But test pilot praises JSF's performance as aircraft AA-1 begins roll manoeuvres
Lockheed Martin is working to fix fuel system valves in the first F-35 Joint Strike Fighter that have prevented the aircraft being able to take on a full load. "So far we've been flying with about 3,500lb [1,600kg] short of what it will hold," says chief test pilot Jon Beesley.
Although reporting no "significant" issues, Beesley says improvements and repairs have been made to the flight control electro-hydrostatic actuators, which suffered minor leakage, and to the integrated power pack, which combines the functions of the auxiliary power unit, environmental control system and emergency power system.
The test team hopes to take aircraft AA-1 to Edwards AFB, California for emergency back-up system tests, including engine relights, in September-October. Tests above Mach 1, provisionally to start in 2008, "will not be a problem", says Beesley: "The more interesting tests will be for higher-speed flight at lower levels."
Lockheed expects to complete initial airworthiness test flights over the next few sorties, clearing the way for further envelope expansion and system tests. The first manoeuvring flight demonstrations, complete with full-stick rolls, were accomplished on 20 March, during AA-1's ninth flight test.
"It worked exceedingly well," says Beesley, who praises the aircraft and its "robust" handling characteristics. "The aircraft is stiff compared with the [Lockheed] F-22 in which you feel as if you're at the end of a diving board. With the F-35 you're standing at the other end."
Beesley says one peculiarity is the design of the splitterless inlet, which "picks up an extra 2,000lb thrust [9kN]" as the aircraft accelerates between 80kt (150km/h) and 100kt for take-off. The jump in thrust is "definitely noticeable in the cockpit," he adds.
Aircraft AA-1 is also being used for fuel dump tests to help Lockheed with final design decisions on the carrier variant. The aircraft is also undergoing speedbrake test work. Although not fitted with a dedicated speedbrake, the F-35 is designed to be slowed using a combination of leading- and trailing-edge flaps, as well as rudder.
Speaking at the Society of Experimental Test Pilots meeting in San Diego, California, Beesley also praised the F-35's Pratt & Whitney F135 that produces "perfect linear thrust" throughout its 40,000lb-plus power range. To date the aircraft has reached 340kt/M0.78, +3g and a 16º angle of attack.
Source: Flight International
