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Aviation History
1926
1926 - 0100.PDF
O'Malley were perhaps the most conspicuous of the R.A.F. pack. From the standpoint of Rugger as it should be played it could not be called great football, though at any rate it was a hard tussle fought to the finish in the best spirit: vigorous thrusting and hefty tackling in plenty, but clean play throughout. One came away from Twickenham, however, with a feeling that the Army XV will come out on top when they meet the Navy and the R.A.F. respectively on March 6th and 27th, unless a vast improvement in team-work takes place meanwhile in both the sides playing last Satur- day. The teams were :— The Royal Navy.—Shipwright S. Hoskin (H.M.S. Vivid), back; Lieutenant H. C. Cumberbatch (H.M.S./M.H.23), Sub-Lieutenant T. S. Lee (H.M.S. Tiger), Sub-Lieutenant R. W. Armytage (H.M.S. Pembroke), and Lieutenant M. Richmond (H.M.S. Victory), three-quarter backs ; Lieutenant C. R. Garrett (H.M.S. Victory) and Able-Seaman C. R. Knapman (H.M.S. Vivid), half-backs ; Master-at-Arms W. G. E. Luddington (H.M.S. Thunderer), Able-Seaman W. Paddon (H.M.S. Vivid), Lieutenant R. D. Fricker (H.M.S. Thunderer), Lieutenant G. C. F. Branson (H.M.S. Excellent), FEBRUARY 18, 1926 Lieutenant P. B. R. W. William-Powlett (H.M.S. Savage), Lieutenant D. Orr-Ewing (H.M.S. Vivid) Lieutenant A. A. Havers (H.M.S. Pembroke), and Sub-Lieutenant H. T. Armstrong (H.M.S. Excellent), forwards. The Royal Air Force.—Flying-Officer C. B. Wilson (No. 22 Squadron, Martlesham Heath), back ; Pilot-Officer the Earl of Bandon (No. 4 Squadron, Farnborough), Squadron- Leader C. N. Lowe (No. 602 Squadron, Renfrew), Flight - Lieutenant O. C. Bryson (Cadet College, Cranwell), and Flying-Officer S. H. G. Trower (Northolt), three-quarter backs ; Flying-Officer P. J. Chambers (Cadet College, Cran- well) and Squadron-Leader J. C. Russell (No. 3 Squadron, Upavon), half-backs ; Flight-Lieutenant J. S. Chick (Experi- mental Section, R.A.F. Farnborough), Flight-Lieutenant E. F. Turner (No. 502 Squadron, Belfast), Flight-Lieutenant T. Rose (No. 13 Squadron, Henlow), Corporal N. WY. Johnson (Record Office, Ruislip), Corporal M. G. Christie (R.A.F. Depot, Shrewsbury), Pilot-Officer J. G. Franks (No. 56 Squadron, Biggin Hill), Leading-Aircraftsman J. F. Hampton (Record Office, Ruislip), and Flying-Officer C. J. S. O'Malley (Technical Training School, Halton), Forwards. Referee.—Mr. T.'H. Vile. _, 3 ^ $ CORRESPONDENCE The Editor does not hold himself responsible for opinions expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters intended for insertion in these columns. METAL v. WOOD. [2121] The articles in THE AIRCRAFT ENGINEER by Messrs. Green and Short on metal construction are valuable summaries of first-hand experience, and are particularly interesting because they bear on a subject which is treated sometimes in a more or less controversial way which generally has the effect of obscuring real issues. If it were not for the difficulty of obtaining good spruce, the enormous rejections, and the obvious drawbacks of having to import it from a great distance, a closer comparison of wood and metal as structural materials would be very interesting. The situation, however, is dominated by the necessity of not being dependent on the supply of long lengths of good spruce. In other words, metal spars and struts are becoming necessary, and it seems that this is the point upon which to concentrate. When satisfactory spars are obtain- able in metal—and by " satisfactory " is meant many things, such as ease of production and moderate cost for small numbers, etc.—the spruce difficulty will be over as far as wings are concerned, and for ribs, leading and trailing edges, etc., wood is entirely suitable and obtainable in any national emergency in the necessary quantities. It may be said, therefore, that apart from the main members, the use of metal can be determined by ordinary tou&idera-tions, such ;is cost, maintenance, etc. In the case of fuselages, it is not easy to see what advantages can be claimed for metal construction, if an adequate supply of 3-ply wood is obtainable. It is certainly very doubtful if the combined lightness and stiffness of the 3-ply and wood fuselage can be obtained in metal. The question of length of life in hot climates remains to be answered, for the present position is that there is practically no experience of metal under these conditions, whereas the wood and 3-ply fuselage, suitably protected, has already proved itself to be thoroughly satisfactory in hot climates. It may, in future, be necessary to depart from this form of construction for supply reasons, but apart from this necessity it seems a highly desirable type to retain. Major Green makes an interesting comparison of wood, Duralumin and steel as materials. This comparison is a difficult one to make owing to the uncertainty of the ultimate strength of the steel. If a rectangular beam of spruce with a compressive strength of 5,000 lb. per sq. in., is tested it will develop a fibre stress of about 8,000 lb. per sq. in. before failure. An ordinary spar section may not quite attain this figure, but will in general exceed 7,000 lb. per sq. in. Similarly the figure given for Duralumin is the approximate yield stress of this material, the ultimate being largely in excess of this. Thus wood and Duralumin have a large reserve of strength against actual failure of the structure, since their load factors are calculated on the low figure. If an aircraft were seriously overstressed, compression " shakes " would appear in wood, and in both wood and Duralumin deformation would occur without failure of the structure. It would be interesting to know to what extent this reserve against failure exists in the steel-strip spar, when its factors are calculated on the " Proof Stress." Presumably it would be considerably smaller. Our firm has recently been testing metal spars, for a certain machine, and in making check tests on the actual spruce spars used in the same type, it is certainly striking to notice iii every case the great margin of strength against actual failure over that calculated. Metal spars, however, have got to come, and it will be interesting to watch their evolution. Steel has the advantage of being a more home-produced material, while Duralumin, as pointed out by Mr. Short, has certain structural and manu- facturing advantages—is well adapted to float construction, and is likely to be improved in its physical characteristics. While weight of structure is naturally of great importance, it can be exaggerated. An easily produced and cheap metal spar woud be worth adopting, even if it were 10 per cent, heavier than wood. It would in fact be more valuable in most cases than a difficult and costly spar weighing 10 per cent, less than wood. The effect on the total weight of the aircraft would be small in either case. Stag Lane Aerodrome, C. C. WALKER. Edgware. February 11, 1926. METAL CONSTRUCTION. [2122] I have read with interest Mr. Oswald Short's notes on my article in THE AIRCRAFT ENGINEER on steel construc- tion for aeroplanes. There is little doubt that in case of emergency it would be possible to obtain supplies of bauxite from Northern Ireland, and that in time we should be able to manufacture our own supplies of aluminium. Unfor- tunately, the time taken in getting going would be serious, and unless we had large supplies of aluminium there would probably be a serious shortage, for a time at least. There is scarcely the same chance of shortage of steel, and in any case we should be in such a hopeless position without steel that it would not much matter whether we could make aero- planes or not. With regard to Mr. Short's other point, the question is whether it is safe to work to a higher stress than the proof stress. In the British Standard Specification 2L3 the proof stress is given as 13-5 tons to the square inch. I am well aware that it is possible to obtain stresses that are higher than the minimum proof stress when testing spars, but I am not at all sure whether it is wise to work to a higher stress, particularly when reversal of stress will occur. There are many samples of aluminium alloys that are a good deal above the present specification, but this is equally true of steel I have some recent tests of atrip steel which gave a proof stress of over 80 tons to the square inch, as against 55 tons, which is the figure I used for comparison with Duralumin. I have little doubt but that the strength of aluminium alloys will gradually be improved in the same way as the present-day high-tensile steels are being developed, but at the present time I do not think that we are justified in basing our designs of Duralumin spars on a higher figure than I gave in my article. It, therefore, seems to me that we can make lighter spars usingisteel, and we are also freed from the possibility of having to re-organise our source of supply in case of war. Coventry. F. M. GREEN. February 15, 1926. 92
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