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Aviation History
1956
1956 - 1371.PDF
FLIGHT, 21 September 1956 523 NEW ELECTRA DATA Estimates for Lockheed's Turboprop Airliner SUCCESSFUL operations with Viscounts augur well for the^ widespread introduction of turboprops into the American airline field. Seven of the 12 main U.S. domestic airlines arenow committed to turboprops for medium-haul operations, repre- senting very many ton-miles of capacity payload to be sharedbetween two types of aircraft—the Viscount and the larger Electra, deliveries of which are to begin in 1958. The process of development begins, of course, long before theaircraft is in service, and each published change of performance or specification must (with a commercial airliner) be regarded in thelight of the competition that the performance presents to the aircraft's contemporaries. Revised weight and performance datafor the Lockheed 188 Electra, which were foreshadowed in our Commercial Aircraft issue of July 6, are consequently of quiteconsiderable interest. The structural-design gross weight of 113,000 lb and the landingdesign-weight of 95,650 lb remain as quoted at that time; more recently released are the maximum zero fuel weight of 80,910 lband an operating weight of 59,272 lb. This latter figure is the aggregate of an empty weight of 56,000 lb and operating equip-ment which weighs 3,272 lb. Additional equipment which must be carried in the international version of the Electra is responsible 40 deg F) day. Consideration of take-off at the maximum weightof 113,000 lb shows that field lengths of 5,820ft and 7,240ft respectively are required. Normal day-to-day operation (withoutcritical failures) at a typical configuration—take-off weight of 112,000 lb, 66 passengers and their baggage, maximum cargoloading and 34,600 lb fuel—would require about 3,920ft for the Electra to become airborne on a standard day. The normal landing weight of the Electra will be 85,030 lb,for which a field length of 4,920ft is required at sea level and normal temperature. This field length is based upon the require-ments of U.S. Civil Air Regulations, and includes a factor of 0.6, but does not take into account any form of reverse thrust.At the maximum gross landing weight of 95,650 lb this length is increased to 5,400ft. Landing with two hours of fuel in thetanks would account for 7,200 lb of the total landing weight of the domestic version, and 7,340 lb in the slightly heavier internationalversion. An interesting comparison can be made between the cost-rangecurve shown on this page and that shown in Flight for July 6. It will be seen that the earlier figures have been increased by anappreciable amount. The first Electra is due to fly in October 1957 and, by means Operating costs of the Electra as a 66-seat international and domestic custom version (1, and 40 D,) and an 88-seat international version (h) or 85-seat domestic version (D2) are compared on the right. The take-off performance curves below are drawn to Civil Air Regulations "j requirements, which make provision for engine failure at the critical take-off point followed £ 3 5 by automatic feathering of the 13ft 6in diameter Aeroproducts four-blade airscrew. 8| 1 1 1 1 1 1 1 « 30 7 6i j 1 1£ 1—__JL-—f~~—— i_^-——* 1 825 5 4 3 2 1 0 85 90 95 100 105 UO 115 TAKE-OFF WEIGHT (IbXIOOO) o * O <z'-.hi tt —I i TAKE-OFF RUNWAY LENGTH ,—•— - ''ij R1OO O li.il ftr1 Id STANDARD DAY / + ' 40'F^ - _——•-~ T»un*pn DAY SEA LEVEL 10 1i 1, D2 —*- « 1 -. • • <" 500 POO 1,500 2D00 2500 3C00 FLIGHT DISTANCE (similes) for an additional 665 lb to bring the operating equipment total to4,408 lb; this may be broken down into crew and crew baggage 1,090 lb; passenger and service equipment 1,794 lb; removablegear 340 lb; marine equipment 590 lb; navigation equipment 75 lb; unusable fuel and oil 324 lb, and consumable oil 195 lb.The total payload of the Electra of 18,000 1b may be comprised of the weight of 66 passengers (custom version) and 7,110 lb offreight baggage, but operation with additional passengers up to a payload of 21,638 lb is permitted. Reference to figures quoted asat April this year show that an increase in design take-off weight of 3,000 lb, of design landing weight of 2,250 lb and in operatingweight of 2,000 lb have been made. So much for weight differences; what of the effect upon per-formance? The April figures remain largely unchanged. The mean cruising speed is given as 406 m.p.h. at optimum altitudeand zero wind conditions—in fact the actual cruising speed varies between 410 m.p.h. at short ranges and 400 m.p.h. over themaximum stages of about 2,600 miles. A slight improvement on the performance figures quoted earlier is, however, apparentfrom a study of the payload-range curves, which show that the 21,638 1b payload may be carried up to 2,300 miles cruising at80 per cent of the normal rated power available—figures that substantiate the maker's claim for the Electra's ability to operatethe longest medium-haul distances—necessary on the longer U.S. domestic flights. More comprehensive figures are now quoted and a curve given(it is reproduced on this page) to show the take-off field lengths required under varying conditions. In drawing the curve it hasbeen assumed that an engine fails at the most critical point in the take-off run, whereupon the airscrew feathers automatically.Performance at sea level for a standard day and for standard plus 40 deg F temperatures are shown. With a take-off weight of97,432 1b necessary for a 1,000 mile flight, a field length of 4,080ft is required on a standard day, and 4,900ft on a hot (standard plusof a pre-planned programme, the production rate is scheduled to reach 132 aircraft per year by late 1959. The number of aircraftat present on order is 128. The rise of a third turboprop airliner star—the Britannia—hasrecently been observed (without much need for a long-range tele- scope) in the U.S. skies; and despite Bristol's insistence that theElectra and the Britannia "are not comparable, the Britannia is a much larger aircraft," the Electra performance yardstick is sureto figure in an assessment of the British challenger by the president of an American airline with a cheque-book for equipment-pur-chasing in his pocket. CONTINENTAL CONSTRUCTORS' CONFERENCE TPHE second European Aeronautical Congress is to be held atA Scheveningen, Holland, from September 25 to 29. The dele- gates represent the technical-scientific branches of the aircraftindustry in countries associated with A.I.C.M.A. (Association Internationale des Constructeurs de Materiel Aeronautique), andmembership of the Congress is also open to those engaged on aeronautical work in Austria, Finland, Greece and Yugoslavia.Papers on many different topics will be given, several of the most important dealing with the introduction of jet propulsioninto civil aviation, a subject which has been recommended for particular study. There will also be visits to places of aeronautical interest, and(as mentioned in our issue of August 24) a demonstration of the S.N.C.A.S.E. S.E.210 Caravelle and the Fokker F.27 Friendshipat Schiphol Airport, Amsterdam. -,.-.,.-. .*-..• ->:.»- ^
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