but it's a chebby lol
from Av-Week:
USAF Researchers Flying Pulse Detonation Engine-Powered Aircraft
Aviation Week & Space Technology
03/08/2004, page 30
Stanley W. Kandebo
New York
Test flights should help demonstrate potential of pulse detonation engines
Flights of Fancy
An experimental pulse-detonation-powered aircraft should begin test flights next month at Mojave, Calif., now that the FAA has issued it an airworthiness certificate.
Powered by a pulse detonation engine (PDE) developed by the Air Force Research Laboratory's Combustion Science Branch, the aircraft, a Rutan LongEZ, will be flown by pilots from Burt Rutan's Scaled Composites.
The aircraft is expected to make 3-10 short flights. During each "we'll probably fly a few circles and land to show that the PDE concept is viable. There'll be no cross-country flights," said Fred Schauer, a research engineer within the Laboratory's Propulsion Directorate.
The purpose of the tests is three-fold: to propel an aircraft using a PDE, to investigate the acoustical and vibrational effects of a PDE on an aircraft and pilot, and to help demonstrate the potential of PDEs. The tests are not part of an engine technology demonstration; the flight test powerplant is a research tool.
PULSE DETONATION engines are essentially tubes in which fuel and air are admitted into one end and then detonated, creating a high-pressure wave that travels at supersonic speeds down the length of the tube, causing burning rates of thousands of meters per second and a pressure rise of 30-100 atmospheres. As exhaust gases are expelled at the far end of the tube, the process repeats. In comparison, pulsejets used by Germany during World War II did not use a detonation process and peak pressure rises were only about 2-3 atmospheres.
PDEs offer the potential to propel missiles and manned aircraft at speeds up to about Mach 4. Commercial gas turbines also could benefit from pulse detonation technology; if substituted for the core of a conventional gas turbine engine, the resulting hybrid powerplant could show a fuel efficiency improvement of 10% or more. The Air Force has been examining PDEs, in an in-house program, since the late 1990s, the Navy even longer.
A LongEZ (foreground), fitted with a four-tube pulse detonation engine, is expected to make 3-10 flights. The engine will run on standard aviation gasoline during the trials.
The upcoming flight tests are a joint effort between the Air Force Research Laboratory's (AFRL) Combustion Science Branch, Innovative Scientific Solutions Inc., the AFRL Air Vehicles Directorate and Scaled Composites.
The engine to be used in the upcoming tests is a modified four-cylinder General Motors automobile engine that will run on standard aviation gas. Four PD tubes replace the cylinders and two sets of cylinder heads have been installed so that there are eight valves per tube. "It's basically an off-the-shelf engine," Schauer said. The flight test engine is similar to pulse detonation powerplants the Combustion Sciences Branch has been researching for several years.
Three engines were fabricated for the upcoming tests. The first was run under static conditions on a teststand, while the second was installed in a LongEZ for structural and acoustic tests. The third engine is the flight test article. Installed, it should be capable of propelling the LongEZ at about the same cruise speeds as the 108 hp. Lycoming engine it replaces, Schauer said. "When the engine detonates, it provides 1,200 lb. at peak thrust. Of course, the average thrust is lower and also depends on ambient temperatures and pressures," he explained.
REGARDLESS, RESEARCHERS classify the flight test PDE as "basically functionally equivalent" to the powerplant it replaces. That means that during the upcoming flight trials, researchers believe the aircraft will stay in the middle of its flight envelope, reaching a speed of about 150 kt.
Static thrust of the fight test-configured, four-tube pulse detonation engine was measured at Wright-Patterson AFB, Ohio.
Engine noise is a significant issue with PDEs and the flight tests are expected to provide significant data in this area. "You have a Mach 5 shock wave coming out of each tube 20 times a second," Schauer said. Noise around the aircraft is expected to be about 150 dB., equivalent to the noise generated by a conventional gas turbine using its afterburner. Noise in the cockpit is expected to be about 130 dB., so hearing protection will be required by the pilot.
Overall, USAF research has been directed at examining detonation, instrumentation and measurement techniques as well as developing the methods used to study PDEs. "All this has been shared with industry," Schauer said.
USAF work also has been focused on exploring the potential operating envelope of PDEs. "We've been successful in stationary detonations; we've also been doing some collaborative tunnel testing with NASA to see if we can do detonations under supersonic conditions," he explained.
Nozzle work also is a priority item for researchers. "You can't efficiently use conventional nozzle designs because they're for steady-state systems," Schauer said. PDEs are currently anything but that. In a PDE, "you go from an under-expansion to an over-expansion many times a second," Schauer noted.
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