This post is one in a series on the development of the F-35. Click here for a Flash graphic with system cutaways. Click on Read More to read the entire post on that system and check out next week's special coverage of the program in the Dec 12 edition of AW&ST.
Dorsal auxiliary air-inlet doors, which open in STOVL mode to increase mass flow into the engine and generate an additional 7,000lb of vertical thrust, were found to flutter in semi-jetborne flight, causing premature hinge wear. Photos: Lockheed Martin
The initial fix was to modify operation of the large lift-fan door forward of the auxiliary inlet (see picture above) to stay fully open to higher airspeed on short take-offs to "shelter" the clamshell doors. Instead of closing to the 35° mid position at 125kt the aft-hinged lift-fan door now stays fully open at 65° (see below) to 170kt on take-off, and begins to open to 65° at 160kt on approach to landing.
Meanwhile, the auxiliary-inlet door actuator and mechanism has been redesigned to make them stiffer, moving the natural frequency of the doors significantly higher. Aircraft BF-1, the first test F-35B to be modified with the redesigned door system is scheduled to return to flight by January. Back to F-35B Graphic or on to Bulkhead