THE AUTOGIRO

Evening Post, Volume CX, Issue 151, 24 December 1930, Page 3

THE AUTOGIRO

(By Juan de la Cierva.)

HOW IT FUNCTIONS

INVENTOR'S DESCRIPTION

CHANGING- AVIATION

(Copyright.) Because most persons already know what the autogiro is, how it looks, how i it works, I am not going to enter into a detailed description of the autogiro - as such. Instead, I shall try to convey • briefly the philosophy of the autogiro, as an introduction to its theory. I have been working many years on the conventional aeroplane. lam a ' great enthusiast of the aeroplane, for • I think it is the most marvellous invention of modern times; but a long, time ago I came to the conclusion that the 'plane had fundamental limitations due to its own nature. I tried, therefore, to produce a new system of flying, free from those limitations. I thought that the aeroplane could be improved quantitatively in every direction, but my thought was and still is that no improvement can change the very nature of the aeroplane and its qualitative limitations. After a certain amount of theoretical work, I reached the conclusion that the only method for removing those fundamental limitations was to make the wings relatively independent of the frame or body of the machine, so as to make it possible to keep them going fast through the air while the machine could be going slowly or even be stationary. I saw the possibility of achieving this result without the introduction of mechanical complications such as those which inevitably occur in helicopters, ornithopters, or generaUy speaking, flying machines with driven wings. I started then the study of a very primitive autogiro which was related to the existing machine only by the fundamental idea of freely rotating wings. FAXN_UL PERIOD. I am not going to explain in detail the long and painful experimental period through which the autogiro has passed to reach its present development. I point out to you only that I did not achieve success at all until I had the idea of articulating the blades of the autogiro so as to let them flap freely, since there were too many mechanical and aerodynamical problems that could be solved only in. that way. The main problem I solved in this way was the dis-symmetry of the reactions on opposite blades, since there is a single group of them rotating in the same direction. On one side of the machine the speed for a given point of the blade will be the addition of the general speed of advance of the machine, and the peripheral speed, while in the opposite, will be the difference. To balance the lift in those two opposite planes by means of controls that would periodically change the incidence of the blade is a most difficult problem, but this solution of the articulation does it automatically and in a very simple 'way. The aerodynamics of the autogiro appears as a very complicated problem, if one realises how difficult are the problems involved in the calculation of ordinary propellers, considering the autogiro can be likened to a propeller with three or four more parameters. It is a propeller which is advancing through the air with a great obliquity and with blades which are free from flapping. The speed and the incidence at every point of every blade at every moment is different. I cannot attempt here to make a detailed analysis of the aerodynamical qualities of the autogiro and compare them with those of the ordinary aeroplane. Nevertheless, and in answer to an extended criticism of the autogiro, I want to point out to you that there is no fundamental, reason why the autogiro should be aerodynamically inferior to the aeroplane-»-NO STALLING. It has been said that since the speed of the blades of the autogiro through the air is higher than the corresponding speed of the wing of a eonvential aeroplane, the energy expended will be greater. The autogiro, because of its special qualities in landing, is free from the necessity of having big wing surfaces and, in consequence, can utilise very high wing loadings, which means higher aerodynamical efficiency. By its aerodynamical nature the autogiro is not subject to any of the risks of stalling. Tho wings always move fast through the air, whatever the speed of displacement of the fuselage. It can be stopped in the air for ono moment without losing completely its lift. If by; a sudden manoeuvre, the pulling back of the stick, the machine is brought to a standstill in the air, the wings still continue rotating under the action of the • inertia for the first moment, and they still give a certain amount of life which makes the machine fundamentally different from the aeroplane, which, when it is stalled, loses all grip on the air. Since the movement of the blades continues even when the machine is not moving with any forward speed, the autogiro can become a parachute at the will of its pilot. A most interesting aerodynamic problem can be pointed out in this connection. I had predicated as far back as 1921, by theoretical considerations, since confirmed by experiments which have been checked by the officials of several Governments, that the efficiency of the autogiro as a parachute is considerably higher than that of the ordinary parachute. As a fact it does not need discussion, but I should like to point out to you that its efficiency as a parachute is as high as three times that of an. ordinary parachute formed by a disc of the same diameter of its rotor. SMOOTH FLIGHT. The physical explanation of that phenomenon is that, contrary to what most aerodynamicists think, the mass i of air influenced every second is much ■ larger than that corresponding to the volume equal to the product of the surface of the rotor by the speed of i descent. The ordinary parachute prac- '. tically has an efficiency corresponding to the optimum in this assumption and, : if one considers the great amount of • energy wasted in the complex vortexes ■ in its wake, it is obvious that a much '. greater efficiency can bo achieved by a : parachute, like the autogiro, in which 1 the flow is much more smooth and regu- ■. lar. My theoretical results are that < the optimum possible parachute would t havo an efficiency equal to six times " that of the disc and the present auto- ] giro achieves about 50 per cent, of < that optimum. _ Structurally the autogiro is based on ] a very different principle than the aeroplane. The wings of the aeroplane are constructed in such a —;ay as to resist stresses of rigidity, whereas the autogiro is a flexible structure; s_d.den changes in incidence or speed do not-.-increase the structural stresses in the ' same measure as they increase those . of an. aoroplane. The centrifugal force ■ which keep tho blades approximately - horizontal acts as a spring on long i travel, and gives the autogiro the ' quality of a much greater comfort, a smoothness in flight which is thoroughly ' different from the feeling that is produced in the flight of an aeroplane in bumpy weather. Many people ask whether the autogiro can fly in bumpy weather. The answer is that the autogiro is much less sensitive to bumps than is an ordinary aeroplaa* because pt£ jteHgfcpr__ii__.fhßri_gl^ t