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Aviation History
1948
1948 - 1725.PDF
OCTOBER 14TH, 1948 FLIGHT 465 heads and difficult operating standards, the Brabazon iB showeditself capable of making a profit operating westbound across the North Atlantic against the average head wind which was52 m.p.h. at 35,000ft. Eastbound with prevailing tail winds it should be better still. The Ambassador and the Constellationwere also potentially profitable propositions. In conclusion, the discussion in this section could be summedup as four essential requirements : — - (1) Reduce overheads.(2) Increase utilization. * • ••» • y > *; (3) Maintain standards. . ;--•••.. (4) Match aircraft to routes. The Problem of Future Power Plants Mr. Masefield said that one of the outstanding questions ofthe hour was the form of power plant which was likely to prove most satisfactory for various classes of transport aircraft.From the point of view of commercial operations, the ques- tions which stood out in considering any new form of powerplant were: What will it cost per annum? What are its powers of earning revenue? What are its qualities in bad weather?He then went on to examine three types of modern power plant applied to hypothetical airframes in comparison with astandard piston engine. They were the compound piston engine, the turboprop and the turbojet. Both short and long-range possibilities were analysed, and for the shorter stage types four twin transports, each of 28,000 1b gross weight,were considered. (1) A twin Merlin transport, two 1,500 h.p. Merlin 35 engines. (T.M.T.)(2) A twin Merlin helicopter with similar engines. (T.M.H.) (3) A twin Dart transport with two 1,500 e.h.p. Dart turbo-props. (T.D.T.) (4) A twin Derwent transport with two 3,900 lb. staticthrust Derwent turbojets. (T.J.T.) The weights and performance characteristics of the fouraircraft were tabulated as shown on this page. The assumed prime costs for complete power plants, excluding airscrews,which were representative but not precise makers' figures and tended to be on the high side, were: Merlin—£7,000 (£4.7 per h.p.) ;•- Dart—£12,600 (£8.4 per h.p.) " - Derwent—£7,000 (£4.7 per h.p.) •The fuel, load and range of the helicopter had been deliber-ately restricted to ensure maximum performance over the short stages for which it was most suited. Taken all round, the.weights and performances showed up the turbine types remark- ably well. On examining the twin Derwent transDort with thesame standards for allowance and fuel reserves as had to be assumed for the other two twin transports, it was found thatat present standards the amount of fuel required for taxy, climb, descent, diversion and stand-off would occupy morethan the tankage provided, a minimum pay load of 3,000 1b having been specified and the gross weight having been fixedby take-off requirements. In other words the aircraft was completely inflexible and its economic possibilities were maderidiculous by the fuel consumption on diversion and stand-off. WEIGHT ANALYSIS TWIN-ENGINED SHORT-RANGE AIRCRAFT COMPARATIVE PERFORMANCE DATA TWIN-ENGINED SHORT-RANGE AIRCRAFT Weights in Ib Power plant and systems ... ... Operating equipment Passenger equipment Basic (with crew, fixtures) ... Maximum oil capacity Maximum usable fuel capacity Corresponding payload Usable fuel with capacity payload ... Capacity payload Disposable load Gross Pre-flight fuel allowances Maximum take-off and landing ... Twi n Merli n Transpor t (tw o standar d pisto n engines ) 8,300 6.200 2,350 1,750* 18,600 19,850 350 20,200 4,870 3,000 0 7,870 7,870 28,070 70 28,000 Twi n Merli n Helicopte r (tw o standar d pisto n engines ) 9,615 6,270 2,350 2,000t 20,235 21,485 240 21,725 3,315 3,000 0 6,315 6,315 28,040 40 28,000 Twi n Dar t Transpor t (tw o turboprops ) 8,450 3,900 2,350 2,000t 16,700 18,030 60 18,090 7,000 3,000 2,130 7,870 10,000 28,090 90 28,000 Twi n Derwen t Transpor t (tw o turbojets ) 8,500 4,100 2,350 2,000t 17,050 18,530 50 18,580 6,550 3,000 1,680 7,870 9,550 28,130 130 28,000 1. Total take-off power 2. Meto power 3. Cruising powerassumed 4. Meto power for cruise 5. Operating height at start of cruise re-gime 6. Operating height at end of cruise re- gime 7. Assumed av. cruising fuel consumption... 8. Assumed specific cruising fuel con-sumption 9. Cruising speed at take-off weight ... 10. Cruising speed at 85 per cent take-off weight II. Cruising speed at 70 per cent take-offweight 12. Cruising consumption at 85 per cent take- off weight... 13. Air miles per gallon14. Theoretical still-air range at operating height, no allow-ances 15. Estimated take-off distance to 50 feet on full power at max. take - offweight Units e.h.p. e.h.p. e.h.p. per cent feet feet Ib hr Ib/ e.h.p./ hr m.p.h. m.p.h. m.p.h. Ib/mile a.m.p.g. statutemiles feet Twi n Merli n Transpor t (tw o standar d pisto n engines ) 3,000 2.480 1,340 54 10,000 10,000 615 0.458 212 220 227 2.80 2.57 1,740 2,000 Twi n Merli n Helicopte r (tw o standar d pisto n engines ) 3.000 2,480 1,340 54 2,000 2,000 615 0.458 110 • 112 114 5.50 1.29 603 Nil Twi n Dar t Transpor t (tw o turboprops ) 3,000 2,730 1,340 49.2 17,000 26,000 880 0.655 264 270 227 3.26 2.48 2,140 2,000 Twi n Derwen t Transpor t (tw o turbojets ) (7,800 Ib) 3.000 variable variable variable 30,400 40,200 2,490 1.335 343 350 355 7.1 1.14 922 2,00') The only hope for such a machine would lie in improved airtraffic control. Round figures of interest for the fuel consumptions of trans-port aircraft standing off at 5,000 ft. at 180 m.p.h. were: — Piston-engine types: ij per cent of landing wt. per hr.Turboprop types: 2% per cent of landing wt. per hr. Turbojet types: 6J per cent of landing wt. per hr.In order to continue with his comparison, Mr. Masefield therefore assumed in the case of the turbojet transport animprovement in air traffic control, and by the use of automatic landing procedures (1) no diversion to an alternate airport tobe contemplated, (2) 30 minutes stand-off at operating height to be an adequate emergency reserve. Following a detailed analysis of the four types a cost sum-mary was prepared as follows: — Fixed Annual Costs, £ ... Hourly Cruising Costs, £ Take-off and Landing Costs, £ ... T.M.T. 44,735 23.35 57.02 T.M.H. 46,745 25.28 31.37 T.D,T, 50,245 23.92 58.37 T.J.T. 44,485 33.50 47.78 For a production run of 150 aircraft, the cost per pound ofgross weight for the four types was respectively £2.5, £3.0, £301, £2.5. For a utilization for. 3,000 hours with two hours betweenlandings, the operating costs for the four types would be: — Per annum, £ Per hour, £ Per still-air stage mile, £ Block speed (still air) m.p.h., £ T.M.T. 200,255 66.8 0.406 164 T.M.H. 164,745 54.9 0.560 98 T.D.T. 209,445 69.8 0.346 202 T.J.T. 223,200 74.5 0.268 i78 * Non-pressurized, t Bus-type seating for additional passengers. Pressurized. B 19 With a 3 per cent addition for dead flying the results wereplotted as comparative U curves for operating costs per revenue ton per hour. The general conclusions which^ could be drawn from thesurvey of shorter range aircraft were: — First, because of its high consumptions at low speeds andheights, the plain jet aircraft could not be a commercial proposition in the present stateof air traffic control—except (Continued on page 470)
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