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Aviation History
1919
1919 - 0904.PDF
ij ins. below the line of thrust. With the machine in flying position, the centre of gravity of the machine occurs at a point i ft. 4.6 ins. behind the axle. When at rest on the ground, a straight line from the wheels to the tail skid makes an angle of II° 15' with the centre line. The tail consists of a small divided horizontal stabilizer with elevator flaps hinged to the trailing edges, a triangular vertical fin (3 ft. by 3 ft. 6 ins.) and an unbalanced rudder (3 ft. 10 ins. by 2 ft. 7^ ins.). The engine is a Curtiss model K-12 12-cylinder V-type, with cylinders cast en bloc. Aluminium is used extensively in its construction. The bore and stroke is 4J ins. and 6 ins. respectively, and the rated horse power at 2,500 r.p.m. is 400. Ignition is by two high-tension double spark " six- cylinder " magnetos, located at the forward end of the engine, and driven through flexible couplings by beveled gears from a vertical shaft. Two Duplex carburettors are used, located between the groups of cylinders. They are supplied with an auxiliary altitude hand-controlled air valve, and also with non-back-firing screen. Without oil or water, the engine weighs 680 lbs. ; the dead weight per rated horse power being 1.7 lbs. The petrol con sumption is at the rate of -55 lbs. per brake horse power per hour, and the oil, .03 lbs. per brake horse power per hour. The tractor screw is 9 ft. in diameter, and when the machine is in flying position, the tips clear the ground by 8£ ins. The general specifications of the follows :— Span, top and bottom planes .. Overall length Overall height Chord, top plane Chord, bottom plane Gap Stagger Weight, fully loaded Useful load Performance Service ceiling Maximum ceiling Climb in 10 minutes Climb in 10 minutes (light load) Sea 5,000 Level. ft. High speed (m.p.h.) .. 160*5 158-5 Low speed (m.p.h.) .. 59 68 "2 Economical (m.p.h.) 80 85 Rate of climb (ft. per* minute) .. .. 2,390 1,690 Time of climb .. .. 0 2-5 JULY 10, 18-B biplane 37 ft. sfins 23 ft. 4 ins. 8 ft. 10J ins 4 ft. 6 ins. 4 ft. 5ft. 1 ft. 4i ins 3,001 lbs. 1,013 lbs. 22,000 ft. 23,000 ft. 12,500 ft. 16,000 ft. 10,000 15,000 ft. ft. i57'S 155 73-6 79-8 92 100 1,040 580 6-3 12-9 1919 are as . 20,000 ft. 152 86 118 210 27 Endurance (high speed) .. 283 miles 1 -75 hours Endurance (economical speed) 536 , 6-7 If H H H H THE STRESSES IN BRACED STRUCTURES WITH RIGID JOINTS IN regard to the article by Mr. John Case under above title, published in our issue of May 29, 1919, we have received the following queries :— SIR,—It is with great interest that I have read Mr. John Case's article in FLIGHT on " The Stresses in Braced Structures with Rigid Joints," and hope to use the vital information therein practically in the near future. For some time it has appeared to me that the general practice (in small machines) of rigidly, or semi-rigidly attaching interplane struts to the top or bottom of the main spars is not a good one, and this especially so in all metal design. Being a young engineer, and not the pure mathematician that might be desired, I now write in the hope of being en lightened on a few points, should you be sufficiently interested, and for which I can assure you I shall be more than obliged. (i) Am I right in understanding that if in para. 7 " General Equations," all the couples are taken as zero, the case reduces to that oi a structure in which every individual element has pin jointed ends ? (ii) Secondly, that if in Fig. 7, M'. 23, M. 12, M. 01, M'23, etc., are all zero, M'. 3, etc., will then equal M. 2, etc., re spectively, and the case will reduce to that having continuous spars with pin jointed struts ; i.e., the one you appear to recommend. (iii) The results of the simple case worked out in para. 3 are very convincing, but surely the couples acting on the strut BB' in Fig. 1, where the spars ABC and A'B'C are continuous throughout the joints, would not be so serious. An actual example of this case also would make your theory more conclusive. (iv) Finally, should not the two equations (25) be as follows :— MI2 = M'j - M, and M1,, = N, - N,1 and not as printed. • Yours faithfully, B. A. DUNCAN. Ely, Cambs. SIR,—I was much interested in Mr. John Case's article in FLIGHT of May 29 on " The Stresses in Braced Structures with Rigid Joints " as I am at present engaged on work of a somewhat similar nature. I note that he mentioned in the article that the trigonometrical and hyperbolic functions H m R 33 Keeping Her Hand in. BY way of keeping up practice, and incidentally to help to give the Victory Loan a fillip the Armstrong-Whitworth rigid airship R 33 this week carried through quite a respect able little tour over England. The trip was timed for about 36 hours, the starting-point being Pulham Air Station at 8 ajn. In less than an hour and a half Swaffham was reached. Peterborough was passed before eleven o'clock, and Grantham and Nottingham by midday. Making Liver pool in the evening, the Victory Loan ship passed seaward. required in solving problems of the nature referred to have been tabulated by Mr. Arthur Berry, but does not mention in what book or periodical these tables have been published. I should be very much obliged if you could supply this information. G. W. HIGGS WALKER. Hendon, N.W. We have submitted these queries to Mr. John Case, whose replies follow.—ED. In replv to Mr. Duncan's queries :•— (i) Yes'. (ii) Yes. M'a = M2, etc., unless there be " offset" couples due to the lift-wires. In this case the difference be tween M'3 and M.2l etc., will equal the applied couple. &f* (iv) Yes. I am obliged to Mr. Duncan for pointing out the slip in equations (25) which should read as he says. (iii) The example which I chose was, deliberately, a rather extreme case for the purpose of calling attention to what may be a serious matter, and also because it was easy to work out. When the spar is continuous over a strut the couples applied to the latter will certainly be reduced ; from one or two cases which I have worked out one can say that the effect is of the order of half that shown in the example given. This would be serious enough, for it must be remembered that, when the load on a strut is approach ing anywhere near the crippling load, a very small end- couple will be sufficient to bring about failure. Certainly struts do not often break in the air, but that is because they are always more or less pin-jointed ; in practice they deflect long before the crippling load is reached and the addition of any (small) end-couple will greatly increase the stress and hasten failure. In civil engineering—bridges—where_ the members are all rigidly rivetted together, it is usually the compression members which give trouble ; the collapse of the old Quebec bridge was due to secondary stresses in a compression boom. With regard to Mr. Walker's query : the tables referred to were compiled by Mr. Arthur Berry, King's College, Cam bridge, and have been published confidentially, during the War, in Air Board Publication C.I.M. 9, and in the handbook of Strength Calculations, written by Pippard and Pritchard and published by the Air Ministry. I suppose in due course these documents will be made public. m m On Tuesday R 33 returned to her moorings, having covered the 900 miles mapped out in 31 hours. Dwellers in the Midland towns passed over were vastly interested in" this novel visitor. Yatesbury and Wyton Aerodromes Closed. THE Air Ministry announces that the R.A.F. Eastern aerodrome at Yatesbury has been closed. All machines landing at Yatesbury should, therefore, nse the Western aerodrome. The aerodrome at Wyton has also been relin quished by the R.A.F. 9C4
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