|Crucial Test Coming for HyFly Hypersonic Cruise Missile
Aviation Week & Space Technology
HyFly hypersonic missile faces key final test after fuel shortage limited penultimate flight speeds
An upcoming test of the HyFly hypersonic cruise missile demonstrator will be the development team?s final chance to prove enabling technologies for a Mach 6 strike weapon.
This comes on the heels of a fuel-system issue on the second-to-last test, which prevented it from accelerating well-beyond Mach 3.5.
Key to the test of HyFly?a Defense Advanced Research Projects Agency and Office of Naval Research project with Boeing and Aerojet?is the performance of the missile?s rocket-boosted ramjet-scramjet propulsion system and its advanced ceramic matrix composite (CMC) construction. Also known as a dual-combustion ramjet (DCR), the system is based on an innovative cycle comprising a ramjet that burns liquid hydrocarbon fuel (JP-10) in a subsonic ramjet to generate a fuel-rich gas that is then burned in a supersonic-combustion ramjet.
The recent test, conducted on Sept. 25 out of the Naval Air Warfare Center?s Weapons Div. site at Point Mugu, Calif., was the first to assess the DCR in flight.
Previous drop tests in January and August 2005 proved the separation characteristics and rocket-booster performance. Ground tests of the flightweight DCR, conceptually developed by Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., were successfully performed in June 2007 by Aerojet in its direct-connect test facility in Orange, Va.
HyFly?s multiple inlets feed air to the subsonic ramjet before the mixed reactants pass as fuel into the scramjet at the missile?s rear.Credit: BOEING
?That was the final ground validation of the material [CMC] system in which we were able to simulate airflow into the ram inlet,? says Dick Johnson, Aerojet executive director of airbreathing systems.
The test showed good, ?steady operating performance at Mach 6 for around 240 sec.,? he adds. Tests were also conducted at Mach 3.5 and 4.1.
The entire engine, comprising a ram-combustor with six inlets in the forepart and a 9-ft.-long scram combustor aft, is made of a lightweight, high-temperature CMC specially developed by Aerojet.
?We tested 20 different types of material in small coupons and in a wind-tunnel environment, and the final material was far superior to anything else we tested,? says Johnson. He adds that, aside from flow path concerns, ?the other main challenge in the engine was materials to handle the Mach 6 environment.?
The Sept. 25 flight test was intended to demonstrate DCR takeover, fuel control and climb and acceleration to Mach 5.
?Everything worked fine, including the separation from the launch vehicle (F-15E), control acquisition, boost, inlet cover separation, booster separation and DCR ignition,? says Johnson. ?But we didn?t have enough fuel to accelerate the vehicle from the takeover point. There was nothing inherently wrong with the missile itself, and we accomplished 90% of what we were looking for.? Johnson adds that without accelerating to Mach 5, ?we didn?t really stress the engine material sufficiently.?
The next, and final, test is set to occur around the end of October and is targeted for a run at Mach 6, as well as gathering general flight-performance data and measurements of terminal accuracy.
HyFly is being evaluated as a potential high-speed weapon for both air- and ship-launch against options that include Boeing?s scramjet-powered X-51A and Lockheed Martin?s turbine-powered Rattlrs. It is considered slightly lower risk as it has a lower Mach number at which the engine can be started (M3.3), compared to a pure scramjet.
Evidence for this was gathered in 2004 during tests in the Arnold Engineering Development Center?s Aerodynamic Propulsion Test Unit in Tennessee, which marked the first time a fully integrated hypersonic cruise missile engine using conventional liquid hydrocarbon fuel was tested at critical flight takeover conditions, meaning that the rocket was boosted to air-breathing at Mach 4.