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Aviation History
1935
1935 - 0679.PDF
March 28, 1935 Supplement to m CS^CT U 332a FLIGHT ENGINEERING SECTION Edited by C. M. POULSEN No. 110 /Volume X\ l No. 2 ) 10th Year March 28, 1935 THE AUTOMATIC PITOT: AILERON CONTROL Application of the Gyroscope : Avoidance of Errors Due to Accelerations By G. R. M. GARRATT, M.A. (CANTAB.) IN a recent article in these pages* there appeared a description of the automatic pilot which is now exten sively used throughout the Royal Air Force. For various reasons, however,, it was only possible at that time to describe that part of the mechanism which controls the rudder and elevators, and while it is true that the per formance of many aircraft is entirely satisfactory for most purposes when fitted with automatic rudder and elevator control only, it cannot be denied that a very appreciable improvement in the control results from the employment of the aileron control in addition. For many purposes the control of the ailerons is absolutely essential if complete stabilisation is required. Where a high degree of stabilisation is required, such as is necessary, for example, in accurate aerial surveying, full gyroscopic control of all three axes is essential, no matter what degree of inherent stability may be possessed by the machine. Unless the ailerons are controlled, the damping by lateral oscillations and the ; correction of a disturbance is influenced solely by the characteristics of the aeroplane. However, in the case of a machine the ailerons of which are controlled, the damping of an oscillation is considerably improved, and it is probable that the initial disturbance will never reach the same magnitude as in the case of a machine with uncontrolled ailerons. The accuracy of con trol which can be achieved by a human pilot is limited by the fact that he can detect a disturbance only after it has grown to a considerable magnitude, and quite a considerable time interval must elapse before he is able to apply the necessary correcting movements to the aircraft controls. The. gyroscopic pilot, however, detects the slightest devia tion or disturbance instantaneously with its occurrence, and almost simultaneously applies the necessary correcting movements to the controls. Consequently, the effect of an y given disturbance is kept within very small limits and a Ver y high degree of stability is achieved. *THE AIRCKAFT ENGINEER, July 24th and August 30th, 1934. There are several possible forms which a mechanism de signed to control the ailerons of an aircraft might take. It might, for example, be designed to carry out flat turns or to bank the aircraft to the correct angle during a turn. It might be made directly or indirectly dependent upon the direction of apparent gravity, or it might employ a gyroscope, the spin axis of which might serve as a datum to which disturbances of the aircraft are referred. But while various simple mechanisms might be devised with partial success to relieve the pilot to an appreciable extent, the gyroscope alone stands pre-eminent as an instrument of precision, capable of maintaining a perfectly stable datum and capable of controlling the aircraft with the utmost accuracy, no matter how violently the machine may be dis turbed by prevailing conditions. In view of its standing as an instrument of precision the gyroscope was chosen as the fundamental unit when the work of developing an accurate aileron control was first commenced. In the description which follows, the manner in which the somewhat complex principles of the gyroscope have been applied and the manner in which the compara tively large accelerations experienced on an aircraft have been prevented from disturbing the accuracy of the datum will be made clear. The reader will be assumed to have at least a superficial knowledge of the principles of the simple gyroscope. A brief account of the properties of the gyro scope was given in the previous article, but for a more detailed account the reader must refer to a text-book of mechanics. The familiar applications of the gyroscope, such as, for example, the stabilisation of a ship, make use of the dynamic stability of the gyroscope directly for achieving the required stabilisation. For aircraft purposes, however, the gyroscope forms only a stable datum. Deviations from the datum are detected by sensitive air valves which govern the movements of the control surfaces of the aircraft. Accurate definition of the vertical is the underlying prin ciple of the aileron control. By means of the gyroscope and
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