STOVL pedigree gives Rolls-Royce key technology edge

As the manufacturer of the world’s only operational short take-off vertical landing (STOVL) engine, Rolls-Royce has established unique STOVL expertise, which is being extended by the company’s current work in developing the STOVL technology for the Lockheed Martin F-35 Joint Strike Fighter (JSF).

The company’s experience is drawn from the bank of knowledge accumulated in developing and producing the Pegasus, powerplant of the unique Harrier/AV-8B family of tactical fighters. This 21,500-23,800lb thrust turbofan last year surpassed 1,500,000 flying hours in service with UK, US, Spanish, Italian, Indian and Thai armed forces.

STOVL technology development dates back to the early 1950s, when military leaders foresaw the rapid onset of weapons capability that would necessitate a new breed of defence fighters able to launch themselves from less accessible bases. Project teams in the US and Europe studied a range of concepts, but only the Pegasus-powered Harrier survived to successfully enter service.

This turbofan has four rotating nozzles, two on each side, that allows bypass air and exhaust gases to be vectored downwards. It also incorporates contra-rotating engine spools to minimise the gyroscopic effect on hovering stability.

First STOVL patents were registered in 1956, the Pegasus ran in 1959, and the Pegasus-powered Hawker P1127 (to become Harrier) flew for the first time the following year. The first operational squadron of STOVL fighters entered service with the RAF in 1969, and two years later, the US Marine Corps became the first export customer, later becoming the first operator to take the highest-powered production standard Pegasus, the 23,800lb 11-61/F402-RR-408.

The Pegasus-powered Harrier first won its combat spurs during the Falklands conflict in the South Atlantic, when it proved its worth as a naval fighter. It has since proven its value in a number of combat scenarios, notably during the Gulf War, where STOVL capabilities allowed AV-8Bs to continue combat operations when the airfield was temporarily closed to other fixed wing operations because a disabled aircraft blocked the runway. AV-8Bs were able to continue takeoffs and landings from either end of the airfield, in less than 3,000 feet.

Recognising the need to replace wide range of fighter and strike aircraft, the United States initiated the JSF programme, the largest ever Department of Defense acquisition programme. The STOVL variant is one of three variants derived from a common design to ensure an affordable high-performance aircraft.

From its formal launch in 1996, Rolls-Royce has been involved in all main propulsion system elements of this project. During JSF’s Concept Demonstration phase, Rolls-Royce provided a range of components that enabled Lockheed Martin’s X-35B prototype to prove its STOVL capabilities. Rolls-Royce supplied a LiftFan, driven by a shaft from the engine via a geared clutch, and a swivelling nozzle providing horizontal thrust for forward flight that can turn through 90 degrees to redirect the engine’s exhaust flow down for vertical lift.

The contract covering the design and development work of the STOVL elements for the F-35 during the System Development and Demonstration (SDD) phase of the program is worth $1 billion to Rolls-Royce over 10 years. Rolls-Royce will manage the STOVL work from Bristol, England, while involving teams from Indianapolis in the US as well from the UK site.

The JSF will be used by the U.S. Air Force, Navy and Marines, as well as the U.K. Royal Navy and Air Force. Canada, Denmark, The Netherlands and the United Kingdom have signed up to the SDD programme.