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Aviation History
1955
1955 - 1730.PDF
FLIGHT, 2 December 1955 849 CORRESPONDENCE The Editor of "Flight" does not hold himself responsible for the views expressed by correspondents in these columns; the names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. "The Epoch of Air Power" From Marshal of the Royal Air Force Sir John C. Slessor. 1MOULD you allow me to comment on one sentence of your "" report in the issue of November 18th on the discussion after the Sir George Cayley Memorial Lecture, in which I am quoted as saying "certainly, of course, in time the front-line strength of air power would be entirely 'unmanned'"? This, I think, gives an impression more definite than I in- tended to convey. It may be that in a future which is probably not as near as many people think the strategic bomber will give way to the long-range ballistic rocket, and the home-defence fighter to the ground-controlled guided missile. But the push-button age is not just round the corner. Air power must preserve its flexibility, and it is too early to assume that even in a push-button age there will be no place for the manned bomber or fighter. In the tactical, maritime and trans- port roles, I do not think the front line of our air power will ever be unmanned—anyway, in any foreseeable future. I must apologise for giving a misleading impression, which it is sometimes easy to do in the thrust and parry of discussion after a lecture. London, W.I. J. C. SLESSOR, M.R.A.F. Supersonic Bale-outs IS one to assume that the news that a Hunter pilot had success-fully baled out at supersonic speed was released to the Press by the Air Ministry? If so, why was the Ministry apparently unaware that at least one, and probably two, American pilots had ejected at supersonic speeds and survived the ordeal? So far as I know, no reference was made in British newspapers to the American escapes, one involving a Grumman Cougar and the other a North American F-100. One is led to infer that the Air Forces concerned are slow to exchange information on such incidents. Surely this is wrong. There is nothing to be lost, and a great deal to be gained, from an international sharing of all experiences yielding data on prob- lems of survival at high speeds and altitudes. Publication of such data in the aeronautical Press (subject to normal security .regula- tions) is also to be recommended, as a means of ensuring that survival information reaches squadron aircrews without delay, instead of filtering slowly through "official channels." London, W.I. ROGER BAKER. Helicopter Rotor PracticeI HAVE now read Mr. Payne's valuable and interesting paper [mentioned in his letter in Flight for November 11th] entitled The Stiff Hinged Helicopter Rotor and have come to the con- clusion that we are both after exactly the same thing. We are agreed that the way to get the best out of a rotor which is operating in asymmetric flow is to load it asymmetrically and that, to do this, one must have a rotor arrangement which is capable of transmitting moments to and from the remainder of the helicopter. We are also agreed that this same ability to transmit moments is desirable in order to achieve stability in hovering flight and I personally believe that, in allowing a forward e.g. offset, it will produce static stability in forward flight. The only point at which we are at variance is the engineering method to be adopted. Mr. Payne wants a rotor blade which has a "soft" point somewhere near the root where the desired elastic stiffness is superimposed upon a mechanical hinge by means of, say, a torsion bar. I want a blade in which the desired elastic stiffness is provided by the blade itself in bending. Mr. Payne's method certainly makes the mathematical analysis easier; in fact, my colleagues used the analogy of bending at a point in order to predict the behaviour of a hingeless rotor; he is also quite right in saying that the degree of stiffness required is not high. It is dependent, of course, upon the degree of e.g. offset required. So far as I can see, the only "quarrel" I have with Mr. Payne s thesis is over his reference to rigid rotors. Of course a rigid rotor is structurally impossible; there is no such thing as a rigid rotor except in theory. I have certainly never termed my rotor "rigid," it is a hingeless rotor in which the differential lift and drag loads are taken in bending. . vt f I believe that it is necessary to improve the fatigue life or helicopter rotors and that the way to do this is to make them into smooth, continuous structural members without joints and with no sudden changes of section, and to keep the operatingstresses below the levels required for long life. The introduction of a mechanical hinge in a blade produces allthe requisite ingredients for fatigue failure. In addition, no journal can be designed economically for long life if it is sub-jected to high radial loads coupled with a very small angular travel; it merely becomes a "Brinelling" machine. In any case,the introduction of a hinge, whether "stiff" or "loose," does not prevent the blade from being subjected to comparatively largebending stresses along its length due to variations in flow distribu- tion across the rotor disc. However, I agree most emphatically with Mr. Payne that hismethod can readily be applied to existing articulated rotors and that flight experience could be gained this way with little trouble. With regard to scale effect on hingeless rotors, it seems to methat if disc loading, static margin (stability) and number of blades are kept constant, then the bending moment at the blade rootswill vary as the all-up weight to the power of three over two. Since, however, larger helicopters are likely to have severalengines, a larger number of blades can conveniently be introduced. Both these factors will tend to reduce the adverse growth in bladeroot material weight and I have no doubt that, as with fixed wings, we shall find that blade weight will turn out to beapproximately a constant percentage of all-up weight in a given performance bracket. I regret that I am not in a position to publish any work onhingeless rotors at the present time, but I am gratified to see the most valuable contributions being made by Mr. Payne and lookforward keenly to seeing his ideas reach fruition. Holywood, Co. Down. F. H. ROBERTSON. A Famous Balloonist IN the very charming little parish Church of St. Peter, EastBlatchington, Seaford, Sussex, is a commemorative plaque: — "This tablet is placed here to the memory of The Famous AeronautHENRY TRACEY COXWELL for many years a resident of this Parish '.Died Jan. 5 1900. Aged 81 years. Of the many remarkable balloon ascents made by him for scientificpurposes during his long career the most notable was from Wolver- hampton, September 1862 when he reached an altitude of seven milesthe greatest height ever attained by man. Erected by his widow." It would be interesting to know more about this pioneer. London, E.C.4. JAMES LAWRIB. [We have a photograph of this particular memorial, and it is reproduced below. Coxwell (1819-1900) made numerous scientific- research ascents with James Glaisher, F.R.S., first hon. treasurer of the Aeronautical Society. In their 1862 ascent from Wolver- hampton, a height of about 37,000ft was probably reached, though both aeronauts temporarily lost consciousness owing to lack of oxygen after making their last observation at 29,000ft.—Ed.] IN BRIEF ' , We learn that A. Cdre. A. H. Wheeler is still anxious to find a Wolseley Viper engine for the S.E.5A, which is waiting, power- less, in the Shuttleworth Collection of historic aircraft. The memorial tablet referred to above by Mr. James Lawrie. sS «=» ACCB wrs?r. TO TM« MCWC THE '"(\HOVSi K MA MY r£AM$ A tt€Sif*em Of rttm DiecJ .laii.S.IgOO Aged SI Of TM£ MANY C'W SCIENTIFIC ASCCRTS MA8C BY H EHMRfNCk Ht» MMtO HE WAS FIOM wenx mm*4awf®*,mm»rtmm.ft 11tc M AITITUOC ©# ©gvett MIMES »r«5MT £¥E» TYMM£0 @Y ttl
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