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F-35C tailhook design blamed for landing issues

Jan. 17, 2012 - 08:59PM   |   Last Updated: Jan. 17, 2012 - 08:59PM  |  
Lockheed Martin has traced issues with the F-35C's tailhook problem to design and is correcting it, the company said.
Lockheed Martin has traced issues with the F-35C's tailhook problem to design and is correcting it, the company said. (Lockheed Martin)
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Lockheed Martin has traced the Navy F-35C Joint Strike Fighter's troubles with catching a carrier's arresting gear wires to the tailhook design.

Efforts to fix the problem are well underway, a top company official said.

"The good news is that it's fairly straight forward and isolated to the hook itself," said Tom Burbage, Lockheed program manager for the F-35 program. "It doesn't have secondary effects going into the rest of the airplane."

Moreover, the rest of the design of the tailhook system, which include the doors and bay that conceal the device and other ancillary hardware, is sound, Burbage said.

"What we are trying to do is make sure that we got the actual design of the hook is optimized so that it in fact repeatedly picks up the wire as long the airplane puts itself in position to do that," he said.

A preliminary review has already been completed and was done in conjunction with the Naval Air Systems Command and F-35 Joint Program Office.

Burbage said the hook system is already being modified in accordance with the new test data.

"We're modifying the hook to accommodate what we found so far in test," Burbage said. "The new parts, we expect to have them back in the next couple of months."

Tests with the newly modified tailhook should start at Lakehurst, N.J, in the second quarter of this year, Burbage said.

That will give the F-35 program another set of data to study to make sure the new design works as promised. However, until those tests are done, there is no ironclad guarantee that the redesign of the tailhook will work, but Burbage said he is confident of that the modified design will be successful.

"The big test for this airplane is not until the summer of '13 when we take the Navy jet out to the big deck carrier and do actual traps at sea," Burbage said.

Burbage dismisses claims that the F-35C will be unable to land on a carrier as falsehoods.

"That's patently not true," he said.

Richard Aboulafia, an analyst at the Teal Group, Fairfax, Va., said the claim that the F-35C could never land on a ship was always highly dubious.

"They turned the YF-17 into a carrier plane, why couldn't they correct carrier-hook problems here?" he said. "This does not appear to be a killer problem."

Flight testing is designed to uncover and fix problems with a new aircraft, Aboulafia said.

"This is the kind of problem that might come out during the flight testing of a carrier-based plane," he said.

Aboulafia added that the F-35 is an extremely ambitious program with its three variants — technical problems are par for the course.

The reason the problem with the hook arose in the first place is because of the inherent constraints of building a stealth fighter, said Burbage. The F-35 is the first naval stealth fighter and as such, Lockheed had the unique challenge of designing the jet with a tail-hook that had to be concealed when it's not being used.

Because the tail-hook has to fit within the outer mold line of the F-35, the device had to be fitted further forward on the jet's ventral surface than on other naval aircraft, Burbage said. The result is that the hook behaves differently than on previous fighters like the F/A-18.

In an ideal world, an arresting-hook will catch a wire 100 percent of the time, however in the real world that doesn't happen due to various dynamic forces, the veteran former Navy test pilot said.

In the case of the F-35, one of those dynamic forces includes the way the wires react when the jet passes over them. The wire reacts in a sine wave pattern, Burbage said. "The time differential between when the main gear rolls over the cable and the time the hook picks up the cable on a more convention airplane, there is more time for that wave to damp out," he said. "In the case of the F-35, one of our design constraints is that hook just has to be closer to the main landing gear than on a conventional aircraft because of the requirement to hide it inside the airplane."

Another factor that effects landing on a carrier is the sheer force of the impact from a carrier landing. Unlike conventional land-based aircraft, naval aircraft don't flare on landing. While the landing is on a more precise spot, it causes the tail-hook to oscillate vertically- which increases the chances that it won't catch a wire, Burbage said. The dampening of that motion has to be tweaked, he said.

The shape of the hook itself also has an effect on the probability of catching a wire, he added. All of these are being tweaked to increase the chances that the F-35C will catch a wire on a carrier's deck.

"We're doing a redesign of the hook to increase the probability the hook will engage the wire a high percentage of the time," Burbage said.

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