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Aviation History
1911
1911 - 0363.PDF
APRIL 22, 1911. position of g, the aeroplane will glide at an angle of incidence greater than that of horizontal flight, and therefore with a de creased speed and an increased gliding angle. On the other hand, with increased thrust we may expect it to fly at a decreased angle with increased thrust. Its speed, if this be so, will be increased as the thrust increases. It might be possible to so place the thrust line that this increased speed did not result in an upward trajectory, or that, since the power of rising upwards is necessary, the increased speed will make the trajectory only slightly inclined upwards. If we can do this, as seems quite possible, we could have a machine which, without changing the area of the planes or their angle relative to the machine, would fly faster with increased thrust and would glide at a lower speed *o ensure safety in landing. This lower speed would, however, be obtained at the expense of the gliding angle, and the decrease of landing shock due to slower speed might be counterbalanced by increase of shock due to increased gliding angle. In landing, however, the elevator could flatten out the trajectory. Something might be done by having two sets of propellers, the thrust line of the first set, to be used alone in normal flight, passing through the centre of gravity ; and the thrust line of the second set, to be used in conjunction with the first set for speed flying, passing above the centre of gravity. As an alternative, they might be used separately by means of a special clutch on the engine shaft. The idea seems, at any rate, to be worthy of experiment. Air Currents. [1142] I was standing the other day at a place where the surface of the ground ran somewhat as in the diagram. There was a series of undulations—ridges with valleys between —and the wind was blowing across them. As I stood there I tried to visualise the path of the air currents, which would more or less follow the contour of the ground, though air coming up the valleys would give a slight general upward trend. It was evening, and just then a hawk came in sight flying home dead into the wind. When first I saw him he was as at A, gliding on without a wing beat, upborne and pro pelled by the upward current of air. When he arrived at B I thought, " Now he will flap," but no, the bird knew better than that; instead, he glided down at a sharp angle to C to within a few feet of the ground, and a very little flapping brought him to D, where he again encountered an upward air stream, and sailed away forward and upward with out spread wings ready to repeat the manoeuvre at the next dip. He was followed at distances by some ten other birds, which all went through the same process. Of course, the reason for this procedure was evident enough. Finding at B that the wind became unfavourable to soaring flight he glided downwards (and forwards) to C, where, being close to the ground, the wind was weaker and consequently the work easier. Incidentally he saved himself the work of flapping from B to C. What struck me as worthy of note was the in genious way in which he managed to place himself in the strongest air currents when favourable, and in the weaker when he had to fight against them, thus using the force of an opposing wind as deflected by the ground to both support him and propel him home. This surely points a lesson to cross-country flyers, who by adopting similar tactics might save much petrol and increase the distance traversed in proportion. The navigator of the future will have to take these things into consideration. Richmond, Natal. V. K. VYVYAN. ffpGHT Aerial Sign Posts. [1143] In view of future air traffic I should like to suggest that gas companies be approached all over the country with a view to having the cardinal points of the compass and the name of the place painted on the top of gasometers. I understand that railway companies are to be approached as to having the names painted on station roofs, which I think is a good idea. W. H. NORTON. Redhill. The Dipping Front Edge. I.1144] Your foot-note to Mr. A. A. Griffiths' letter (1036) opens a large field for argument as to which is the most efficient type of dipping entering edge. There are at least three, if not four, different types. Fig. 1 represents the Bleriot or blunt entry type, with the hump. By " hump " I mean when the top and bottom surfaces are the greatest distance apart at or just before the centre of the camber (see Fig. 8). Fig. 2 shows the Maurice Farman type, with the hump, but a sharp entry. Sir Hiram Maxim, after his numerous experiments with various types of aerofoils, seems to have decided that this type is the most efficient. In Fig. 3 we see the Wright type, without the hump, i.e., the under and top surfaces of the planes are parallel at the front. Fig. 4 shows the type of plane Mr. Roe used in his early machines when he created the world's record of flying with only 9-h.p. (a record which has not yet been beaten). It will be noticed that there is a slight dipping edge, a slight hump and a sharp entry. They were very similar to those advocated in articles published in FLIGHT a short time ago, li Can we Fly Faster for Less Power ? " A section of the Kaufmann Demoiselle-type monoplane wing (illustrated in FLIGHT, page 35, Vol. Ill) is shown in Fig. 5. The maker evidently has been trying to obtain a perfect stream-line entry. Personally I favour Type 2, as it must enter the air with much less shock than the blunt entry, and therefore offer less resistance (Figs. 6 and 7). Of course I know that in the first case the " hump " (taking the definition given above) was introduced for con structional purposes, but I think it has been kept, through it proving itself so efficient in practice. Fig. 8 shows a section of the average bird's wing, from which it will be seen that it has a comparatively sharp entry and a large hump. It would be interesting to hear some other correspondents' views on this subject. Manchester. SKY PILOT. Mathematics of the Cambered Plane. [1145] With reference to " Mathematics of the Cambered Plane," published in FLIGHT (NO. 108), in which you give several very useful formulae, the following results derived from your " lift and loading " formulae may be of interest:— The angle # for the latest 30-h.p. Nieuport monoplane loaded at 4-7 lbs. per sq. ft. (allowing 200 lbs. for pilot, &c.) at 66 m.p.h. works out at 120 ; for a Bleriot, 5 lbs. per sq. ft. at 60 m.p.h. to 15- 50; R.E.P. to 170 ; and a Breguet " Cruiser " (fully loaded) at 5 • 1 lbs. per sq. ft. and 53 m.p.h. to 200 ; while the M. and H. Farman machines (ordinary type) work out at <r 50 and 11 • 50 respectively. If the angle of declination is taken as the average declina tion of upper and lower surfaces, I should think the first four results are too high and the last two about right, i.e., the practical load per square foot (in the first four cases) is con siderably greater than the theoretical load. Newcastle-on-Tyne. C. DAN BURRELL. 365
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