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Aviation History
1949
1949 - 1379.PDF
AUGUST 4TH, 1949 f LIGHT 74" THE MAMBA MARATHON FLIES Britain's Third Turboprop Transport Completed THE Handley Page Marathon, powered by ArmstrongSiddeley Mamba airscrew-driving turbines, becameBritain's third turboprop airliner to fly within twelve months when it took off from Woodley airfield, Read- ing, on July 21st. As a result, Britain finds herself in the unique position of having had three turboprop transports airborne before anyone else in the world has flown one. The 22-seat M.69 Mamba Marathon is a direct develop- ment of the piston-engined Marathon airliner currently in production for the Ministry of Supply and British Euro- pean Airways. It is basically the same except that it is powered by two Mamba turboprops each developing 1,010 h.p. and 307 lb of jet thrust. Whereas the Hermes V fills the need for a large turbo- prop airliner, and the Viscount and the Apollo for a medium-sized type, the Marathon is small and much cheaper to buy and therefore opens up the market to feeder airlines and even, perhaps, to charter companies. It has been specially designed and built—through the backing and foresight of the Ministry of Supply—for journeys requiring a still-air range of up to 770 miles. As the production lines of Handley Page turn out stan- dard Gipey Queen-powered Marathon airliners for B.E.A., and 82,000 1b Hercules-engined Hermes IVs for B.O.A.C., their experimental departments are busy developing and perfecting the Mamba Marathon and the Hermes V. Con- sequently, should the airlines later elect to replace or aug- ment their present new equipment with turboprop air- craft now in the experimental stage, the country will be saved a large amount of money because both piston and turboprop variants of these two types of aircraft are iden- tical, except for their engine installations. Not only can the Mamba Marathon and the Hermes V be built on the same jigs and with the same tools as are used to construct the earlier marks now in production, but the airlines may effect an economy because they will only need to train their ground crews to deal with new engines, and will not have to spend hundreds of pounds in converting their air- crews to an entirely new aircraft. A description of Mara- thon progress appeared in the May 17th issue of Flight. More than three years have been spent on the design and construction of the Mamba Marathon, but its initial A 17 flight was seri- ously delayed by the troubles which befell the designers — the late Miles Air- craft, Ltd. The Marathon has a thin wing so the jet pipe of the Mamba engine cannot be buried within the aerofoil section ; consequently it must be carried—not very attractively—over the top of the wing. To test the aerodynamic effects this installation would have, a 5/6th scale nacelle was built some time ago of plywood and fitted to the wing of an Aerovan. This Aerovan (actually the prototype) was extensively flown and the data accumulated was ultimately used to advantage. . ...- New Performance Standards Flying at 10,oooft, the Mamba Marathon will cruise at 260 m.p.h. and if it were used on the British European Air- ways' internal services, it could cut travelling time by about one half. Calculations show a take off in 700yd and climb-away at 2,100ft a minute. Should one engine cut when the take-off run is well advanced, the climb will still be 600 ft/min. The calculated service ceiling of the Mamba Marathon is 35,000ft, and on ,one engine it is 16,oooft. Consequently, if advantage is to be taken of performance at high altitudes, production versions would have to be pressurized. Designs have been prepared for cabin pres- sure with maximum differential of z\ lb/sq in. Normal still-air range is 770 miles and the maximum still-air range is 900 miles. It is said that the Mamba- powered Marathon would be able to compete economically with the. Gipsy Queen version. It will carry 18 passengers and 540 lb of luggage for 770 miles at 260 m.p.h. as com- pared with its forerunner's 500 miles at 175 m.p.h. with the same load. For a distance of 500 miles the Mamba Marathon could carry 22 passengers and over 1,000 lb of luggage or freight. As a freighter it .could carry 5,470 lb for 500 miles, or 4,370 1b for 770 miles. Having over
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