Dead simple on paper but very tricky to build, the hypersonic scramjet engine gets a boost from a new jet-fuel-based design. Mach 8 here we come?
You don’t run this wind tunnel. You fire it. With the help of air pumped to 160 times atmospheric pressure and a highly explosive combination of hydrogen, oxygen, and a megawatt generator, the tunnel, set in a suburban Long Island business park, can reproduce the hellacious conditions an aircraft would encounter while traveling 20 miles above Earth at 5,300 mph–Mach 8–a speed at which the violent airstream packs enough energy to soften and melt solid nickel alloys.
Bolted to a massive copper support in the center of this torture rig is the focus of the HyTech project: a 6-foot-long, 200-pound prototype of a NASA- and Air Force-developed jet-fuel-powered scramjet (supersonic-combustion ramjet) engine called GDE-1 that could, by 2008, propel a small unmanned airplane to 5,000 mph and beyond.
Such hypersonic capabilities-particularly when powered with conventional jet fuel-could eventually lead to a new generation of long-range bombers, fast-reaction cruise missiles, and a space launch system that could cut the cost of propelling astronauts and payloads into space to one-hundredth of today’s prices.
That is, of course, assuming that the Pratt & Whitney engineers who built the thing can light it-and keep it lit.
The hypersonic (at least five times the speed of sound) velocities that the engine is striving for have until now only been feasible with single-use hydrogen- or hydrocarbon-fueled ramjet engines that in most cases would be destroyed by the end of the flight, making them suitable for missiles but not much else. Scramjet test engines -which improve upon ramjet performance and reliability but are much harder to engineer-have been around for decades, but their success rate has been dismal, and they have usually burned dangerous and unwieldy hydrogen for fuel. (Ramjets slow air traveling through them to subsonic speeds, while scramjets keep airflow above supersonic speeds-hence, the difficulty keeping them lit.) But this new engine, being tested at the cutting-edge facilities of aeronautical engineering firm GASL, runs on JP-7, a significantly more manageable kerosene-like jet fuel, and it has a unique cooling system that is key to its performance under hypersonic conditions. HyTech is slowly edging toward success, with several tests over the summer that have come close to a previously unattainable milestone: actually starting and sustaining combustion amid supersonic airflow.
Simply testing for that achievement is almost as hard as accomplishing it. Producing Mach 8 airflow through a 6-foot-diameter test chamber like the one at GASL takes a lot of energy-its facility is a labyrinth of tanks, ducts, and valves all designed to spit out a blast of air at incomprehensible speeds for up to a minute at a time.
The inflow end of the wind tunnel is connected to a bank of truck-size steel cylinders that hold a total of 20 tons of air at 2,400 pounds per square inch. The exhaust end is connected to a spherical 48-foot-wide steel vacuum tank behind the building. First, the air is pumped out of the sphere, simulating the near vacuum above 80,000 feet. Then, compressed air from the tank farm flows through a hydrogen- and oxygen-fueled heater that raises the temperature to more than 4,000
Photograph by Tom Tavee
Pat Fischer, the Bellagio’s surveillance director, flanked by banks of VCRs (left) and computers (right).