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Aviation History
1927
1927 - 0207.PDF
31, 1927 Supplement to FLIGHT ENGINEERINGSECTION Edited by C. M. POULSEN March 31, 1927, CONTENTS Aircraft Performance. By J. D. North, F.R.Ae.Soc. Wiring Lug Design. Bj-C.Chapleo Technical Literature 25 EDITORIAL VIEWS When the publishers of FLIGHT decided to issue with the last number in each month a special section devoted to the more technical aspects of flying, it was hoped and intended that this section should be mainly devoted to an interchange of ideas among our designers and constructors, an inter- change which, looked upon from a broad viewpoint, could only be for the common good of the industry and consequently for the improvement of British aircraft in general. It is with regret that we have (tome to the conclusion that British .incraft designers do not individually realise that for THE AIRCRAFT ENGINEER to fulfil its intended functions, a certain amount of co-operative effort is required on their part. We do not, of course, for one moment believe that they have failed to assimilate the view put forward by Mr. North some time asjo, that if there are 10 designers and each 'Ontributes his share of knowledge to the common stock, lie stands, on an average, to receive nine times as much as he rives. •A few aircraft designers have supported us admirably, none more so than Mr. North, who has been an almost uninter- ruptedly regular contributor since publication of the second issue of THE AIRCRAFT ENGINEER, and to them our thanks are due. But out of the 20 or so chief aircraft designers of the British industry, but a very small percentage has come forward in the manner which we had hoped for and—not unreasonably, we think—expected. Private appeals by the Editor have, met with promises, but unfortunately the paper cannot go to press on promises. Let us see what publication °J a " Black List" will do. The firms from whose chief designers we have as yet had nothing include : The Blackburn Aeropime & Motor Co.; The Fairey Aviation Co.; The Gloster Aircraft Co.; H. G. Hawker Engineering Co.; George Pamall * (1°-, A. V. Roe & Co.; S. E. Saunders, Ltd.; and ShortBr °s;, Ltd. "6 r.now that THE AIRCRAFT ENGINEER is greatly appre- ciated -n the drawing offices of the industry and by many of °ur tefanically-minded readers outside the industry, but if aU the designers do not " do their bit," the paper will fail to •jcbievi- its maximum of usefulness. Moreover, it is not quite air to ' -ave it to a few energetic ones of our designers to do all of keeping " The Industry's Paper " going.the AIRCRAFT PERFORMANCE. The Airscrew. By J. D. NORTH, F.R.Ae.S. (Continued from p. 6.) The most elementary conception of an air propeller is an instrument for imparting a sudden rise of pressure to the column of air passing through it as the aircraft advances. In the figure the fluid motion is streamline except for the pressure suddenly added at the "' actuator disc." The reaction at the actuator disc (the integral of this pressure) is equal to the momentum imparted to the wake, while the lost energy in the race is, of course, equal to the kinetic energy of the race. Since the momentum is proportional to the added velocity, and the kinetic energy to the square of the added velocity, it is obvious that losses from this source will be reduced by the lowest possible added velocity, i.e., by OUTFLOW STREAM /AIRSCREW ^~—• __—— INFLOW STREAM " — DIRECTION OF AIRCRAFT Fig. 15 (reprinted from June 24,1926, issue). making the actuator disc as large as possible. The funda- mental inefficiency of any direct form of " combustion-jet " propulsion is obvious. The air screw, a mechanical device for producing the pressure at the artificial " actuator disc " from the rotating shaft of the engine, demands a certain mean /V\" helix angle," and hence a certain pitch-diameter ratio I — I for efficient working. With aeroplanes and engines as we know them, these two requirements are incompatible. A compromise diameter has to be chosen to give a minimum sum of " jet " and " screw " losses. For a given forward velocity, however, it will be obvious that the added velocity in the race will be a constant if the diameter of the propeller increases as the square root of the horse-power, and that it / Vwill operate at the same value of ( -^- = J ) if the angular \nD 188a
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