Paris 2011: Multi-mission Supersonic Stealth May Be Possible, but Is the F-35 Affordable

Paris Air Show » 2011
June 19, 2011, 8:30 PM

The Lockheed Martin F-35 development program has met or exceeded the revised flight-test schedule that was written following a technical baseline restructuring (TBR) last August, according to Lockheed Martin officials. But some significant technical issues remain, and affordability continues to be a key concern for the new-generation combat aircraft.

The Pentagon is expected to make further adjustments to the F-35 development and production plan shortly. Since around this time last year:

 • the fourth low-rate initial production batch was contracted, comprising 31 aircraft costing from $127 million to $158 million each, depending on version;

 • Israel confirmed that it would receive 19 F-35As worth $2.75 billion;

 • after a defense review, the UK switched its order from F-35B STOVL versions to F-35C carrier landing versions;

 • the Pentagon ordered a further stretchout in production, added 13 months and $4.6 billion to the development phase, and put the F-35B STOVL version on a “two-year probation.” Lockheed Martin and Pratt & Whitney admitted four F-35B development problems, but described solutions for each one;

 • the new head of the F-35 Joint Program Office (JPO) said the projected costs to produce and sustain the F-35 were “simply unacceptable.” He also said that initial operating capability cannot be achieved in 2016, as planned;

 • night-vision problems with the Israeli-designed helmet emerged. The F-35 has no head-up display (HUD), so this helmet is the pilot’s primary flight display;

 • work on the alternative F136 engine stopped when Congressional funding lapsed, although the GE/Rolls-Royce team pledged to continue the program on its own dollar;

 • the last four of 13 development aircraft made their first flights, and the first two F-35A production aircraft (AF6 and AF7) were delivered;

 • static testing was completed five months ahead of schedule with no failures (but a bulkhead on the F-35B fatigue test article cracked).

In a recent briefing, Steve O’Bryan, Lockheed Martin vice president F-35 customer engagement, talked up progress. “We’re seeing very reliable flight-test airplanes. We are 20 percent ahead of the TBR on flight tests, and 30 percent ahead on test pilots,” he said. The development fleet has already flown more than 350 times this year, and more than 800 times in total. Another 500-plus test flights are scheduled this calendar year. (O’Bryan did not mention the in-flight generator failure last March, which was attributed to excess lubrication, but did not materially affect flight-test progress).

 “Software stability is good compared to legacy platforms,” O’Bryan said. The Block 1 software, which provides an initial training capability, is now flying on the next two production F-35As (AF8 and AF9). They are due for delivery to Eglin AFB, the F-35 training base, shortly. The pace of mission system software development will be accelerated by the addition of another test line manned by 190 people this summer, as mandated by the TBR.

The Block 2 software is now being loaded into the CATbird flying test bed. This adds about one million lines of code (LOC) to the six million already written for Blocks 0.5 and 1. Block 2 provides the F-35 with networking capability and therefore “an initial war-fighting capability.” It will be on the low-rate initial production (LRIP) Lot 3 and 4 jets.

Eventually, another two million LOC must be written and tested for the definitive Block 3 with full data fusion, which should be flying by 2015 in time for initial operational test and evaluation the following year. To speed the process, the TBR re-allocated three of the early LRIP jets to mission systems software development (and another three to other development tasks).

The first flights tests of the F-35’s low observability have produced “very, very good results,” according to JPO chief vice admiral David Venlet. Development aircraft AF3 flew against radars and signature measurement devices on the Nevada Test Range and validated the results previously achieved in ground tests.

Now the challenge is to replicate the same degree of stealth on each aircraft off the production line. And, for sure, the first two production aircraft–AF6 and AF7–did recently pass the stealth test in the anechoic chamber and in pole testing.

The F-35 pilot’s helmet is supplied by Vision Systems International (VSI), a U.S.-based joint venture between Rockwell Collins and Elbit Systems. O’Bryan said it is flying successfully in daytime flight, although there have been reports of jitter in the projected symbology.

In addition, the challenge of providing night vision by importing medium-wave infrared imagery (MWIR) from the aircraft’s distributed aperture system has proved difficult so far. Therefore, Lockheed Martin has recently issued an RFP for “traditional” night-vision goggles hoping that this unanticipated add-on would require only a minimal modification of the aircraft’s cockpit displays.

An alternative view of F-35 development progress was offered by the U.S. Government Accountability Office (GAO) in its latest audit of the program two months ago. “As of December 2010, about four percent of F-35 capabilities have been completely verified by flight tests, lab results, or both. Only three of the extensive network of 32 ground test labs and simulation models are fully accredited to ensure the fidelity of results,” the GAO reported.

“Engineering changes continue at higher than expected rates...and more changes are expected as testing accelerates,” it added. Software development is a moving target, it noted; the total lines of code predicted to be needed for the F-35 is already 40 percent greater than originally anticipated.

What of the troubled F-35B program? Was U.S. Secretary of Defense Robert Gates being unduly pessimistic when he spoke of the possible need to “redesign the aircraft’s structure and propulsion...changes that could add yet more weight and more cost to an aircraft that has little capacity to absorb more of either.”

According to O’Bryan, reliability problems with the STOVL version’s lift-fan actuators and rudder pedals that limited flight test sorties last year have been overcome. A design to strengthen the auxiliary inlet doors so that they can be opened at high speed (250 knots) has passed preliminary design review, and will be flight tested early next year. Driveshaft spacers that solve a thermal expansion problem have already been fitted to the five development aircraft. The problem of unexpected heating at the wingtip roll-post actuators will be solved by adding extra insulation. Additional cooling air may be supplied to the lift-fan clutch, which has also been overheating slightly.

A steel patch has been designed to strengthen the F-35B rear fuselage bulkhead, which cracked during ground durability tests. But this adds a bit more weight to an aircraft that may already be uncomfortably close to the maximum for vertical landings with a full weapons load, the so-called bring-back margin.

The weight that was saved in the big redesign of the F-35 structure in 2005 was driven by the F-35B’s power/weight ratio, but was evidently not enough to address this problem. The contractor and the prime customer (the U.S. Marine Corps) are still discussing what the final margin should be.

Could Pratt & Whitney provide some increased thrust in the F135? Possibly, but this might further raise engine operating temperatures and possibly negate the fixes to the driveshaft, clutch and roll post actuators described above. The F-35B may need all of the two years “probation” that has been directed by the program office.

A total of 63 aircraft have now been ordered in four LRIP lots. At Fort Worth, a further two final assembly stations are being added this summer, making seven and thus supporting a rate of four aircraft per month.

“Our learning-curve [reduction] is world-class,” O’Bryan claimed. Direct Touch Labor has declined from 250,000 hours for the first SDD aircraft to close to 100,000 hours today. This trend encouraged Lockheed Martin to agree to fixed prices for the 32 aircraft in LRIP 4. Negotiations for the 35 aircraft in LRIP 5 will start shortly.

Replacing seven legacy fighters (F-16s, F-18s, F-111s, A-10s, AV-8s, Tornados and AMXs) with one design was never going to be easy, especially when supersonic stealth was a key design driver. The F-35 program is proving that it can be done, although at a slower pace and a much higher cost than originally predicted. The total development tab is now predicted to be a breathtaking $56.4 billion. Setting that sunk cost aside, whether the F-35 can be affordably produced and operated still remains to be seen.

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