The first flight of F-35 BF-1, the first short-take-off, vertical landing (STOVL) version of the Joint Strike Fighter, has slipped from May to June as a result of the most recent test failure of a Pratt & Whitney F135 engine, JSF program director Gen. Charles Davis said on Wednesday at Aviation Week's Defense Technology and Requirements conference.
At that point, the engine will have been cleared only for conventional take-off and landing (CTOL) operations: studies of the most recent failure have confirmed that the problem is linked to loads in a STOVL mode in which the low-pressure turbine (where the failure occurred) is driving the lift fan. "Our plan is to re-clear BF-1 for STOVL operations, but we had not intended to do STOVL testing until December 2008 anyway." Later engines in the program feature modifications which are expected to eliminate the problem.
The biggest challenge in the program today is manufacture, Davis said. "I'm worried about getting the manufacturing lines down the learning curves," he told the conference. The JSF is showing some of the problems that have afflicted the Airbus A380 and Boeing 787 programs (although no major delays are manifest yet). Work is being performed out of sequence - for instance, many of 650 brackets in the wing are currently being installed after the wing has been mated to the body. Behind such problems are issues such as "requirements received late to schedule" - that is, by the time the design of a part has been finalized it is too late to ramp up production as planned.
Davis is also concerned about the complex integrated subsystems on the JSF, in which separate auxiliary, secondary and emergency power systems and environmental control are packaged into a single subsystem. "We're working closely with them", he says.
A bigger potential problem was raised by Lt Gen Raymond Johns, USAF deputy chief of staff for strategic plans and programs: the USAF won't be able to afford its planned 110 JSFs a year under its projected total obligational authority (TOA). F-16s, he said, "will be coming out of the force at a rate of 100 a year from 2014. With our TOA, we can buy 48 JSFs per year, and the fighter force declines to 1400 aircraft."
Currently, JSF plans call for the US total buy to reach 130 aircraft in 2015, with deliveries in 2017. The USAF does not have an internal solution to the problem, which would almost halve US purchases of the JSF in the peak production years with consequent effects on the production cost. "I can't take more people out," Johns said, "because I'm playing football with ten players as it is, and we don't know where to go with infrastructure. It's a question of the right level of gross domestic product to go to defense."