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Aviation History
1914
1914 - 0147.PDF
FEBRUARY 7, 1914. from a gust suddenly arising and coming in from the outside of the curve. This would have the effect of suddenly increasing the deflecting force to a degree perhaps beyond what the velocity and radius demand. The downward movement of the wing has the effect of bringing the centre of the keelplane below and to the rear of the centre of gravity, through which the various axes of rotation of the whole sy>tem pass. A gust coming in from the convex side would now, therefore, have the effect of reducing the bank, and holding the machine into the gust, l»th movements tending to safely. In turning into the wind a sudden gust would have the effect of increasing the bank, and holding the machine into the wind. The increased amount of banking would automatically increase the deflecting force, thus preserving the necessary conditions for circular motion. A sudden cessation of the wind would have the effect of decreasing the bank and giving an outspin for safety. In turning down wind, the conditions are identical with those arising when an inward sweeping gust suddenly arises in " still air," and which I have already referred to. 51. I have already observed that not one of these movements increases head resistance to flight; on the contrary, I believe that in practice the velocity will be found to increase when turning. It will be obvious that the banking reduces the lift of the wings, and a loss of altitude would in the ordinary way result—the loss of lift is, however, converted into a centripetal force which when compounded with the propeller thrust may give increase of speed sufficient to counteract the loss of lift. Nothing but actual test, however, can show whether such a result is obtainable. I have often noticed birds turning, not only without loss of altitude, but with apparent gain. 52. When gliding, birds always retire the wings for descent at angles steeper than the ordinary gliding angle and advance them for ascent. Birds fly without any apparent difficulty in a cabri attitude, the reason being that the raised wings raise the centre of the keel- plane, and so counteract the effect of the low tail. In any case, the absence of a rudder or anything in the nature of a vertical fin near the tail reduces the danger of the cabri attitude. Such a result in an aeroplane would mean that the machine might safely climb cabri, and so avail of the full power of the propeller thrust. 53. Further than this, the fact that incidence could be altered in flight would obviate the necessity for the machine to take the cabri attitude, in order to obtain support, in the case of a failing engine. 54. When flying obliquely across a regular wind, the windward wing may be retired ; this holds the machine into the wind and corrects for drift without increasing head resistance. Correction by rudder increases head resistance. I have frequently seen rooks gliding in this way at tremendous speeds right across a gale of wind. When extra weight is taken, such as a passenger or more, the [AUsg balance of pressure and gravity can at once be adjusted by advance or retirement of the wing*, thus enabling the machine to fly always under the most favourable conditions. Greater liberty for disposing of loads is also allowed—once in the air the pilot can immediately bring the machine to a level keel. This is the plan the birds adopt when carrying food, &c. 55. The investigation of the problem of turning in the air has been confused by a false analogy, drawn from the case of steering a boat, because the rudder and bows reaction produces spin, it is thought proper to follow the same plan. There is a true analogy in this—that the naval architect makes use of kinttic force to deflect his ship j this mut be the case either in the air or on the water from the very nature of the laws of circular motion ; but for stability he depends on static conditions. The plan must also be followed in the air. 56. In considering and comparing systems used by birds with systems which may be safely adopted on artificial flying machines, it must not be forgotten that birds get propulsion from their wings, i.e., the thrust is applied directly to the centre of gravity, whereas in artificial flying machines the thrust is applied directly to the face of the propeller blades, which is usually situated at some distance from the centre of gravity, and hence capable of taking up a lateral component. 57. It follows, therefore, there are certain movements used by birds which cannot be imitated on aeroplanes. I believe birds do sometimes depress the inside wing tip, as described by Dr. Hankin, and possibly give the tip a negative angle of incidence, but, I believe, that this is a nicety of control into which we cannot follow them. Birds have not got a shrieking propeller thrust to deal with —we have. 58. When all controls are exercised by the the wings, and by the wings only, the machine must follow a natural path determined by the attitude of the wings. With independent rudder and elevator, the machine may be and almost invariably is in practice forced into a path other than that which the wings lay down for her to follow— a proceeding naturally attended with great risk. The vol piqui, for instance, would be an impossibility with wing control. Quick descents could, of course, be made, but they would be a con sequence of the alteration of the natural gliding angle of the machine. It has been suggested to me that there are certain constructional difficulties in the way of building a full-sized machine on the lines I have described. Speaking as a practical engineer, I can say that I have designed a full-sized machine with a factor of safety of eight in all the component parts; that the weight is not above the average, and that a considerably higher factor of safety could be allowed without making the weight excessive. ® ® ® ® Iff ilf . i iL^Jb timfilfl' Phatet by Mr. E. L. N. Ltveson Onuer. The above snaps are of considerable historical interest from the fact that they show the scene at Buc uoon the occasion when Peeoud for the first time "looped the loop" on his Bleriot. On the left Pegoud is seen pointing out to those concerned the exact spot where he Intended to make his first loop. In the centre picture Is the late M. Perreyon, and in the righfhand picture from right to left MM. Pegoud, Djmenjjz and Perreyon. 147
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