USAF Scramjet Hits Mach 6, Sets Record

s122604 writes "The [X-51A Waverider]'s scramjet engine accelerated the vehicle to Mach 6, and it flew autonomously for 200 seconds before losing acceleration. At that point the test was terminated. The Air Force said the previous record for a hypersonic scramjet burn was 12 seconds. Joe Vogel, Boeing's director of hypersonics, said, 'This is a new world record and sets the foundation for several hypersonic applications, including access to space, reconnaissance, strike, global reach and commercial transportation.'"

Comments

Why so short bursts?

[Henriok]

Why are these engines burning for such short times? Are these engines so early in development that they really can't get them to be stable and safe for more than 12 seconds? Sounds a lot like fusion: it works but it's not yet useful.

Re:Why so short bursts?

[shadow349]

Are these engines so early in development that they really can't get them to be stable and safe for more than 12 seconds?

Are you talking about the scramjet or the events at Kitty Hawk in 1903?

Because Wilbur already had the first chance, Orville took his turn at the controls. His first flight lasted 12 seconds for a total distance of 120 feet (36.5 m) - shorter than the wingspan of a Boeing 707.

Re:Why so short bursts?

[bkaul01]

Scramjets have no moving parts; it's a duct and a fuel injector. That's it. Wear is a non-issue here.

Figuring out what shape that duct needs to be in order to get stable combustion, however, is far from a trivial problem; it's not just the fluid dynamics of the supersonic flow that must be considered ... thermodynamic losses can be large enough to quench the flame, and where in the duct those losses occur is as important as their magnitude. With most sorts of engines, second-law analysis is only something you look at to refine the efficiency of the technology once it's mature and functional. With scramjets, it's critical to making them work at all. Building one of these, with all our modern computer modeling technology, is kind of akin to building the first rockets with no computers at all.

Jet - Scramjet - And Questions!

[Anonymous Coward]

• Jet engines still have propellers to compress air, into which the propellant is injected where this mixture then ignites.
• Scramjets just use their immense speeds to do the compression with a funnel, but that also means they need more conventional means to reach these high speeds (such as getting a ride on a B52 plus gravity)

Questions

• What is the fuel efficiency per kilometer traveled?
• Can a scramjet reach escape velocity, or get close enough so that additional oxygen for the fuel doesn't make up more than half the payload?
• Did they find a new way to lose heat at supersonic speeds? Otherwise these rides will remain short ones.

Re:Jet - Scramjet - And Questions!

[MartinSchou]

Can a scramjet reach escape velocity

If it is capable of propelling whatever it's carrying to 11.2 km/s (just under Mach 33 at the Earth's surface). Since this one only goes to 6, there's still a ways to go.

Just as a foot note - if you're travelling at 11.2 km/s in a circle with a 6,378 km radius (Earth's equator), you will experience an acceleration opposite to gravity of 19.67 m/s^2 (aka 2 g). Just slightly slower if you do it at an altitude of 10 km (19.64 m/s^2). At the altitude this one reached, you'd hit 19.6 m/s^2

Re:Jet - Scramjet - And Questions!

[BJ_Covert_Action]

With regards to question 3, they have developed some pretty tricky ways to help cool the engines and the body of the vehicle. For instance, they cool the engines by circulating the JP-7 fuel through the body to absorb some of the heat to help bring it to the combustion point. This is very similar to how rocket nozzles are currently cooled to slow melting/failure:

The scramjet will circulate the fuel behind engine walls to cool the structures. Without such active cooling, the temperatures in a scramjet could reach 5,000 deg. Fahrenheit, high enough to melt virtually any metal on Earth. Solving the cooling challenge is a major AFRL/Pratt & Whitney achievement.

Source

My wager is that the entire vehicle took thermal control into its design considerations and it uses a combination of geometry, aerodynamics, and fuel management to help sink heat at an appropriately high rate to prevent too much for a build up. However, since I don't have the design specs, and I doubt anyone outside of the military will, for awhile at least, I can only speculate. You also have to understand that at those speeds, your gas dynamics become a problem of rarified gasses and heat management becomes a very tricky problem indeed, one that can't be approached by traditional cooling means. So in summation I would guess yes, they have probably found some very cool new ways to sink heat at hypersonic speeds.

Re:Interesting...

[Pojut]

Scramjets aren't exactly easy to test in the lab.

Hell, even normal jet engines are tough to test. Have you seen the equipment used to keep those things stationary while testing them? Holy fuck .

Amazing

[maillemaker]

It's amazing to me that they can make a machine who's parts are GLOWING they are so hot and the metal still functions without failing.

Re:For those of you who don't know how fast Mach 6

[vlueboy]

Mac 5 melts aluminum steadily
Mac 6 melts steel

And don't forget that keeping this friction heat down also requires a good deal of power.