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Aviation History
1956
1956 - 1408.PDF
560 FLIGHT, 28 September 1956 The Friendship's Field Performance ON the eve of publication of the Commercial AircraftNumber of Flight (July 6) we received and were able toinclude in our explanatory notes some information relating to greatly improved take-off and landing performance figures forthe Fokker Friendship. To the operator beset by terrain diffi- culties, Fokker suggest that the reduced field lengths required—about 90 per cent of the previous estimates—could be decisive where new equipment decisions are being made and might bringthe aircraft within the consideration of the range of companies who could not previously contemplate the use of a fast modernturboprop. The airfield performance of the 32-seat Friendship at maximum landing and take-off weight compares very favour-ably with the 24-seat DC-3 which it has, in part, been designed to replace. Where the DC-3 required a field-length of 4,500ftto take off at full load, the F.27 will require a guaranteed length of only 3,850ft; similarly, the landing field length required is aguaranteed 3,000ft over the DC-3's 3,400ft. Estimated take-off and landing performance curves are shownon this page. The calculations have been made on the basis of the American Civil Air Regulation requirements which for take-off assumes that the critical engine fails at the critical point in the take-off run, whereupon the airscrew automatically feathers.The altitude figures given in parenthesis relate in every case to take-off in hot-day conditions—those drawn show performanceat international standard atmosphere plus 15 deg C—and include the use of water-methanol injection into the two Dart 511 turbo-props. It may be seen from the graph for take-off field length that the estimated values for the maximum take-off weight of34,520 lb and a demonstration weight of 33,000 lb are 3,640ft and 3,220ft respectively; while the new guaranteed field lengths atthese weights are 3,850ft and 3,400ft. The landing field length requirements shown on the graph arealso drawn to C.A.R. requirements, which exclude the benefits of reversed thrust. The figures are given for the most forwardcentre of gravity position (24 per cent of the aerodynamic mean chord) and provision has again been made for the increasedfield lengths required with higher-than-standard temperatures. An interesting feature of the Friendship is that because tandemwheels are used the maximum mainwheel load of 8,100 1b is very much less than that of the DC-3. The mainwheel tyres areinflated to 79 lb/sq in and the nosewheel tyres to 61 lb/sq in, although optional pressures of 60 and 40 lb/sq in can be used. The reason for the use of a collector tank in the_ Friendshipfuel system—which has been the subject of speculation by some operators—has recently been explained by Fokker as being neces- ISA+I5*C 26 28 29 3O 31 32 33 34 TAKE-OFF WEIGHT (lb«l,OOO) 2,000I 25 26 27 28 29 3O 31 LANDING WEIGHT (lb« I.OOO) 32 33 34 Marked improvements in the take-off and landing field lengths pre- viously quoted for the Friendship are shown in these new estimated performance curves, which are plotted to the requirements of Civil Air Regulations 4b. The sea level standard day take-off field length of 3,640ft at the maximum all-up weight of 34,520 Ib is particularly noteworthy. Fokker's guaranteed field lengths are given in the text. sary to prevent flame-outs as a result of entrained air in the fuel.Unlike the piston engine, they say, the turboprop has no car- burettor to bleed air from the fuel at the engine and the collectortank has been introduced to act as a separator—the released air is vented back to the main integral tanks. Aerated fuel, it ispointed out, can be caused by flying in bumpy conditions or during a side-slip, and in these conditions the trapped air maycause the supply to the collector tank to be interrupted. NEW U.S. AIRCRAFT ELECTRICAL EQUIPMENT OIX sizes of hydraulic-powered electrical power packages rang-•^ ing from 0.5 to 3.0 kVA output have been developed by Vickers Incorporated of Detroit, Michigan. The units are lightand compact, and are claimed to show improved efficiency when used in place of a conventional inverter in providing A.C. powerfor new or additional systems. Typical applications are power supply for the co-pilot's instruments in multi-engined aircraft, oremergency A.C. power when the only power source is a ram-air- turbine hydraulic pump. Normally, power is supplied by the flowavailable in the aircraft hydraulic system—which is claimed to be made generally without any changes to the system—full flowis demanded only briefly and infrequently. (This conception makes an interesting comparison with the long-range versions ofthe Britannia, the Messier hydraulic pumps of which are driven electrically.) The alternator is a 120/208-volt, three-phase, Y-connected unitgenerating at 400 cycles/sec at 8,000 r.p.m. It is capable of continuous operation between temperatures of —65 to +250 degF, and, as there are no brushes, it can be used at altitudes up to 55,OOOft. The reduced size and weight over conventional genera-tors are obtained from elimination of the exciter and slip rings. Performance data for the six Vickers models are as follows: — kVA 60 120 no160 180 240 Duty cycle Continuous Continuous Continuous Continuous 5 minutes5 seconds Speed(r.p.m.) 5,700-6,300 4,000 4,800-7,200 5,700-6,300 6,0006,000 Air pressure required(in of water) None 6 6 11 11 11 Power factor .75 .75 .75 .75 .75 .75 A much larger, very heavy duty machine is the G-180 160-kVAalternator manufactured by Jack and Heintz (who are, inter alia, responsible for the complete electric system of the Douglas DC-8).The power rating of 160 kVA is claimed to be the highest ever designed, but will make provision for aircraft requirements forthe next few years, including nudear-powered aircraft. Jack and Heintz say that the benefits derived from the use of a large single-source machine over a multi-generator installation—the elimina- tion of components and complexity with a reduction in weight—make it attractive for today's multi-engined aircraft. (Lett) Driven by a Vickers constant-speed oil-hydraulic motor, this 1-kVA generator meets electrical power requirements tor aircraft instruments or emergency use. (Right) The Jack and Heintz 160-kVA generator can be driven directly, by con- stant-speed drive, or by gas or air turbine.
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