Experience from flight testing has eviscerated the argument that the F-35 program architects used to support high concurrency, with fat production contracts early in the test program: that modeling and simulation had advanced to the point where problems would be designed out of the hardware. In fact, the F-35 is having just as many problems as earlier programs, which means that there is no reason to expect that it will not continue to do so.
The “quick look review” (QLR) panel was chartered by acting Pentagon acquisition boss Frank Kendall on Oct. 28, eight days after top U.S. Air Force, Navy and U.K. Royal Air Force operational test force commanders jointly expressed their concern that the F-35 would not be ready to start initial operational testing in 2015, as envisaged in the delayed test program adopted in January.
Kendall was looking for an assessment of test progress, as well as a look at “concurrency risk” – the concern that problems discovered in testing will result in expensive modifications to aircraft that are produced before the fixes can be designed, tested and implemented in production.
The QLR was submitted on Nov. 29, beforE Navy Vice Adm.Dave Venlet, the JSF program director, disclosed some of the fatigue issues in interviews with AOLDefense. Its existence anD some of its findings were reported by Bloomberg’s Tony Capaccio early last week.
The most positivE thing that the QLR has to say about the program is that the team “identified no fundamental design risks sufficient to preclude further production.” That is, they don’t say that the program should be terminated, or that production should be halted until problems are fixed. But the team concludes:
Since flight testing started to pick up speed in June 2010, 725 engineering change requests have been initiated, of which 148 are ready to incorporate. On average, it takes 18-24 months between the identification of a change and its implementation in production. JSF production orders started three to four years earlier than other fighters, and even under the current plan, close to 200 aircraft will be on order by the halfway point in flight testing.
Many of the issues described by the QLR have been reported, but not in detail. Others have been played down by the program. The following are four of the “big five” issues that have already surfaced. (The fifth is classified, but dollars to doughnuts it has something to do with stealth.)
We knew that the helmet-mounted display was in trouble. A simpler alternate HMD was ordered from BAE Systems in September, but it does not meet the requirement for “through the airplane” zero-light visibility provided by the electro-optical distributed aperture system. (Yes, that EO-DAS, that makes maneuvering irrelevanT.)
Today, the killer problem with EO-DAS is latency: the image in the helmet lags 130 milliseconds behind sightline movement where the spec is under 40 ms. (So the video is where the pilot’s head was pointed an eighth of a second ago.) That can’t be fixed without changing the JSF’s integrated core processor – the jet’s central brain – and the EO-DAS sensors. Even the backup helmet faces buffet and latency issues, simply for symbology.
The underwing fuel dump system on the JSF doesn’t get fuel clear of the aircraft surfaces, so that fuel accumulates in the flaperon and may get into the integrated power package (IPP) exhaust. That creates a fire hazard, particularly on a ship deck after landing. Fuel dumping has been banned except in an emergency. Two unsuccessful modifications have been tried on the F-35B.
The IPP – the cause of a grounding this summer, after a “catastrophic failure” caused IPP parts to puncture a fuel tank – is turning out to be unreliable. It’s supposed to last 2,200 hours, but so far in the flight test program, 16 IPPs have been removed and replaced – a process that takes two days of 24-hour work.
The arrester hook issue has been reported. In the first round of tests, the hook failed to catch the wire once. The QLR notes that tests of a minimal modification – a reprofiled hook with different damper settings – set for April “represent only the initial stages leading into full carrier suitability demonstrations.”
Studies are already underway of changing the hook’s location – the basic problem is that the designers put the hook closer behind the main landing gear than that of any current or recent Navy aircraft, even the tailless X-47B – but that will have “major, direct primary and secondary structural impacts”.
The QLR report predicts more problems, based on experience so far, historical data, and the collapse of the “test is validation” orthodoxy.
F-35 flight tests have not gone beyond 20 degrees angle of attack, and higher-than-predicted buffet loads have been experienced. So far, severity has been similar to current aircraft but it is experienced over a large part of the envelope. Exploration of the high-AoA envelope does not start until the fall of 2012 and full results will not be available until 2014. Excess buffet can accelerate airframe fatigue, and induces jitter in the HMD.
One editorial observation, not from the report: aerodynamic issues are a challenge on a stealth aircraft because some of the standard fixes – fences, strakes and vortex trippers, for instance – can’t be used.
Other risks are individually less severe but cumulatively could result in substantial modifications. They include thermal issues – like the current speed restriction – and an untested lightning protection system, which at least until late 2012 means that the aircraft is not allowed within 25 nm of predicted lightning. (That is expected to cancel 25-50% of training events at Eglin AFB.) Weight margins for all versions are paper-thin.
The full QLR is densely packed and makes fascinating reading. Personal view? What keeps going through my mind is Gus McCrae from Larry McMurtry’s Lonesome Dove, after one of the Hat Creek outfit has ridden into a nest of water moccasins:
“Eight sets of bites, not countin’ the legs. Ain’t no point in countin’ the legs.”