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Aviation History
1927
1927 - 0113.PDF
February 24, 1927 Supplement to FLIGHT ENGINEERINGSECTION Edited by C. M. POULSEN February 24, 1927 CONTENTS Comparison of Aircraft Performances. By H. A. Mettam, M.A., A.F.R.Ac.S Fineness. By F. M. T. Reiily, A.M.I.A.E., A.M.I.Ae.E., A.M.I,P. .„ Technical Literature 13 15 17 OUR CONTRIBUTORS Mr. H. R. Mettam, who is Chief of the Stress Department of the Westland Aircraft Works, Yeovil, contributes to the present issue an article on " Comparison of Aircraft Per- formances." The article is really in reference to our trans- lation of Prof. Everling's article on " Comparative Quantities in Aircraft Statistics," which was published in our November 25, 1926, issue. The article has for its object the derivation of the " Ever ling quantities " in British symbols and units and the correlation of them with methods of performance comparison already in use in this country. There can be no doubt that the use of unfamiliar symbols and units is a prolific cause of irritation, and may often result in the total disregard of an article or paper on that very score, and for that reason we are extremely glad to have Mr. Mcttam's article, which should do much towards helping those of our readers who may have been " put off " by the strange symbols and units used in the original article to a better understanding of Prof. Dr. Everling's arguments. At the same time, as we pointed out in our introduction to the article in the November 25 issue, the " Everling Quantities " are intended for comparison between various machines, not only our own machines between each other, but between British and foreign aircraft. That being so, it is surely better to '" standardise " the units in such a way that the same units can be employed in all countries. As Prof. Everling first suggested the quantities, and as the continental system is fairly widely adopted, we considered it logical to retain the original units and symbols in the translation of his article. Mr. F. M. T. Reiily deals with the subject of " Fineness," and draws attention to the importance of careful design. He throws a good deal of blame upon bodies, and illustrates some which do certainly not appear to be; perfectly streamlined. At the same time it is, we think, only fair to bear in mind the fact to which Mr. North has referred, i.e., that the question of body shape is largely out of the hands of the aircraft designer, who has to provide a machine in or on which certain loads of a certain nature have to be carried. Mr. J. D. North has sent us a further instalment, but as the material, and more particularly the illustrations, arrived too iate, it has not been possible to include the article. It will be published next month. COMPARISON OF AIRCRAFT PERFORMANCES. By H. A. METTAM, M.A., A.F.R.Ae.S. In view of the Editor's decision to make use of the " Everling quantities " when describing British and foreign aircraft in FLIGHT, it is of interest to derive these quantities in British symbols and units, and to correlate them with methods of performance comparison already in use in this country. For a full description of the Everling quantities reference should be made to the article by Prof. E. Everling on " Comparative Quantities in Aircraft Statistics," as translated in THE AIRCRAFT ENGINEER for November 25, 1926. The names suggested therein, " high-speed," " dis- tance " and " altitude " figures will be used, together with the expression " wing-power" which will be measured in the British units of horse-power per square foot of wing surface. The three quantities which measure the aerodynamic merit of the aircraft for the requirements of high speed, distance or altitude are defined by Prof. Everling, in non- dimensional forms. The only change to be made when using British symbols is due to the fact that the German coefficients for lift and drag—Ca and Cw—are double the English coefficients ki and Ay. It is, therefore, very simple to define the three required quantities in British symbols so that they will be directly comparable with the quantities given by Prof. Everling in German symbols. If T) is the propeller efficiency and ki and k^ the lift and drag coefficients, these definitions become— " High-speed " figure = — 2k j) " Distance " figure = rj — Altitude " figure = /2k Each of these figures can be derived from the standard equations for level flight as in Prof. Everling's article, and the resulting formulae are given below— 2kD ~ 147000 X H>. X f(h) D ~ 375 X L _ W W.f(h) 1 WA X18-95 If 100a
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