Hypersonic jet ready for launch [British design will launch tomorrow]

A new jet engine design able to fly seven times the speed of sound is scheduled to launch over Australia on Friday.

The scramjet engine, known as Hyshot III, has been designed by British defence firm Qinetiq.

If successful, it could pave the way for ultrafast, intercontinental air travel, and substantially cut the cost of putting small payloads into space.

It is the first of three test flights planned for this year by the international Hyshot consortium.

The first Hyshot engine was launched in 2001 but the test flight failed when the rocket carrying the engine flew off course.

A supersonic combustion ramjet, or scramjet, is mechanically very simple. It has no moving parts and takes all of the oxygen it needs to burn hydrogen fuel from the air.

This makes it more efficient than conventional rocket engines as they do not need to carry their own oxygen supply, meaning that any vehicle could potentially carry a larger payload.

However scramjets do not begin to work until they reach five times the speed of sound.

At this speed the air passing through the engine is compressed and hot enough for ignition to occur. Rapid expansion of the exhaust gases creates the forward thrust.

To reach the critical speed, Hyshot III will be strapped to the front of a conventional rocket and blasted to an altitude of 330km before being allowed to plummet back to Earth.

On its descent the engine is expected to reach a top speed of Mach 7.6 or over 9,000km/ hour.

Making sure the flight happens correctly is incredibly difficult, according to Dr Allan Paull, project leader of the Hyshot programme at the University of Queensland.

"You are dealing with extremes of conditions. You're working out on the edge and with a lot of the stuff no one has ever tried [it] before," he told the BBC News website. "You've got to expect things to go wrong".

If everything goes to plan, the experiment will begin at a height of 35km. As the engine continues its downward path the fuel in the scramjet is expected to automatically ignite.

The scientists will then have just six seconds to monitor its performance before the £1m engine eventually crashes into the ground.

The scramjet will not provide forward thrust during the flight, necessary if the engine is ever to power a vehicle. But the test will be enough to show that burning starts automatically and to verify trials already done in a wind tunnel.

"The wind tunnels operate for milliseconds," Dr Paull explained. "The difficulty is whether or not you can even see the supersonic combustion in this period of time."

Although the Qinetiq engine has never left the ground it is more realistic than previous Hyshot experiments.

It has a more efficient air intake on the front and can operate over a greater range of speeds. It also scoops air into the combustion chamber at a lower temperature, closer to that needed in a commercially useful engine.

If the test flight is successful, it will be followed four days later by the test flight of another Hyshot engine designed by the Japanese Aerospace Exploration Agency (Jaxa). This will be followed in June by the launch of an engine that will fly at Mach 10, designed by the Australian Defence Science and Technology Organisation (DSTO).

The Hyshot tests will bring the idea of a commercial scramjet one step closer to reality.

In the first instance these would probably be used to launch satellites into low earth orbit but many have speculated that they could also allow passenger airlines to fly between London and Sydney in just 2 hours.

Although this vision maybe many years off, it was given a huge boost when Nasa successfully flew its X-43A plane over the Pacific Ocean in 2004. The unmanned aircraft flew at 10 times the speed of sound, a new world speed record.

The team at the University of Queensland is also currently designing a vehicle that can fly under its own power.

If the plane works, it could be flying over the Australian desert within the next two years.

The Pratt & Whitney J58 engine was a nine-stage, axial-flow, bypass turbojet originally developed in the late 1950s to meet U.S. Navy requirements. It was the first jet engine designed to operate for extended periods using its afterburner. The J58 generated a maximum thrust of 32,500 pounds -- more than 160,000 shaft horsepower -- and was the most powerful air-breathing aircraft engine yet devised. The J58 was specifically tailored for operation at extreme speeds, altitudes, and temperatures, and was the first aircraft engine to be flight qualified for the Air Force at Mach 3. At maximum output the fuel flow rate in the J58 is about 8,000 gallons per hour and the exhaust-gas temperature is around 3,400 degrees. The J58 was only used on the Lockheed YF-12 interceptor and its descendents, the A-12 and SR-71.

The J58 required the use of a special AG330 engine starter cart to spool the engines up to the proper rotational speed for starting. The cart was powered by two unmuffled Buick Wildcat V-8 racing car engines which delivered a combined 600 horsepower through a common gear box to the starter drive shaft of the aircraft engines. The J58s had to be spun up to about 3,200 RPM for starting.

The variable-geometry inlets for the engines were quite complex and intricate. The most prominent feature was a hydraulically-actuated conical spike which was automatically moved forward or aft by the Air Inlet Computer as required to keep the supersonic shockwave properly positioned in relation to the inlet throat. Working in conjunction with a series of bypass ducts and doors, the spike prevented supersonic air from entering the inlet and maintained a steady flow of subsonic air for the engine. At Mach 3.2 cruise the inlet system itself actually provided 80 percent of the thrust and the engine only 20 percent, making the J58 in reality a turbo-ramjet engine.

At the speeds the SR-71 operated, surface temperatures were extremely high due to aerodynamic heating: 800 degrees at the nose, 1,200 degrees on the engine cowlings, 620 degrees on the cockpit windshield. Because of the operating altitudes, speeds, and temperatures, Lockheed designers were forced to work at the cutting edge of existing aerospace technology, and well beyond in many cases. Many features and systems simply had to be invented as they were needed, since conventional technology was inadequate to the task. New oils, hydraulic fluids, sealants, and insulations were created to cope with the ultra-high temperatures the craft would encounter. A new type of aviation fuel, JP-7, was invented that would not "cook off" at high operating temperatures, having such a low volatility and high flash point that it required the use of triethylborane as a chemical ignitor in order for combustion to take place. The fuel itself was rendered inert by the infusion of nitrogen and then circulated around various components within the airframe as a coolant before being routed into the J58 engines for burning. Link; http://www.hill.af.mil/museum/photos/coldwar/j58.htm

robertpaulsen:

Call me crazy, but why not 86 the scramjet, increase the payload, and use the rocket all the way to Mach 7?

You also need rockets when you go exoatmospheric. But a scramjet (very roughly) requires half the combustibles by weight and volume that a rocket does, as it need not carry oxygen, it gets it from the atmosphere.

I read papers on SCRAMJET theory in school in the 1960s, but only recently has it started to be practical in engineering terms.

oxcart:

Heh, on the screen name. That's a great photo of the static test. There are some similar shots of the X-43 statics around, but it's not as big, so not as spectacular.

The loudest thing I'm aware of is the pulse detonation engine they were playing with a Wright-Pat. They had to abandon plans for a manned test flight. The Germans had a sound weapon in the lab in WWII, and it was not as loud as the PDE.

d.o.l.

Criminal Number 18F

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.