Last week, the Secretary of Defense, Robert Gates, announced that he had placed the short take-off/vertical landing (STOVL) version of the F-35 Joint Strike Fighter on “double secret probation.” The prime contractor, Lockheed Martin, has two years to fix problems with the air frame and engine. It is noteworthy that the Secretary said that the other two parts of the F-35 program for the Air Force and Navy are proceeding satisfactorily.
Building a STOVL aircraft is an extraordinarily challenging undertaking. The aircraft has to be able to operate in both vertical and horizontal dimensions, have a useful operational range and carry a meaningful payload. The same power plant engine must be used to power the aircraft in both flight modes. Only two STOVL systems have ever been deployed, the Harrier and the Yak-38 Forger, and the latter was a failure. The former was a notable success particularly in the Falklands war and Operation Iraqi Freedom. But the Harrier is based on 1960s technology. The Harrier production line closed in 1997 and remanufacture of older versions into the current Harrier II Plus configuration ended in 2003.
A new STOVL aircraft is needed. But to meet emerging threats and new mission requirements, it must have stealth characteristics, a supersonic speed and the kind of advanced avionics that can cope with the modern battlefield. This is particularly difficult when one is building a plane that can also land like a helicopter. This further complicates aircraft design. A hinge flap on an inlet door had to be redesigned when it compromised the F-35B’s stealth characteristics.
What exactly are the F-35B’s current problems? As the Secretary noted, they include both structural and engine issues. Apparently, a bulkhead cracked during testing. While it has been redesigned, additional testing of other structural elements to ensure against a repeat of the problem is ongoing. Lockheed has said that resolving structural issues will not require replacement of the aluminum structures, a move that could add cost and weight.
The engine problems are more challenging, which is to be expected given the nature of the power plant required by a STOVL aircraft. In vertical flight mode some of the components of the lifting portion of the power system have not operated as expected, creating mechanical and heating issues. These are not fundamental technical problems but questions of component design and subsystem integration. The engine manufacturer asserts that it can fix these problems without adding weight or cost.
It is likely that the Lockheed team will be able to resolve the issues that have delayed the STOVL portion of the F-35 program. The challenge is to do it while the clock is ticking.
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