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Aviation History
1990
1990 - 0848.PDF
TECHNICAL: PROPULSION Burbank hushes HeavyLrft 707s The first Boeing 707 to be fitted with a Burbank Aero nautical II (BAC II) engine hushkit has arrived at the company's California factory to undergo conversion. The aircraft, a Boeing 707- 324C of UK airfreight specialist HeavyLift Cargo Airlines, arrived from Southend last week and is undergoing flight trials to estab lish baseline pre-hushkitting engine performance before conversion and certification. The BAC Stage 2 hushkit will cut down noise from the front fan by increasing the inlet sur face area which can be acousti cally treated. The area is enlarged by adopting the inlet profile de signed by BAC II for its Stage 3 hushkit for the McDonnell Douglas DC-8-62/63. This re moves the 707's distinctive na celle blow-in doors and produces a continuous inlet surface area to be coated in acoustic material. The front-fan bullet is similarly enlarged with a collar or fairing. BAC II says that the 707 system also incorporates design features of the kit developed by sister company Burbank Nacelle' for the Stage 3 McDonnell Doug las DC-9 Pratt & Whitney hushkit programe of ABS (a partnership of Airborne Express, BAC and SanFran), and in the Stage 3 Boeing 727 hushkit pro gramme with Valsan for Federal Express. The Burbank company also says that the Stage 2 hushkit equipment "... will be retained and fully incorporated as part of a Stage 3 Boeing 707 hushkit which is now in final design". The redesigned nacelle retains the "dog box" covering over the fan casing, which contains a short discharge duct for transfer ring fan air forward. Stage 3 noise treatment will involve acoustic treatment of the main body of the Pratt & Whit ney JT3D, including low- and high-pressure compressors and turbine sections. Extra bypass ducting is also likely to feature in the Stage 3 design. HeavyLift technical director Jim Keith says that the modifica tion is expected to produce slight improvements in specific fuel BAC II stage II hush kit for Boeing 707 Blow-in doors Existing production nacelle BAC II noise reduction nacelle stage ll/stage III consumption of "hopefully around 1.5 to 2%", as well as thrust performance improve ments of "up to 3%". Reductions in noise signature will bring equivalent perceived noise deci bels down across the range to 104.EPNdB on take-off, 98.9EPNdB on sidelines and 107.9 on approach. HeavyLift and BAC II hope that aircraft fitted with the hushkit will see restrictions lifted from the current maximum of 25° landing flap at maximum gross landing weight for simi larly treated 707s to 35° or beyond. • The aircraft will be temporar ily registered in the USA for the conversion and Federal Aviation Administration supplemental type certification (STC) before returning to the UK in mid-May. The aircraft will undertake 80h of flight testing as part of the certification programme. # Nordam, a Tulsa, Oklahoma- based aerospace company, has received hushkit orders for 60 aircraft and options on a further 51 Boeing 737-200 shipsets. The Pratt & Whitney JT8D hushkits have been ordered by Inter national Aircraft Services and Cuaff, Lippman Leasing and an undisclosed leasing company. • Nordam will hold the STC for the system for which Pratt & Whitney is the programme's technical director. A final hushkit will be selected in May 1990, with FAA certification ex pected in 1991. Of the other Pratt & Whitney noise-reduction programmes, the DC-9 collaboration with ABS has been successfully flight- tested on an Airborne Express DC-9 and is scheduled for FAA- certificated flight testing in May 1990. STCs for the DC-9-10 and DC-9-30 are expected later this year. The system will involve respaced inlet guide vanes, ex haust gas mixer and external noise suppressor. The Federal Express/Pratt & Whitney Boeing 727-100 hushkit system for JT8D-7 en gines was granted an STC in May 1989 and testing for a kit for lightweight 727-200s using the same kit has been completed. A new hushkit for heavyweight 727-200s, using an external noise suppressor, is scheduled for testing next month. • Volvo looks for resonance cure Compressor resonance prob lems continue to plague Volvo Flygmotor. The phenom enon appears the likely cause of last month's Saab Viggen crash in Sweden and has already forced Saab to delay a resumption in flight tests of the new Volvo- powered Gnpen fighter. The Swedish Air Force says that the Viggen's RM8B engine failed when blades in the low- pressure compressor broke free, and Volvo suspects that vibration caused the blade failure. The accident was similar to one which occurred in 1988, suggest ing that the problem is not iso lated in the RM8B engine fleet, the Swedish defence ministry says. Several RM8B engines were removed from service for inspec tion and service manuals of others have been investigated. The Air Force refuses to say how many Viggens were grounded as a consequence. Volvo says that the cause of the latest crash has yet to be confirmed and the accident report is as yet unpublished. The Air Force believes that it can be cured without the need to impose performance limitations on the Viggen, and the defence ministry says that some Viggens are back in service. The troubled RM12 engine, developed by Volvo and General Electric for the Gripen, which suffers from compressor res onance, is to be modified. In the meantime, Volvo recommends limiting Gripen performance in forthcoming flight tests with un modified engines. • NEWS IN BRIEF ENGINE TESTBED Froude Consine has handed over a complete testbed to Alfa Romeo, Italy. The single-cell unit can test turboprop or turboshaft engines. Two dynamometers—an F47 and an HS150—serve the cell, and each has been installed on a trolley to enable them to be wheeled in and out, depending on the engine to be tested. lb FLIGHT INTERNATIONAL 21-27 March 1990
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