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Aviation History
1917
1917 - 0728.PDF
IGHT JULY 19, ANSWERS CORRESPONDENTS [As a number of letters reach us signed with initials only, some of which do not give a complete address, 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 Full name and address, which will not be published, must always be given.—ED.]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, Strand, 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. G. W. B. (Gosport).—It is not possible, from your sketch to decide what type of machine is represented. The tail planes and tail outrigger do not somehow look correct. The tail booms Would scarcely converge, as shown in the sketch, both in plan and side elevation. L. H. R. (Cricklewood).—It is impossible to state in general terms the increase of speed obtainable with a variable angle of incidence. The advantages of the variable angle are that for any given speed of which the machine is capable the correct angle can always be found, at which the body is in a horizontal position, thus offering a minimum of resistance. That the fixed angle of incidence does not and cannot give maximum efficiency throughout the entire range of speeds will be readily understood when it is realised that, in a machine having its angle of incidence fixed, there is only one speed at w'hich the maximum efficiency is obtained, namely, the speed in horizontal flight at which the machine flies with its body horizontal. Any change in the speed caused by a variation in power through the intermediary of an alteration of the angle of incidence (the flight path is assumed to be horizontal) necessitates a change in the attitude of the whole machine, which again means that the flight path is no longer parallel with the centre line of the body. The result is that the air, instead of flowing along the top and bottom of the body and causing skin friction only, strikes it at an angle, on top at higher speeds and on the bottom at lower speeds. For example, suppose a machine, flying with its fuselage horizontal, will maintain a horizontal flight path with its engine on three-quarter throttle. Now, if the throttle is opened fully the angle of incidence will have to be diminished in order to keep the flight path horizontal, or, in other Words, to prevent the machine from climbing. As the angle of incidence is fixed it can only be diminished by changing the attitude of the whole machine, that is to say, by letting it fly "tail high." Again, for flying at low speeds, the engine is throttled doWn, and the angle of incidence increased by letting the machine fly cabri, i.e., with the tail down, a position which always carries With it the possible danger of a tail slide in case of engine failure. In both cases the air, instead of caus- ing skin friction only, exerts a pressure on the detrimental surface presented by the top or bottom of the body in the " tail high " or " tail low " position respectively. One the most successful machines with variable incidence Was the French Paul Schmitt biplane, which established several world's records in the summer of 1914, before the outbreak of war. A similar machine, fitted as a seaplane, is now, we believe, being built and successfully flown in America. A. U. (Cadet, R.F.C.).—During the War we are not per- mitted to publish illustrations of British machines, anc£ cannot, therefore, assist you in the matter of identification of the various types. We were under the impression, how- over, that the R.F.C. had already issued charts showing the various Allied aeroplanes and that these charts Were available- for members of the Flying Services. Probably, on making: inquiries, you may be able to obtain them from your Com- manding Officer. A. R. M. (Tooting).—The World's duration record for aa aeroplane with pilot only on board Was established by the German aviator, Reinhold Boehm, on July nth, 1914^ Starting from Johannisthal aerodrome at 5.52 p.m. on a Friday, he did not land until 6.4 p.m. the next day. The machine he used was an Albatros biplane with 75 h.p. Mercedes engine. At the start of the 24 hours 12 mins. flight the machine carried 600 litres of petrol and 50 litres of oil. M. P. L. (Clapham Commoner—The reason for the differ- ence in the angle of incidence of the right and left hand wing: tips of the Albatros Dl, described in " FLIGHT " recently, is- that, When the engine is running, the torque tends to rotate the machine around its longitudinal axis in the opposite direction to that of the rotation of the engine. As the engine is a right-hand one, it follows that there is a tendency for the machine to tilt over to the left. As the angle of incidence of the left wing tip is 40 and that of the right wing tip 2°, the left wing lifts more than the right, thus providing a. restoring couple. This alteration in the angle of incidence is employed by many designers, although there are some who prefer to have the angle of the two wings the same, but to connect the ailerons up in such a manner that When* the control lever is held centrally the ailerons provide the restoring couple. Your second question regarding the send- ing up of aeroplanes before raiders arrive cannot be dealt with in the short space available in this column. Sound Waves. We have received from McE. (CrickleWood) the following r " Concerning the discussion in " FLIGHT " recently about sound waves, Mr. S. T. G. Andrews, B.Sc, seems to think that the sound rises as the machine approaches. " Several of my friends whom I have asked are sure that the sound falls as the aeroplane approaches. As we are near the Beatty School of Flying we have Caudrons and Wrights passing over us every day, and I have spent considerable time making sure of the fact C. A. H. (Barnet) noticed." X. Y. Z.—An allowance of ^8 for uniform is made when you join the R.F.C. Cadet Corps. On obtaining your commission this amount is increased by £42, bringing the total allowance.U P to £5°- E. J. Mel. (Gillingham).—The function of the dihedral angle was explained in our " Answers to Correspondents " column on page 130 of our issue of February 8th, 1917. When a flat plane moves through the air parallel to its chord, i.e., with no angle of incidence, it gives no lift. As the angle of incidence is increased the lift increases, approxi- mately in the same proportion, up to a certain angle. When this angle is exceeded the lift begins to decrease again. So with a cambered plane, except that for the latter the angle of no lift is generally negative, a cambered section giving a certain amount of lift even at no angle of incidence. The chief advantage of staggering the planes of a biplane is that by so doing the view in a forward and downward direction is improved. Also there is a slight gain in efficiency attending the employment of staggered planes. W. D. K»-(Sanderstead).—The identification marks of the various belligerent countries were described and illustrated in our issue of September 14th, 1916. P. W. S. (Maida Vale).—For an elementary book on aero engines, we can recommend " Aeronautical Engines," by F. J. Kean. A copy may be obtained from the offices of " FLIGHT/' the price being 6s. 6d., post free. , .. 728
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