New design changes raises pressure on future of F-35B variant

Flight International ^ | 12/01/11 | Stephen Trimble

[sukhoi-30mki]

New design changes raises pressure on future of F-35B variant

By Stephen Trimble

Lockheed Martin and Pratt & Whitney have revealed the extent of design changes required to release the short take-off and vertical landing F-35B from a newly imposed "probationary" status within two years.

The Joint Strike Fighter programme is now cleared to spend another $4.6 billion partly to correct structural and propulsion design flaws in the F-35B. But patience is swiftly cooling with the specialised variant ordered by the US Marine Corps.

While the US Air Force's conventional take-off and landing F-35A and the US Navy's F-35C carrier variant are "proceeding satisfactorily" in tests, Secretary of Defense Robert Gates says the Marine Corps' prized stealth fighter is "experiencing significant testing problems".

The F-35B's troubles appear to have been recognised by the programme's international partners. UK Prime Minister David Cameron shelved plans in October to buy the type in favour of the carrier-based F-35C, leaving only Italy as a potential buyer among the nine major partners.

© Lockheed Martin

Three months after Cameron's decision, Gates announced the two-year probation order, seemingly giving the USMC and Lockheed one last chance to fix the F-35B's problems.

Lockheed first has redesigned one of six major bulkheads that cracked on the BH-1 ground-test aircraft less than 10% through a 16,000h durability test in November. The company now adds that "other locations of similar design" on the F-35B are also being evaluated.

In a positive sign, Lockheed has determined that aluminium material did not cause the cracking problem. Cracks formed on the aircraft's Alcoa-supplied No 496 bulkhead, where the fuselage attaches to the main landing gear. This created a "large stress concentration", Lockheed says. The company's decision to convert the bulkhead structure from titanium to a lighter-weight, aluminium alloy in 2004 was not a factor, it says.

P&W, meanwhile, is making three changes to the propulsion system engaged only during STOVL operations. The driveshaft, lift-fan clutch and actuator for the roll-post nozzles as currently designed meet Lockheed's original specifications, says Bennett Croswell, P&W's vice-president for F135 and F119 programmes.

But experience in flight-testing has revealed that each of the three components encounter surprising conditions.

In STOVL mode, the driveshaft contracts and expands more than expected, and the actuators for the roll-post nozzles are blasted by more heat than anticipated. Plates in the clutch fan, meanwhile, touch unexpectedly during normal flying mode, which "very infrequently" creates more heat than the clutch is designed to tolerate, Croswell says.

Gates says the F-35B's possible redesign could "add yet more weight and more cost to an aircraft that has little capacity to absorb more of either".

Croswell, however, believes the propulsion redesign can avoid penalising the aircraft's price tag or performance. "From a cost and a weight standpoint, [the impact] will be minimal," he says. In the case of the driveshaft, P&W's goal is to reduce the cost of the strengthened, Rolls-Royce-supplied component as a result of the redesign, he adds.

The STOVL variant was always expected to pose the hardest design challenges of the three F-35 models. It is the first fighter to blend stealth features, supersonic speed and advanced avionics with the unique ability to take off within roughly 250m (820ft) and land vertically.

Such capabilities make the F-35B essential for the USMC, which lacks aircraft carriers with catapult launchers and relies on fighters to support relatively lightly armed ground units.

But the variant's unique performance requirements drove a major redesign in 2004 that became the first in a series of delays and cost overruns reported by all three F-35 variants.

In flight tests, the F-35A and F-35C both exceeded a greatly reduced set of flight-test goals in 2010, but the F-35B notably struggled. Although the BF-1 flight-test aircraft achieved its first vertical landing in March 2010, reliability problems slowed the pace of flight tests. In late September, Lockheed grounded the F-35B to fix a critical issue with a hinge opening the auxiliary inlet door for the lift-fan.

It would be nearly four months before the BF-2 flight-test aircraft completed another vertical landing on 6 January.

If such lapses continue, the F-35B programme could be cancelled. Gates announced on 6 January that tests for the F-35A and F-35C variants would be decoupled from the STOVL version. The US Navy, meanwhile, will buy 41 more Boeing F/A-18E/F Super Hornets over the next three years and slash planned orders for the F-35B from 61 to 20 over the same period.

Lockheed has already received $37 billion to develop and test three variants over nine years, plus contracts worth roughly $10 billion more to deliver 62 jets in the first four lots of low-rate initial production (LRIP). So far, only 10 of 13 flight-test aircraft have been delivered and none of the LRIP fighters.

[WaterBoard]

Story does not mention that they will have to retro-fit the decks of all ships carry the F-35B because the extreme heat from the VSTOL warps the deck plates.

[Walkingfeather]

Oh geez are you kidding?

[Vroomfondel]

ping

[MontaniSemperLiberi]

I was wondering what they were going to do with all those old shuttle tiles.

[SZonian]

Source?

I’m not aware that any STOVL testing has been performed on carrier decks.

[Tonytitan]

Not only does it warp the deck plates of ships, it can destroy flight line and runway concrete also. Pointing the exhaust nozzle of the most powerful jet engine ever built at something other than empty space does such things.

[Walkingfeather]

Yikes

[A.A. Cunningham]

Such capabilities make the F-35B essential for the USMC, which lacks aircraft carriers with catapult launchers and relies on fighters to support relatively lightly armed ground units.

Brilliant bit of writing there Trimble. The Navy owns all CVNs, LPHs and LHDs, not the Marine Corps.

[A.A. Cunningham]

Story does not mention that they will have to retro-fit the decks of all ships carry the F-35B because the extreme heat from the VSTOL(sic) warps the deck plates.

Assumes facts not yet in evidence. Send Trimble your resume. You write like he does.

[BwanaNdege]

Is the heat that much more than for Harriers?

[BwanaNdege]

Exactly!

The Corps wants STOL aircraft for forward deployment, placing them closer to the front lines thus giving shorter reaction times.

When you’re getting pounded by the enemy, SOONER close air support is BETTER CAS!

On the other hand, it is nice having the capability to have fixed wing air support as a part of an amphibious assault group, able to operate off of an LHD, LHA, etc. The Navy does not always have CV’s near a Gator Navy task force.

[sukhoi-30mki]

Why is it that US LHD’s don’t have ski-jumps?? All other Harrier users seem to have it.

[Yo-Yo]

Assumes facts not yet in evidence.

Take it up with the Office of Naval Research.

[WaterBoard]

Assumes facts not yet in evidence. Send Trimble your resume. You write like he does.

I don't think you really deal in facts given the timber of your writing style.

Anyway, adults are having a conversation here, if you would like a source for this, I will be happy to provide one.

"Nearly three two years ago, the U.S. Navy discovered that the engine exhaust heat from its two newest aircraft, the tilt-rotor MV-22 and the vertical takeoff F-35Bs, was too hot for the deck plates on some of the carriers. The gas turbine engines of both aircraft, which blow their exhaust right on to the deck of the carrier while waiting to take off, caused high enough temperatures to the steel under the deck plates, to possibly warp the understructure. The navy also discovered that the exhaust heat problem varied in intensity between different classes of helicopter carriers (each with a different deck design.)

The navy sought a solution that would not require extensive modification of current carrier decks. This includes a lot of decks, both the eleven large carriers, and the ten smaller LHAs and LHDs. This began looking like another multi-billion dollar "oops" moment, as the melting deck problem was never brought up during the long development of either aircraft. Previously, the Harrier was the only aircraft to put serious amounts of heat on the carrier deck, but not enough to do damage. But when you compare the Harrier engine with those on the V-22 and F-35B, you can easily see that there is a lot more heat coming out of the two more recent aircraft. Someone should have done the math before it became a real problem."

[WaterBoard]

Still waiting on an apology.

Deck Damage

The Pentagon’s Gilmore said in his report that the engine and power-systems’ exhaust on the Navy and Marine versions is powerful enough to pose a threat to carrier personnel. The blasts also may damage shields used to deflect heat on the deck, including on the CVN-21 carrier, the Navy’s most expensive warship.

“Early analyses of findings indicate that integration of the F-35 into the CVN-21 will result in damage to the carrier deck environment and will adversely affect hangar deck operations,” Gilmore wrote.

The Navy model’s exhaust area is larger than the Boeing planes’, making the jet-blast deflectors used during launch “vulnerable to warping and failure,” he wrote.

Exhaust from the Marine Corp version’s integrated power system deflect downward and may be “a hazard to flight deck refueling, munitions, personnel and equipment” located on catwalks, the report said.

Lockheed spokesman Chris Giesel said tests conducted with the JSF Program Office and the Navy “are showing positive results regarding compatibility of the F-35’s exhaust with carrier decks and tarmac surfaces. The study will conclude in spring 2010.”

http://www.bloomberg.com/apps/news?pid=newsarchive&sid=a6gq84TiIFcA&pos=9

[WaterBoard]

VSTOL(sic)

Since you don't know much about naval avaition, VSTOL refers to Vertical and/or short take-off and landing.

http://en.wikipedia.org/wiki/V/STOL

[magslinger]

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[Oystir]

This variant is not related to chicken flu?

[lbryce]

Well, you’ve got to give credit to the awesomely futuristic wonder craft that is the J-20 in all its unattainably advanced technological superiority,where it seems one singular J-20
could all by itself vaporize the combined forces of America’s military establishment in one fell swoop for whatever assistance it provided in getting the F-35B variant, a veritable bi-plane in comparison with the J-20, (J as in Junk) in breathing new life in getting the project approved.