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Aviation History
1950
1950 - 1133.PDF
713 " It is definitely worth while to cut out two en- gines at 5,000ft where stacking problems are en- countered."—The Vickers Viscount demonstrates its ability to fly with two engines feathered, in this case ©a Qoe.iide. aircraft at the ramp for clearance. It was pointed out thattaxy speed of jet aircraft is fast—approximately 30 m.p.h. Thirteen gallons per mile are required for taxying, not allow-ing for start-ups and slow-downs. What turn-round time should be allowed in any operationalstudies on turbine aircraft in view of the special engine charac- teristics and the quantity of fuel having to be handled ? Turn-round time contingent upon speed of refuelling. Inthis connection, jets will never stop at a refuelling point without refuelling. Engine Design and Maintenance What are the man hours and material costs involved in over-haul and line maintenance of a typical turbine unit as com- pared with a reciprocating engine ? (In answer to question, attention was called to papers*read at recent S.A.E. meeting.) For new, experimental jet units, considerably lower time and costs were incurred inmaintenance. There is less which requires attention. Man- hours and cost on jets are one-half of those required forhigh-powered piston engines, according to BRISTOL repre-sentative. Cost of overhaul also varies according to where work is done—airline or manufacturer—and location. What are the existing actual service periods between overhaulsfor jets, and what is anticipated in the future, and at what dates ?RotLs-RoYCE will give a warranty of 1,500 hours on parts. No difficulty is anticipated in getting 500 hours whenaircraft go into airline service, and manufacturers hope to extend that to 800 hours. What, in general, are the large items of equipment that wouldbe involved in the overhaul and maintenance of turbine air- craft ? Test establishments may have to be adapted to highernoise levels. What inspection periods may be applicable to turbine engines, and what parts are principally involved ? Replacements involved are listed in S.A.E. Paper No. 456. What total life before retirement is anticipated for turbineengines, and what life is anticipated for components retired at shorter periods ? No definite data on jets. BRISTOL said the longest com-pressor life is 800-900 hours, and the longest accumulative life on a whole engine 750 hours to date. DE HAVILLANDanticipate 2,000 to 3,000 hours on turbine blades. Are there airscrew problems peculiar to turboprop installationsthat are liable to cause trouble (e.g., reliability, large size, balancing, etc. ? The turboprop uses a smaller shaft and blades 50 lb lighterthan on corresponding piston engines, because of lack of vibration. There is a limit, however, to how much morecan be cut. HAMILTON STANDARD thinks it depends onability to minimize engine-excited stresses. Higher speed, higher gradient may be problems. Orientation of shaft axismight be changed to mitigate this. Caution was expressed against depending too ranch on absence of vibration. Theneed for good dynamic balancing will persist. It will not ordinarily be possible for the operators to do this balancingthemselves in the field. Much depends on experience. How will the failure rate be likely to compare with thatachieved on piston engines ? How well does the jet maintain its initial power rating and fuel consumption throughout itsservice life by comparison with piston engines ? . ._- • See " Flight," May 4 and 11 ~~ _ ;/ British failing rates have been "very gratifying." Initialfuel consumption does deteriorate by about 2 per cent, which is not considered serious. Has engine and airscrew controllability for turboprop com- binations been developed to a point where it is satisfactory for commercial operation ? Yes. Both British and Americans agreed. What will the power-control system on both turbo jets andturboprops be like ? Will it be adequate, simple and reliable ? HAMILTON STANDARD is working on electronic develop-ment. BRISTOL have short-circuited control problems byseparating the turbines which run airscrew and compressor. CURTISS-WRIGHT hope to simplify electronic system sub-stantially, but operators were found to be unwilling to trust too much to electronics, and simple, speed-sensitive typesfound much favour. They expressed a desire for controls which operate despite failure of auxiliary systems. What are the advantages and disadvantages of installing powerplants in pods as against conventional wing installations, par- ticularly for jet turbines ? BOEING strongly advocated '' pods'' because they giveclean-swept surfaces; simplify maintenance problems and change-over of engine types; isolate engines in the eventof fire; give better control of noise level; give aerodynamic "dams" at wing tips to reduce aerodynamic loss. AVRO CANADA said their JETLINER had, in effect, a pod with avery short neck. Passenger Comfort and Safety In the event of sudden decompression, what procedures willhave to be. followed by the crew? Can passengers be pro- tected ? Will special provision have to be made to allowvery rapid descent of the aircraft to safe altitudes ? No insurmountable problems are anticipated. What is the risk involved for passengers sitting in the plane of the turbine disc, and how necessary is it to seat passengers clear of the noise cone of the jet exhaust ? What e.g. problems will arise from these two conditions ? Present regulations do not prevent seating passengers in the plane of the airscrews, although many passengers prefer to avoid such seats. No reason was adduced to believe that the turbine discs would be more of a problem. The " Problems of blow-out are under control. Restarting will be no problem at 20,000ft and aircraft may be brought down to this level."—Combustion chamber of the Armstrong Siddeley Mamba turboprop. (This British design is also the subject of a licensing agreement in America).
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