF]

Hat tip. It's blogger speak.

Ah sorry, I really must stop voting for the Luddite Party :D

[J Tiers]

Not a turboprop, I know the sound. I tend to listen, I tend to look around when I hear a radial, not for TPs..... Saw a nice staggerwing Beech go over at minimum altitude while I was up in Ohio a couple weeks ago.

This looks like a widebody, twin, definitely a high bypass by the look of the engines. Can't be sure, I remember the sound from being at the airport, but not the aircraft, so I always see it as it is climbing away, no good idea of scale, nor of altitude.......

[oldtiffie]

Well why not Evan, I have shown that pretty much every post you've made here in relation to the propagation of shock waves, including your diagram, is wrong. But I'll confess I'm not holding my breath for you to write those magic words :rolleyes:

Peter.

I AM surprised - truly.

I do hope you aren't waiting for Evan to say "I love you"?

Careful what you wish for - he might just do it!

Its more likely than his admitting that he's wrong - and apologising!!

It may happen at those higher ethereal planes.


Ethereal Plane
The Ethereal is often likened to an ocean, but rather than water it is a sea of boundless possibility. It consists of two parts: the Border Ethereal which connects to the Inner and Prime Material planes, and the Deep Ethereal plane which acts as the incubator to many potential demiplanes and other proto-magical realms. From a Border Ethereal plane a traveler can see a misty greyscale version of the plane from which they are traveling; however, each plane is only connected to its own Border Ethereal, which means inter-planar travel necessitates entering the Deep Ethereal and then exiting into the destination plane's own Border Ethereal plane. Many demiplanes, such as that which houses the Ravenloft setting, can be found in the Deep Ethereal plane; most demiplanes are born here, and many fade back into nothingness here. Unlike the Astral Plane, in which solid objects can exist (though are extremely rare) anything and everything that goes to the Ethereal Plane becomes Ethereal. There is also something here called the Ether Cyclone that connects the Ethereal plane to the Astral Plane.

In Dungeons & Dragons Third Edition, there is canonically one Ethereal Plane attached to each Material Plane; use of the Deep Ethereal is an optional rule

And pigs might fly!!


"The time has come," the Walrus said, "To talk of many things: Of shoes and ships and sealing wax, Of cabbages and kings, And why the sea is boiling hot, And whether pigs have wings." THROUGH THE LOOKING-GLASS, (1872).
Lewis Carroll (1832 – 1898), English writer, mathematician.

[jugs]

Pete, thanks for the interesting info, we have certainly moved on since stringfellow.

You should hang your head in shame, for daring to argue with 'the god EVAN' whose word is law & is always correct.

He probably designed the airbus in his shed between posts on here ! (12/ day)
Not bad for an ex photo copy mechanic

You should also take note of his modesty


I probably build at least 3 times as much stuff as you do (and most other people).

A true god amongst us.

john
:)

[Evan]

Well why not Evan, I have shown that pretty much every post you've made here in relation to the propagation of shock waves, including your diagram, is wrong

No, you haven't.



Shock waves in supersonic flow may be classified as normal or oblique according to whether the orientation of the surface of abrupt change is perpendicular or at an angle to the direction of flow. A schlieren photograph of a supersonic flow over a blunt object is shown in the illustration. Although this photograph was obtained from a supersonic flow over a stationary model in a shock tube, the general shape of the shock wave around the object is quite typical of those observed in a supersonic wind tunnel, or of similar objects (or projectiles) flying at supersonic speeds in a stationary atmosphere. The shock wave in this case assumes an approximately parabolic shape and is clearly detached from the blunt object. The central part of the wave, just in front of the object, may be considered an approximate model of the normal shock; the outer part of the wave is an oblique shock wave of gradually changing obliqueness and strength. See also Ballistic range; Wind tunnel.

http://ixian.ca/pics7/shock.jpg

http://www.answers.com/topic/shock-wave


Note that "normal" means at a right angle or perpendicular. One of the problems in photos of shock waves is that the area imaged is not large enough to show what happens at any distance away from the model in a wind tunnel. Wind tunnels that operate in the transonic and higher regime are very limited in size and the models are made to occupy as much of the volume as possible. Shock waves shown standing normal to the air flow are really just a very small segment of a swept back overall shape.

An example of a shock wave that is swept along with the flow of gas is the appearance of thrust diamonds in a supersonic exhaust. The shock wave is reflecting from the extreme density change at the flow boundary of the exhaust and the atmosphere.

This is a series of Schlieren photographs of the shock wave produced by a blunt faced object at transonic velocities ranging from Mach 0.6 to just over Mach 1. That is the precise flight regime of Jet transport aircraft. All of the images show approximately the same shock wave shape which is a small segment of a parabola just in front of the test object. They also show the oblique shock typical of the transition zone from the surface normal to the flow and a surface oblique to the flow.

http://ixian.ca/pics7/shock3.jpg
http://www.nasaimages.org/luna/servlet/detail/nasaNAS~2~2~7360~109006:

I have selected the image showing the wavefront at Mach 0.6 which is when the sound waves are sufficiently compressed by the Doppler effect to begin to form an incipient shock wave. Since the wind tunnel isn't large enough compared to the model to show more than a very small portion of the wave front I have fitted a parabolic curve to the image. A parabolic curve quickly begins to approximate a straight line either side of the origin as the descriptive equality is Y=X^2. The parabolic curve correctly describes the extended portion of the compression wave.

http://ixian.ca/pics7/shock2.jpg

If the test object were more representative of the actual shape of the nose of an aircraft the obliquity of the compression wave would be much more pronounced.
Take it or leave it, that is how it works.

[PeteF]

No, you haven't.

Take it or leave it, that is how it works.

No it is NOT how it works Evan, you are confusing subsonic pressure waves with supersonic shock waves. Now give it up. I was going to let this die to preserve your dignity, but if you insist on pursuing this then fine. Let me say then, you are WRONG, I have proven you WRONG, and the reason you are WRONG is because of a fundamental misunderstanding that shock waves do NOT propagate at the speed of sound, they travel FASTER!

I am not about to cut and paste every post of yours here so here's just one when discussing a theoretical situation of an aircraft in Mach 1 flight and accompanied by an incorrect diagram:


From the viewpoint of the observer at A the shockwave would emanate at a 45 degree angle to the rear of the aircraft.

With regards to shock waves that is just plain and simple WRONG! At Mach 1 the Mach angle is (very close to) 90 degrees. The angle of the shock wave does not in fact become 45 degrees until approximately Mach 1.4.

As I said Evan, I was going to just let it slide, and I certainly wasn't after any form of apology as has been suggested. But what frankly pisses me off Evan is that it takes me quite a lot of my time to respond to this type of thing. Now while you clearly don't have much going on in your life, I do. That's fine, I'm happy(ish) to try to pass on what to me is pretty useless knowledge. However it's the true height of arrogance and rudeness on your behalf to not even bother to actually read the references I provide to support what I'm saying. I know you haven't bothered reading them, because they clearly point out the difference between subsonic pressure waves and supersonic shock waves and indeed provide the precise formula to determine the Mach angle!

As for this absolute crap about blunt nosed objects, that has NOTHING, ZERO, ZILCH to do with what you were saying previously, so please don't try your usual smokescreen on me old mate. Duck and weave all you like. You were WRONG in your understanding plain and simple. Whether you are man enough to actually admit it is up to you, but one way or the other get over it, and move on.

Edit: If I seem a bit P.O.ed you'd be right. I spent this morning off the BB with Dennis pointing out the difference between subsonic and supersonic wave propagation. It took a few messages back and forth, but credit to Dennis, he could see the difference and I presume that was what his H/T comment was relating to. However I have absolutely no intention of spending another night until 0200 patiently trying to explain this and finding suitable references if you can't even be arsed reading them Evan! Please do yourself a favour and go back to the references I provided to see why the two waves are different. You largely have to abandon all previous assumptions about pressure waves when looking at the behaviour of shock waves.

[Evan]

At Mach 1 the Mach angle is (very close to) 90 degrees. The angle of the shock wave does not in fact become 45 degrees until approximately Mach 1.4.


Correct. However, the Mach angle only refers to the angle at which the wave stands to the surface immediate to where it is produced.



No it is NOT how it works Evan, you are confusing subsonic pressure waves with supersonic shock waves.

You may be confused but I am not.

A shock wave is a compression wave in the limit. The pressure gradient across the compression wave simply becomes steeper as the rarefaction zone and the compression zone merges to form a discontinuty. You will note that the above wind tunnel images include pressure waves above mach 1. Note also that there is NO significant difference in the appearance or shape of the pressure waves above mach 1 and those below mach 1, which I have consistently referred to as INCIPIENT shock waves.




Now give it up. I was going to let this die to preserve your dignity, but if you insist on pursuing this then fine. Let me say then, you are WRONG, I have proven you WRONG, and the reason you are WRONG is because of a fundamental misunderstanding that shock waves do NOT propagate at the speed of sound, they travel FASTER!


Yes they do, but only as long as they are driven. Once the shock wave is no longer driven it decays exponentially to sonic velocity. This occurs only a short distance away from an aircraft since the aircraft is the driver of the shock wave. As soon as the shock wave is travelling in free air it very rapidly decays to a simple pressure wave. That happens within 10 wing spans distance from an aircraft at multi sonic velocities and within a span or so at mach 1.

Driven shock waves are not usually discussed in aerodynamics as they are more of a concern to weapons designers and blasters. Nevertheless, the principle is the same.


As for this absolute crap about blunt nosed objects, that has NOTHING, ZERO, ZILCH to do with what you were saying previously, so please don't try your usual smokescreen on me old mate. Duck and weave all you like. You were WRONG in your understanding plain and simple. Whether you are man enough to actually admit it is up to you, but one way or the other get over it, and move on.


Seems to me that the original question I asked was about a blunt nosed aircraft. It has everything to do with this discussion.

Why do people become so rude when faced with the possibility they are mistaken?

[Todd Tolhurst]

Is Evan still arguing? I'm gonna need more popcorn.

[dp]

A significant difference between shock waves and pressure waves is that in pressure waves, only the pressure moves (the molecules are displaced but return to the original position). With shock waves, the air moves. And shock waves can move very much faster through the air than pressure waves as they are not limited by molecular impact to propagate. They move, in fact, at the speed of the object that is creating them. Shock waves are also incredibly thin in cross section. Shock waves decay to pressure waves. It's the law.

There are some very interesting photos of nuclear blasts where shock waves are generated and race out ahead of the pressure wave. They are nearly vertical to a very high altitude.

[Evan]

Driven shock waves such as those produced by explosives are always normal to the direction of travel. They remain as shock waves until the pressure behind the shock wave falls below the pressure in front of the wave. Then they almost instantly decay to a pressure wave.


With shock waves, the air moves.

Not according to NASA.


Shock waves are generated which are very small regions in the gas where the gas properties change by a large amount. Across a shock wave, the static pressure, temperature, and gas density increases almost instantaneously. Because a shock wave does no work, and there is no heat addition, the total enthalpy and the total temperature are constant. But because the flow is non-isentropic, the total pressure downstream of the shock is always less than the total pressure upstream of the shock; there is a loss of total pressure associated with a shock wave. The ratio of the total pressure is shown on the slide. Because total pressure changes across the shock, we can not use the usual (incompressible) form of Bernoulli's equation across the shock. The Mach number and speed of the flow also decrease across a shock wave.


http://www.grc.nasa.gov/WWW/K-12/airplane/normal.html

[dp]

Not according to NASA.

It doesn't move as in a stream, it is displaced. This different from a pressure wave where the molecules compress adjacent molecules while passing on the initial disturbance. The molecules vibrate in place.

A shock wave passing down a tube can evacuate the tube by displacement, with the tube refilling from behind the wave. The original occupants of the tube being ejected permanently out and with sufficient velocity they cannot return to their original location.

[Tinkerer]

Gees.... think they'd of at least dusted and swept the crumbs off the floor before taking the photos. :D

[PeteF]

You may be confused but I am not.

Seems to me that the original question I asked was about a blunt nosed aircraft. It has everything to do with this discussion.


Well then I'll have to presume option B then Evan, and you're not going to like that one!

Actually nobody asked you Evan, you asked me. Remember? In fact I really don't think too many people here are actually too interested in your constant pontifications about subjects you know nothing about. People here can use Google just as well as you. You have been proven wrong Evan. No more smoke screens. You clearly did not understand that shock waves behave differently to subsonic pressure waves, yet you STILL persist in arguing!

[PeteF]

Just for the record Evan, and this is not even all of your errors and misunderstandings in this post! I can only eat breakfast for so long and the number of errors you have made is far longer than the time it takes me to eat!


If the aircraft is flying 100 knots below Mach 1 in a 100 knot head wind the sound it emanates will be retarded according to the velocity of the aircraft and the velocity of the head wind after it leaves the aircraft. The sound will assume some of the characteristics of a shock wave.

Wrong.


From the viewpoint of the observer at A the shockwave would emanate at a 45 degree angle to the rear of the aircraft. Since it is traveling at the speed of sound outward from the aircraft AND the medium that is carrying the compression wave is traveling at the speed of sound relative to the observer for every metre that the shock wave moves away from the aircraft the medium carrying it moves a metre away from the observer.

Wrong and wrong

http://ixian.ca/pics7/mach.gif

Wrong


The problem inherent in that statement is that it ignores the time it takes for the wave to propagate. While the wave is propagating the medium is moving in the scenario you proposed and in the diagram I drew. That will indeed "carry back" the wave. In the image of the jet the jet is moving and the medium is stationary in respect of the camera. Once the wave leaves the jet it appears to propagate outward in a straight line. Since the medium isn't moving you are looking at the position of the shock wave as it propagates through the stationary medium at the velocity of the jet. It is propagating forward along with the jet. That is why it appears to be straight.

Wrong


I have a question for you to answer.

If a shock wave is to appear to stand vertically out from an aircraft for any significant distance how fast must it travel and in what direction?

Hint. It cannot be instantaneous, therefore it cannot be moving perpendicular to the aircraft.



Wrong.


There are other factors that influence the slope of a shock wave at all Mach numbers including the transonic regime. The only time the shape of the frontmost shock wave will resemble a portion of a circle is if the object producing the shock wave resembles a flat plate, otherwise known as a "bluff body". Real world aircraft are not built that way so another calculation enters the picture. It is the calculation of shock wave obliquity. This effect causes the wave to slope back from the foremost point of the aircraft. The finer the angle of the nose the greater the sweep back of the shock wave at all mach numbers.

Wrong

... ok this is getting tedious as I've finished breakfast. I didn't realise it would take THIS long :rolleyes:


I probably build at least 3 times as much stuff as you do (and most other people).

Woops, sorry, that's probably not wrong ... just extraordinarily arrogant.

But I'm just going to leave it there Evan, the point has been made.

[Evan]

A shock wave passing down a tube can evacuate the tube by displacement, with the tube refilling from behind the wave.

You are talking about a driven shock wave. The shock wave doesn't do the work. It is pushed along by expanding gas and it is that gas the pushes the contents out of the shock tube. A shock wave traveling in free air does not displace the air. To do so would be doing work.


You have been proven wrong Evan. No more smoke screens. You clearly did not understand that shock waves behave differently to subsonic pressure waves, yet you STILL persist in arguing!


I am discussing, you are arguing. I am very well accquainted with the subject of shock waves long before this discussion. It is a subject of great interest to me and has been for many years. It is directly applicable to astronomy.

http://metalshopborealis.ca/pics5/bowshock.jpg

Most interesting is how a shock wave can form even though no part of the wave is in communication with any other part of the wave. A shock wave isn't an "object". It is a compression wave that can be modeled in one dimension and frequently is. The very term "shock wave" comes from the fact that it is a form of wave.

[Evan]

Quote myself:
I have a question for you to answer.

If a shock wave is to appear to stand vertically out from an aircraft for any significant distance how fast must it travel and in what direction?

Hint. It cannot be instantaneous, therefore it cannot be moving perpendicular to the aircraft.



Wrong.



Wrong? You display a very basic lack of understanding of general science.


Woops, sorry, that's probably not wrong ... just extraordinarily arrogant.


It is the truth. Why is that arrogant?

[Thruthefence]

"
Just kidding it's a Head-up Display (HUD), a very cool piece of kit. They present images focussed on infinity on this screen so you can look through it to the world outside"

Now, If it would just 'paint' volcanic ash.....................................

[A.K. Boomer]

Woops, sorry, that's probably not wrong ... just extraordinarily arrogant.







Pete your just like another "club member" You have the stick to-it ness that it takes to keep keeping on around here,

But that particular statements of Evan's really isn't arrogant - Iv been hanging around here far to long and have seen what the guys built, To me it wasn't boasting - it was just plain fact.

Ok --- enough of a corner ring cool off --- DING DING - in goes your mouth piece - get back out there and move your feet a little more - his left jab is nothing but watch the right upper hook! :)

Also keep a close eye peeled for "distractions" - he's a master...

[Todd Tolhurst]

I am very well accquainted with the subject of shock waves long before this discussion. It is a subject of great interest to me and has been for many years. It is directly applicable to astronomy.

But, as we have seen, your knowledge of astronomy is not all-encompassing. You'll recall your unfamiliarity with the meaning of the word "metal", as used in astronomy. Essentially, you failed a basic vocabulary test. You argued that one at length as well -- obfuscating, moving goalposts, changing the subject, and finally, simply going silent when confronted with unimpeachable authority. I don't recall hearing "I was wrong" then.

[Evan]

The other shoe drops.
That is your opinion.
I'll not discuss it here, again. I made my point.


You argued that one at length as well -- obfuscating, moving goalposts, changing the subject, and finally, simply going silent when confronted with unimpeachable authority

Invariably people who are losing the argument resort to that accusation.

[PeteF]

I have written these words before and will again.

"You are correct. I am wrong."

So tell me Evan, just how many times does it take to be proven wrong before you do write these words? I can count at least 10 occasions on this thread where you're been proven to be flat out wrong, used correct data but in entirely inappropriate circumstance, or (as you attempted to do in your last post) tried to discredit a widely accepted generalised statement by a pedantic absurdity.

All of my examples, with the exception of the analogies, were in relation to aircraft Evan.


I am very well accquainted with the subject of shock waves long before this discussion.

Yes of course you were Evan, just like everything else you think you're an "expert" in. :rolleyes: That would explain why you couldn't even tell the difference in behaviour of a shock wave compared to a sub sonic pressure wave. You knew NOTHING about the topic and your posts simply illustrate that.

Edit: The reason your statement was arrogant Evan is because most people here hold down full-time jobs and simply don't have the time. Something it would appear you have far too much of!

[Evan]

The reason your statement was arrogant Evan is because most people here hold down full-time jobs and simply don't have the time. Something it would appear you have far too much of!


I am disabled, officially. I have the parking pass. I don't use it though if I can avoid it.


All of my examples, with the exception of the analogies, were in relation to aircraft Evan.


And? We are discussing shock waves. The physics do not change regardless of how they are produced.

Speaking of which, everything you have said and claimed is discredited utterly by your assertion that my above statement is wrong.

[PeteF]

I am disabled, officially. I have the parking pass. I don't use it though if I can avoid it.

And? We are discussing shock waves. The physics do not change regardless of how they are produced.

Speaking of which, everything you have said and claimed is discredited utterly by your assertion that my above statement is wrong.

I am well aware of your situation Evan.

Ha! That's just too much Evan. YOU claimed and stated SPECIFICALLY that at Mach 1 a shock wave is produced at a 45 degree angle. That is plain and simple BS. Totally false. Forget trying to get me to bite on your latest pedantic tripe, I have given the formula to calculate the Mach angle now several times Evan.

[Todd Tolhurst]

The other shoe drops.
That is your opinion.
I'll not discuss it here, again. I made my point.


I'm sorry -- what was your point? That you were right, and every other authority was wrong, including the actual working astronomer I contacted to obtain the correct definition? Oh yeah, you made a point all right. But probably not the one you think you made.



Invariably people who are losing the argument resort to that accusation.

So then, logically, why would I resort to it, as I demonstrably won the argument?

[dp]

Time to lock another one.

[PeteF]

Time to lock another one.

Yes I think so Dennis. I must say I'm really disappointed in this, and in future will head the warnings given to me by others. I started the thread by saying that I don't like posting OT topics on this board and this is just a reminder as to why. I thought the original link may have been of interest to the readers here, and it seems it was. I also don't mind trying to answer questions if I can, but this has degenerated into little more than Evan hijacking the thread with a know-it-all attitude about a subject he very clearly knows nothing about, then once again demonstrating he is incapable of admitting when he is mistaken, in spite of overwhelming evidence to prove that is the case. Banging my head against a brick wall is ugly, and makes me angry and disappointed; life's too short for that.

I started the thread and would now also ask for it to be closed.

[Evan]

YOU claimed and stated SPECIFICALLY that at Mach 1 a shock wave is produced at a 45 degree angle.

You find a picture of a shock wave at any mach number that is perpendicular to the flow for more than 2 times the width of the generating object and I will admit that I was wrong about that.

In the mean time you still have some serious explaining to do about your comment that I was wrong about the propagation velocity of a shock wave. Instantaneous means just that and that is impossible. The shock wave must curve and when it is traveling in free air will assume the shape of a cone. I have provided factual evidence in the form of actual images of the effect and yet you still dispute it.

Furthermore, you have taken the discussion and rapidly made it a personal attack on myself instead of a dissertation of fact to support your claims. I really don't care much but it does nothing for your argument and only reflect poorly on yourself.

My comment about being disabled was given because I would like nothing better than to be able to get a paying job. I can have a job in a CNC equipped machine shop tommorow if I were capable of doing it. Unfortunately even a good friend can't have an employee that needs to take a 30 minute break every hour.

I believe Dennis' comment about closing this thread was related to Todd. He has revealed his old habit of trolling for an argument. I was wondering how long it would take.

[PeteF]

Evan if you didn't quite understand my calling for the thread to be closed, here's the deal. I'm over this "discussion" as you like to put it. I come on the net to relax and maybe even learn something. Occasionally I'm able to share something back, this was one of those moments. I don't know what your deal is with wanting to constantly argue, bicker and generally piss people off, maybe you think people will be impressed, I don't know, I don't care, that's your business.

You have zero knowledge of this field, to the extent that you don't even know what the images actually represent that you post, I'm just not even going to go there but I did get a laugh. You STILL can't tell the difference between a pressure wave and a shock wave :rolleyes: You have been shown to be wrong on so many points I've literally lost count. If you're not mature enough to be able to admit it and instead try to contort the "discussion", create a straw man, or wriggle out some other way, well again that's your problem and I won't make it mine.

Quite what your disability has to do with this I have absolutely no idea, nor why you should choose to bring it up. Given that I sent you a PM several months back wishing you luck on what I understood to be a significant specialist appointment I was clearly already aware of your situation. What you may not be aware of is that for the majority of this year I have also been unable to work. Quite why is my business and unlike yourself I choose not to share that with the members here, fortunately it's nothing too serious, though the seemingly never ending run of bad news was only added to today. Never mind.

Trolling for an argument? Oh the irony.

[Todd Tolhurst]

I believe Dennis' comment about closing this thread was related to Todd. He has revealed his old habit of trolling for an argument. I was wondering how long it would take.

Pot, Kettle. Kettle, Pot.

[Evan]

Quite what your disability has to do with this I have absolutely no idea, nor why you should choose to bring it up.

You brought it up by suggesting I had too much spare time unlike people that work for a living.



You STILL can't tell the difference between a pressure wave and a shock wave

Still avoiding the key issue I see. Nothing that you have to say at this point has any credibility until you explain how a shock wave can remain normal to the air flow. If it did then what is the velocity vector and rate of propagation?

If you cannot answer that then you have zero understanding of the phenomenon and further no understanding of transport phenomena in general.

[J Tiers]

Quote myself:
I have a question for you to answer.

If a shock wave is to appear to stand vertically out from an aircraft for any significant distance how fast must it travel and in what direction?

Hint. It cannot be instantaneous, therefore it cannot be moving perpendicular to the aircraft.


Evan, I have stayed out of this up to now.

It isn't clear to me, despite your mention of "appear to", that you are really distinguishing between the apparent and actual movements.

But, every part of a wave can be moving exactly perpendicular to a moving object, and yet it may not appear as a "line" at 90 degrees to the path of that object.

Because there is a time element, (and a finite speed as you point out) the wave is viewable as generated in successively created infinitesimal pieces. The earlier parts of the wave are moving at 90 deg to the path, AT THE POINT OF THEIR GENERATION at a finite speed. After any given amount of time (during which the object has moved some distance "x") they have expanded at 90 deg a certain distance "y".

because they have finite speed, the "apparent" shape of the wave is a cone moving with the object, even though no individual point of that cone wave may have a velocity component along the path (the "x" dimension).

The "movement" of the cone along the path is "apparent" because the "locus of points within the wave" travels. But each point of the wave can still be simply expanding at 90 degrees (or 85 deg, etc) to the path.

If the physics of the situation define the path of the "individual pieces" of the wave to be at 80 deg or any other angle, that doesn't change the "apparent" vs "actual" movement disparity.

As far as a shock wave, it is my understanding that the shock wave decays to an "ordinary" pressure wave, at which point it is not profitable to discuss it as a shock wave. The shape of the wave is not important to the discussion after that point.

[Evan]

The "movement" of the cone along the path is "apparent" because the "locus of points within the wave" travels. But each point of the wave can still be simply expanding at 90 degrees (or 85 deg, etc) to the path.


Yes, of course. As I also pointed out it can be modeled as a 1 dimensional phenomena because no part of the wave is "connected" to any other part. For the wave to appear normal to the aircraft as it flies the propagation velocity would have to be infinite. That applies to a pressure wave and shock wave. A shock wave is nothing more than the limit case of a pressure wave. Obviously, infinite propagation rate is impossible. Therefore the shock wave will trail the aircraft as I show in the diagram.

[PeteF]

Still avoiding the key issue I see. Nothing that you have to say at this point has any credibility until you explain how a shock wave can remain normal to the air flow. If it did then what is the velocity vector and rate of propagation?

If you cannot answer that then you have zero understanding of the phenomenon and further no understanding of transport phenomena in general.

HA HA, oh dear or dear Evan, this is classic, you just cracked me up. What a pathetic attempt at creating a straw man. I emphasised the last bit just for my amusement. You have again and again been shown to be wrong, now you confuse Mach angle with normal shock. Oh dear, you really do have absolutely no idea do you? Thanks for the laugh mate, I really needed that. So, Evan, since I have "no understanding of transport phenomena", precisely what licences and qualifications do YOU have in this field?

Edit: "As far as a shock wave, it is my understanding that the shock wave decays to an "ordinary" pressure wave, at which point it is not profitable to discuss it as a shock wave. The shape of the wave is not important to the discussion after that point." Jerry, yes that's correct.

[Greg Q]

This has been such fun. Except for the part about the magic 8-ball crystal gizmo which predicts the captain's odds.;)

Pete, you are smarter than the average bear. I have discussed high speed aerodynamics with hundreds of guys and can report that your grasp of the subject is both uncommon and accurate.

The HUD said "no" again tonight, so back to the Empty Arms Motel for me...

GQ

[Evan]

HA HA, oh dear or dear Evan, this is classic, you just cracked me up. What a pathetic attempt at creating a straw man. I emphasised the last bit just for my amusement. You have again and again been shown to be wrong, now you confuse Mach angle with normal shock.

I don't think you know what "normal shock" means.


...can report that your grasp of the subject is both uncommon and accurate

Ain't Google wonderful? Trouble is you can't trust everything you read. I have been studing this for many years. I refer you to pages 333 to 342 in Transport Phenomena by Bird, et al. where shock waves are discussed. Looks like my copy is now worth $125.00. I paid $14.95 for it.

[Evan]

Just so others don't lose sight of the mistake you made that goes to the heart of this discussion I reference it here.


http://ixian.ca/pics7/question.gif

"Wrong" is the wrong answer. Now, who is confusing Mach angle and normal shock? What does the word normal mean in this context? Any idea?

[PeteF]

I have been studing this for many years.

So what's that telling us Evan, you're a slow learner, because you've demonstrated again and again you have NO knowledge of this field. So, once again, Evan, you try to discredit me, now what licences and qualifications do YOU have in this field?

You really are a funny guy Evan, I really like the way some things seem to have finally twigged for you, then you turn it around to make it appear as if I was the one who made the statement. You constantly build straw man arguments, but sorry I won't buy into them. Let me remind you of (yet another) error you made, which seems to be at the heart of your complete misunderstanding of this subject.


Correct. However, the Mach angle only refers to the angle at which the wave stands to the surface immediate to where it is produced

Absolute BS Evan, complete and utter crap. The Mach angle is the angle between the forward velocity of the object and the shock wave produced. You have zoomed in on a special case of oblique shock that's called, surprise surprise a "normal" shock, and somewhat bizarrely extrapolated that out to apply to all shock waves. That is just plain wrong and simply demonstrates once again that you really don't know what you're talking about.

So just how long are you planning to continue demonstrating your complete and utter ignorance of this subject anyway? It's a good refresher for me, so you can continue making a fool of yourself just as long as the thread remains open. I think it's pointless, and would prefer it closed, but that's up to you I suppose.

[PeteF]

This has been such fun. Except for the part about the magic 8-ball crystal gizmo which predicts the captain's odds.;)

Pete, you are smarter than the average bear. I have discussed high speed aerodynamics with hundreds of guys and can report that your grasp of the subject is both uncommon and accurate.

The HUD said "no" again tonight, so back to the Empty Arms Motel for me...

GQ

Cheers big ears!

I hope you managed to hack into the porn channel ;) I don't know if you guys got the memo down there some years back that we were all to stop hacking into the porn channels as they had a "list" of guys who were doing it. They may as well have just reproduced the seniority list :D

[oldtiffie]

......................................

......................................

It's a good refresher for me, so you can continue making a fool of yourself just as long as the thread remains open. I think it's pointless, and would prefer it closed, but that's up to you I suppose.

Peter.

Once a thread is started it belongs to everybody and nobody and seems to have a life and direction of its own.

I can't see where its present stage bears any resemblance to your excellent OP:

As much as I'm not keen on constant OT threads, I know there are a lot of people here who are also interested in aviation, so thought some may be interested in this.

http://www.gillesvidal.com/blogpano/cockpit1.htm

Pete

at:
http://bbs.homeshopmachinist.net/showpost.php?p=579926&postcount=1


The only one with the authority and ability to "close" or "lock" a thread is one of the moderators - which for all practical purposes is George Bulliss.

If a thread is "not too bad" in George's opinion he seems to let it run its course until it "Peters out" (sorry - but that is an OZ expression meaning to just fade out into oblivion).

I suggest that you both PM and email George Bulliss asking for the thread to be either "deleted" (probably unlikely as it is still of interest to some) or "locked" where it can still be read but no further postings made to it.

Alternatively, you may either "block" all posts by Even in which case he can read your posts but you cannot read his.

Perhaps a better result would if you could "persuade" Even to block you and you posts.

But, on the other hand, if you were to stop posting to Evan specifically, he would not have been "invited" to reply - but if he has something to say he will say it and keep "saying" ad infinitum and ad nausium.

These "last man standing" contests are exercises in futility and best ignored or avoided.

In my opinion, for what its worth. you've made your points very well and can well afford to let the matter rest.

[PeteF]

These "last man standing" contests are exercises in futility and best ignored or avoided.

In my opinion, for what its worth. you've made your points very well and can well afford to let the matter rest.

Thanks Tiffie, I know one thing for sure is that Evan will always want to have the last word and I'll never "win" that one ;)

One thing I've learnt, particularly when flying with guys, is if anyone ever feels it necessary to declare themselves an "expert" in a field, they almost always aren't. Indeed it seems a person's actual knowledge is inversely proportional to the amount they quack on about how much they know. I just see constantly correcting Evan's complete ignorance as boring reading for those who are not involved in the field. I appreciate it's up to George, and he's probably laughing just as much as everyone else at Evan, so I guess it will stay.

Thanks for the thoughts, I'm glad you liked the initial intention of the thread and it's a shame Evan has hijacked it, as it will certainly cause me to think twice about ever posting any OT topic like this again.

Pete

[oldtiffie]

Thanks Pete.

I certainly did not regard your excellent article and your posts as being OT or not of interest to me at all - and I'd guess that many here have a direct or indirect interest in "things aviation" as they are technology items that do include things technological and machined/machining etc. and as such are well within the ambit and bounds of a non-OT item on a BBS such as this.

My last (I think) flight in an airliner was on a "DH Comet 4" of which the predecessors had bad habits of dropping into sea or of flying into solid objects. That I got plucked just 3 months after being married and flown into a ship in a war zone didn't help much either. Suffice to say that my last night in bed at home was a bloody side "different" to my first night on that ship as I had to "hit the ground running" as it were on some technology that needed a lot of "attention" in very short order!!!

I've done my time on the Flight Deck of an aircraft carrier ("Melbourne") where I had the landing mirrors on my slate to look after. After seeing a few of the "mishaps" there as well as "on the wires", over the side and having a lot of trust in others and technology when on the catapault quite put me off air-craft. Being sprayed with AVCAT from jet engines that may or may not have ignited is something I'm not anxious to repeat. Being in company with other carriers as well as small-ship "helos" when both the Brits and Yanks (Canucks and Indians too) had lottsa Carriers too was quite an education. Lottsa land-based Air Force air-craft as well.

My family spent 14 years at Woomera in the 50's. I spent some time up there as part of my Apprenticeship at LRWE/WRE at Salisbury SA (which abuts ans works with RAAF Edinburgh. We had Brit "V" Bombers ("Victors" and "Valiants") as well as Sabres, Meteors, Canberras and all of the missile testing firing and tracking stuff too.

I do admire aircraft and those that fly them - but terra firma will do me.

After the Navy, I won't go near a ship - naval or otherwise - as I've had my fill of them too. I think I've had to use Sydney ferries twice and gone out in FIL's boat to see that we'd got it right when we did it up as well as two fishing trips - and thats it.

But having said all that, if you've got any more items like the one that you started this thread with you will have my attention as you put your explanations very well.

Many thanks.

[PeteF]

Tiffie, your last flight was on a Comet? You haven't flown since?

Yeah neither the Comet, nor the Melbourne shared the best of reputations :p

I think we're both trodden similar ground, though I'll claim to have followed some time after! My "past life" was in electronics and I also did some work for the WRE or whatever they call themselves this week. The company I worked for also supplied some test equipment out there. Interesting.

Likewise I worked for and was taught to fly by the guys at RDU at Edinburgh. There's a very cool museum at Woomera (well last time I was there, it's going back a while come to think of it :( ) It's not so much what they have, but the fact that it's just laying about on trestles to pick up (and wander off with if anyone was that way inclined). Not a glass cabinet in sight. They had a logbook from the Mercury program I read from cover to cover. Amazing stuff. You really get the impression they would say "I wonder what would happen if we did this ... " A bit like this http://www.youtube.com/watch?v=6Y52E4sU-t0

[oldtiffie]

Yeah Peter.

HMAS "Melbourne" has a striking career - sinking two destroyers (HMAS "Voyager" and the USS "Evans") - by ramming them in peace-time with 82 + 74 = 156 killed. I was not on Melbourne when she "hit" but I was ashore on standby for/to "Voyager" - if required. Close call.

http://en.wikipedia.org/wiki/HMAS_Melbourne_(R21)

I was on "Voyager" when she "blew" two/both boilers and had to limp into Hong Kong for repairs. We had people with all sorts of excuses for wanting to be flown home!! Can you believe it. Most of 'em had just as good excuses to go with us from home!!! The "pace" was pretty hot and the funds were pretty low!! etc. (fill in the blanks).


On 30 April, burst tubes in the "B" boiler damaged the ship, forcing her to limp to Hong Kong for six weeks of repairs.[1] Over 300 sections of tubing had to be replaced in both boilers, with the cause of the damage confirmed to be oil contamination of the boilers' feed water.

from: http://en.wikipedia.org/wiki/HMAS_Voyager_(D04)

I re-examined my "flying" and sure enough, I did some more after the "Comet" effort. I flew to and from Adelaide (~ 1995) for a family birthday and to Sydney (~ 1996) for a Navy "Facilities Officers" conference. I flew to Canberra for another. That's it for any "big" stuff". A friend of mine has a light aircraft and I could not refuse a trip from Tyabb (VIC) around Westernport and Port Phillip. His son used to fly it on the "King Island" run. That son later was lucky enough to be recruited by Qantas and flew "long haul" (his son married an Air Hostess). His initials are CB.

I was pleased that you had been to Woomera. Great place in its hey-day - as was LRWE/WRE (part of "Supply" then and DSTO now). We wanted for nothing as regards the laboratories and workshops, tool and instrument shops etc. The Toolroom was all Cincinnati grinders and Swiss Schaublin mills and all "Starrett" and "Moore & Wright" tools etc.

While in the shops and on the ranges at Woomera I saw the Brit "Black Knight" (ballistic) rockets, the "Blue Steel" "stand-off" bombs (on the Valiants and Victors) as well as "Sidewinder", "Sea Slug" and other missiles. It was quite a prank to play on new people at the Tech Areas aerodrome to have them between the front of the hangars to watch a "Jindivik" pilotless target air-craft take off and after the PTA took off and they were watching it, the "pram" that the PTA left behind nearly ran over 'em!! (Happened to me too). Another - out past "E" range was having a pilotless RC "Meteor" take off and it took quite while to realise that my eyes were OK and that there wasn't a pilot in it. The Meteors were used as tracking targets for the "Sidewinder" missiles on the "Sabres". Once in a while the missiles were set to fire with a setting to pass below the Meteor. Every once in a while the "setting" was not working and the missile went straight up the jet exhaust (one of two) on the "Meteor" followed by a flash of flame and lot of debris, some very embarrassed people - and some very amused ones (me included). Some of the bombing runs were pretty spectacular too.

http://en.wikipedia.org/wiki/Blue_Steel_missile

http://en.wikipedia.org/wiki/Black_Knight_(rocket)

http://en.wikipedia.org/wiki/Sidewinder_missile

http://en.wikipedia.org/wiki/Sea_Slug_missile

http://en.wikipedia.org/wiki/Vickers_Valiant

http://en.wikipedia.org/wiki/Handley_Page_Victor

http://en.wikipedia.org/wiki/CAC_Sabre

http://en.wikipedia.org/wiki/Canberra_bomber

It was a great time to be an Apprentice and a Tradesman. Life at home in Adelaide/Salisbury was pretty good but it sure got a whole lot better when we went to Woomera and had to live in the Single Men's Quarters and Mess. Suffice to say that I had to live there too even though my family had a residence there. Mum worried too much (with good reason), Dad said to let off stream and sow a few wild oats (which we sure did) and that if we had enough money to get into strife to keep enough to get out of if as so far as he was concerned if we wound up in court or gaol we could get ourselves out!! Mum used to scan the "Gibber Gabber" (local paper) to see if we were "listed". We weren't, but that was through sheer good luck and was not through lack of trying. It sure did sort out some "Mothers boys" in amongst some and some took to it with gusto. Once they had the bit between their teeth there was no stopping them!! And weren't their mothers surprised when they got home!!

Going back to Adelaide/Salisbury/LRWE/WRE was not only quite a let-down it was a bloody great relief too - 'specially to my parents.

There were a lot who were only too pleased to see me leave and join the Navy - me included!!

I volunteered for the then new "Oberon" class submarines (built in the UK) as it really appealed to me. I had everything going for me and was all but "in" (the Submarine service - like General Service - was all by volunteer and selection) but as I was already a Chief Ordnance Artificier, I was too senior as the submarines preferred to train and select/promote their own Chieks from their own personnel. I was offered the job with every chance of being re-promoted to Chief if I "dropped back" a grade which I was not prepared to do. So I missed out and often regretted it. My wife was pretty pleased that I missed out - I can't imagine why though!!

http://en.wikipedia.org/wiki/HMAS_Ovens

http://en.wikipedia.org/wiki/Oberon_class_submarine

I don't fore-see me taking to the skies again any time soon.

[Evan]

You have zoomed in on a special case of oblique shock that's called, surprise surprise a "normal" shock, ...

Well, you just proved you don't know what a "normal shock" is.

Define:normal "A line or vector that is perpendicular to another line, a surface, or a plane"

Funny thing is that I already told you what it means quite a while back. You aren't even reading what I post.

Since you don't understand something as basic as what the mathematical meaning of "normal" is the rest of your diatribe is meaningless.

[jugs]

Well, you just proved you don't know what a "normal shock" is.

Define:normal "A line or vector that is perpendicular to another line, a surface, or a plane"

Funny thing is that I already told you what it means quite a while back. You aren't even reading what I post.

Since you don't understand something as basic as what the mathematical meaning of "normal" is the rest of your diatribe is meaningless.

Pete you may as well ignore Evan you cant stop him with fact or truth, he has a "special kind of mind" that see's a different normal to the rest of us.

There is a forest fire heading his way but He'd rather try any thing to prove he's right & your wrong

john

:)

[PeteF]

Give it up Evan, your cover has been blown. You've been caught with your pants well and truly down as not knowing the first thing about this subject and instead trying to BS your way through. I thought maybe you'd had the good sense to let it drop, but nope, back you come to keep digging yourself into a deeper hole!

Your knowledge of the subject has been shown countless times to be absolutely zero, your meaningless reference to esoteric texts and bizarre claims that you'd been "studying" the subject for years seen for what they were; crap. Now, since you can't even find something I've said that's inaccurate you're down as low as making stuff up ... and then discrediting it. How terribly novel. Desperate maybe, but novel just the same.

Sadly you gave the game away right from the start Evan with this nugget.


From the viewpoint of the observer at A the shockwave would emanate at a 45 degree angle to the rear of the aircraft. Since it is traveling at the speed of sound outward from the aircraft AND the medium that is carrying the compression wave is traveling at the speed of sound relative to the observer for every metre that the shock wave moves away from the aircraft the medium carrying it moves a metre away from the observer.

Now let me tell you that as long as my clacker points to China, nobody, and I mean NOBODY who had even the vaguest knowledge of the subject would EVER make a statement like that, never mind somebody who had been "studying" the subject for years. Unfortunately that turned out to be pretty much the highlight from you and it was all very much down hill from there, rather spectacularly at times!

Now, as if you hadn't made a big enough dick of yourself already, I've got some bad news for you old mate. You chose to direct me to a text that you believed I couldn't possibly have, and you'd be right. Sad really, because apparently contained within this weighty tome was the answer, for here was the source, the mother-lode of all wisdom on this subject. Well ... according to you anyway. So I had a bit of a think about this little problem and realised that while I didn't have it, I knew somebody who possibly would. And guess what? I was right. So sitting here, right now, is a copy of said text. Sadly I see I shouldn't have even bothered because Bird barely mentions the subject!!! There are about 6 pages devoted to the topic, and, rather hilariously, it's not even related to aircraft. Instead he discusses how a gas flowing through a venturi will go supersonic at the throat. Woopee! I could have asked the 18 year old lad next-door what his go-kart could do if I wanted to know that! And just so you don't think I'm making this s#%t up Evan, I can even see the sentence where you're hanging your hat. "The simplest of many possibilities is a stationary normal shock wave, shown schematically in ..." etc So THAT'S what you've been "studying" all these years Evan? What do you do, study one word per year? 14.95 you say? I reckon you were ripped off!

Evan I have no doubt you have a lot of knowledge in many different areas, but let's face the facts mate, this ain't one of them. :rolleyes:

[Todd Tolhurst]

Well, you just proved you don't know what a "normal shock" is.


I don't know Pete's mind, Evan, and I suspect you don't either. However, his words hardly prove that he's ignorant of the meaning of the word "normal". He said:



You have zoomed in on a special case of oblique shock that's called, surprise surprise a "normal" shock


So, your argument is that by saying that a normal shock is a special case of an oblique shock, Pete believes that normal means "ordinary" or "regular". How do you parse that sentence to come up with your conclusion?

And while I don't know squat about shock waves (you and I may have that in common), I can Google as well as you can, and I find a lot of passages like this one:



A Normal Shock, though, is generally a special case of a common Oblique Shock that typically occurs on supersonic airplanes and rockets, as discussed to the right.


Somebody has certainly proved that he doesn't know what a normal shock is, but it ain't Pete.

[Evan]

So THAT'S what you've been "studying" all these years Evan?

How droll. As if I have just one book.

[Evan]

And while I don't know squat about shock waves (you and I may have that in common), I can Google as well as you can, and I find a lot of passages like this one:


Quote:
A Normal Shock, though, is generally a special case of a common Oblique Shock that typically occurs on supersonic airplanes and rockets, as discussed to the right.



I can also find instructions on how to build an antigravity platform.

[Evan]

A normal shock is NOT a special case of an oblique shock.

From NASA:



If the shock wave is inclined to the flow direction it is called an oblique shock. On this slide we have listed the equations which describe the change in flow variables for flow past a two dimensional wedge. The same changes and oblique shocks occur downstream of a nozzle if the expanded pressure is different from free stream conditions. The equations presented here were derived by considering the conservation of mass, momentum, and energy for a compressible gas while ignoring viscous effects. The equations have been further specialized for a two-dimensional flow (not three dimensional axisymmetric) without heat addition. The equations only apply for those combinations of free stream Mach number and wedge angle for which an attached oblique shock occurs. If the Mach number is too low, or the wedge angle too high, the normal shock equations should be used.

http://www.grc.nasa.gov/WWW/K-12/airplane/oblique.html

Just another indication that Pete has been learning about shock waves from all the wrong places.

[Todd Tolhurst]

No doubt. But probably not on page 219 (http://books.google.com/books?id=_NCz9iZIugYC&lpg=PA219&ots=S7Y2Sy3Ric&dq=%22normal%20shock%22%20%22special%20case%20%22o blique%20shock%22&pg=PA219#v=onepage&q=%22normal%20shock%22%20%22special%20case%20%22ob lique%20shock%22&f=false) of Fundamentals of Compressible Flow, S. M. Yahya, 2003:



When the direction of flow is inclined at an oblique angle to the shock wave it is known as "oblique shock wave". Normal shock wave discussed in Chapter 6 is a special case of oblique shock wave in which the wave angle is 90 degrees.


(emphasis mine).

I await your next obfuscation.