Boeing and Lockheed Martin have completed government-required flight testing of their respective Joint Strike Fighter (JSF) concept demonstrators. Both teams are on track to submit results from the final phase of short take-off and vertical landing (STOVL) testing as addenda to their engineering and manufacturing development proposals by the 15 August deadline. Selection of a winner is scheduled for 26 October.
Lockheed Martin completed the government-required flight testing on 16 July with a short take-off, transition from wingborne to jetborne flight and vertical landing at Edwards AFB, California. The X-35B demonstrator remained in STOVL mode, with the shaft-driven lift fan engaged, throughout the flight. Boeing completed required testing on 1 July with a series of short take-offs of the direct-lift X-32B. It had accomplished first transition to a vertical landing on 27 June at NAS Patuxent River, Maryland. Touchdown weights were 12,700-13,200kg (28,000-29,000lb).
Both teams continue testing to achieve company objectives. Lockheed Martin did hope to complete "Mission X" last week, which required a short take-off, switch to conventional propulsion mode, acceleration to supersonic speed, then a return to STOVL mode and transition to a vertical landing.
Boeing also flew supersonically last week. The X-32B demonstrator is not capable of vertical and supersonic flight on the same mission, as the inlet cowl and undercarriage doors were removed and lift-improvement strakes added for STOVL testing, precluding supersonic flight.
Boeing has not performed a vertical take-off and says it is not a requirement.
Lockheed Martin is still discussing with the JSF programme office the desirability of ferrying the X-35B to Patuxent River for sea-level testing on the STOVL variant. All testing so far has been conducted in the high desert of California, at 2,500ft (760m) altitude, involving a thrust loss of about 2,500lb (11kN).
In the 16 July test, the X-35B landed vertically on the pad at Edwards at a weight of around 15,000kg, including just under 900kg of fuel, says test pilot Simon Hargreaves. "That's more than twice the Harrier's hover weight at this altitude." The aircraft had earlier performed a vertical take-off at nearby Palmdale at 16,100kg, including over 2,270kg of fuel.
Hargreaves says the aircraft experienced no Harrier-style "suck-down" or loss of lift just before touchdown, and no evidence of hot-gas reingestion in the hover. The temperature rise measured in the inlet was just 3°C(6°F), says Lockheed Martin, confirming that relatively cool air from the lift fan, behind the cockpit, does prevent engine exhaust reaching the inlets.
Source: Flight International
