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garagemark
01-05-2013, 06:06 AM
I was watching a show on History last night (Modern Marvels). It was all about speed. What piqued my interest was the rocket test track at Holloman Air Force base. A five stage rocket shooting down it holds the worlds land speed record at 6453 MPH, set in 2003. The three steel rail track (narrow gauge and wide gauge) is 50,788 ft long. But what interested me is that over the entire almost 51,000 ft, track width tolerance is held to a staggering .0025. Yes, 25 thou.

So, my normal confusion module kicks in, and I start asking myself things like:
How do they get two huge pieces of railroad track that straight in the first place? Railroad track probably isn't best known for its "precision".

And how can the track possibly KEEP that kind of tolerance? Holloman AFB is in New Mexico... hotter than the devil during the day and colder than a witches boob at night. Surly a 50,000 foot ribbon of steel will move side to side more than .0025 with thermal changes.

Even with modern lasers and other technology, I find it hard to imagine something, actually two somethings that straight and parallel over it's entire nine and a half mile length. So how do they do it? :confused:

luthor
01-05-2013, 06:54 AM
Is that .025" or .0025"? Makes a lot of difference.

rock_breaker
01-05-2013, 06:56 AM
I agree with the "how did they do it?", rails are installed using angle plates and bolts that permit slipage thus accomodate linear expansion/contraction, Perhaps they used concrete ties for the support as opposed to wood. Just guessiing that the ties were partially buried to help control the lateral movement, but holding that tolerance is a mystery.
.

vpt
01-05-2013, 08:04 AM
This is the one that myth busters does tests on?

browne92
01-05-2013, 09:24 AM
First, I'm guessing this is not your garden variety RR track. Probably machined flat on at least 2 sides (top and inside), if not all sides. That would at least give you the ability to measure down to .025"

Second, wouldn't most of the expansion/contraction be end to end and not width? Carefully computed gaps between the rail ends would take care of this.

There may also be some pretty strick rules regarding conditions when the track is used. No rain, no clouds, temperature between such and such.

Remember, this stuff wasn't nailed down by prison inmates with sledge hammers. This is the best mil-spec RR track your tax dollars can buy! :D

A.K. Boomer
01-05-2013, 10:12 AM
yeah It's the structure that's holding the rails together that need's to be considered and I bet their not typical wood ties - might be reinforced cement with studs sticking out so the rail is bolted to it, and their probably like tap-roots going way into the ground,

Im sure the rail is totally specialized too as in being seamless with overlaps that will not give vertically but will allow for linear expansion and contraction...

At those speeds I'd be more interested in hearing what the vertical deviation is for how many feet, I bet that puts the rail to rail deviation to shame...

Tony Ennis
01-05-2013, 10:19 AM
I bet it was machined in situ.

Lew Hartswick
01-05-2013, 10:41 AM
Next time I pass through Alamogordo I'll see if I can find anything about it.
...lew...

Optics Curmudgeon
01-05-2013, 10:43 AM
Read this: http://www.dtic.mil/dtic/tr/fulltext/u2/a105778.pdf, it tells all. The procedures are much the same now as then, only with better measuring methods.

chipmaker4130
01-05-2013, 10:55 AM
I bet it was machined in situ.

Hey, is that in China?! :D

loose nut
01-05-2013, 11:19 AM
Was there someone (as in crazy person) riding that.

Lew Hartswick
01-05-2013, 11:43 AM
Read this: http://www.dtic.mil/dtic/tr/fulltext/u2/a105778.pdf, it tells all. The procedures are much the same now as then, only with better measuring methods.

Thank you, thank you, Now I won't have to check. That pretty well answers all the above questions. I won't claim to follow all the math etc. but read most of it.
...lew...

PaulT
01-05-2013, 12:58 PM
Its pretty obvious, they just scraped it in.

danlb
01-05-2013, 02:10 PM
Was there someone (as in crazy person) riding that.

Yep. Crazy person did indeed ride it. I understand that a lot of the initial knowledge about human tolerance for high G situations came from there.

Dan

barts
01-05-2013, 02:37 PM
I'm sure they have a nice laser interferometer setup to do this; I've error-mapped robot track rails before to easily .001 with such rigs.

- Bart

Machine
01-05-2013, 03:20 PM
Looks like they tension the track so that as long as it doesn't go above 140 deg F, it remains in tension; thereby eliminating thermal distortion. Also, according to the referenced link, they developed a super duper precision grinder on wheels to grind the track to the high precision required. We were talking about why surface grinders were needed in another thread, and this application is an interesting "twist" on what they do best.

Although I haven't read the whole thing, one thing I didn't see them mention is the curvature of the Earth. Did they conform to the curvature or did they level the Earth to achieve true flatness? A ten mile track could experience quite a bit of "bending" due to the Earth's curvature in that distance, unless corrected. Also, another interesting aspect is that as the projectile rides along the rail it should experience a Coriolis acceleration. According to a diagram of the track, it's orientated North/South, which means anything riding along the track would be subjected to Coriolis forces. Probably negligible or accounted for in the track design, but interesting to think it has to be factored in for something moving that fast.

danlb
01-05-2013, 03:39 PM
It was a good read, though the mathematics were somewhat beyond me.

I, too, was impressed that they have a 10 mile length of steel under that much tension. Doesn't steel expand a few percent in 140 degrees? Imagine the size of the anchors.

They noted that one rail ( around the 41000 feet mark) appeared to be installed "backwards", thus showing a larger than normal deviation. How does one remove and replace a 39 foot section of track that is under that much tension? It boggles my mind.


Dan

tdmidget
01-05-2013, 08:48 PM
It's probably not possible to relate this test track to modern railroad rail. Railroads do not have to worry too much about their rolling stock becoming airborn. This is a real possibility at 6000+ mph.

Modern railroad rail is called CWR, continous welded rail. It is delivered in 1/4 mile lengths and when in place is it welded so that a length may be as much as 100 miles long, if no switches or other interruptions are encountered. It is bound to wood or concrete ties, by spike in the wood and held by Pandrol clips on concrete. The ties stabilize the gauge. The ballast, which is carefully chosen for it's ability to interlock and form a ridged base, prevent the ties and therefore the rail, from moving sideways. This requires that all expansion be upward, nor longitudinal. Rail must be welded, if not installed within a certain range of temperatures that might be encountered in service. Rail is ground to remove defects and maintain the profile. This minor material removal extends the life of the rail substantially.
I suspect that this rail at Holloman bears no resemblance to railroad roadway.

tdmidget
01-05-2013, 09:01 PM
Read this: http://www.dtic.mil/dtic/tr/fulltext/u2/a105778.pdf, it tells all. The procedures are much the same now as then, only with better measuring methods.

The rail shown in the link is not railroad rail. It is what is known as "crane rail" , used for overhead cranes. It is flat on top where railroad rail is crowned with a radius. The gauges are obviously not close to standard . It shows the Sled bearing on the rail at 6 points, including from below, where railway rail only needs 1 critical and 1 other quite loose.

garagemark
01-06-2013, 07:07 AM
Sorry this thread escaped me shortly after posting. Things happen. And yeah, I inadvertently added an extra zero to the measurement in the text. However, it is still for all intents and purposes a staggering piece of engineering.

OC, fantastic document! Just about explains it all. And as usual some of it it is well above my head. Thanks.

One more thing. When doing these ultra high speed runs, These guys install a plastic canopy over the track for almost it's entire length and then fill it with helium. Of course it is blown to bits as the sled shoots through it (the videos are awesome), and I understand why it's done, though just putting this thing together would take a while. But I'm curious as to why helium as opposed to other inert gasses. Helium is more scarce way more expensive than some other gasses, and to purge a ten mile long tube would seem to cost an inordinate amount.

Oh wait, it's government run. Question answered.

Obviously I am also slack in my knowledge of gas properties... though my wife says differently.

Ed P
01-06-2013, 08:40 AM
It shows the Sled bearing on the rail at 6 points, including from below, where railway rail only needs 1 critical and 1 other quite loose.

That's because a railway uses two rails, the sled only uses one. Which brings up the question, why did they go to the expense of building two rails along the entire length. They explain why there is a third rail along a portion of the track but never explain the second rail.

Ed P

A.K. Boomer
01-06-2013, 10:21 AM
I didn't read it - but for those who thumbed through most of it, Now im not thinking about the rails at all - Im thinking about the wheels, was there any mention of them - how big were they and what were they made of? what kind of RPM's would they be spinning to cover over 6,000 mph? ---!!!

at those speeds why would you not just forgo the wheel deal and adapt to magnetic levitation ??? Or was the entire point to still be connected to the ground for the "land speed record"

or maybe it might be a weight acceleration thing due to only having so much distance to get it done - yet wheel weight no matter the size takes twice the energies to get moving and twice the energies to stop, so I guess it would come down to what all the guts of the internal levitation system weighs ?

there's one draw back as I would think the sled would have to be built for massive amounts of downforce so the entire unit does not turn into a kite, and with good wheels you have that covered with copious amounts of overkill - but with levitation you just might exceed the lifting capabilities and grind the apparatus directly into the exciter coils ???

becksmachine
01-06-2013, 11:19 AM
I didn't read it - but for those who thumbed through most of it, Now im not thinking about the rails at all - Im thinking about the wheels, was there any mention of them - how big were they and what were they made of? what kind of RPM's would they be spinning to cover over 6,000 mph? ---!!!

at those speeds why would you not just forgo the wheel deal and adapt to magnetic levitation ??? Or was the entire point to still be connected to the ground for the "land speed record"

or maybe it might be a weight acceleration thing due to only having so much distance to get it done - yet wheel weight no matter the size takes twice the energies to get moving and twice the energies to stop, so I guess it would come down to what all the guts of the internal levitation system weighs ?

there's one draw back as I would think the sled would have to be built for massive amounts of downforce so the entire unit does not turn into a kite, and with good wheels you have that covered with copious amounts of overkill - but with levitation you just might exceed the lifting capabilities and grind the apparatus directly into the exciter coils ???

Someone correct me please, but I think the reason they are called sleds is because they have runners, not wheels.

Dave

Optics Curmudgeon
01-06-2013, 11:30 AM
Exactly, the sled runs on what are called "slippers", the design depends on the experiment. Some sleds are monorails but the majority are on two rails. The slippers wrap around the rails and the whole experiment is designed to be lift neutral. Efforts have been made to make Bernoulli effect air cushion slippers, I don't know how far that's gone. At the terminal end of the run the slippers are leaving a rooster tail of sparks.

A.K. Boomer
01-06-2013, 11:59 AM
Someone correct me please, but I think the reason they are called sleds is because they have runners, not wheels.

Dave

that makes perfect sense - was hard for me to wrap my head around the RPM's of a wheel at that speed and what a lightweight solution to the problem runners would be , so im guessing although levitation would be superior in a frictional sense the amount of weight one would have to add to achieve this for the accelerated part (sled - craft - whatever) would not be worth it - also the expense would get crazy im sure.

so did anyone read what the material of the runners are made of, teflon or something?

Edit; Just looking real quick - the fastest tip speed for a flywheel type structure I found is only about half of what would be needed to run with the speed of that rocket sled @ 2,990 mph
http://www.grc.nasa.gov/WWW/RT/2003/7000/7725konno.html

but years ago I remember a totally different looking storage device (in a popular mech. issue)
and it was more of typical flywheel like structure (actually more like a rounded off button) and although it's mass was light it spun at incredible RPM's and was much larger in diameter in comparison - not to say it would hold up enough weight on one side to make it an actual wheel of sorts as that's an entirely different can O worms...

Optics Curmudgeon
01-06-2013, 01:51 PM
so did anyone read what the material of the runners are made of, teflon or something?


The examples I've seen were stainless steel of some sort, I've only been involved in the preparation for one of these tests, and examining data afterwards. I might actually get to be there for one someday. I've never asked about the earth curvature thing, I can see arguments for the straight case but on the other hand if the track follows the curvature the gravity vector will always be straight down on the track. There are so many other forces involved that are bigger I don't see them worrying about it. I vote for physically straight, being easier to align optically.

rkepler
01-06-2013, 02:51 PM
Here's a (rather short) video from the track where the speed maxed at 10K km/h.

https://www.youtube.com/watch?v=p5iX1c9NuU0

Sandia Labs has a smaller sled run used quite a bit. I used to use a rifle range nearby (the track in in Area III and I used the Zia R&P range) and once in a while you would hear them fire it during the day. They used to fire it for "Family Day" (one day every 5 years when employee family was allowed to come out and see where dad/mom worked). I was kid of weird to see the sled start at one end and reach the other before you heard the rocket fire and the noise travel down the track.

on edit: Wanted to add that the sled facility used by Mythbusters is at the Energetic Materials facility outside Socorro, run by NM Tech. I'm not sure how many sleds there are in New Mexico, I know of 3 (4 if you count some real small ones up in Coyote Canyon), but then there's a lot of empty space around here. The example I use to illustrate that is that in 1945 they exploded the first atomic bomb here because 1) nobody would notice and 2) nobody would care - it's New Mexico!.

A.K. Boomer
01-06-2013, 03:17 PM
O. C. That's amazing you were involved in something like that,,, can you imagine the speed of a wheel's top (if you could get one to hold together) ---- of any size it's going to be double that of the craft - 12,000 mph + !!! I guess you can compare it to trying to launch a rocket off of a really fast jet,

I wonder what the equilibrium speed is for our gravity and size (curvature) of our planet?

what kind of speed does it start to pull on the rails with skid retainers VS using the rails with the main load carrying skids.

keeping a track physically straight will load the rails no matter the speed whilst following the curvature will eventually have to totally unload the track and pull against gravity on the rails... but at what speed? how much of a "drop" from straight is 10 miles following the curvature? hmm

ckelloug
01-06-2013, 06:13 PM
garagemark,

The reason that they use helium is due to the low density. It takes less rocket power for the sled to shove aside helium than air. Only hydrogen is lighter
and I think we can all guess why they don't use that.

--Cameron

Paul Alciatore
01-06-2013, 07:41 PM
Ditto on helium being the lightest gas that could be used. It would be difficult and really expensive to create a vacuum chamber that long.

As for the expense, they probably have their own production facility. Take it from the air and it winds up back there. If you introduce it from one end, it would push the air out the other so there would not be a lot of waste. Probably 1.5 to 2 times the volume of the tent if the test starts as scheduled. They would have to keep a positive helium pressure after purging so any delays would waste more.

A.K. Boomer
01-06-2013, 08:01 PM
I wonder if the sled makes chipmunk noises as its passing though the helium?

tdmidget
01-06-2013, 11:01 PM
Ditto on helium being the lightest gas that could be used. It would be difficult and really expensive to create a vacuum chamber that long.

As for the expense, they probably have their own production facility. Take it from the air and it winds up back there. If you introduce it from one end, it would push the air out the other so there would not be a lot of waste. Probably 1.5 to 2 times the volume of the tent if the test starts as scheduled. They would have to keep a positive helium pressure after purging so any delays would waste more.

Helium is not separated from air. There is virtually NO helium in air. It comes from gas wells in, guess where?, Northern New Mexico.

rkepler
01-07-2013, 08:47 AM
Helium is not separated from air. There is virtually NO helium in air. It comes from gas wells in, guess where?, Northern New Mexico.

I think it comes from other natural gas fields in Oklahoma and Texas. NM wells don't have that much helium.

But I'd never heard of running a sled through helium. I know some blast effects are best done under helium as things scale better and have seen some shock tube work done with it. Anyone have link to some images or something? It'd be interesting to see how they set it up.

Paul Alciatore
01-07-2013, 10:39 AM
I wonder if the sled makes chipmunk noises as its passing though the helium?


No, but the rider does.

Paul Alciatore
01-07-2013, 10:45 AM
Helium is not separated from air. There is virtually NO helium in air. It comes from gas wells in, guess where?, Northern New Mexico.

Oops, my mistake. Please pardon me.

Paul A.

Mcostello
01-07-2013, 10:12 PM
If the rider made only chipmunk noises it would still be awesome, otherwise it would be the worlds longest--------------oooooooooooooohhhhhhhhhhhhhh SSSSSSSSSSSSSS HHHHHHHHHH ************ ****************.