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Aviation History
1964
1964 - 1063.PDF
600 FLIGHT International, 16 April I9i4 AIR CO E R C E The Short-Haul Contenders IT came as no surprise when Mr Hugh Conway, joint managingdirector of Short Bros & Harland Ltd, last week disclosed hiscompany's answer to the problem of finding the optimum DC-3 replacement: a 30-passenger, twin-turbofan project known as the PD.65. This brings to 11 the total of European aircraft and pub- lished projects aimed broadly at this most studied of all transport- aircraft markets. One of the entrants is Short's own Sky van. More- over, the United States—which probably has by far the greatest potential requirement for general-purpose short-haul transports- has become increasingly interested in the immense challenge which the "DC-3 replacement" represents, and between 12 and 20 design submissions are expected in the Federal Aviation Agency's design competition for the optimum local service airliner. Short's approach, as exemplified by the PD.65, has been to develop the simplest possible design consistent with the conflicting demands of high cruising speed and good airfield performance. They have chosen an overall size, payload and field length similar to that of the DC-3. Key to the PD.65's economic sense is availability of the right engine. This is always important with transport aircraft, and is particularly true of small aircraft designed for short stages where the inevitable low utilization and frequent take-offs highlight the importance of low engine capital, maintenance and spares costs, and good full-power fuel consumption. Mr Frank Robertson, chief of preliminary design at Belfast, told Flight International that with the performance in mind for the PD.65 a 5,5OOlb-thrust turbofan was needed. Nearest engine to the hardware stage in this class is the 5,2201b thrust Lycoming PLF1B-2—described in this journal last July 18, and already specified for the SLAT 311A and Weser WFG 614, rival projects from Germany. Another suitable engine is a possible fan conversion of the General Electric T64; and Rolls- Royce and Bristol Siddeley also have "paper" engines in this class. Asked why he had chosen turbofans, Mr Robertson admitted that turboprop projects looked better on paper; but: "You can't sell seats on a turboprop when the other Joe's offering aft-mounted fan aircraft." Given time, he thought, the turbofan would turn out to be very successful. In order to operate comfortably in and out of the sort of grass fields frequented by DC-3s, approach speeds in the 75-80kt range are being talked about for the PD.65. It is hoped to achieve this by putting broad-chord Fowler flaps on the 20°-swept wings. Studies have convinced Short's designers that in this instance, reductions in wing size through drooping, blowing and so forth, do not promise significantly worthwhile gains for the complication involved; also that the modest sweep-back does not greatly affect low- speed lift, but gives a worthwhile drag reduction if more power eventually comes along to push the cruising speed up to Mach 0.75. The present proposal is to cruise at about 400 m.p.h.—Mach 0.6 above 30,000ft, or less than this at the probable cruising height of 10-20,000ft. The PD.65's predicted APS weight (empty prepared for service) is comparable at 19,0001b with the DC-3. Gross weight, at 32,0001b, is some 4,0001b heavier than DC-3s operating under BCARs, and 6,8001b more than DC-3s certificated under American requirements. The PD.65 is designed to do four or five stages of 100-120 s.m. without refuelling, equivalent to one 600 s.m. stage carrying the ALTA payload of 4,6001b, or a still-air no-reserves range of 1,000 s.m. carrying the 7,0001b maximum payload. With the 10,0001b capacity fuel on board, the maximum stage length that can be flown is around 1,200 s.m. Most thorny of all aspects of DC-3 replacement design is direct operating cost. Very few people, it seems, are prepared to say what DC-3s actually cost to operate, and, in particular, to maintain. Views on what a replacement's d.o.c. ought to be range right down Short's PD.65 turbofan powered DC-3 replacement to the outright optimistic figure of "40 cents or less per aircraft- mile" contained in the local-service airliner specification issued by ALTA (the US Association of Local Transport Airlines). Short's main conclusion on costs is that an aircraft of PD.65 size ought to be designed to sell for about £300,000 if the d.o.c. is to be reason- able. Crew costs become an increasingly [large factor in the d.o.c. of short-range aircraft, as the size of the aircraft is reduced. For an aircraft meeting ALTA's plane-mile cost figure, even two-crew costs would form some 35 per cent of the total d.o.c. The PD.65 is arranged for two-crew operation without cabin staff; passengers stow their own luggage in a "pigeon loft" rack as they go in through the door. On a formula basis, the PD.65 has about the same total d.o.c. per aircraft-mile and per seat-mile as a DC-3—although the new aircraft, being considerably faster, is more productive and needs a higher sustained traffic level to get the same passenger-mile cost. Prospects for building the PD.65 depend entirely on Government assistance; it is estimated by Short Bros that the development cost would be less than £5m. The company is reported to have been investigating the possibility of building the aircraft in partnership with an overseas firm, the identity of which has not been disclosed. Short Bros already have agreements of one sort or another in most fields with such manufacturers as Beechcraft, Breguet, Ling-Temco- Vought, Hiller and Lockheed. If Government money is made available for a small jet airliner, someone will have the difficult job of sorting through the rival claims of Shorts and Hawker Siddeley who have a very similar project designated HS.136. Foreign competition to the British projects could come from any of a number of rival designs in Germany and France. Prompted- it is believed, largely by the Australian airlines, Dassault have for some months been testing reaction to a small jet airliner develop- ment of the Mystere 20 designated Mystere 30. Another desig- nation, Mystere 30C, has at various times been mentioned, although it is the Mystere 30 which is now the subject of a firm announcement by the French company. On March 21 Dassault signed with the
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