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16 August 2016

F-35B Test Pilots Complete 31 Land Based Ski-Jump Tests at NAS Pax River

The complexity of flying Lockheed Martin’s F-35B off an aircraft carrier such as the Royal Navy’s (RN) new QUEEN ELIZABETH CLASS (QEC) should not be underestimated.

Pete ‘Wizzer’ Wilson, F-35 Programme test pilot, summarised the 31 ski-jump flight trials that have been conducted to date at Naval Air Station (NAS) Pax River, MD/AUSA and onboard the USS WASP. “The aircraft is really close to perfect, just not perfect yet,” he revealed.

The impetus for this initial land base testing is to conduct preliminary work leading eventually to flight trials at sea. “The driving force is to ensure that the aircraft is cleared for the ship and that the ship can operate the aircraft,” said David Atkinson, BAE Systems lead for the F-35B integration programme. “The flight trials are critical in order to validate the work done by modelling and provide certification evidence so that we can have the best possible envelopes for operating the aircraft from the ship.”

Although on land, the 31 ski-jump take-offs had been conducted during the day and night and with cross winds. However, as Wilson pointed out: “The first time we go to see and take-off from the carrier will be a brand new event; we cannot replicate that exactly ashore.”

The differences include the role and pitch of the ship as well as its motion.

There has been one particular point during the take-off that has focused the minds of engineers and test pilots said Wilson. “Once we are airborne the aircraft will fly nicely; the acceleration up to the ski-jump we know about, but it is the brief one second bit in the middle that we were still working on.”

While there have been flight trials on the USS WASP they did not involve a ski-jump. However, Wilson said that following those trials expectations were high for the QEC trials. He pointed out that the new Royal Navy’s QEC aircraft carriers were much bigger and that was going to prove a very positive factor for the alternative landing method, called Shipborne Rolling Vertical Landing (SRVL). This was a new requirement from the military, he said. “They want to maximise the ‘bring-back’ of extra weight, several thousand pounds if fact which could be unused weapons from sorties including combat air patrols (CAPs). We have done RVLs with similar speeds and techniques, but not from a ship,” he revealed.

The certification of take-offs is of a different scale than on the old HMS Illustrious carrier where the ski-jump was 150ft long and with a 12° upward curve. The QEC is 200ft long with the same degree of curve. Wilson said that the recent testing focus has largely been on the transition of the F-35 during the take-off. “What matters is the airplane is transitioning through maximum acceleration. It recognises that it is on a ski-jump once it has some positive attitude and a pitch rate  although the gear is still in contact with the ground. At that point the airplane recognises that it is on a ski-jump and the thrust switches to ski-jump STOVL to fly away. The thrust has to come forward so the airplane can be supported on its two columns of thrust. This nozzle vectoring is completely autonomous.” He said it is during that second of time in transition from level acceleration to being airborne that has been challenging.

Studies have also been made from the take-off data collated during this time regarding the optimum speed and weight that will allow the best performance.

Said Wilson, “an absolute minimum speed we can fly away at is 65 knots which takes into account sudden gusts of wind of up to 15 knots; we never want to take-off at less that 50 knots.”

He had said that there were different views within the various IPT’s about what should be the correct speed and weight for take-off, varying between those wanting performance and others wishing to maximise load. “We eventually pinpointed around 80 knots at 44,000lbs airplane,” he said.

The conclusion after the 31 ski-jumps in the year between June 2015 and June 2016 was that successful execution the initial phase. “It is a significant milestone to de-risk the project and demonstrate the Control Law concept of take-off from the ski-jump. It is the first step towards clearing full ski-jump envelope as part of the build up to the QEC flight trials onboard,” said Wilson. More testing is due to begin on the amphibious assault ship USS America which has received an upgraded flight deck with thermal coating to protect it from the F-35B’s engine blasts.
Andrew Drwiega