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Aviation History
1913
1913 - 0161.PDF
FEBRUARY 8, 1913. (TQGHT] STABILITY DEVICES. By MERVYN O'GORMAN. Paper read before the Aeronautical Society on Wednesday, January 29th, 1913, Brig. Gen. D. Henderson, D.S.O., C.B., in the Chair. 13- The Wright Stabiliser/ the " Doutre" and other more usual Speed Maintainors.—Among the known devices which purport to keep an aeroplane within its safe limits of speed we may name: (1) the Wright Bros.' automatic elevator control, (2) the "Doutre" (see Appendix), and (3) more important than either, the almost universally used longitudinal Vee, (4) the duck or " S " type aeroplane, (5) screw propulsion, (6) small fly-wheelage. 14. The Longitudinal V as a Speed Maintainer.—It is not usual to ascribe to the longitudinal V, open upwards between main and tail planes, the function of a speed maintainer, but that speed maintenance is one of the chief and most valuable effects of this disposition of planes has been elegantly shown by Mr. Alexander See in six steps, somewhat as follows :— (a) If the speed falls off, the supply of supporting air fails, and the aeroplane cornes downwards. (b) Owing to this descent, the angle of incidence on the air is increased. (c) The increase of angle of incidence causes the centre of total pressure of a Veed aeroplane to travel backwards, and gives rise to a diving couple. (d) This dive having been started, the angle of incidence is thereby made normal again, but the travel being downwards, the machine accelerates. (e) The speed being increased by the acceleration, the support derived from the air is increased, and the descent ceases. (f) The descent having ceased, the angle of incidence is diminished, the centre of pressure of the whole travels forward, giving rise to a " nose-up " couple, which sets the aeroplane level again. T 15. If the speed had at first increased instead of falling off as assumed at (a), the converse of all this is true. Thus, we find it helpful to restate the working of the Vee between main and tail planes by saying that an "aeroplane is guarded from risky longi tudinal movement not when it opposes itself to any pitching, but, on the contrary, when it takes on by itself such pitching up or down as shall secure a constancy of speed ' within limits.' "J We may add that the more sensitively it responds, the less time is there for the speed change to be felt, the less the amplitude of the movements and the less likely are oscillations to occur. The characteristic (Continued from page 127.) ih Fig. 3. increase and decrease of speed of the two dangerous flight paths or phugoids (Fig. 3) (the cusped and the looped) are to be combated all along the line by a really good device. 16. The "Tall First" or "S" Type§ Aeroplane as an improved Speed Maintainer has for some years been more particularly studied of the makers of small models, and I know of no effect of scaling up which precludes the belief that for large craft also the maintenance of air speed automatically is improved by the " duck " form, at least in horizontal gusts. - Much on the lines of the Wright stabiliser is that described in Pat. 10,424, April 29th, 1909. (Motorluftshiff.) The speed of the aeroplane is regulated by an elevator controlled by the air pressure acting on a membrane to steer up when speed rises and down when it diminishes. t Whether this swing back is accompanied by oscillations or not, is, it will be observed, entirely overlooked in this—as was indicated in para, l, p. 126. J Alternative methods of looking at this are to be found everywhere, e.g., the author's paper on Aircraft Problems. Proceedings Inst. Autom. Engineers, March 191 J, p. 285, where the righting couples are calculated for various cases which have been kept simple by assumptions which are set forth. § 1 ventured in 1911 to call this " S '* type after Santos Dumont, the originator, or at least, the first successful flyer with this type. to enter the region of air speed fall off, this 17. The small forward plane is the first altered air speed, and if the gust makes the plane dives in anticipation of the loss of air speed by the mam wings. It thereby causes the main mass to rotate on an axis roughly parallel to and located somewhere near the main wing spars. This rotation of the main mass for a dive is effected the more quickly because it is accompanied by less air damping than the downward acceleration of the main mass itself. (In the case of the " B" type or " F " type of aeroplane where the large mass is in front the damping is greater since the wing loading is necessarily less than that of the front plane of the '* S type.) I give 8 diagrams (Fig. 4) borrowed from the Aerophik of 5omTu3 0*o>n«atKW HToi *€. ' \ 1 [,•••' w> Fig. 4.—Diagrams of Duck or "S" Type Aeroplanes Arrow to show the position of centre of gravity. with machines of this type which have flown, and in addition there are those of Mr. Curtiss, and those who follow in his earlier footsteps, Mr. Barber's Valkyrie, the R. A.F.'s aeroplane S.E. I, the new Bleriot Canard, &c. I see no objection to the type on the score of uncontrolled pitching. 18. In the opposite event of a head-on gust which increases the air speed for the moment, the front plane gets the extra lift first and quickly rises, tilting the aeroplane, and speaking colloquially, it checks an increase of air speed of the aeroplane by setting it forth for a climb. It is probably because so much of the work of a model is effected with a small margin of power and so much gliding comes into the the performance that the "duck" type has had so great a vogue with model makers. It was noticed at the Aero Show this winter that in France there is a recrudescence of the '' duck" in the full-size machine just now. It may survive and I think it may even be important. If it fails it does go on other considerations than the above. 19. In paragraph 7 we have only regarded horizontal gusts, and the up and down directions of travel have been treated as the only remedies for speed fluctuations. The treatment is incomplete unless we can reckon with or utilise the effect of vertical gusts and engine speed variations. 20. Some merit may be found in relation to up-gusts in the " S " type. If we refer to the diagrams of "lift and drag" of wing shapes and select the wing shape for best efficiency for the main wings we may, I think, so choose the loading and wing shape of the front plane that it will be sensitive to changes of speed but less sensitive to changes of angle of attitude. This is possible because we can select with much freedom the angle of attack of the small plane when it is in front, whereas we are restricted to narrower limits of positive angle when the small plane is behind. (To be continued.) l6l
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