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Aviation History
1910
1910 - 0525.PDF
JULY 9, 1910. \fU9El HEAD RESISTANCE. HAS IT BEEN THE CAUSE By R. F. MONOPLANES have been somewhat unfortunate in that the more sensational of the comparatively few fatal accidents have taken place with them, and the public are very naturally led to inquire if there is any factor that has been overlooked in the construction of this type of machine. For my own part I am of the opinion that there is, for I believe that designers of monoplanes have not given suffi cient attention to the stress on the main spars of the wings that is induced by direct head-resistance. Inasmuch as the aeroplane flies nearly edge on, it is commonly supposed that the head-resist ance on the spare is more or less negligible, but my own investi gations, and some little experience in the design and construction of an experimental machine, have led me to the contrary conclusion. Many theories of the cause of the latal accidents to Delagrange and Le Blon have been advanced, but none of them have, to my mind, been convincing, for I was an eye-witness of the former disaster, and feel sure that the failure was neither due to the gyroscopic action of the rotary motor nor to any region of aerial disturbance. It was a melancholy good fortune, too, that enabled me to be able to make an examination of the wreckage of this machine immediately after the accident, and before it had been tampered with by the public, and from this inspection I satisfied myself that although the left wing was broken off about 2 ft. from the body, yet all the stays and connections of the wings on the under side were in sound condition, and that it was not due to any failure on their part that the wing collapsed. I had, as a matter of fact, explained my views on what I consider to be an inherent weakness in monoplane design to several experts prior to any serious accident with such machines, but it was generally received with scepticism, and I therefore thought it best to wait until I had collected something in the nature of practical evidence. The Delagrange smash seemed to uphold my view, but still more convincing evidence was afforded one day at Huntingdon, OF MONOPLANE DISASTERS? MACFIE. on May loth, when Mr. T. Radley met with an accident of a similar nature from which he escaped unhurt. Mr. Radley was flying at a height of 50 ft. from the ground when the machine suddenly executed a cork-screw glide, curving to the right from the aviator's point of view. It was found that the trans verse arms of the right wing were both cracked for a distance of about two feet from B to C (see sketch). The after spar was badly twisted as well as split, and the whole wing was bent back from B to C, as it is here illustrated. In the sketch the dotted line shows the original shape of the wing, and the full line shows its shape after the accident. Mr. Radley is positive that this buckling took place in mid-air, and was not caused by the shock of landing. My explanation of the failure is as follows : The wings of a monoplane constructed on these lines largely depend for their cross-bracing on the fabric itself, and it is not difficult to suppose that the head-resistance, represented by R in the sketch, is capable of straining the wing when it is remembered how great the leverage is through which it operates. The head-resistance, it must be remembered, includes skin friction and possibly a fraction of the aerodynamic resistance if the angle of incidence is considerable. In any case it is quite reasonable to suppose that the head-resistance represents a considerable portion of the total thrust, although it is difficult to say how much that amount is for any given machine. I have, as already mentioned, always believed that more attention ought to be paid to the matter, and to my mind the evidence that I have collected is proof of my contention, for I certainly think that the head-resistance is capable of severely straining the main spars, and of causing them to crack or fracture in extreme cases. Another very important point that deserves to be investigated is the influence of a possible toggle action between the spars and their guy wires, which may in some cases augment the effect of the stress. It will be remembered that there was considerable dis cussion as to why the Delagrange accident could have taken place apparently as the result of fitting a rotary engine, and many people supposed that gyroscopic action had something to do with the matter. It will be recollected, however, that the reason why the rotary engine was used was because it gave greater power, and, therefore, made a higher flight speed possible. This increased velocity would increase the head-resistance, and since the resistance in the direct air increases as the square of the speed, a comparatively slight increase in velocity would be sufficient to account for a considerable augmentation of the pressure, which, it seems to me, the wings were unable to withstand. In principle it is not desirable to emphasise anything in the nature of a fault without offering a remedy, and if I may be per mitted to make the suggestion it is that most modern monoplanes would be improved in this respect by bracing the rear spars direct to the bows of the main frame by means of one or more diagonal wires beneath the wings, or the front spars to a bowsprit. This would enable some of the head-resistance to be taken by a member in tension, and would tend to relieve the bending strain. The new French monoplane, * Montgolfier," with Lieut. Bier in the pilot's seat, who has recently been making some successful flights with this 25-30-h.p. Anzani-englned machine. 523
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