Piloting the Joint Strike Fighter
Testing of the Lockheed Martin F-35 Lightning II (joint strike fighter) is well underway. Ian McInnes catches up with Graham "GT" Tomlinson, BAE Systems' lead test pilot for the STOVL variant, to find out how it flies.
Ian McInnes: Having flown the Harrier, what was your initial reaction to the short take-off and vertical landing (STOVL) variant of the F-35?
Graham Tomlinson: The Harrier family of aircraft remains a miracle of technology and design which, by the time it retires, will have been hovering for more than half the history of powered flight. It has provided unmatched capabilities and flexibility of basing, with accepted penalties for the pilot in terms of workload and training. But it is also necessary for Harrier pilots to obey some hard-learnt golden rules; break them and it would bite.
The F-35 brings 21st century technology to the table. It retains the flexibility inherent in STOVL aircraft but adds stealth, large increases in performance and capabilities, and – for the first time – offers a STOVL aircraft that looks after the pilot, not the other way round.
Workload is dramatically reduced, training requirements are slashed, and a cocoon of safety protects the pilot from human errors and omissions. The pilot is now able to concentrate fully on the mission tasks in the knowledge that the take-off and landing tasks are trivially easy.
IM: Technical issues aside, did you enjoy flying the aircraft, and what pleased you in particular?
GT: Early flight tests are all about predicting behaviour. We do that using rigs, simulators, wind tunnels and computer-based analysis, and then confirm that the real behaviour is a close match. We move cautiously in small steps, checking the match through real-time telemetered data to the control team experts. The most pleasing thing from this perspective has been how good our predictions have been.
Purely as a pilot, the most satisfying features have been the rock-solid handling and stability of the aircraft, coupled with brute performance that slightly exceeds our requirements. Pilots always like thrust.
All STOVL aircraft encounter non-linear behaviour close to the ground, caused by hot air bouncing back up and interfering with aerodynamics and propulsion characteristics. I'm greatly encouraged that our experiences of this so far have been as good as we could have hoped; it is far more benign than in the Harrier family. It will undoubtedly remain an area of interest as we expand the wind envelopes for low speed take-offs and landings.
IM: Did the F-35 training simulation preparation make your flight easier when the real thing came around?
GT: Like many fly-by-wire aircraft, the joint strike fighter uses on-board models of aerodynamic and propulsive effects to decide which flight control surfaces or engine parameters provide the best way to satisfy the pilot's demands. These same models live in our simulators, which provide amazingly accurate representations of the real thing.
In the design years we used the simulators to refine the way the aircraft responds, and this gave us a deep understanding of how the joint strike fighter flies. Now we use the simulators to rehearse missions; it boils down to practice makes perfect. The pilot gets to practice the "monkey skills" he needs to hit test points accurately and consistently, and we hook up the simulator to the control room team so that everyone gets to practice. We emphasise the communications, the rhythm of the mission, the expected areas of interest (the new bits) and we throw in practice failures to create emergency training. It is all very realistic and beneficial.
IM: How much time did you log on F-35 simulation before taking the real aircraft out?
GT: I'd estimate between 1,000 and 2,000 hours; more than enough to feel completely at home in the aircraft before we turned a wheel.
IM: Did any elements of the aircraft's performance surprise you?
GT: I was surprised by how little the aircraft varied from the predictions. Good surprise.
It also surprised me that the aircraft copes so well with the airflow disturbances created by the huge door above the lift fan, which generates destabilising airflow for the rudders and tails.
The upside of the door is that it scoops flow into the lift fan intake and adds significant thrust. The downside is the non-linear flow over the rear of the aircraft at conventional speeds where we convert from a conventional aircraft into a STOVL aircraft. The compromise seems to have been made just about right, as we retain satisfactory control through the conversion process (opening the doors and spinning up the lift fan). This will be another area of interest as we expand the conversion window from our initial heart-of-the-envelope speeds.
IM: Were you happy with the cockpit in this aircraft or will some of it take some getting used too?
GT: All three joint strike fighter variants have identical cockpits. It is a bare cockpit with few switches, focusing on the mission tasks. The basics of starting up, getting airborne, flying and landing the aircraft are trivially easy. The F-35 in STOVL mode flies remarkably like the family of joint strike fighter in conventional mode. A single button commands the conversion, which is then fully automatic.
The mission elements are dominated by a 20x8in touch screen display and by the helmet-mounted display, which replaces the heads-up display of legacy fighters. Voice activation is in the pipeline for some functions, and obviously the legacy Hands On Throttle-And-Stick philosophy has been retained. Getting the best from the mission systems will undoubtedly require a degree of familiarity and practice for the service pilots, but the gut feeling is that the videogame generation will quickly adapt to the full potential of the sophisticated sensor suite.
IM: So what did it feel like to you to fly the F-35 STOVL? Did it seem like just another job or a lot more than that?
GT: You get tied up in the professionalism of the team and don't have much time to think about the job dispassionately. There's a lot to do in flight test because we double and triple check everything, and do everything slowly and steadily with a continuous flow of information between pilot and control room. We also have lots of extra instruments and test kit to shepherd and analyse. So yes, it is just a job when you are actually involved in doing it. It is when you sit back afterwards that you realise what fun it is, how lucky we are as individuals to be involved at this early stage of testing and how the UK's heritage of STOVL aircraft has propelled us to the forefront of testing of this latest incarnation.