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Materials & Assembly

Shockwaves Caused Crash of DARPA Hypersonic Aircraft

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williamlweaver
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100x Performance Factor
williamlweaver   4/26/2012 7:41:18 AM
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I recall several publications and reporters reveling in the "failure" of the HTV-2 test back in August. But the ability to withstand forces 100x greater than design specifications and still manage to deploy a controlled abort should be a success in everybody's metrics. Controlled flight at Mach 20 for 3 minutes should have provided a wealth of telemetry. And these are the unclassified tests.... exciting.

TJ McDermott
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Re: 100x Performance Factor
TJ McDermott   4/26/2012 10:41:33 AM
One learns most from failures.

Droid
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Re: 100x Performance Factor
Droid   4/27/2012 10:08:33 AM
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I absolutely agree...this was a fantastic accomplishment.  After all, the whole point of testing something is to determine potential failure modes.  Simulations give us a fantastic set of tools to better predict failure, but there is really no subtitute for an actual real world test.  So often, we discover important variables or interactions that were not anticipated by simulation.

kenish
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Re: 100x Performance Factor
kenish   4/27/2012 12:43:12 PM
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In the early days of SPICE (circuit simulator), the late Bob Pease had a rant in his weekly column.  He published a circuit to simulate in SPICE and pointed out a certain resistor dissipated negative power!  He said he couldn't wait to put together the real circuit and watch it get colder by the minute.  He speculated on the breakthroughs it would bring to food and beer storage.

Then he got serious and made the point: simulations are a good tool but no substitute for hands-on prototypes.  Of course simulation software has made huge advances in all disciplines but Pease's point still rings true today.

Jerry dycus
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Re: 100x Performance Factor
Jerry dycus   4/27/2012 12:56:01 PM
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  What I don't understand is why they want these? 

 It makes the same sense of a big planing powerboat or a cavitating submarine, a fuel hog and nothing can be done about it.

 Why not go higher and avoid the drag, go even faster?

As far as forces the heat could have weakened the sructure or even mellted it like the X-15's titainium?  tail did 60 yrs ago.

burn0050
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Re: 100x Performance Factor
burn0050   4/27/2012 1:34:55 PM
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This is a DARPA project. Being able to fly that fast in the atmosphere means that it can outrun anything shot at it (SAM, bullets, etc.) - so that it could get somewhere fast and drop a payload (bombs, etc.). It could also be used to catch anything in the air (planes, missiles, etc.). It would also be extremely difficult to track or anticipate. Even a laser would have a hard time hitting it, especially if it is making random micro adjustments to its flight path. LA to NY in 12 minutes means that it could get to North Korea in under 30 minutes.

 

Jerry dycus
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Re: 100x Performance Factor
Jerry dycus   4/27/2012 4:59:59 PM
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  Avoiding missles, etc doesn't count if it can't get there and burns up on the way. Far better is skipping off the atmosphere or full space flight, both are far easier to do, have far more range, payload. And they are far safer from countermeasures.

There is not much that can withstand 5000F or so the ship has to endure. If you make it bigger for payload, the drag, heat just increases.

I'm having a hard problem find metals, etc that can withstand just 1500F with a decent lifetime which hasn't been easy. Much less the temps a hypersonic craft has to endure.

Over 2500mph just isn't smart in the atmosphere and this, every test before proves this. No?

So please tell me how far can they go and how much payload can they carry?  Enquiring minds want to know? 

burn0050
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Re: 100x Performance Factor
burn0050   4/27/2012 5:29:22 PM
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All they need to do is get some materials from one of those UFO's at Area 51 - problem solved! :)

I guess the point is that you'll never know if you don't try. I'm sure they learned a lot about shockwaves that will probably be useful in other applications, including slower speed craft.

It seems to me that ceramics is the answer here - our current technology can handle 2k-3k degree temperatures. I'm not sure how they would hold up to shockwaves since they can be brittle, but at that speed and temperature they may actually be a bit more flexible.

Flying fast within the atmosphere has its applications - there will be times that going out of the atmosphere simply isn't practical - short range applications, for example. I cannot imagine the sonic properties of something travelling Mach 20, it would certainly not be a stealth vehicle; but when you're going that fast you don't need to be stealth.

 

 

 

Ann R. Thryft
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Why didn't engineers correctly predict shockwaves?
Ann R. Thryft   4/26/2012 2:21:52 PM
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I guess what's not clear to me is, why was the aircraft designed to withstand shockwaves 100 times LESS strong than it actually experienced? I'm especially surprised since this was apparently the second flight, not the first. Why didn't engineers do a better job of prediction?


Charles Murray
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Re: Why didn't engineers correctly predict shockwaves?
Charles Murray   4/26/2012 8:12:37 PM
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That's a good question, Ann. The fact that it travelled successfully for three minutes might indicate that the shock wave was a sudden anomaly shortly before it failed (I can't imgine any design standing up to 100X loads for three minutes). Still, it's hard to imagine why no one foresaw a shockwave of this magnitude.

Ann R. Thryft
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Re: Why didn't engineers correctly predict shockwaves?
Ann R. Thryft   4/27/2012 12:43:57 PM
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Chuck, I was also guessing that the 100x shockwaves might be an anomaly. I just assumed that we knew a lot more about their potential force after all this time, and could therefore compute the relevant loads.


ervin0072002
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Re: Why didn't engineers correctly predict shockwaves?
ervin0072002   4/27/2012 9:15:13 AM
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Hey Ann,

 

The reason is our ability to predict turbulence. Some simulation software has gotten close. But to date we can only predict tested conditions. The facts behind turbulence are still largely guessed and even after a good bit of aviation history we are still working on the kinks. I have been to several meetings with mathematicians that are leaders in this field. It's difficult for them to predict with any great accuracy. Yes 10000% error is outrageous but it's possible in a field we are infants on.

 

Ann R. Thryft
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Re: Why didn't engineers correctly predict shockwaves?
Ann R. Thryft   4/27/2012 1:39:18 PM
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ervin, thanks for the explanation. I'm surprised that we're still infants in this field after so many decades of aviation history. That's unnerving, especially considering this is a DARPA project.


Charles Murray
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Re: Why didn't engineers correctly predict shockwaves?
Charles Murray   4/27/2012 6:53:57 PM
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Good points, Ervin. That actually does explain to some degree how a 10,000% error could occur.

Akmose98
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DARPA Hypersonic Aircraft
Akmose98   5/11/2012 10:37:17 AM
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The test duration reminds me of oner of the large rocket motor manufacturers comments after the exit nozzle exited 50 milliseconds into the test, "all test objectives were met"

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