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Aviation History
1993
1993 - 1793.PDF
level of 388kN (87,2001b) to 350kN. To date, the engine has achieved record thrust levels of 469kN in runs at Peebles. Work on the 747 testbed may include making the first-class and business-class seating areas into an onboard, mobile, briefing room. "We could use this during our cold-soak tests in Fairbanks, Alaska, and for our high-altitude/ lapse-rate tests in Casper, Wyoming," says Chappell. "We may also be making one of the underfloor con tainers into a flyaway unit for spare parts, and so on." The 747 is held by GE on a ten-year lease, but could be used for testing engines well beyond 2003 if the FTO finds that the aircraft is as useful as it hopes. TYPICAL TESTING Average test sorties for the 707 have grown over the past five years, from around 2.5h to 4.5h and more today, says Beeler. Given the even greater endurance po tential of the 747, in me chanical and human terms, the trend towards longer test sorties is likely to be maintained. Flight International joined GE's 707 testbed for a routine test flight of the CFM56-5B. Flight 22 was aimed at meet ing 17 targets on the test card. These included establishing the engine's per formance level at altitude, relative to guarantees, and to establish a preliminary power-management strategy for certifica tion testing of the Airbus A321, which is due to enter service early in 1994. In addition, the flight was designed to collect data throughout the envelope to create and validate an engine-performance model, as well as determine various spe cific characteristics of the engine. The 8h flight began with a lapse-rate take-off, in which the lapse in engine power with speed and altitude is carefully measured during the take-off and climb- out. Before take-off, the engine was stabil ised at minimum idle for 20min before lining up on the runway. The throttle was then advanced to 70% Nt (fan speed) before brake release in The GE90's first flight is the focus of FTO activity advance of being run up to maximum take-off thrust. The other three engines were at low power settings for take-off as the single CFM56-5B, in this case, generates about the same thrust as two JT4s. The -5B is rated at 133.5kN, or 138kN, depending on digital engine-control setting. Following take-off, the crew put the aircraft into a climb out over the Sierra Nevada mountain range, where it settled into a race-track pattern for most of the day's testing. This included an exhaustive series of steady-state power-calibration checks at various speeds and altitudes beginning at 15,000ft (4,500m) and 280kt (518km/h) indicated airspeed. Blade-tip clearance in the low-pressure turbine was checked against baseline spec ification at various speeds, while cruising at between 10,000ft and 15,000ft. The 707 was then taken up to 35,000ft for a series of transient tests in which the full- authority digital engine control (FADEC) was failed deliberately for specific modes. These occurred during a lmin, slow acceleration to maximum cruise thrust; a sudden chop from cruise power to idle, then stabilised for 20s; followed by a burst to maximum take-off power, again stabilised for 20s. The test flight programme also included a series of airstarts and quick re-lights. The airstarts were performed at various conditions, rang ing from 31,000ft and Mach 0.45 to 10,000ft and VM0 (maximum design-operating speed. Quick re-lights, con ducted at 5,000ft and VMiN (minimum speed) higher-altitude were classified as if light-off was within 30s. Airstarts were achieved using both windmilling and starter assis tance, with residual exhaust-gas tempera tures reading between 80° and 100°C. With fuel running low, the 707 was returned to Mojave for a series of ground- test transients of the FADEC, before it was shut down for the day. So much data had been collected by the time the aircraft touched down that new recording tapes had to be despatched to the test bed for the final series of tests before the engines were shut down. At the time of Flight International's visit, the test team had amassed almost 70 flight hours of assessment on the -5B. The programme, when complete, is expected to total about 120h. £1 like the airstarts, successful achieved The Boeing 747 testbed will eventually replace the "hard to maintain" 707 machine 28 FLIGHT INTERNATIONAL 21 - 27 July, 1993
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