Shape of things to comeV-1 engine design for hypersonic plane

V-1 lives, sort of.  The restless minds at DARPA offered a $2 million contract for initial development work on the Vulcan zero-to-Mach-4 hyper pulse-jet engine. The Vulcan program, according to a DARPA announcement last year, is to feature a normal turbine mode used to get an aircraft moving and up off the runway. Once the regular jet starts showing signs of strain, the Vulcan should start working as a Constant Volume Combustion (CVC) engine — either of “pulsed detonation” or “continuous detonation” type, using high-pressure air scooped from the front end of the fast-moving unit.

A pulse detonation design would see the interior of the Vulcan filled with an explosive fuel-air mix and this detonated — with the process rapidly repeated. Lewis Page writes that, in essence, the engine would be setting off a bunker-busting-size bomb inside itself, perhaps eighty times a second. This would be a much more advanced version of the “Argus” pulse jet which powered Hitler’s V-1 flying bombs during the closing stages of the Second World War.

The even more imaginative continuous detonation concept would use flow designs to feed fuel/air mix toward the point of explosion at the propagation speed of the detonating shockwave. The shockwave headed toward the front of the engine should then become stationary, and the explosion should keep on exploding — hence the designation “continuously detonating” — out of the back of the engine as long as the fuel/air supply was sustained. In this case, the bunker-busting-size bomb would turn into a sustained, constantly exploding fireball.

In either method, the inside of the engine would get much too hot even for jet turbine components to survive: this is why DARPA specify that the turbine drive should be “cocooned” in order to preserve it.

It appears that Alliant Techsystems (ATK), makers of innovative jets and rockets to NASA and the U.S. military, convinced DARPA they can build Vulcan. The Pentagon has given ATK $2,913,613 “to perform Vulcan Program, Phase I.”

The Vulcan program may offer some consolation to advocates of hypersonic planes at DARPA. The plans for such a plane appeared doomed last year, when the proposed Blackswift hyperplane was canceled. The Blackswift was seen as a successor to the elegant cold war-era SR-71 Blackbird spyplane, and it would have been capable of doing barrel rolls at Mach 6 from a standing runway start. Since we mentioned the Blackswift, we should also mention the X-51 Wavedriver, a scramjet demonstration vehicle for hypersonic (Mach 7, around 8,050 km/h) flight testing. The X-51 is a descendant of earlier efforts, including the Advanced Rapid Response Missile Demonstrator and the liquid hydrocarbon-fueled scramjet engine. DARPA had viewed X-51 as a stepping stone to Blackswift. The Blackswift was canceled, but the X-51 program goes on, with four test flights scheduled this year.

Pages says that Blackswift was a bit of a long shot, and so too may Vulcan be. Many DARPA projects, because of their push-the-envelope nature, never make it past Phase I.