X-51 Waverider Makes Historic Hypersonic Flight

[Astronuc]

X-51 Waverider makes historic hypersonic flight
http://www.af.mil/news/story.asp?id=123206525

/26/2010 - EDWARDS AIR FORCE BASE, Calif (AFNS) -- An X-51A Waverider flight-test vehicle successfully made the longest supersonic combustion ramjet-powered hypersonic flight May 26 off the southern California Pacific coast.

The more than 200 second burn by the X-51's Pratt & Whitney Rocketdyne-built air breathing scramjet engine accelerated the vehicle to Mach 5. The previous longest scramjet burn in a flight test was 12 seconds in a NASA X-43.

Air Force officials called the test, the first of four planned, an unqualified success. The flight is considered the first use of a practical hydrocarbon fueled scramjet in flight.
. . . .

http://en.wikipedia.org/wiki/Boeing_X-51

http://www.boeing.com/defense-space/military/waverider/index.html

www.youtube.com/watch?v=VZUwKX3_uE4

 

[sanman]

Wow, this is pretty amazing. I wonder if there are any practical commercial applications for it beyond military and space uses. For example, could airliners one day carry passengers and goods around the world at hypersonic speeds? Perhaps a hypersonic version of the Concorde could succeed where the original failed, since hypersonic propulsion would allow you to cross the globe at much more conveniently shorter travel times. Plus these days there's a lot more globalization than there was during the time of Concorde.

I feel that mass-market interaction helps any technology evolve faster - be it microchips, combustion engines, or carpentry. PCs were considered quite inferior to mainframes and minicomputers when they first appeared. And yet they quickly evolved, so that today the biggest and fastest supercomputers all run on microchips designed for PCs. Intercontinental transport could then be a useful mass-market for hypersonic propulsion technology to ride on and evolve through.

Eventually, hypersonic engine technology could become so refined and robust that it would be the lower-stage of choice for space launches. The hypersonic flyback booster would then become the mainstay for routine spaceflight.

A key constraint in international long-distance flights is the ability to overfly land. As I recall, Concorde was banned from doing that by many countries, because of the noise pollution its sonic booms posed on the ground. So then would a long-distance hypersonic wave-rider aircraft be able to fly high enough so that its noise would not be heard signficantly on the ground?

 

[Cyrus]

A key constraint in international long-distance flights is the ability to overfly land. As I recall, Concorde was banned from doing that by many countries, because of the noise pollution its sonic booms posed on the ground. So then would a long-distance hypersonic wave-rider aircraft be able to fly high enough so that its noise would not be heard signficantly on the ground?

That's right, but there is another problem - heat. Getting a hypersonic airplane to fly continuously from one part of the glob to another without melting is no easy task. And it has to do not one, but many flights over and over again without melting. The X-15 went about those speeds and was made of Iconol-X. Damn expensive, and not robust enough for regular use.

 

[sanman]

That's right, but there is another problem - heat. Getting a hypersonic airplane to fly continuously from one part of the glob to another without melting is no easy task. And it has to do not one, but many flights over and over again without melting. The X-15 went about those speeds and was made of Iconol-X. Damn expensive, and not robust enough for regular use.

Maybe ablation is the answer, as with spacecraft heat shields?I realize that the more harsh the usage conditions, the more difficult it is to achieve reusability.

X-15 testing was done long before modern innovations like plasma aerodynamics, modern ceramics, etc.

But if the Space Shuttle can do it repeatedly while traveling through much higher speeds and using technology developed over 30 years ago, then why can't a mere Mach-6 craft do it using the latest technology?

 

[Cyrus]

But if the Space Shuttle can do it repeatedly while traveling through much higher speeds and using technology developed over 30 years ago, then why can't a mere Mach-6 craft do it using the latest technology?

But the amount of time the space shuttle spends reentering the atmosphere at high speeds is trivial compared to a sustained hypersonic vehicle (hour or more flight time). Also, look at picture of any hypersonic vehicle, you won't find space tiles on it.

Also, ablation means it goes away after use. You don't want to reheat shield after ever flight.

 

[sanman]

Maybe the solution will be in a combination of things - eg. high-temperature ceramics or boron nitride, plasma aerodynamics, and regenerative cooling.

This latest X-51 test showed some unforeseen heating in the aft of the engine bay - any speculations on what the cause was?
Was it perhaps a buildup of heat in the engine that was propagating rearwards? (in which case, why only rearwards?)

 

[Cyrus]

Maybe the solution will be in a combination of things - eg. high-temperature ceramics or boron nitride, plasma aerodynamics, and regenerative cooling.

This latest X-51 test showed some unforeseen heating in the aft of the engine bay - any speculations on what the cause was?
Was it perhaps a buildup of heat in the engine that was propagating rearwards? (in which case, why only rearwards?)

I would imagine that heat has a hard time moving forward when your going faster than the speed of sound.

 

[Borek]

I would imagine that heat has a hard time moving forward when your going faster than the speed of sound.

I would imagine that could be a problem when you move faster than light, at least there is a good reason why transfer by radiation would be affected.

 

[sanman]

I would imagine that heat has a hard time moving forward when your going faster than the speed of sound.

Hmm, well, isn't heat/phonon propagation relative to the reference frame of the material it's in? The aircraft itself is moving, but is stationary with respect to the heat propagating from its engine. Maybe the flowstream is transferring more heat rearwards through its combustion. Maybe the exhaust stream is expanding faster than the vehicle is moving ahead of it, and thus transferring more heat to the aft end.


Actually, regarding heat management - what about the idea of phase change materials? Is it feasible to have a phase change material with a sufficiently high specific heat capacity that it can absorb heat to mitigate temperature change on the aircraft? After all, when the aircraft is at lower speed, then the atmosphere could be cooling it, and the phase change material could absorb cold. Then when the aircraft accelerates to hypersonic speed and heats up, the phase change material would absorb heat. Maybe that might be enough to buy the aircraft a couple of hours of stress relief during hypersonic flight, when used in conjunction with other technologies.

 

[Cyrus]

Hmm, well, isn't heat/phonon propagation relative to the reference frame of the material it's in? The aircraft itself is moving, but is stationary with respect to the heat propagating from its engine. Maybe the flowstream is transferring more heat rearwards through its combustion. Maybe the exhaust stream is expanding faster than the vehicle is moving ahead of it, and thus transferring more heat to the aft end.

Ah, you're thinking about the heat spreading within the material of the aircraft itself. I was thinking about heat from the engines combustion chamber propogating forward in the air mass. Now that I see what you mean, its a bit more interseting of a problem .

Actually, regarding heat management - what about the idea of phase change materials? Is it feasible to have a phase change material with a sufficiently high specific heat capacity that it can absorb heat to mitigate temperature change on the aircraft? After all, when the aircraft is at lower speed, then the atmosphere could be cooling it, and the phase change material could absorb cold. Then when the aircraft accelerates to hypersonic speed and heats up, the phase change material would absorb heat. Maybe that might be enough to buy the aircraft a couple of hours of stress relief during hypersonic flight, when used in conjunction with other technologies.

I don't know, this isn't an engineering analysis and doesn't have any sound basis behind it.