AFRL engine, hearing protection technology land at Air Force museum

  • Published
  • By John Schutte
  • 711th Human Performance Wing
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  The first aircraft to fly by pulsed-detonation engine power, and associated hearing protection technology--both developed at the Air Force Research Laboratory-- were welcomed by the National Museum of the United States Air Force in a ceremony held August 25 at the Museum Annex at Wright-Patterson Air Force Base. 

The PDE developed by AFRL's Propulsion Directorate logged a record-breaking manned flight on January 31 at Mohave, Calif. With test pilot Pete Siebold at the controls of the modified Long EZ aircraft manufactured by Scaled Composites, the PDE achieved a speed of over 120 mph and 60 to 100 feet altitude, producing more than 200 pounds of thrust, marking the first successful flight powered by pulse detonation technology.
 
During the flight, Siebold wore an Attenuating Custom Communications Earpiece System (ACCES) integrated with a standard military flight helmet for acoustic protection from the extremely loud engine. The deep-insert custom-molded ACCES technology is a product of an earlier collaboration between the 711th Human Performance Wing's Warfighter Interface Division, Battlespace Acoustics Branch and Westone Laboratories, Inc., under a Cooperative Research and Development Agreement. 

The demo flight culminated a collaborative effort led by the Propulsion Directorate and its on-site contractor Innovative Science Solutions, Inc. (ISSI) and supported by AFRL's Human Effectiveness and Air Vehicles Directorates. The team overcame a multitude of technical challenges to prove that pulse detonation is a feasible technology that would be more economical and less fuel-hungry than traditional jet engines.
 
"This is a great day for your team and the team at the museum," said museum director Major Gen. (Ret.) Charles D. Metcalf.
 
The PDE is unique because instead of burning fuel for propulsion (known as deflagration), an air and fuel mixture is ignited and detonated in repeated, controlled explosions inside open-ended tubes resembling exhaust pipes. When detonation moves through the tubes it creates a supersonic shockwave that continually pulses and generates thrust.
 
Researchers from the 711th Human Performance Wing determined acoustic exposure limits and provided the hearing protection system. Noise levels in the cockpit of the PDE-driven aircraft reach 130 dB compared to about 100 dB for a typical fighter jet, said AFRL research audiologist John Hall. Without ACCES protection, a PDE pilot would be unable to communicate with crew and would suffer hearing loss after only two flights. 

In presenting the hearing protection system to the museum, Siebold said ACCES technology "allowed the flight to take place and me to retain my hearing."
 
The PDE project demonstrated that the engine could sustain an aircraft, withstand extreme acoustic pressure during detonations, and that the pilot and ground crew could be protected from high noise levels. 

Both technologies were developed using off-the-shelf components--the PDE incorporated an 8-cylinder automotive engine and ACCES leveraged Westone's commercially available communications equipment used by musicians.
 
The increased-thrust PDE could be capable of powering future aircraft up to four times the speed of sound, according to Dr. Fred Schauer, PDE program team leader.
 
"This engine offers the capability of static to near-hypersonic flight with good supersonic efficiencies. PDEs could make sense for missions that require efficient supersonic cruise and/or boost from low to high speeds," Dr. Schauer said.
 
Scaled Composites and AFRL have a history of collaboration reaching back to June 2004 when Scaled Composites launched the first private manned vehicle beyond the Earth's atmosphere. In that flight, test pilot Mike Melvill--wearing ACCES earplugs--guided SpaceShipOne to a record-breaking altitude of 328,491 feet or approximately 62 miles.
 
"The PDE plane is way loud, so the AFRL Propulsion Directorate and Scaled Composites came to us to figure out how to protect the pilot," Hall said.