PRATT & WHITNEY hopes to win approval from the US Air Force by the end of this year to flight-qualify the F100-229A, a radically improved version of the -229. The US engine builder says that the $40 million qualification effort would allow a large-scale retrofit programme of McDonnell Douglas F-15Es and Lockheed Martin Block 52 F-16s, producing life-cycle savings of up to $400 million. The engine could be available for export after 2000.

Most of the improvements, and most of the potential savings, are tied to a new fan module at the heart of the upgrade. The module has many design elements of the F119, in initial production for the Lockheed Martin/Boeing F-22. The fan has boosted airflow by more than 10%, reducing turbine temperatures by nearly 50¡C and allowing inspection intervals to be increased from 4,300 cycles to 6,000.

The three-stage fan module is longer by around 150mm, and is slightly larger in diameter, but still fits into the original -229 engine envelope, thanks to repackaging of accessories and a slimmer oil tank.

The fan module is fitted with integrally bladed rotors and bowed stators, again derived from those of the F119. It also has a one-piece cast inlet, which reduces the part counts by around 300 and increases ruggedness. "We've been able to take the inlet vanes off and produce far more stall margin than we'd expected," says PW229A engineering manager Jeff McAnally. P&W cannot reveal exactly what improvements have been achieved. The tests have shown, however, that the fan stalls substantially later in the afterburner cycle.

The engine is also strengthened to meet the USAF's new high-cycle-fatigue requirements, issued after fan failures in operational engines. This adds around 68kg to the weight, most accounted for by the strengthened fan.

P&W says that the improvements could offer a 30% increase in turbine durability or be translated into additional thrust growth to around 151kN (33,900lb), up from the current 130kN with afterburner, "-or it could add 5% range to the typical USAF air-to-ground F-15 mission", McAnally adds.

Source: Flight International