A performance comparison of operational VSTOL propulsion systems

Composite aircraft employing Vertical and Short Takeoff and Land (VSTOL) capabilities offer a possible solution to many of the challenges facing our aviation system today. But the development of these vehicles has been relatively slow. Several military VSTOL aircraft have been deployed, including the Yakolev YAK-36 Forger and the McDonnell Douglas AV-8 Harrier. While the YAK employs a separate propulsion system for vertical lift and for forward thrust, the Harrier employs a single high bypass turbofan engine which uses thrust vectoring for both vertical and forward flight.

The Rolls Royce Pegasus engine development began in the late 1950s. The engine has seen service in various models of the Harrier as the F-402- RR-402, the F-402-RR-406, and the recently operational F-402-RR-408. This thesis will discuss the design evolution of the series, as well as compare performance for engines within the series. Performance will be compared for each engine in the series to assess areas of strength and weakness, and each engine will be compared to each other in the series. Performance comparisons will consist of vertical lift capability for engines in the series both unaided and with the use of thrust augmenting water injection for various temperatures throughout the ambient operating temperature range of the aircraft.

Performance increases have primarily been realized by increasing the operating temperature of the engine, reducing both reliability and engine life. Further performance increases in the Pegasus engine will be challenging without significant redesign.