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16 AIRCRAFT ENGINEERIN G January, 1940 Preliminar y Investigations into the Effects of Air-Intak e Shape on Power at Altitude By S. Riess IT H the increasing speed of modern (6) Dynamic pressure at the place of the In this article the results of some experi- aircraft it becomes pertinent to give air intake ζ. W menta l work that had been started in some more thought to the correct (7) Air temperature at the carburettor air Poland just before the outbreak of wa r are shaping of carburettor air-intakes. intake θ. given. Unfortunately the work has had to All the above values should preferably be The intake manifold or boost pressure of a be abandoned, though the author hopes taken by recording instruments. The air-speed supercharged engine at a given altitude H, recorder should be carefully calibrated before fitted with a hundred per cent efficient air tha t it may be taken up and continued in test. For the determination of the dynamic intake, may be derived from the formula this country in order that the investigation pressure at the carburettor intake an air-speed p = Σ (η + ζ) (i) ma y be carried to completion H H recorder wind-tunnel-calibrated in millimetres where p is the boost pressure, of water head should be used. Σ the compression ratio of the super It may incidentally be noted here that the charger at the altitude H, This may be caused by some of the following above procedure might be used for checking the Η the total (dynamic and static) factors : blower compression ratio and the validity of pressure in the carburettor air (1) Air intake efficiency. empirical formulæ evolved for correction of intake in still air a t the altitude H, (2) Blower efficiency. tha t ratio with change of air-intake tempera and ζ the dynamic pressure at the place of (3) Airscrew efficiency. ture. The supercharger compression ratio can the carburettor intake created by (4) Error in estimating the true value of be found from formula (2). th e aircraft velocity. C . Supposing the speed of the aircraft is equal to It should be noted here tha t ζ is not equal to zero, the boost pressure will be : Measurements of the aircraft's speed near the th e pressure corresponding to the aeroplane's ground by classical methods may be generally P" = Σ η (3) H H H speed as its value is determined by th e air flow accepted as a reasonably good test of the I n this instance η is equal to the static near and around the air intake. correctness of the adopted values of C and pressure corresponding to the altitude H. The actual intake manifold pressure of the airscrew efficiency. The results of most of The increase of manifold pressure due to the engine will be different, as th e actual carburettor the m check up fairly well with calculated values. dynamic pressure will be equal to : intake pressure ζ' will generally fall below the I t is the top speed at critical altitude that P' -P" = Σ ζ' value of ζ. H H usually causes surprise to the designer, the From this we find P' = Σ (η + ζ') (2) results often falling below expectations. It is, H H I t is clear from the above formula; that the therefore, very important, in this regard, that critical altitude of a supercharged engine some method be evolved for checking carburet depends on the value of the factor ζ and may be tor air-intake efficiency instead of allowing it to As a measure of the carburettor intake increased by fitting a suitably shaped efficient be estimated by more or less personal opinions. efficiency the ratio ζ' to ζ may be taken. It air intake. follows then that this efficiency is as follows: This is important as it has an appreciable Tes t Procedure effect on the performances of aircraft, increasing The following data should be recorded in the critical altitude and power of the engine and fuel throttle level flights at altitudes near the Results of Tests maximum speed and rate of climb of th e aircraft critical one: a t and above the critical altitude. Two such flight tests have been made and (1) Flight altitude H. valuable data obtained. Unfortunately the Some experimental flights tend to prove, (2) Aircraft speed v. author is not in a position at present to publish however, that the actual increase in perform (3) Absolute intake manifold pressure p. all these data. Nevertheless it may be stated ances of the aircraft due to th e dynamic pressure (4) Engine r.p.m. n. tha t in both flights carburettor intake efficiencies factor falls in some instances much below (5) Total pressure at the carburettor air of not more than 50 per cent have been obtained. expectations. intake η . Th e Daniel Guggenheim Medal, 1939 The Daniel Guggenheim Medal for 1939 has A t the meeting which confirmed the award directors designated by the American Society of been awarded to Donald Wills Douglas, Presi for this year Dr. J. C. Hunsaker, of the Mechanical Engineers, the Society of Auto dent of the Douglas Aircraft Company of Massachusetts Institute of Technology, was motive Engineers and the Institute of the Aeronautical Sciences. The recipient of the Santa Monica, California. The medal, which elected Chairman of the Board of Award to award is chosen by the directors and foreign is t o be presented a t the Honours Night banquet succeed Dr. George W. Lewis. Major Lester D. of the Institute of the Aeronautical Sciences on representatives from England, France, Germany, Gardner was elected Vice-Chairman and Januar y 26, 1940, is given to Mr. Douglas " for Holland, Italy and Japan. Mr. Elmer A. Sperry, Jr., Secretary. outstanding contributions to the design and The recipients of the Award have been: The Daniel Guggenheim Medal Fund was construction of transport airplanes." 1929, Orville Wright; 1930, Dr. Ludwig established in 1928 to provide a gold medal and Mr. Douglas is an Honorary Fellow and past Prandt l of Germany; 1931, Dr. F. W. Lan- certificate to be presented annually in recogni president of the Institute of the Aeronautical chester of England ; 1932, Jua n de la Cierva of tion of notable achievements in the advance of Sciences. He received the Collier Trophy for aeronautics, in commemoration of the support Spain ; 1933, Dr. Jerome Clarke Hunsaker; 1935 in recognition of his development of twin- given by Daniel Guggenheim to the advance 1934, William E. Boeing; 1935, Dr. William engined commercial transport aeroplanes. The ment of aeronautics through donations to Frederick Durand; 1936, Dr. George William same year he delivered the Wilbur Wright Lewis ; 1937, Dr. Hugo Eckener of Germany; Memorial Lecture in London before the Royal universities and for the encouragement of civil Aeronautical Society. 1938, A. H. R. Fedden of England. aviation. The fund is administered by nine
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Jan 1, 1940
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