F-35 Cancelled, then what ?

[John Farley]

B STOVL flight control software - background

The B’s flight control software which provides the handling characteristics that the pilot sees during the STOVL speed range (regardless of the airframe aerodynamics or lift system forces present at any time) is a very well developed and tested aspect of the overall programme.

If I can convince some posters of that it may help them have confidence in the handling queries that crop up here from time to time and stop some people feeling that if they can’t see a video of a particular manoeuvre on YouTube then there has to be a future problem being covered up by L-M or others.

My personal position is that I know nothing about programme costs, politics, support issues and timescales and all those other things that may be right or wrong with the programme. However I do know a bit about the flight control software because I went to the first meeting about it in 1971 (yes 1971) and was associated with its development from then until I last flew it in the VAAC Harrier in 1999.

In 1971 the RAE scientists at Farnborough were looking to improve on what the pilot experienced in the Harrier, which at that time had then been in service for two years. The elephant in the room was asking the pilot to control both thrust amount and thrust direction with his left hand. They wanted (correctly) to get rid of the nozzle lever to avoid the pilot boob of moving the wrong lever. It was after all only a matter of time before any of us did that (one day I stop-cocked the engine instead of selecting the reverse thrust angle but was lucky enough to have a few knots on at the time and the dying whine woke me up).

As befitted a research establishment the RAE were not looking to mod the Harrier fleet but to start with a clean sheet of paper about what the pilot should be given in any Harrier replacement which turned out to be the F35B. I won’t bore you with the very large number of “what does the left hand do and what does the right hand do” ideas during a whole raft of possible STOVL manoeuvres, however we flew most of these options in the VAAC Harrier from the completely digital rear cockpit, the front cockpit having normal Harrier controls for the safety pilot.

In the end the preferred option (for all except Harrier pilots) turned out to be “the left hand controls speed and the right hand controls height”. The team found even non pilots could use this system without training. Result. Harrier pilots had of course learned to use the nozzle lever which (they thought) made them better that non nozzle aviators and turkeys don’t vote for Christmas.

The capability of the VAAC aircraft as a design tool had to be experienced to be believed. It was possible to sit in the hover on this single channel 100% authority flight control system and wobble the stick to see what you thought of (say) the roll control sensitivity, feel you would like a higher value, then select that parameter on a panel in the cockpit and while the system was engaged and flying the aircraft (!) dial up the higher value and have another wobble on the stick. Do optimisation systems come any better?

(Before anybody gasps at the apparent risks of such a system let me assure you that the boffins knew what they were doing and had installed an independent monitor to keep the aircraft safe regardless - but that is a whole other story and not relevant to this thread).

By 1999 a lot of JSF project office personnel and others had flown the optimised system and it is a matter of history that this RAE (later DERA and later still QinetiQ) STOVL flight control system was taken up by the JSF team for the B.

So please relax. There may well be issues over the whole JSF programme but the B’s STOVL flight control system is not one of them and don’t forget that in decelerating to the hover every intermediate speed is experienced!