F-35B - Roll Posts
5:26 PM on Dec 09, 2011
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.
Both use engine bleed air for roll control in the hover, but where the Harrier uses wingtip puffer jets the F-35B has more powerful nozzles in the wing that provide both roll control and a significant amount of vertical thrust - about 1,850lb each.
One of latest STOVL issues to emerge involves overheating of the nozzle actuators embedded in the wing. The roll posts duct engine bleed-air at high pressure and temperature from the compressor to mid-wing, where thrust is modulated for roll control using fast-acting nozzles. Seals are leaking, increasing temperatures in the nozzle bays and overheating the rotary actuators. Thus limits the time the aircraft can spend in jet-borne flight at speeds below 60kt.
The solution is to instal insulation blankets to keep heat away from the actuators and to switch to a potting material, or sealant, on the actuator components that can cope with the higher than anticipated temperatures. An actuator redesign is under way and will be introduced into production engines in late 2012.
There are doors that close over the roll posts for stealth in up-and-away flight, and they are perforated to allow heat to escape. These doors are cracking in high-speed flight, so stiffeners have been added, beginning with test aircraft BF-3.
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