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Aviation History
1917
1917 - 0674.PDF
I/LIGHT) JULY 5, 1917. INDENTS J [As a number of letters reach us signed with initials only, some of Which do not give a complete addtggs, we would point out that such communications cannot be dealt with in our columns. Full name and address, which will not be published, must always be given.—ED.] Notice to Correspondents in General. Applications for commissions in the Royal Naval Air Service should be addressed to the Director of Air Services, Admiralty, S.W. The necessary form and conditions of entry can be obtained from the Secretary of the Admiralty. Applications for commissions in the Royal Flying Corps should be sent to the Director-General of Military Aeronautics, Hotel Cecil, Stran* W.C. Those who wish to enlist in the R.N.A.S. should apply to the nearest naval recruiting station or to the R.N.A.S. Drafting Office, Crystal Palace, S.E. Skilled mechanics are taken whatever their army classification, but unskilled men are only taken if they are classified Bi, B2, or Ci. Recruiting for the R.F.C. is closed for the time being, and any enquiries should be made to the Officer Commanding, Royal Flying Corps Depot, Farnborough. Enquiries with regard to appointments in the A.I.D. should be addressed to the Chief Inspector, Aeronautical Inspection Department, Hotel Cecil, W.C. 2. C. H. J. (Sutton Coldfield).—We should say that the machine represented in your sketch is an R.E.. although the sketch is not clear enough to enable us to determine the series number. Yes, the other machine is a Nieuport scout. During the war it is not permitted to publish scale drawings and descriptions of modern machines, and we cannot, there- fore, at present supply you with the scale drawings you require. R. C. P. (Leyton).—The centre of head resistance of an aeroplane is determined by taking the resistance of the various items, such as wingSi body, struts, chassis, &c. and considering the moment of each item, the centre of thrust being generally taken as the centre of moments. In an idealjnachine the thrust, the resistance, and the lift should all pass through the centre of gravity. In a good many machines the centre of thrust is slightly below1 the centre of resistance, the couple thus set up being counteracted by another couple formed by having the centre of gravity slightly ahead of the centre of lift. With this disposition the machine will, when the engine is switched off, have a tendency to dive, thus getting on to its proper gliding path. If the centre of resistance were below the centre of thrust, the machine would have a tendency to drop its tail on switching off, which is, of course, undesirable. As a general rule the thrust-resistance and weight-lift couples are to be kept as small as possible, since otherwise the machine may have a tendency to pitch. I H. J. W. (Goodmayes).—You do not state whether you refer to variable camber or variable incidence. We take it, however, that ygag^ave in mind the former. There are several difficulties to overcome in producing a variable camber, valuable-^is that feature would be on a modern aeroplane where a wide speed range is a necessity. In the first place, the operating gear required to turn a wing section having the characteristics desirable for high speed into one giving very great lift for slow landing, would necessarily be com- plicated and fairly heavy, so that the extra lift obtainable •with the deep camber would be almost, if not quite, used up in lifting the weight of the operating gear. Several methods have been tried, some with internal lever arrangements which were intended to arch the section between the spars, while in others the rear spar was dropped, thus increasing both the camber and the angle of incidence. We have no information regarding the practicability of either of these types. Another and simpler way of altering the camber is to hinge the entire trailing portion of the wing after the fashion of an aileron, but although this is a much simpler proposition mechanically, a section having at some point a sudden break in its curves cannot be so efficient as one in which the change of curvature is gradual. A difficulty inherent to any type of variable camber is that ci so attaching the fabric covering that it will adhere closely to the curvature of the ribs at any point. Sound Waves. We have received from Mr. S. T. G. Andrews, B.Sc, the following communication :— " I see that a correspondent, G. B. P., in this week's paper, gives what he calls an explanation of the sounds heard as an aeroplane approaches and recedes from an observer, and contradicts a statement previously made—but which I do not recollect—that the sound rises as the aeroplane approaches. " Surely this is merely a simple application of Doppler's principle. As the aeroplane approaches, it follows up the waves which it has first sent out in the direction of the observer, and consequently a greater number of waves are crowded together in a given length of air, and as a result a greater number are received per second than the number sent out, and the pitch rises. When the aeroplane is receding it draws away from the waves, and consequently a smaller number are received than the number sent out and the pitch falls. " An easy way of verifying this is to put a whistle in the end of a rubber tube some 6 ft. long. Then if the tube is whirled in a horizontal circle around the head while blowing into the open end an observer standing a short distance away will hear most distinct rises and falls in the pitch as the source, that is the whistle, approaches and recedes. "It is also capable of fairly easy mathematical proof, taking into consideration the velocity of the wind in addi- tion." W. D. (Maidstone).—The method of attaching the con- necting rods of a rotary engine to the crank shaft differs somewhat. In the accompanying sketch is shown a fairly typical arrangement, i.e., that of the 100 h.p. monosoupape wi) Gnome. There is a so-called master connecting'rod, which has a big end of the shape Shown, to which all the other con- necting rods are attached by means of the wrist pins shown. The wrist pins have a small peg near one end, which prevents the pin from turning. The details will, we think, be clear from the sketch. G. M. (Kenley).—There have been cases of transfer such as you refer to, but they are very rare. If you are eligible you would be more likely to obtain a commission in the R.F.C. Y. Z. (Hampstead).—You will find all the information you desire in the Aviation Pocket Book, which can be bad from " FLIGHT " offices for 5s. post free. Wireless (Hendon).—A simple explanation of the various instruments used in wireless telegraphy is given in " The Elementary Principles of Wireless Telegraphy." It is pub- lished in two little volumes which can be ordered from . " FLIGHT " offices for 4s. post free. •»• ^
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