Boeing is said to be stealing ahead of rival Lockheed Martin in the $219bn Joint Strike Fighter (JSF) project, in which Britain is a partner. The perceived difficulties of servicing an innovative turbofan driveshaft and gearbox arrangement proposed by Lockheed Martin, teamed with British Aerospace, are behind the claims.
US aerospace giants Boeing and Lockheed Martin are each leading competitive JSF demonstrator programmes, the X-32 for Boeing and the X-35 for Lockheed Martin. One will be chosen to go into production following a ‘fly-off’ between prototypes in 2000. Construction of the demonstrators and their engines has already begun. The aircraft is scheduled to come into service in the US in 2008.
In the demonstrator programme, both companies will develop three JSF variants for the US Air Force, US Navy, US Marine Corps and the Royal Navy. The US Marine Corps will use a short take off and vertical landing (STOVL) version of JSF, as could the Royal Navy. The US Navy will use a catapult take-off (CTOL) variant of JSF, and the US Air Force will use a conventional take-off version. Both teams will build concept demonstrators for the STOVL and catapult launched versions.
Propulsion arrangements on the Boeing demonstrator appear simpler than Lockheed-Martin’s and this is the key to Boeing’s supposed lead.
BAe was included in Lockheed Martin’s JSF bid largely due to its vertical takeoff expertise gained in its development of the Harrier. However, the system the X-35 will use to hover and land vertically is considerably different from the Harrier’s four directional jet nozzles.
The X-35’s main engine has a single directional nozzle at the rear, which rotates from the horizontal to the vertical to provide thrust for hovering. This is assisted by a linked, but separate, two-stage lift fan further forward in the fuselage.
The forward lift fan is driven by a 27,000hp central drive shaft from the main engine, through a clutch and gearbox. Harry Blott, Lockheed Martin’s vice-president and deputy programme director for the X-35 programme, was proud of the X-35’s lift fan at Farnborough earlier this month, saying it had exceeded lift expectations by 5%.
The involvement of Blott, who has a background in the US Marines Corps, also brings credibility to Lockheed Martin’s more complicated engine concept.
Affordability was central to Lockheed Martin’s X-35 concept. Blott says: ‘The government forced both companies to do technical work to reduce costs.’
Dave Palmer, Lockheed’s JSF project manager in Fort Worth, Texas, is sanguine about the X-35: ‘Our shaft-driven lift fan allows the most restrictive customers the US Marine Corps and the Royal Navy to really operate comfortably. We think that this concept for STOVL flight is very benign.’
However, according to a California-based consultant: ‘The Marines are very dubious about that shaft-driven lift fan and ask how it’s going to be serviced in the field. They feel the X-32 is going to be a much simpler airplane to deal with. There is already a perception that Boeing is ahead in the JSF competition because its engine arrangements are simpler.’
The Boeing X-32 uses the same Pratt & Whitney PW119 turbofan. But to switch from horizontal cruise to hover, air flow is closed off to the engine’s rear nozzle and a lift module mounted midway along the fuselage comes into play; this has two swivelling nozzles and is much more like the Harrier arrangement.
There is no forward lift fan, as on the X-35. Additional minor jets, as on the Harrier and X-35, will keep the aircraft stable in the hover.
Whatever the perceived advantages and disadvantages, both aircraft will be at the cutting edge of STOVL technology. A British engineer involved in JSF says that while both the X-32 and X-35 will be ‘quite unstable’ in the hover, the air jets and ‘fly-by-wire’ controls will ensure they stay straight and level.
And whichever engine is used, the mechanics of Boeing’s and Lockheed Martin’s demonstrator aircraft will be the same.
Meanwhile, the JSF programme has been called into question in the US as being over-ambitious. Last April the US Department of Defence’s air warfare branch released a ‘talking paper’ by George Schneiter, the Pentagon’s director of strategic and tactical systems, which criticised the JSF programme’s ‘unrealistic expectations’.
It said the project’s participants ‘may be getting more caught up in the salesmanship and beginning to believe the rhetoric, as opposed to facing the realities of the technical and programmatic problems’.
The paper criticised the lack of common parts between the JSF’s F119 engine and a version of the same engine used in the US Air Force’s F-22 fighter. The JSF version of the F119 has more risks because of increased thrust requirements, the paper said.
But despite this high-level criticism, BAe remains upbeat about the project’s prospects. A spokesman for BAe hints that it wants to remain in the programme even if STOVL technology does not cut the mustard in either Boeing’s or Lockheed Martin’s offerings.
‘We’re looking at something that’s a long time in the future, he says. ‘The fact that the Royal Navy has expressed interest in the STOVL version of JSF is of great interest to everyone in the UK, but we are interested in the total JSF programme.’