F-35 Cancelled, then what ?

[SpazSinbad]

F-35B Ski Jump Trials NAS Patuxent River 2015

Salty Dogs & Funky Jets October 2015 Mark Ayton
"...Ski Jump Trials
Her Majesty’s Ship Queen Elizabeth (R 08) is fitted with a ski jump like no other: a new design tailored to be used by very expensive new aircraft. Launching a 60,000lb F-35B off a ski jump requires some serious maths, engineering and testing.

The F-35B ski jump test campaign should have started in March of this year, but was delayed due to brutal sub-zero temperatures and snow that blighted Patuxent River at the time. Aircraft BF-01 was originally assigned to conduct the ski jump events but was unable to remain at Pax while the weather improved. It was already scheduled to deploy to Edwards Air Force Base, California to conduct wet runway and crosswind testing.

The test programme comprises two phases, the first of which eventually began on June 19 when BAE Systems test pilot Peter Wilson conducted the first take-off using the ski jump at Pax with F-35B BF-04. Sqn Ldr Edgell told AIR International: "Phase 1 is a risk-reduction phase designed to highlight any significant hardware or software updates that may be required prior to commencing the bulk of testing. It comprises 29 ski-jump launches.

"Phase 1 will ensure our models and predictions are correct. If anything needs addressing we can do so in a timely fashion and then go into the 140-sortie Phase 2."

The ski jump used on HMS Queen Elizabeth has a curved leading edge designed to simultaneously launch an F-35B upward and forward with a greater take-off weight and less end-speed than required for an unassisted horizontal launch aboard an LHD-class amphibious assault ship, such as USS Wasp (LHD 1).

The reader may be surprised to learn that the ski ramp built at Pax River is based on the type used on the Invincible-class aircraft carriers which is a little bit shorter (50ft) and slightly shallower (0.5º) than the ramp on Queen Elizabeth-class carriers. Sqn Ldr Edgell explained: "The Pax River ramp design process dates back to 2005 but, at the time, the Queen Elizabeth ramp profile was not known. Analysis conducted in 2005 showed we simply needed to use a ramp with a profile that allows us to stay just under the predicted F-35B ultimate loads and the Invincible-class ramp achieved this."

Pax River’s ramp allows the test team to make adjustments for different profiles and encompass everything below the ultimate loads of the aircraft. "Though the verification of our models during phases 1 and 2 we can tweak the control laws to work off other types of ramp, none of which are the same," said Sqn Ldr Edgell. When the aircraft comes off the end it is ballistic and accelerates to the fly away air speed, typically 10-20kts higher than launch speed, and therefore reduces ground roll.

"There’s a fine line between ensuring we have suitable gear loads and fly away speed," explained Sqn Ldr Edgell.

"We want lots of margin on both of those. To achieve margin for gear loads we need to be slow, i.e. start right at the bottom of the ramp. To achieve margin on minimum fly away speed we need to start towards the back of the run-up. We blend the two aspects together and meet in the middle to gain the safest launch spot. For the very first sortie, our spotting distance will be conservative and will launch the jet off the end of the ramp straight into a previously flown flight condition."

Such regimes have been flown several times during short take-offs at the field and STOVL departures.

Sqn Ldr Edgell explained an interesting fact about the take-off : "You can be lined up three, four, five hundred feet back from the start of the ramp and as you slam the throttle forwards, the jet doesn’t know it’s about to go up the ski jump. It waits for certain triggers to alert it to the fact it’s going off the ski jump, at which point its flight control system moves the horizontal tails and the nozzles into the optimum position. It needs to hit 45 knots going up the ramp.

"The throttle needs to be above 65% ETR, with 6 degrees of attitude and a pitch rate of 6 degrees per second. At that point it moves all of the effectors into the right place. Bear in mind the ski jump at Pax is only 150 feet long, so the aircraft hits all of those parameters with less than 100 feet remaining. By the time it goes off the edge of the ramp all the surfaces and the nozzles are at the optimum position, the aircraft rotates up to the optimum pitch attitude to fly away. It’s pretty clever stuff."

Sqn Ldr Edgell described the launch process: "You slam the throttle and guard the stick. There is no input on the stick required. As the aircraft moves down the tramline of the deck you track the centre line with your feet, just like any other carrier deck take-off, but there’s no pitch input required. The jet flies away. It’s effortless." In the event of any kind of malfunction, the pilot takes control and manually flies off the edge of the ramp, which is why he must guard the stick during the roll.

There is no significant part for the pilot to play in the take-off – the result of a design philosophy to minimise the pilot’s workload. A good example is tracking the centreline on a rolling pitching deck at night. That’s a challenge in a Harrier but in the F-35B it’s his only task so he should do a much better job. The administrative burden on the pilot has been significantly reduced: in this situation to an effortless level.

Phase 2 will introduce crosswinds, external stores, asymmetry, minimum performance (minimum deck) launches from the bottom of the ramp, and simulated performance degradation all to increase the aircraft’s flight envelope in Block 3F configuration. That’s imperative work for the UK which will undertake first-in-class flight trials on HMS Queen Elizabeth in the final quarter of 2018...."

Air International OCTOBER 2015 Vol.89 No.4