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Aviation History
1925
1925 - 0709.PDF
OCTOBER 29, 1925 THE CIERVA "AUTOGIRO" Noteworthy Lecture at the Royal Aeronautical Society IF the attendance at the Royal Aeronautical Society is anycriterion, British aviation circles can be assumed to be keenly interested in the new method of flight invented by the Spanishengineer, Senor de la Cierva, as represented by his " Autokro " which was demonstrated at Farnborough last week It issate to say that of rerent years no lecturer at the Royal Aeronautical Society has drawn an attendance approachingthat of Thursday of last week, October 22. The lecture room was filled by 5.30, and still people continued to arrivethe late comers having to be satisfied with standing around the room, whilst a large number were obliged to remain in S6 l1^6;1"00?1- The Director of Civil Aviation, Air Vice-Marshal Sir Sefton Brancker, was in the Chair In introducing Senor de la Cierva, Sir Sefton said that hethought undoubtedly the future would regard October 22nd as a very significant date in the history of the Royal Aero-nautical Society, and he would go as far as to say that Senor de la Cierva's invention would be found to represent thegreatest step forward in aeronautical development since the Wright brothers piloted their first power-driven machine.Before asking Senor de la Cierva to give his paper, he would ask Major Wimperis to say a few words concerning the lecturer,but before doing so he thought it only fair to state something about the lecturer which probably even Major Wimperis didnot know, and that was that Senor de la Cierva had been a member of the Spanish Parliament, and that, therefore, incriticising the invention, they would have to be prepared for acrimonious replies. Major H. E. Wimperis said that Senor de la Cierva hadbeen interested in the design of aircraft for a considerable number of years, and that he had built no less than thirtysuccessive models. The machine which had been obtained for tests at the Royal Aircraft Establishment was the propertyof the Spanish Government, to whom they were greatly indebted for the loan of the machine and for the opportunityto make exhaustive tests. As regards the future of the •" Autogiro," all that could be said at present was that this•would depend upon the load carried per horse-power, and data of that kind. Senor de la Cierva, speaking in French/said he regretted hewas not sufficiently familiar with the language to be able to speak in English. He expressed his very great indebtednessto the British technicians for the assistance they had given him, and he was also extremely grateful to " Le Grand Pilote," .Capt. Courtney, whose extraordinary skill had resulted in the very good demonstrations which had been given. Senorde la Cierva was received with vigorous applause. Sir Sefton Brancker agreed to read Senor de la Cierva'spaper, as the lecturer did not feel sufficiently at home in the English language to read the paper himself. Senor de laCierva began his experiments in 1911, at the age of 15, commencing with gliders. Needless to say, he had a number ofcrashes, and all, or nearly all, could be attributed to a loss of flying speed. In 1918 he built a large three-engined machine,which was wrecked through loss of flying speed. His many mishaps due to that particular cause resulted in Senor de laCierva looking for other means of obtaining lift than the normal aeroplane wing, and the actual idea of fitting a wind-mill in place of ordinary wings occurred to him in 1919. The original machine, however, had wings which obtained theirpropulsion from beating or flapping. A number of lantern slides were then shown, illustratingthe windmill as applied to the evolution of the present Cierva " Autogiro." The first machine built was provided withtwo four-bladed windmills mounted one above the other, but revolving in opposite directions. The windmills were notdriven by the engine, but were rotated by the forward speed of the machine. The four blades of each propeller were rigidlybraced, the idea of hinging the four blades not occurring to de la Cierva until later. It was found that although the topwindmill came very close to the predicted performance as regards speed and lift, the lower windmill only attained some-thing like two-thirds of the predicted performance, so that it was evident that there was considerable interference betweenthe two windmills. This fact led Senor de la Cierva to concentrate in the future upon the development of the singlewindmill, and in machine No. 2 but a single lifting screw was employed. This was a three-bladed affair, and it was foundthat, although the machine would lift, it always tilted over to the right and side-slipped. In machine No. 3, five rigid blades were employed in thewindmill, and the elevator was divided in the centre, the idea being to use the two elevator flaps independently tocounteract torque. The fuselage was suitably strengthened up to take the twisting stresses arising from this type ofelevator. It was found, however, that although the divided elevator did effect an improvement, the machine still had atendency to roll to the right and side-slip. The idea of hinging the blades of the windmill, relyingupon centrifugal force to oppose the lift on the blades, first occurred to Senor de la Cierva early in 1922. Machine No. 4,therefore, incorporated this idea. It had a four-bladed windmill with the blades hinged, the hinges being placed atan angle of 2° to the axis of the windmill. Control was still found difficult, and it was found that the method adoptedfor tilting the windmill axis to counteract torque required greater force than could be exerted by the pilot. MachineNo.25 had a three-bladed windmill, but the blades were rotated in the opposite direction—that is to say, anti-clock-wise as ^viewed from above. This arrangement had the effect of stopping the tendency of the machine to lean over GOTTINGEN429 -5 0 ANGLE of INCIDENCE-DEGREES to the right, and, moreover, the action was entirely auto-matic. By now Senor de la Cierva had succeeded in convincingthe Spanish authorities of the practicability of his invention, and machine No. 6 was, consequently, built at the expenseof the Spanish Government. This machine was similar in all but very minor details to the one flown by Courtney atFarnborough last week. The wing section employed in the windmill blades was stated to be Gottingen No. 429. [For the benefit of our readers we give a graph showingthe characteristics of this wing section. The section and the data from which the curves were plotted were obtainedfrom Vol. I of the " Ergebnisse der Aerodynamischen Versuchsanstalt zu Gottingen." No dimensions of the sectionare given in this work, the usual practice of Gottingen being to print on photographic paper through the templates usedin making the wind tunnel models, thus obtaining a silhouette of the particular section whose template was used. Thismethod, while giving a good picture of a section, obviously does not give the dimensions, but it will be seen that thesection is a bi-convex one, probably intended to be sym- metrical. From the lift coefficients obtained at negative 709
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