DTi’s Bill Sweetman sums up some of the current problems and news on the JSF.
JSF Delays Pile Up
Posted by Bill Sweetman at 8/11/2008 6:59 AM CDTGraham Warwick’s report on the latest delays to hit the JSF flight-test program undercuts most of the optimistic predictions made by industry and government leaders earlier in the summer. It’s now clear that problems with the F135 engine and other issues have forced another delay in the start of the “build-down” flight tests that precede the demonstration of the F-35B’s short take off, vertical landing (STOVL) capability.
This sequence of 20 flights, reaching progressively lower speeds, was planned for the first quarter of 2009, and as recently as mid-July (at the Farnborough air show) Lockheed Martin program vice-president Tom Burbage said in an interview that these tests and the first vertical landing would be carried out in the first quarter. (So did JSF program office director Gen. Charles Davis in a June interview.)
Now, the build-down tests won’t start until the second quarter and the location for the first vertical landing – which had been planned to follow a move from Fort Worth to Patuxent River – is once again open. DTI’s prediction in our last issue that a vertical landing would not happen until well into the second quarter now looks optimistic.
The first F-35B, BF-1, will complete a few more sorties and then remain grounded until it is ready to start build-down tests, alongside the next test aircraft, BF-2. Meanwhile, AA-1 – the first F-35A, but reflecting the pre-2005 design – is grounded by cooling problems, but will go to Edwards later this year to perform noise tests – because some export customers are worried that the JSF’s noise level will force them to relocate their fighter bases.
But what apparently won’t happen is what Burbage predicted in July: that the program’s flight rate would reach 12 sorties a month “early next year”. Indeed, it looks like the program will have logged fewer than 100 flights in total by the end of the first quarter of 2009. (The log stands at 56 flights, with 15 more due on BF-1 before it goes down for upgrades.)
To put it another way, the program will have 98 per cent of its test sorties remaining by the end of March 2009, with just over three years to the scheduled initial operational capability (IOC) date with the Marines.
Export customers, apart from the Royal Navy, are not directly affected by delays to the STOVL program. However, because the Marine IOC date has always been the first of the three versions, the flight-test program has been arranged in that sequence. Unless that gets changed, delays in STOVL testing are likely to affect progress with subsequent stages, including the testing of mission equipment on F-35A and F-35B prototypes.
The current problems also invalidate Lockheed Martin CEO Bob Stevens’ comments to an investor group at the end of May. Among other things, Stevens told the Wall Street audience that “we are committed to flying the STOVL mission by the end of this year and we will be scored as to whether we do or don’t do it.”
The abruptness of the slippage means one of several things. It could be that bad news is not making its way freely up the management chain – one of the problems that ultimately doomed the A-12 Avenger II, Fort Worth’s last major all-new program. Alternatively, the challenges causing the latest slippage were not predicted, or a mix of both factors could be in play. Either way, it’s not good news.
Lockheed got the chance to comment on some of this:
Component Failures Impact F-35 Flight Testing
Aviation Week
Aug 8, 2008
By Graham WarwickLockheed Martin continues to struggle to gain momentum in flight testing of the Joint Strike Fighter, with the first F-35 again grounded by component failure and while the second aircraft heads toward a hiatus in flying that will last into early next year.
The issues will not affect the overall schedule, says Lockheed, but they are preventing key risks being retired early. These include additional noise tests funded by the Australians at a time when the F-35’s environmental impact has become an issue for some international partners.
The first F-35, aircraft AA-1, is grounded awaiting the repair of nacelle vent fans designed to keep the engine bay cool on the ground. The situation has echoes of the overheating problems that dogged the F-22, but Lockheed says it is unique to AA-1.
“The issues we are dealing with are independent of the thermal management system,” says deputy program manager Bobby Williams. “Nothing is on the critical path, but the earlier we get the data the better.”
The problem involves repeated failures of the nacelle vent fans that force air through the space between engine and airframe to prevent heat from damaging the structure.
While the fan failures may be unrelated, thermal management is the “biggest challenge” in the F-35, says Daniel Kunec, JSF program office director, air system integration. “It is the most limiting feature, and there are still some challenges to be overcome,” he told an AIAA propulsion conference in July.
Originally designed for the canceled Boeing Sikorsky RAH-66 Comanche, the vent fans are unique to AA-1. “They are one-off fans that were never fully qualified because AA-1 is a one-off,” says Williams. AA-1 was built before a redesign to reduce the F-35’s weight and is not production standard.
The fans are surrounded by fuel, which is colder than the ambient air, and in the heat and humidity of Fort Worth, Tex., condensation is coating circuit cards inside the units and causing corrosion. The fans are being repaired by supplier Hamilton Sundstrand, but the “long pole” delaying a return to flight is applying a new conformal coating to the cards.
Williams says the problem does not affect the second F-35, production-standard aircraft BF-1, as the vent fans were relocated during the redesign to make them more accessible, avoiding the condensation issue. He expects the fans to be back in AA-1 by the end of August, after which “a couple more flights” are needed at Fort Worth before the aircraft can make its delayed ferry flight to Edwards AFB, Calif., for testing.
Williams plays down concerns about overheating in the high desert of Edwards, although AA-1 does not incorporate design changes made to improve the F-35’s thermal management. These include larger engine fuel pumps, which will be introduced during early low-rate initial production to provide the full thermal management capability.
Thermal management is a particular issue for the stealthy F-35. “There are very few areas to reject heat. We can dump it or burn it,” says Kunec. “Every component has a heat budget and everything is cooled by fuel.” The heated fuel is either burned in the engine or cooled by heat exchangers in the engine fan duct. “The massive fuel/air heat exchanger is our saving grace for coming close to specification.”
Based on lessons learned with the F-22, Williams says, the F-35 has a requirement to operate on the ground for 60 min. on a 120F day, with fully heat-soaked fuel and a full solar load. At the end of 2005, the short takeoff and vertical landing (Stovl) F-35B could not meet the requirement, but after redesign now meets the specification, says Kunec.
Meeting specification at the end of a mission remains a challenge for the Stovl variant. “The lift fan is a huge heat source and at the end of the mission there is little fuel left to use as a heat sink, so there is a strong peak in temperature,” says Kunec. The requirement is to operate for 30 min. after landing. “We meet that with no margin,” says Williams.
Already delayed more than a month, AA-1’s deployment to Edwards is to perform inflight engine shutdown testing over the dry lakebed. The deployment will also be used to collect additional noise data requested by Australia. Several countries face public concerns over the noise produced by the F-35, which with 40,000 lb. of thrust is considerably more powerful than the F-16 it will replace. In Norway, there are concerns noise issues could force construction of a new base to avoid local opposition at existing facilities.
“We are working the environmental issue, but we are not doing anything from a design standpoint,” says Kunec, adding, “There is a lot of misinformation on F-35 noise.” Near-field noise level is comparable to legacy fighters, he says. Lockheed has said the noise footprint that reaches the base perimeter is less severe, but Kunec says far-field or community noise “is at or close to the highest level.” Flyover noise data collected with AA-1 at 1,000 ft. “is right at the top, but then everything over 90-100 dB. is a problem,” he says.
On the emissions front, “NOx [nitrogen oxides] levels are way beyond any previous aircraft because of the higher combustor temperatures,” says Kunec. But while NOx will be significantly higher, carbon monoxide and unburned hydrocarbon levels will be significantly lower.
While AA-1 remains grounded since completing its 45th flight on July 23, aircraft BF-1, the first Stovl F-35B, has logged nine flights since its June 11 debut and has about 15 more flights in conventional takeoff and landing mode before it too ceases flying, for scheduled upgrades. A decision to delay hover pit testing to January means the aircraft will not fly again until the second quarter of next year. A second F-35B, BF-2, will roll out on Aug. 17, but not fly until early next year.
The plan was to conduct pit testing of the Stovl propulsion system in late October and return to flight in November, but program officials have decided to delay the tests until after a redesigned Pratt & Whitney F135 engine is installed. This has pushed full-power hover pit work back to January, but will avoid the need to repeat tests, says Williams.
To minimize the impact, initial tests opening the Stovl propulsion system doors in flight will now be conducted before BF-1 is grounded, instead of after. These will involve opening the doors one at a time and checking handling qualities, says Williams. Electromagnetic-effects tests planned for later in the program have also been brought forward and will be performed while BF-1 is on the ground for upgrades.
Lockheed now plans to begin “build-down” flight tests in Stovl mode in the second quarter of 2009, but a date for the first full vertical landing has yet to be agreed. The original plan was to ferry BF-1 to the U.S. Navy’s Patuxent River, Md., test center to perform the first vertical landing. “We are having ongoing discussions with the JPO on how we do the first vertical landing and we have not finalized a plan,” says Williams
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August 12, 2008 at 10:41 am