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Aviation History
1989
1989 - 0212.PDF
US Navy delays T-45 production The L'S Navy is flying a T-45 Goshawk trainer, above, tpith an uprated engine to uprate the aircraft's F405 turbofan, below, if required Development problems with the US Navy's McDonnell Douglas T-45 Goshawk trainer will delay the programme by up to six months, says the US Navy. The award of a limited- production contract to McDon nell Douglas has also been deferred "until we get a good report card," the Navy says. What the Navy describes as "a total aircraft performance problem" with the T-45 was revealed in a recent report on initial flight-test results at the US Navy's Patuxent River Naval Aviation Test Centre. The aircraft was found to be underpowered, and to have in adequate longitudinal stability, poor stall characteristics and pitch-up on airbrake deploy ment. Other less significant points such as unsatisfactory cockpit switch locations are also being addressed (see Flight, January 21, page 5). "All of the problems are correctable, but we are disappointed to have problems which the test community would call major," the T-45 programme office tells Flight. Hawk derivative The T-45A Goshawk is devel oped from the successful British Aerospace Hawk, but the modifications for carrier use have added 1,3001b weight. Also, the Navy specified a derated engine to reduce life- cycle costs. The export-variant Hawk 60 is powered by the 5,7001b-thrust Rolls-Royce Adour 861, but the l,3001b-heavier T-45 has the F405-RR-400, which is the 861 derated to 5,4501b thrust. The simultaneous weight increase and thrust decrease has made the T-45A underpowered. The Navy says that it agreed to the derated engine choice because of the increased life and McDonnell Douglas calculations of the T-45A drag. "We allowed the design to go forward. . . presuming their figures were accurate," says a Navy source. "One of the things we are doing now is verifying drag predictions through flight test." The F405 is to be rerated to 5,7001b. This is a one-rfbur job entailing adjustment to the fuel control unit and turbine gas temperature controller. Mean while, flight testing is continuing using the derated engine with the bleed-air system closed off. This provides a 5-7 per cent thrust increase. A further solution, described by the Navy as a "very deep" backup, would be to go to a "high-build" standard and give the engine some of the per formance extras of the Adour 871, the 5,8451b-thrust engine used in the single-seat BAe Hawk 200. The Adour 871 has a higher-speed LP compressor, an improved combuster, a beefed-up exhaust mixer, and single-crystal turbine blades. Uprating possible Rolls-Royce tells Flight that rating an Adour to a level between that of the 861 and that of the 871 could be done should a customer require it. Adopting the 871 would provide the necessary thrust, and derating it would then increase the life. However, the "deep backup" solution would probably delay the programme further because of the extra testing required. The US Navy test pilots also identified a problem with exces sive engine spool-up time, a safety factor should the aircraft go low on a carrier approach. The solution is to install control logic which prevents idle thrust —normally 5 per cent—going below 15 per cent when the gear is down. At present a simple throttle detente is being used, "which works fine," says the Navy. Spool-up time will be reduced from 5 seconds to 2 seconds. The T-45's longitudinal stability problems have been most apparent on the approach, according to the Navy. They are apparently caused by higher trim changes resulting from the longer main landing gear legs and the twin-wheel nose gear with catapult equipment, which has higher drag than that of the Hawk. Initial solutions include fitting a 4in end cap to the fin, which is already 6in taller than the Hawk's, and restoring the two ventral fins. The ventral fins are fitted on all other Hawks, but were not originally fitted to the T-45 because of concerns about the "banjo effect" of arrester gear cables bouncing up and stripping the fins. The new ventral fins will be located slightly differently to those on the Hawk, and , and Rolls-Royce has identified options designed ("We hope," says the Navy) to avoid the "banjo" problem. The Navy is also concerned about the T-45's stall perform ance, which is also critical on a carrier approach. "We have not yet properly balanced the maximum lift co-efficient of the aircraft with roll-off during stall," the Navy says. The Navy specification requires that, during the approach to the stall, the aircraft must be controllable to stay within 30° of bank. "Right now we are in the 45°-50° area, and that is exces sive," says the Navy. "It is a matter of keeping the ailerons flying as you approach the stall. The problem does not lend itself to rigorous analytical solution". It will probably be solved by installing a further wing fence to inhibit spanwise flow and maintain aileron authority. . • Critical tests passed While there has been a number of problems, the Navy also points out that the T-45 has passed many critical tests, including the harsh 24-5ft/sec drop test needed for carrier operations. Reliability has also been good, the aircraft having been flown four times in one day during its first operational test last November. The Navy says that McDonnell Douglas is responding well to the fixes. The $143 million 24-aircraft limited-production contract for the second batch of T-45s was due last December (the first, in FY 198 8 was for pilot pro duction of 12 aircraft). This will now be delayed until May or June. "We are not going to buy it until we have flown it satis factorily," the Navy says. 18 FLIGHT INTERNATIONAL, 28 January 1989
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