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Aviation History
1947
1947 - 0912.PDF
528 FLIGHT JUNE 5TH, 1947 ALL-WINC AIRCRAFT Their Advantages, Development and Problems Outlined Before the R.Ae.S. J. K. Northrop. T HE Wilbur Wright Memorial Lectureto the Royal Aeronautical Society is held annually, and the custom is to have a British lecturer alternating with one from abroad. For the last few years this has meant an American lecturer every other year. In 1941 the lecture was given by Juan Trippe; in 1943 by Edward P. Werner; and in 1945 by T. P. Wright. This year's lecturer was John K. Northrop, who is head of one of the most famous American aircraft firms. Its work on all-wing aircraft development goes back to the years before the war, and has now reached in size the XB-35 bomber of 172ft span. HE thirty-fifth Wilbur Wright Memorial Lecture was de-T •M~ livered before the Royal Aero- nautical Society last Thursday by Mr. John K. Northrop. The lecturer began by examining to what extent the all-wing type of aircraft is worth while, traced its development so far as his own company is concerned, and concluded by examining the more serious problems still outstanding and some of their possible solutions. Mr. Northrop said there was a tre- mendous background of development in tailless aircraft, but little outside that of Horten brothers in Germany and of Northrops in America in the all-wing type. Improved efficiency was the factor which had inspired his company's work. The extremes in size explored and satisfactorily flown by Northrops to date ranged from the '' buzz bomb '' of 29ft span to the XB-35 long-range bomber of 172ft span. Explaining the size of the bomber, Mr. Northrop said: "It is consider- ably larger than would be necessary to provide ample space for passenger and crew comfort and,.ample volume for payload, be it cargo or bombs. It was designed larger than necessary because we desired to keep the wing loading comparatively low in this first large experimental venture. It has a normal gross weight of 165,000 lb, an overload gross weight of 221,300 lb and sufficient volume within the winga *H ' - = envelope so that the maximum gross weight at take-off might well be in- creased to over 300,000 lb, somewhat over half of which could be devoted to bombs, fuel and miscellaneous payload. It may be seen, therefore, that there is a practical range of size within which the aD-wing aircraft can be used. If the requirements of space and volume do not permit the full use of the all-wing principle, a rudiment- ary nacelle may be added without losing its economic advantages." Comparisons In comparing all-wing and conven- tional aircraft, Mr. Northrop made the assumption that spans of compara- Cnuising power same speed. Cruising range at same or higher speed. Power for high speed at same speed. High speed at power. 60 81.5 6% 20% 40% 60% 80% t ConventionaJ aircraft corresponds to JOO per cent. Fig. 2. Graph of performance characteristics of al!-wing aircraft tive aircraft having the same gross weight were equal, and that the com- parison was confined to large bombers and transports with maximum veloci- ties up to approximately 500 m.p.h. so as to neglect compressibility effects. '' Based on these assumptions and on the following proved data on the all-wing type, a comparatively simple analysis of advantages may be made. '' The ratio of the minimum para- site drag coefficient (Omi,,) for all- wing aircraft to that for conventional: types is approximately 1:2. Mini- mum drag coefficients for a number of large bomber and transport aircraft average approximately 0.023. The minimum drag co- efficients for several all-wing types have been measured both in model and full- scale configurations and vary from less than 0.010 to about 0.0113, which is the figure for the XB-35, including armament protuberances, drive "-•'• shaft housings, rudi- mentary nacelle for gun emplacements, and so on. 140% 160% "The ratio of ,$•• 113 141 107 118 120% maximum trimmed lift coefficient (Cj^^) for all-wing to con Fig. 1 The Northrop "Buzz" bomb and the XB-35 shown to scale.
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