Sustained hypersonic flight above speeds of Mach 5 by vehicles using air-breathing, jet-fuel-powered engines could become achievable within the next dozen years.
Successful recent ground tests of jet-fueled, ramjet/scramjet demonstrator engines by Pratt & Whitney Rocketdyne and Aerojet represent important progress toward flight-testing of three separate hypersonic-vehicle programs.
In September, Pratt & Whitney Rocketdyne (PWR) completed 10 months' testing of a sub-scale combustor for a hydrocarbon-powered, dual-mode ramjet engine designed to operate over a wide range of Mach-number speeds -- that is, multiples of the speed of sound.
Using JP-7 jet fuel, PWR ran the combustor successfully at a variety of Mach numbers from Mach 2.5 to Mach 6.0, demonstrating "desired operability and performance" at each speed, the company said.
"No engine, to our knowledge, has (previously) demonstrated a range from as low as 2.5 to a high of 6.0," said Michel McKeon, PWR's hypersonics and advanced programs manager. "The FaCET (Falcon Combined-Cycle Engine Technology) engine demonstrated a very wide Mach range, with high performance. This really shows the technology lends itself to application for a variety of different things."
A dual-mode ramjet transitions between subsonic and supersonic modes of operation. Because air entering the ramjet slows down as it goes through the engine, at lower Mach numbers some of the air enters the combustor at subsonic speeds even though the aircraft is traveling faster than the speed of sound, McKeon explained.
At higher Mach numbers, all of the air goes through the engine at supersonic speeds. "'Scramjet' basically means that all of the air is moving at supersonic velocity" through the combustor, said McKeon.
Together with PyroDyne, Aerojet also is developing a turbine-based combined-cycle engine it calls the PyroJet, which the companies hope will operate throughout a speed range from zero to Mach 10. The aim is to provide an engine that will transition smoothly from subsonic turbojet operation through to dual-mode ramjet/scramjet operation.
Now, for all manufacturers, the main challenge isn't demonstrating that their hypersonic engines can fire. To sustain hypersonic flight, the engines will need to fire for several minutes at a time, not just the few seconds that the companies have achieved so far.
Kemo D. (a.k.a. no.7)