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24-01-2013, 13:10
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חבר מתאריך: 13.11.04
הודעות: 16,823
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כתבות חדשות ב AVIATION WEEK על ה F-35, ינואר 2013
F-35 JSF Testers Report Progress, Problems
http://www.aviationweek.com/Article..._p26-537603.xml
Amassing flight hours and test points at an accelerating pace, the F-35 Joint Strike Fighter program faces the question of whether it is completing the right tests at the right time. As it enters 2013 with a focus on high angle-of-attack and weapons testing, the program is still falling behind in clearing the capabilities its customers require. Lockheed Martin exceeded its development flight-test goals for 2012. But a report by the Pentagon's director of operational test and evaluation (DOT&E) reveals this was helped by bringing forward test tasks from future years. Aircraft deficiencies and software delays prevented the program from achieving some test objectives set for 2012 and required to deliver capabilities to the services now beginning to train pilots on the F-35.
But according to the DOT&E report, through November 2012, the program had completed only 78% of the test points planned for the year. The addition of test points to investigate new problems, for regression testing of aircraft and software fixes, and for tasks brought forward from future years pushed the test points accumulated to 35% above the total planned (see F-35 Flight Testing table).
The report says horizontal-tail scorching and delamination and higher than expected airloads on open weapons-bay doors has restricted testing of all variants. Afterburner operating restrictions and delayed aerial-refueling disconnects have affected the conventional-takeoff-and-landing (CTOL) F-35A. Testing continues on a redesigned clutch, driveshaft and doors for the short-takeoff-and-vertical-landing (Stovl) F-35B, and the tailhook is being redesigned for the F-35C carrier variant (CV).
“We are using 18 aircraft to conduct the equivalent of three development flight-test programs and one mission-system program,” says J.D. McFarlan, F-35 test and verification vice president. “We expect it to eventually include 8,000 flights and 60,000 test points. So far we've collected 22,000 of those, so we are around 36% through the test program.” Across the three variants, there are 12 aircraft in the flight-sciences test fleet. Another four are assigned to mission-systems testing, with two more—Stovl production aircraft BF-17 and -18—about to join and complete the flight-test stable based at Edwards AFB, Calif., and NAS Patuxent River, Md. Together they had logged 4,243 flight hours by Jan. 7, with the Stovl aircraft logging 1,309 of those hours and conducting 381 vertical landings.
Tests to clear the F-35A “clean wing” flight envelope for the Block 2B initial combat capability—to Mach 1.6/700 kt airspeed, 9g maneuvers and 40,000-ft. altitude (see F-35 Capability Plan table)—are wrapping up. The next step will be to clear the envelope with internal weapons-bay doors open, he says. Release of the Block 2B envelope is planned for mid-2015. Expanding the flight envelope to 50,000 ft. for the Block 3F full combat capability is planned for 2016, when development testing is scheduled to finish.
High angle-of-attack testing is underway at Edwards AFB using aircraft AF-4 equipped with a spin-recovery parachute. Where the F-16 is limited to 26 deg. alpha by its fly-by-wire flight-control system, the F-35's limiter is set at 50 deg. and the aircraft has been flown to 73 deg. to ensure there is sufficient pitch authority. “We have to really slow down to get those pitch conditions—100 kt at 40,000 ft.,” says McFarlan. “Pilots are pleased with the ability to get the nose down from high angle of attack.”
The DOT&E report says alternative trailing-edge flap settings are being explored to improve flying qualities during the approach to the carrier. Pilot surveys show handling qualities improve with 15-deg. flap deflection, but flight tests indicate 30-deg. flaps are needed to meet the 145-kt. maximum-approach-speed requirement. Burbage says the F-35C's flight-control system uses the flaps to keep the aircraft stable on the approach glideslope, taking out the lag from the pilot's inputs. A new tailhook for the CV will undergo its critical design review within a month and is scheduled to be installed in test aircraft at Pax River by year-end. After the F-35C had problems catching the arrester cables, the hook point, shank and dampers were redesigned. The concept was demonstrated last August at NAS Lakehurst, N.J., when aircraft CF-3 made five successful engagements, McFarlan says.
While live-fire testing in the first F-35, aircraft AA-1, at China Lake, Calif., has confirmed the redundancies and reconfiguration capabilities of the flight-critical systems, it has also shown that ballistic damage to polyalphaolephine (PAO) coolant and fueldraulic lines can cause fires. The report says the program office may reconsider installing the PAO shutoff valve, but not the fueldraulic fuses removed in 2008. The onboard inert-gas-generating system already is being redesigned to address deficiencies in fuel-tank inerting.
Stovl F-35Bs will return to the assault carrier USS Wasp in August for a second round of sea trials in stronger winds. “We will also bring along weapons,” he says. The DOT&E, meanwhile, says weapons integration has been limited by deficiencies in the radar, electro-optical targeting system, sensor fusion and helmet-mounted display.
In ground durability testing, only the F-35A airframe has so far completed a full 8,000-hr. lifetime. In December, fatigue tests on the F-35B were halted for a second time after the discovery of multiple cracks in a bulkhead flange during the 7,000-hr. inspection. Previously, a crack in a carry-through bulkhead was found after 1,055 hr. of testing, and McFarlan says Stovl test aircraft at Pax River will have to go through structural upgrades beginning this year.
Lagging JSF Software Development Worries Pentagon DOT&E
http://www.aviationweek.com/Article...3_p0-536481.xml
Software releases in 2012, the report says, ran late as compared to the schedule adopted after the 2010 technical baseline review, which was carried out in part to correct optimistic projections made before that date. (The program’s leaders had underestimated the amount of regression testing — tests to make sure that changes had not induced problems in previously tested functions — and overestimated test rates and productivity.) Block 1 software is not complete. Lot 2 and Lot 3 aircraft have been delivered “with major variances against the expected capabilities,” the report says.
Software problems are part but not all of the reason for slow progress with weapons integration, along with optimistic and inaccurate assumptions about the need for margins and the availability of instrumentation and range support. “The impact of these delays will potentially require an additional 18 months added to the schedule for weapons integration events,” the report warns.
The F-35C’s transonic acceleration has changed dramatically, increasing by 43 sec. compared to a 65-sec. threshold requirement. Operationally, one impact of this change is on the time at supersonic speed available in any given mission profile: a long, full-power transonic acceleration burns a lot of fuel.The F-35B has a full-page litany of mechanical problems with the powered-lift system, including a couple of issues – redesigning the driveshaft, and a new clutch material — which have large lifetime and maintainability impacts and for which solutions are still in the design stage. There are no showstoppers, but these issues do not point to a low-maintenance system in service. All versions are still restricted in maximum Mach number at altitude because of exhaust heat damage to coatings and structures on the horizontal tail surfaces, a problem that surfaced in 2011. |
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