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Aviation History
1931
1931 - 0702.PDF
FLIGHT, JULY 10, 1931 it would have been very easy for the firm to keep silent about the matter and quietly to go to the various owners and get modifications made without the world in general knowing anything about it. That the De Havilland Aircraft Company, Ltd., should have chosen the other alternative and decided to state in print the actual position is a sign not only of that honesty in dealing with their customers, which has done so much to build up the De Havil- land business, but also of a faith in their products, which faces the facts seriously and frankly, and admits that conditions, particularly overseas, may be such that the load factors hitherto employed, and, generally speaking, found adequate, may need revision. If we look back, it is found that during the last year or so, the De Havilland Aircraft Company, Ltd., has sold something like 200 " Puss Moth " machines, which have flown in the neighbourhood of two million miles. Of notable flights made by " Puss Moths " it is necessary to recall only a few, such as Mr. Caspareuthus' flight to the Cape, Cap- tain Hope's flight to Abyssinia and back, and Captain C. D. Barnard's various non-stop long- distance flights. In none of these did the machines show the slightest signs of structural weakness. Static tests have now been carried out on no less than ten separate " Puss Moth " wings, some taken from machines with months of tropical service behind them, and it is known for certain that all the Strength requirements of the class of aircraft are met. ' ~ The two accidents referred to in Mr. Walker's letter are the only cases of failure in the air, as it is considered fairly certain that the damaged spar in Captain Mathews' machine must have sustained its damage on the ground, a view, we gather, which Captain Mathews himself shares. The Australian accident occurred in clouds, and it is known that a clean machine like the " Puss Moth " can reach very high speeds rapidly. Not only so, but atmos- pheric conditions themselves may, according to a member of the American National Advisory Com- mittee for Aeronautics, occasionally be such that extremely high stresses can be thrown on a fast machine flying into a sharp-edge region of vertical currents, stresses so great that no aircraft ever built would be able to withstand them. The accident, which cost Lieut.-Commander Kid- ston his life, occurred in a pass which is infamous locally for its violent weather, and it is highly prob- able that the machine was thrown about in a manner which would be the exact equivalent of stunting. If, as seems to have been the case, the machine was heavily loaded, it is not surprising that a breakage occurred. A machine is given a Certificate of Air- worthiness for one gross weight for " Aerobatics " and another, and much larger, for normal flying. If, therefore, a machine loaded up to the normal gross weight is, unintentionally, called upon to per- form various evolutions in very rough weather, this may readily become the equivalent of aerobatic evolutions at normal gross weight, and structural failure may be expected. In this connec .on it interesting to learn that the South African accid " showed a fracture of the rear spar in exactly the sam" place where fractures are obtained on static tests witf large incidence loading. From the fact that, as far as can be ascertained the British Air Ministry does not intend to issue an Notice to Ground Engineers about the " Puss Moth' it may be inferred that the Airworthiness Depart ment is satisfied that the load factors of this machine are up to standard. The De Havilland Compam has, however, decided to carry out certain modifica tions with a view to guarding against intentional oi unintentional misuse, so that in future all " PUS! Moth " machines will have not only the load factor demanded by the British Air Ministry but addi tional safety measures, which should guard agains structural failure from conditions of use and handlim which are not readily foreseen. The question will naturally be asked whether ; change in the load factors used at present should no be made? In certain service types the factors havi recently been altered to 9 forward and 6 back, bu although the tendency, in light aeroplanes also, i towards greater and greater speed, there is probabh no reason to change the existing factors, which have on the whole, proved adequate. One firm ha: already taken steps to increase, without, of course being compelled to do so, its " factors of ignorance ' (to quote an expression of Mr. J. D. North's), am should the need arise, any other firm is at libeit to do the same. It will be obvious that mud depends upon the locality in which a light aeroplam is to be used and the manner in which it is to bi used. There is little doubt that certain weather con ditions, of disturbed air and poor visibility, maj constitute a danger in causing an aircraft to get into attitudes not intended. Apart from a strengtheninj of machines to take care of such conditions (am there are manoeuvres which no aircraft ever buil will withstand), it would seem that training in flyinf by instruments might do much to reduce the risk: of certain kinds of flying. The new school recentl) established at Hamble by the Armstrong-Siddele group (Air Service Training, Ltd.) makes provisioi for thorough training in instrument flying, and i may well be that this form of training, which ha: hitherto been regarded chiefly as a specialised forrr of instruction, could with advantage be extended anc taken into more general use. Whether the time hai come for instrument flying to be part of the tests foi an "A" licence may, perhaps, be open to doubt On the other hand, a pilot who includes instrument flying among his accomplishments should be in i position to undertake with a fair degree of safet flights which might otherwise include a not incon- siderable element of risk. In any case, we consider that the De Havillano Aircraft Co., Ltd., has done the whole British avia- tion community a service by drawing attention to a subject which may well become one of very greai importance in the near future. 656
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