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Aviation History
1917
1917 - 0160.PDF
FEBRUARY 15, 191 j. ers J? f 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 pub- lished, must always be given.—ED.] T. N. McE. (Cricklewood). We regret that we are unable to give you any information concerning the meaning of the letters Bu on the Albatros scout. We do not know of any book of scale drawings of aeroplanes, but if you will look through back volumes of " FLIGHT " you will find scale drawings of nearly all the more important machines built up to the outbreak of war. " Mac " (South Shields). The speed of modern seaplanes varies from 70 m.p.h. to about 105 m.p.h., and that of modern aeroplanes from 90 m.p.h. to 150 m.p.h. We have no plans of the scale model tractor you refer to, and to produce " a diagraphm of a seaplane and an aeroplane, showing exactly every part with the exception of the motor," would entail more work than we can afford at the present moment. By looking up back numbers of " FLIGHT " you will find a number of scale drawings of land machines as well as seaplanes. H. C. A. (Horsham). The employment of a small propeller working windmill fashion for driving an electric generator does not, as you quite correctly suppose, make a very efficient drive. As against a direct drive from the engine, there is first, in the case of the windmill drive, a loss amounting usually to some 25 per cent, in the efficiency of the aeroplane propeller. Then there will probably be an equally great loss in the small propeller acting as a windmill, so that all told such a drive is very inefficient. The power required to drive a generator is usually, however, so small in proportion to the horse- power of the engine, that the loss in efficiency is not such a serious matter as might be expected. The windmill drive has the advantage that it is easy to fit without interfering with the engine in any way. For a very large generator the direct drive would probably be preferable. L. M. (Plaistow). The power available for driving other machinery is that delivered by the engine to the belt on its driving pulley, or, if direct drive is employed, that delivered at the engine shaft. Since this power is usually measured by some sort of brake, it is generally known as the brake horse-power, abbreviated to B.H.P. In any machine the ratio useful work total work of effort is called the efficiency of the machine. In the case of an air-screw the efficiency is h.p. delivered by air screw b.h.p. of engine For (example, if the brake horse-power of an aero engine is 3 00 and the useful work done by the air-screw is equivalent to 80 h.p., the efficiency of the air-screw is obviously — = 80 per cent.100 r The Zeppelin airships are equipped with a wireless installa- tion, and, provided his instrument is " tuned " to the same pitch, an English wireless operator can pick up the message, but for communications of any importance a secret code is always employed. There are no examinations of the kind you refer to. If you are over 18 years of age you can apply for a commission in the R.F.C. or R.N.A.S. J. J. M. (Byfleet). The fact that the water in an aero-radiator boils when running the engine for a considerable period whilst the machine is on the ground does not necessarily prove that the body of the aeroplane is not in the slip-stream. When the trans- lational speed of an air screw is zero, in other words when the machine on which it is mounted is standing on the ground, the air screw is no longer acting as a propeller, but as a fan, and may be very inefficient in this capacity. It is quite possible that where the inner portion of the blades of a tractor- screw are acting merely as supporting arms for the blades and not designed to give any thrust, the effect of the slip- stream on the body may be considerably reduced, and that therefore any loss in thrust, due to a smaller portion of the blades doing useful work, may be compensated for by the- attendant diminution in the velocity in the portion of the slip-stream surrounding the body. The problem is an in- teresting one, and might with advantage be discussed further. For this, however, we cannot find space in the A. to C. column. The thrust of a propeller cannot be calculated from the data you give, as the most important factor—the power of the engine—is not stated. If the efficiency of a propeller is assumed, the thrust obtainable can be calculated from the formula : 550XH Ep 1 = V ' where T = thrust in lbs., H = the brake horse-power of theengine, Tip — the efficiency of the propeller, expressed as a decimal, and V = the speed of the machine in ft. per secondsA fair average efficiency for a modern propeller is 75. Cadet R. S. A. (R.F.C.). According to experiments carried out by Mons. G. Eiffel and at the National Physical Laboratory, there is no aero- dynamical advantage in a rearward stagger, i.e., with the upper plane of a biplane set back in relation to the lower. In fact, there appears to be a slight disadvantage attending this arrangement. The reason for adopting it in the machine you mention is that by so doing the pilot obtains a better view in certain directions than would otherwise be possible. W. J. L. (Weston). Apply to the R.F.C. Recruiting Office, The Polytechnic, Regent Street, London, W. Anxious (Huddersfield). Cannot say if there are any vacancies for draughtsmen at the Admiralty ; you should apply to the Director of Air Services, Admiralty, S.W., Stating full particulars. To enlist as a mechanic in the R.N.A.S. apply to the recruiting office. Brook Green, Hammersmith, W. D. S. (Worcester). You can transfer to the R.N.A.S. if you are accepted to be trained as a pilot. The restriction you mention applies- to unskilled mechanics. S. P. (Upper Holloway). For particulars regarding the R.F.C. Cadet Corps you should apply to Adastral House. E. M. G. (Eton). You must wait until you are 18. In the meantime study the subject as much as possible. The R.F.C. Cadet Corps is for those who are being trained as officers for the R.F.C. S. J. (Chesterfield). Apply to Adastral House, E.C., for particulars. If yon are given an interview you may be required to produce your birth certificate and registration card. A. D. P. (Dunston)J Eighteen is the minimumjfor both the R.F.C. Cadets and the R.N.A.S. A. H. (Charlton). There appears to be no reason why you should not applyfor a commission. We understand there will be no vacancies till June. There is no reason to join the wireless section^ifyou can get a commission as flying officer. V. A. (Market Bosworth).! Certainly apply to Adastral House, although there is no- object in worrying about it until you are old enough, as the conditions may be altered by that time. W. W. (Southsea). You would receive pay at the rate of 10s. per day plus 4s.. per day flying pay while you are a probationary Flight Officer under training. When you graduate you will receive a further 4s. per day flying pay. 160
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