Dr Paul Bevilaqua, Chief Engineer of the Lockheed Martin "Skunk Works" is speaking on "Inventing the Joint Strike Fighter". The Australian Government has announced they will order 72 F-35A aircraft.
Dr Bevilaqua developed the F-35-B lift fan for the Short Takeoff / Vertical Landing (STOVL) variant of the Joint Strike Fighter. He discussed the history of attempts to create a vertical landing fighter aircraft. The Harrier is the only successful such aircraft so far, using a ducted turbofan engine, but is not supersonic. The problem was to create an aircraft with the speed of an F-18, but land vertically like a Harrier.
The F-18's engines have only half the thrust needed to land vertically. Also engine's thrust is at the back of the aircraft and so the solution was to balance with with a shaft driven fan at the front. In retrospect this sounds obvious, but as Dr Bevilaqua pointed out that previously engines were either used as a turbojet or turbo-shaft, not both. Research shows the the combination is possible with only a small drop in power.
Interestingly Dr Bevilaqua's initial sketch for the aircraft has the lift fan mounted horizontally in front of the turbojet, with two nozzles to direct the air down, as with the Harrier. The final design for the F-35B has the fan vertical, so no nozzles are required. However, it seems to me this gives up some subsonic efficiency, as the fan is not used in forward flight (as it is in the Harrier). It might be possible to have an annular fan with a clutch. This would be shut down at high speed, but operate as a turbofan at low speed, then with additional doors open, direct air down for vertical landing.
Dr Bevilaqua pointed out that the stealth features of the F-35 are not designed to make the aircraft completely invisible to radar, just hard to spot from some angles.
Dr Bevilaqua related how the design of the VSTOL aircraft was turned into an idea for a conventional aircraft, simply by taking out the lift fan and replacing it with a fuel tank. He related how previous such "joint" designs had a bad reputation in the US DoD due to the TFX project (which resulted in the F-111 which Australia purchased).
One interesting part of the talk was the approach to making the prototypes of the X-35. 3-D printing was used to produce plastic mock-ups of the parts, so the companies making them had a full size template for making metal parts.
Dr Bevilaqua explained that the three variants of the F-35: Airforce, Beach and Carrier have essentially the same fuselage with some different components attached.
Australia is planning to order the conventional take-off F-35A, which does not use a lift fan. Dr Bevilaqua explained that the US Marines have had their own air-support using Harrier aircraft and the F-35B is the supersonic replacement for it. Air support for amphibious operations is very relevant to the Australian Army, which is re-equipping itself to operate from Australia's two new Canberra Class amphibious assault ships. These ships have flight decks specifically designed for the Harrier and the F-35B STOVL aircraft. I have suggested Australia order eighteen F-35b aircraft, to equip the ships.
ps: The event was organised by the American Institute of Aeronautics and Astronautics - Australia. They showed a very cheesy video promoting AIAA and aerospace technology. What got my attention was that AIIA membership is free for school teachers.