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Aviation History
1912
1912 - 0217.PDF
THE INSTITUTION OF AUTOMOBILE ENGINEERS. Abstract of Paper to be discussed on Wednesday, JMarch 13th, 1912, at the Institution of Mechanical Engineers, AEROPLANE at 8 o'clock p.m. UNDERCARRIAGES. IN the first place, it will be as well to consider the principles of alighting. One of the most important rules in connection with this is to bring the machine head to wind before actually touching the ground, as the speed relative to the earth is thereby decreased, and the machine quickly comes to rest. Landing in a side-wind puts heavy lateral strains on the undercarriage, and in a following-wind the speed may be dangerously high. In the case of a machine fitted with brakes and some efficient form of front skid, the danger of alighting with the wind is considerably reduced ; and although the rule _ of landing against the wind should be observed whenever possible, there may be times when this cannot be managed, as in the case of a forced descent when flying low. By G. DE HAVILLAND. nearly vertical as possible. The critical alighting angle is shown on the lift and drift chart of the plane (Fig. l) which, in this case, refers to a two-seated Bleriot monoplane. This and some of the other charts have been prepared for me by Mr. Watts, of the Army Aircraft Factory. It will lie noticed that when an angle of about 15° has been reached, the lift begins rapidly to fall off, while the drift increases, and it is therefore useless to tilt the machine to any greater angle. On reference to the Resistance and Power Chart, it will be noticed that this angle gives a speed of approximately 38 miles per hour, which, in this case, is the lowest possible speed in still air. In modern machines, high speed is obtained more by the reduc tion of head resistance than by using high powers and reducing the - y, > U z VELOCITY. ANGLE OF PLANES TO FLIGHT PATH = a. ANGLE OF AXIS OF MACHINE TO FLIGHT PATH=0. ANGLE OF AXIS OF MACHINE TO HORIZONTAL=7. A. B. C. D. E. F. G. H 0 = 14° 0 = 13° a- 12° a-11" a = tO° 0 = 9° a = 8° MACHINE GLIDING : /3 = ioJ B- 90 B = 8" B = f B- 6° 0 = 5 8 = 4" 1 IN 5-3. 7=10° 7= 8 7= 6" 7= 40 7= 2' 7=-1 7=-4" <* = 7 /B = 3" y— -8' < 11 t c u 0 ft-03 0-M 0-01 DRIFT CO-EFFICIENT. DIAGRAM SHOWING LANDING OF TYPICAL MONOPLANE. A MACHINE LANDS. FLIGHT PATH HORIZONTAL. WHEELS AND SKID TOUCH SIMULTANEOUSLY. Kx = - Dka in. >sq.m xV'„ Fig. 1 When flying across country, a height ot at least 1,000 ft. should be maintained, in order to give sufficient time to choose a suitable landing-ground in case of engine-failure. When descending with the power cut off, it is always advisable to plane down at an angle rather steeper than the best gliding-angle of the machine, as the controls are then more sensitive, owing to the higher speed, while in gusty winds there may be a certain loss of stability if the speed is not kept reasonably high. When a few feet from the ground, the machine is gradually levelled up until the angle of incidence of the planes has almost reached the maximum for lift, and if this manoeuvre is properly timed, the machine will be slow ing up and gradually dropping until the wheels make contact with the ground, without perceptible shock. In the case of a forced landing in a place where the ground is very soft, or where the wheels are liable to meet with serious forward resistance, it is ad visible to level up and take "way "off the machine, and thus diminish the horizontal velocity, so that the actual landing will be as area ot supporting surfaces, which means that the machine possesses a greater speed range. It is doubtful, in the author's opinion, whether special devices will be provided for enabling the surface to be varied in extent, as this would entail extra weight and complication. ^_. If the power plant of an aeroplane were infallible us regards reliability, there would be little necessity for providing a more suitable undercarriage than that in use at the present time, as the pilot would always choose convenient and safe ground for alighting. Even now, engine breakdowns are more the exception than the rule compared with the state of affairs a comparatively short time ago, but as there will always be the possibility of forced landings, the machine must be provided with the best possible form of undercarriage. It will now be as well to consider the conditions that should be fulfilled by the ideal undercarriage :— (<z) Its first duty is to allow the machine to attain its flying speed 217
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