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Aviation History
1916
1916 - 1105.PDF
DECEMBER 14, 1916. [/yens •-if" If in doubt about anything aviatic, write to " FLIGHT " about it. J. W. T. (Eastbourne). The earliest Zeppelin airships were designed so as to enable them to alight on the surface of the Lake Constance, over which the first trials were conducted. The gondolas were boat-shaped, and so designed that when the airship was barely buoyant, they supported part of the weight, and thus enabled the airship to rest' lightly on the surface. It was found, we believe, that considerable difficulties with regard to trim cropped up, and in the latest type Zeppelins, even those employed for sea scouting, there is no attempt at any landing gear whatever. The gondolas have handling rails running along their sides close to the bottom, and when it is desired to effect a landing, this is accomplished by the landing crew, who first catch hold of the tow ropes, and later, when the airship is sufficiently low, of the handling rails, and guide the airship on to the trolleys and rails by means of which she is towed into her shed. J. J, M. (Byfleet). It is not possible to calculate exactly the drift coefficient of an actual machine from knowing its behaviour in the same manner that the lift coefficient can be estimated. With regard to lift, this coefficient can be estimated, since only the lift of the wings is considered. When it comes to the drift, however, not only the wings, but all the other parts of the machine such as body, undercarriage, struts, tail planes, &c, offer resistance, and one does not, therefore, know how great a portion of the resistance is due to the wings, and how much is detrimental head resistance. What can be done, however, is to estimate approximately how many square feet normal to the wind the total resistance of a given machine is equivalent to. For instance, suppose a machine is known to be fitted with an engine developing 100 brake h.p., and to fly at 100 m.p.h. The thrust developed, which must obviously be equal to the resistance, can be found approxi mately from the formula T » ^2— '^, where T — thrust in lbs., H » brake h.p. of engine, Ep - efficiency of propeller, expressed as a decimal, and v = the velocity in ft./sec. An efficiency of • 75 wili be assumed, as this is a fair average. V = 100 m.p.h. = 146 ft./sec. We can then write : T - resistance - ,55° * ">g_x mJS _ 282-5 ibs. The resist- 140 ance of a flat plate normal to the wind is found from the equation R => AAV2, where R «- resistance in lbs., A •= area of plate in sq. ft., and V = velocity in m.p.h. k is a constant, the value of which varies somewhat with the size of the plate. We shall take as an average value of k 0-003. The equation can obviously be written, A - —.f - v— ^ ^ » 9'4 sq. ft. approx. With regard to your second question, it is general practice to include the body in the parts inside the slip-stream, although, as you mention, the inner portion of the propeller arms, for a foot or so out from the boss, does not give any great amount of slip. The majority of fuselages, however, are considerably more than 2 ft. in depth, and engine cowls, where rotary engines are concerned, are usually of about 3 ft. diameter, or over. At any rate, there can be no doubt, that the fuselage does offer very considerably greater resist ance at any speed than it would do had it been outside the slip-stream. H. E. T. (Bradford). There are very few figures available on which to base calculation of fin and rudder area. It is determined by the distance behind the centre of gravity of the machine, by the amount of side area of body, undercarriage, struts, wings (owing to dihedral, propeller, &c. It must be large enough to counteract the inherent yawing instability of the body and the yawing effect of the parts mentioned above that may lie in front of the centre of gravity. In his book. " \'i.. plain- Design," which we can thoroughly recommend, Mr I S Barnwell, now ('apt K.F.C., suggests the following empirical formula: C s x d) - S S x D - I A, where s — area of rudder in sq. ft., d - distance of centre of area of rudder from centre of gravity of machine, in ft., S — area «>1 side elevation of body, aerofoils, landing gear, and propeller, 111 sq. ft.. ]) m distance of centre of this area S Ichind the centre ol gravity, A - area of wings. 111 sq. ft., and C «• a constant. the value of which for tractors Mr. Harnwell gives as 1*7, Some designers place the tail plane of a " pusher " in line with the centre of thrust, while others prefei to have u some 6 iu. above the line ot thrust, the object of the latter disposition being, we believe, to partly counteract any elicit due to I he fact that the tail plane works in the down draught from the wings. So far as we are aware, the book von mention has not vet been published. The best books dealing with wing section and body resistance data are Nouvelles Rtcherches sur la Resistance de t'Air, lis Mons. G. Eiffel, published by Dunod and Pinat, Paris, which can be obtained through " FLIGHT " offices at /2 5£., and the Technical Rtpori ol the Advitory Committee for Aeronautics, 1913-13, which can also be obtained from our offices at 10s. 6d.a post free. H. B. (Fart-ham). I. Through the R.F.C. Cadet Corps. 2. Either. 3. You are hardly likely to get a commission unless you have had military experience. Apply to the Directorate of Miln.ov Aeronautics, Adastral House, E.G., for the necessary forms. 4. No. The R.F.C., if you are accepted, will train you. J. E. (St. Albans). The " wings " are only worn by a pilot who has passed all the tests. In your case therefore you would not be entitled to wear them. , Novice (Wood Green), 1. No ; when on duty you must salute every officer (naval and military) senior to yourself. 2. Yes. 3. Some of the schools are controlled and some are not. Contact (Richmond). For the R.F.C., you should obtain the necessarj form from the Directorate of Military Aeronautics, Adastral House, and for the R.N.AS. from the Admiralty. You would prob- ' ably have to wait another year, and in the meantime had better continue in your present position. A. R. J. W. (Leytonstone). There is no such book published. Vickcrs biplanes are mostly " pushers," but there are Vickcrs " tractors." M- M- (Norfolk). Space does not permit of giving the training in complete detail. You could obtain full particulars* from Adastral House. Of the examples you give, the first officer is in the R.F.C., Special Reserve, having entered as a civilian ; while the second is an Army officer, seconded from the Wiltshire I Regiment to serve with the R.F.C. That also answers your fourth question. F. W. L. (Ashford). It is impossible to 6ay definitely, as your sketch is not very clear. Apparently the machine is a large Sopwith. The attachment is a light skid to protect the ends of the planes when landing. W. A. (Halifax). 1. First obtain commanding officer's permission, then get form from the Admiralty, and when filled up send it to the Director of Air Services, Admiralty, S.W. 2. No. 3. Not so far as we are aware. 4. It depends entirely upon himself. C. E. S. (Gainsboro'). We can only suggest that you should write to Major Mitchell, The Polytechnic, Regent Street, London, W., giving full particulars and asking if there are any vacancies. 1097
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