Pratt & Whitney hopes to test a new adaptive fan variant of its F135 afterburning turbofan in the first quarter of 2013, company officials say.

"We think that'll be a game-changer going forward," says Bill Gostic, P&W vice-president for advanced programmes and technology. Combined with a new very high pressure ratio core, the prototype forms the basis of P&W's entrant into the US Air Force Research Laboratory's adaptive engine technology development (AETD) programme.

With its new prototype, P&W hopes to knock out one of the two incumbent engine-makers developing the US Air Force's ADaptive Versatile ENgine Technology (ADVENT) engine. If everything goes according the company's plans, P&W will supplant either Rolls-Royce or General Electric on AETD - which is a follow-on to ADVENT, says P&W military engines chief Bennett Croswell.

The goal of the AETD is to develop next generation variable cycle engines - the most likely future application is for a next generation replacement for the Lockheed Martin F-22 Raptor, Gostic says. The design goal is to retain the engine performance found on fifth-generation fighters, but to reduce the fuel consumption by at least 30%.

The US Navy is also interested in the variable engine technology, but the service is not as far along in its programme as the USAF. The USN needs a new fighter to replace the Boeing F/A-18E/F in the mid-2030s. USN officials have said that they want greater range and kinematic performance out of their future next generation fighter.

The core of P&W's proposed technology for a sixth-generation fighter engine is partially based on the core of the PW1000 geared turbofan - which the company has dubbed the PW9000 family. The biggest innovation is an adaptive fan in addition to an adaptive turbine section, Gostic says. The combination of those two technologies should yield the better than 30% reduction in fuel consumption that the US Air Force requires.

But while the adaptive engine sections are the most visible technologies, the most difficult part of designing a new fighter engine in the era of stealth is the exhaust system. "It's the long lead item," Gostic says.

The shaping required of a sixth-generation stealth fighter engine will not look like anything that has come before. It is very different from an axisymmetric stealth nozzle found on the F-35, for example, Gostic says. He adds that not only is signature management a real challenge, the engine has to be completely integrated into the airframe. There has been a blurring of the lines between airframers and engineer manufactures in that area, Gostic add. The exhaust is, in many respects, part of the airframe.

One of the advantages of a three stream fan configuration is that it affords a third stream of relatively cool air for signature management. That mean the air can used to cool hot components to reduce the infrared signature - or that air can be fed into the core or afterburners to boost the thrust levels, Gostic says. The ultimate goal is for the engine to be as efficient at low cruise speeds at it would be at high speed supersonic cruise speeds.

Another challenging area is to develop the full authority digital engine control, Croswell says. Modern engine control are a vital part of the aircraft, he says, pointing to the short take-off vertical landing fan and nozzles on the Lockheed Martin F-35B aircraft or the thrust vectoring nozzles on the F-22.

Source: Flight Daily News