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Aviation History
1937
1937 - 1410.PDF
SUPPLEMENT TO 34 FLIGHT MAY 27, 1937 f THE AIRCRAFT ENGINEER component of the force from the tension fields is the same as if the curvature had not altered. This follows since for approximately circular arcs tangents at the mid points of the arcs are parallel to the respective chords. (2) Loads Due to Bending (a) Loads Due to Curvature Produced by Bending. Consider a monocoque section shown in Fig. 9. The My direct stress is given by / = -5- and the load m any stringer My by P = -y- X As where As is the stringer area. The E M curvature of any section due to bend is given by ^ =-y. Thus the compressive loads in a frame due to bending M are given by w = P X -ppr X I where I = frame spacing. These forces act parallel to the plane of the B.M. and in the plane of the frames. They are small, but become of Martlesham and the '* TV /f ARTLESHAM is pleased with it" has long been the |\/l expression used by aircraft constructors when they 1 V A want to impress anyone with the excellence of their latest products. Rarely is one permitted to read the report in which Martlesham expresses its opinions of a new aeroplane; consequently, when Capt. E. W. Percival offered Flight the opportunity to see Martlesham's report on the first of the Mew Gulls to be fitted with Gipsy Six Series II engine and v.p. airscrew, the offer was gratefully received, the only stipulation being that any criticism which the report might •contain should be open to quotation as freely as any points of praise. Trials were made of the machine with three loadings, the e.g. being 20.7m., 17U1., and 15.4m. aft the leading edge. The weight with the e.g. farthest aft was 2,1331b. At this weight and with this e.g. position, the report states, the con trols were well harmonised, light, quick in response and effective. The tail trimming gear was very effective, the engine controls well situated, the flap gear well placed and easy to operate and causing little change of trim. Laterally and directionally the machine was stable under all conditions of flight, whether with engine " on " or " off.'' With the • e.g. in the rearmost position, the machine was longitudinally unstable, but as fuel from the rear tank was consumed, the e.g. moved forward and the instability disappeared. And now for performance. Climbing, with the airscrew in fine pitch, a height of 4,000ft. was reached in three minutes at au I.A.S. of 100 m.p.h. The take-off run against a wind of 5.5 m.p.h. was 300 yards and the landing run, using the brakes, following an approach with flaps down, was 276 yards. Aluminium Alloys A PAMPHLET containing a list of selected aluminium alloys has been issued by the Aluminium Union, Ltd. Tables of mechanical, chemical and physical properties of each of the alloys are included and there are notes on uses arid foundry properties. The brochure may be obtained from the Union at Bush House, London, W.C.2. A New Control Bearing A RECENTLY issued Hoffmann list contains particulars of a new series of ball bearings for aircraft controls. Known as the "C.A." type, and approved by the Air Ministry, the bearings have grease-retaining end shields and a self-aligning movement. Copies of the list are obtainable from the Hoff mann Manufacturing Co., Ltd., Chelmsford, Essex. importance in such cases as side bending on small fuselages with large holes for cockpits. (b) Loads Due to Curvature of Fuselage Lines. (See Fig. 10.) If sections containing the axis of the body are curved appreciably we get loads normal to the frames due to the end loads in the skin and stringers. The magnitude of these normal loads is given by !«( = P X p where R is the radius of curvature of a section of the fuselage containing the axis, and P is the load in a stringer or cross-sectional element of the skin. These forces are inward on the tension side, and outward on the compression side, for positive curvature. It should be noted that if the sizes of adjacent frames are comparable, the frames will deflect approximately equal amounts and will not alter the curvature. < : We are now in a position to calculate all the loads coming on to the frames from interaction with the stringers and skin, and end loads and B.M.s can be obtained from a strain energy calculation. "* j x The stability of the skin-stringer-frame combination needs a separate calculation, and this can be checked for by the method of R. & M. 1679. Percwal Mew Gull At full load the machine stalled at 84 m.p.h. with flaps closed and at 73 m.p.h. with flaps down. With e.g. in the forward position the machine rocked slightly before stalling, but the stall was gentle and straight, both with flaps closed and with flaps down. With the e.g. in the rearmost position, both with flaps open and closed, there was a marked " shuddering " before the stall ; following this, the starboard wing dropped about 20 deg. suddenly. The wing could be raised by the use of the ailerons, but if the machine was left alone the wing would come up unassisted, or the nose of the machine would drop. With all e.g. positions right-hand and left-hand gliding turns could be made satisfactorily, flaps up and flaps down, at 1.2 times the stalling speed. The machine would sideslip satisfactorily, the limit apparently being 20 deg., when the report states the nose fell away. The diving trials disclosed that the Mew Gull is unstable longitudinally (i.e., in pitch) when diving, all controls becom ing slightly less sensitive and heavier. Small movements of the controls, however, give proper response without causing control surface instability or vibration. Recovery from the dive is easily effected. The diving trials, by the way, were with e.g. in rearmost position and the limiting conditions were an I.A.S. of 246 m.p.h. and 2,400 r.p.m., whichever occurred first. So now we know the worst and those who had, secretly or openly, regarded the Mew Gull as something of a racing freak will have to think again. Considering the high wing loading (251b./sq. ft) and short span, the stability and the low stalling speed must be regarded as rather remarkable. It is also worth noting that the controls are effective throughout. Synthetic Rubber Synthetic Rubber, by W. J. S. Naunton. Macmillan, ys. bd. TN this, said to be the first book on synthetic rubber to be -*• published since 1926, Dr. Naunton deals with both the technical and economic aspects. He speaks with authority (as head of the rubber laboratories of Imperial Chemical Indus tries, Ltd., and hon. technical adviser to the Institution of the Rubber Industry) on the technical advances and changes of outlook and policy which in the last ten years have made the large-scale production of synthetic rubber practicable and economically desirable. Having discussed the chemistry of synthetic rubbers and dwelt on the division between rubbers and resins, Dr. Naunton reaches the main conclusion that there is a great held for development of a product which can give better service than natural rubber, though more expensive. VICELESS SPEED
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