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THE values of the load factors used in de‐signing an aeroplane are almost direct measures of its strength. They also affect the weight of a certain portion of the aeroplane structure. Although the percentage of gross weight that depends directly on the magnitude of the design load factors is not as large as might be supposed, it represents a considerable potential pay load on large aeroplanes and therefore warrants careful consideration of the basic question: What is the minimum load factor consistent with safety?

THE serious nature of difficulties which might be encountered in tail spins, was brought forcibly to the attention of the Material Division of the U.S. Army Air Corps, in the Spring of 1926, when Lieutenant E. H. Barksdale lost his life in attempting to determine the cause of difficult recovery from spins in a military aeroplane being flight tested at Dayton, Ohio. Trouble in recovery from spins had been encountered in several instances in foreign countries, and one or two cases had occurred in the United States: however, the problem was not considered as one generally applicable to all aeroplanes, because, in most cases of previous trouble, the aeroplanes concerned possessed unusual design features which were thought to be mainly responsible for their abnormal behaviour. Prior to this time, general conjectures had been made, regarding probable reasons for difficult recovery from spins, but very little in the nature of systematic investigation had been attempted, consequently no generally applicable principles had been determined. Numerous studies had been made in wind tunnels, and it was recognised that the normal aerofoil would rotate automatically under certain conditions, but the magnitude of the forces involved, and therefore the ability of an aeroplane to recover a normal attitude by use of the controls, could not be readily determined by wind tunnel tests. A few flight tests had indicated that the centre of gravity location, with respect to the resultant air force vector on the lifting surfaces, influenced the type of spin and the case of return to a normal attitude.

A gyroscopic control system for aeroplanes and other dirigible objects comprises (1) a pendulous gyroscope having its centre of gravity below the roll axis of the aeroplane, and comprising a frame 7, an outer gimbal ring 5 mounted to turn about the horizontal roll axis on the frame 7, an inner gimbal ring 3 mounted to turn about a normally vertical axis on the outer ring and a motor 1 mounted in the ring 3 to rotate about a normally horizontal spin axis normal to the roll axis; (2) means for operating ailerons in accordance with deviation of the ring 5 relative to the frame about the roll axis; (3) means operable, when the ring 3 precesses from a normal position, relatively to the outer ring 5, to apply, between the outer ring 5 and the frame 7, a torque of a corresponding sign to the relative movement between the rings in a direction to produce a counter‐precession of the inner ring and (4) restoring means for applying a torque between the rings 3, 5 when the inner ring processes relatively to the outer ring in the opposite direction to the direction of precession. The movement of the gyroscope and the angular momentum of its rotor are so related to the forward velocity of the aeroplane, that the gyroscope will, when the aeroplane moves on a curved path, precess in azimuth under the influence of centrifugal force at approximately the same angular velocity as the aeroplane is turning, to maintain the relative relationship between the gyroscope axis and the aeroplane. As shown, the frame 7 is pivoted in a frame 9 mounted on the aeroplane on the same roll axis as the ring 5 which carries a weight 10. (2) Relative movement between the ring 5 and the frame 7 operates due to relative movement between the gyroscope and aeroplane, through a link 21 connected to the ring 5, a piston valve 22 mounted on the frame 7 to supply compressed air to a servo‐motor 27, which operates the ailerons. A lever 29 pivoted on the aeroplane and having a bifurcated end which engages the ring 7 and which is connected to the piston‐rod 28 of the servo‐motor provides a follow‐up mechanism. (3) Relative movement between the rings 3, 5 operates through a link 14 connected to the ring 3 a piston valve 13 to cause a piston 18 mounted on the ring 5 and connected to the frame 7 by a link 19 to apply a torque reaction between the frame 7 and the ring 5 in such a sense as to oppose the gravity torque due to the pendulous weight to limit the relative azimuthal precession of the ring 3. (4) A spring 20 mounted on the ring 5 applies a restoring torque through the link 14 to the ring 3 to cause a precession of the ring 5 about its fore‐and‐aft roll axis and thus return the ring 5 and the weight 10 back to the vertical plane. The mechanism will cause an aeroplane to fly on a curved course without appreciable banking. The apparatus may be modified so that the aeroplane is banked to the appropriate extent in curved flight by providing a torque between the frame 7 and the ring 5 which is proportional to the angular velocity at which the aeroplane is turning.

The problems of older jet aeroplanes as seen by one regulatory authority— the U.K. Civil Aviation Authority (CAA)—are reviewed. Whilst attention is given primarily to airworthiness matters, a number of operational subjects are also considered. The particular problem of structure of the aeroplane is mentioned but the other information which an authority needs is also set out. Attention is paid to the design standard of the aeroplane, the physical standard of the particular aeroplane, and the role of the operator. In the case of imported aeroplanes, especially when they are already old when imported, the intention is to ensure that the standard achieved is not less than it would have been had the aircraft been operated on the British register from the beginning, and is also broadly similar to that of the current generation of equivalent aircraft.

THE high and economical cruising speed already mentioned depends on the aerodynamic “fineness” of the aeroplane (low drag, high airscrew efficiency) and on the horse‐power per unit wing area.

DURING the past 40‐odd years or so, a number of experimental aeroplane types have been invented, visualized, designed, constructed and even flown which, in a quite unorthodox manner, had neither behind the wing nor in front of it any sort of stabilizing and/or controlling surfaces.

THE complexity of the problems which are associated with the lateral stability and directional control of tailless aeroplanes was not realized until rather late.

(Concluded from p. 75)

THERE are so many different considerations to bo kept in mind in connexion with the manœuvring load factor requirements that it might be well to begin by listing the most important of these, as follows:

ONE of the most important tasks of present‐day aeroplane manufacture is the design of economical high‐speed commercial aeroplanes to provide regular and safe services.