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Aviation History
1947
1947 - 1652.PDF
356 FLIGHT SEPTEMBER 25TH, 19 <j The Anglo-American Conference Summaries of Further Lectures : Hazen on Development of Piston Engines and Hafner on Helicopters Factors Affecting Future Development of Reciprocating Engines By R. M. Hazen Mk. HAZEN, who is Director of En-gineering, Allison Division, GeneralMotors Corporation, introduced his Paper with the statement that he proposedto present the viewpoint of the power plant manufacturer on the future of thereciprocating engine by a process of elimin- ation, with more emphasis on practical thanon theoretical factors. To start off with the lecturer postulated that the basic premisesfor this analysis are that every mission, whether military or commercial, which canbe accomplished satisfactorily with pure jet units will be powered with this type, everypossible mission on which the jet engine cannot meet requirements will use airscrew-turbine engines, and that only on sucn missions as cannot be accomplished witheither of these units will the reciprocating engine be used. Accomplishment of missionembraces such factors as speed, range, cost of initial equipment, cost of operation andgeneral performance of the aircraft. Development funds are definitely low ina peace-time economy, continued Mr. Hazen, and their allocation must be devoted todeveloping the simplest type of power whicb may meet requirements, in exploring thevarious sizes needed and developing those tpov due to the greater complication of the pro-duction. The axial-flow unit has been sub- jected to very little emphasis on cost re-duction and an active programme on this type would probably reduce its cost to abouttwo-thirds of its present value. On the subject of fuels in regard to futuredevelopment and supply and the effect on power plant development, the lecturer ob-served that it is more or less obvious that every additional jet- or airscrew-turbinepowered aircraft not requiring high-octane fuel reduces the probability of the fuel com-panies providing development of facilities for higher octane fuel because of the greateruncertainty of its use. Under the heading of "one-way aircraft," Mr. Hazen sug-gested that the pilotless aircraft is an im- portant factor in favour of emphasis onturbine-engine development since it reduces emphasis on the greatest weakness of theturbine, i.e., high fuel consumption, and under-lines the major advantage of low unstalled weight. Perhaps the most glar-ing weakness of the simple jet is its poortake-off and early climb characteristics. There is,however, some evidence that water/alcohol injec-tion and after-burning may give additionalthrust increments whereby take-offs in linewith those given by piston engines can be expected in the futureThe variable range with altitude charai> teristics of the pure jet unit is, pernup.,the least discussed disadvantage of uinnift powered by such engines. We are proneto look at the high-speed sea-level per- formance and the range at the tropopauseand feel rather pleased. The better speci- fic fuel consumptions at sea-level static thanat high speed and altitude are sufficiently' soothing that one is apt to get a'jolt whenit is stated that the range of a jet-propelled "aircraft at sea-level is of the order of one.fifth or one-sixth of the usually quottr 35,000 feet range. After-burning for highspeed, permitting a smaller basic power plant, helps this problem appreciably, aswould a variable nozzle. Multiple low-drag units, some of which may be switched oftat altitude, may be another approach. The airscrew turbine, continued Mr. STAGE WITH VARIABLE SPEED TURBINE-DRIVE CONSTANT-MESH CEARINC, FIXED RATIO ALTITUDE IN FEET Fig. /. Comparative curves of performance for Allison V-I7I0 engine employing diverse types of supercharger. lines whereby the most rapid progress canbe made. The advantages of applying ie- search and development funds to the tur-bine are obvious since major improvements in efficiency, in output for a given size, ineconomical fabrication and use of materials are possible, due to the newness of the pro-duct. In addition, application of such im- provements applies to the power sectionsboth of pure jet engines and airscrew-tur- bines, and, furthermore, provides basic in-formation suitable for the exhaust-turbine necessary in compounding the reciprocatingengine, should this be desired. Production considerations favour thefuture of the airscrew-turbine as compared to the piston-engine. The only importantvariable is the time of prior development and this is, of course, important. The centri-fugal gas-turbine and the piston-engine are both at the stage where only careful produc-tion engineering can lesult in further cost reduction and, in fact, costs may increase VJlTH these precis of two particularly interesting papers—one American and one British—we conclude the series of summaries we have given in recent issues of the lectures delivered before the joint convention of the Royal Aero- nautical Society and the American Institute of the Aeronautical Sciences held in London from September 3rd to September 9th. The Conference has provided a most welcome and extremely valuable meeting ground, not the least important aspect of which has been in the provision of opportunity for informal unfettered con- versation and interchange of ideas to supplement the "official" views given in the lectures- Fig. 2. Schematic diagram of coupling between turbine, auxiliary-stage supercharger and engine-stage super- charger showing, in addition, the induction flow. Hazen, has to meet the tough competitionof piston engines, with all their past his- tory of development, and to succeed, ithas to better in certain respects, and equal . in all others, the qualities to be expectedfrom the piston engine of two or three years from now. The airscrew-turbine hasthe basic advantages of high output per pound of weight, smoothness, low fuel cost,small size, and the important advantage of readily being scaled up or down, once agood fundamental design is developed. In the light of these circumstances, Mr. Hazenobserved that expenditure of engineer^ time and development funds cannot be mPdertaken on an airscrew-turbine without- carefully designing such a unit and compar-ing it with what could be expected from a reciprocating engine of the same developmenttime. His company's developments indi- cated that this should be compared to acompounded reciprocating engine. The Allison V-1710 is selected as theexample of a reciprocating engine only be- cause there is very complete information onnot only the basic design but on various systems of supercharging, and on the un-usual variable-speed hydraulic drive of the auxiliary or first-stage of compression,which made the application of a geared tur- bine for compounding relatively simple-The necessity for concurrent production 0! a single-stage, single-speed version "ithturbo-supercharging, single-stage medium altitude and two-stage high-altitude ver-sions, led to the development of a scf1-'; mtf initial or so-called auxiliary-stage s; vtr
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