GB501014A - Improvements in and relating to helicopters - Google Patents

Abstract

501,014. Helicopters. HAFNER, R., and THOMAS, D. W. Aug. 16, 1937, Nos. 22454/37 and 10839/38. [Class 4] A helicopter includes a rotor constructed to absorb the power supplied to it during flight at a high tip speed and a correspondingly low torque. From one aspect the ratio of torque to thrust of the rotor in stationary hovering has a minimum value 0À09 of its radius. From a second aspect the optimum blade pitch setting for power operation, at least in normal forward flight lies within the autorotational range of pitch settings. From a third aspect, the rotor has blade section and a solidity such that the mean of the minimum torque factors over the working or lifting portion of the rotor disc has a value below 0À09. The torque factor is obtained from the expression [CDP/CL + ¢#CL.#] where CDP and CL are the profile drag and lift coefficients, respectively, and # is the rotor solidity. As shown, the rotor blades 1 are articulated to the hub by flapping and drag pivots and the rotor is constructed in the manner described in Specification 467,589. The aerofoil section chosen of the blades is N.A.C.A23009 and the blades are built with a stressed skin of stainless steel, the general construction being similar to that described in Specification 486,883. The blades are tapered in plan so as to give substantially the optimum lift distribution over the rotor disc and are twisted to keep the mean effective angle of attack correct at each point during flight. The fuselage is shapetl as shown in the Figure, the cross-section at c, c being approximately symmetrically oval, the cross-section being modified towards the nose and tail into unsymmetrical sections which are upwardly directed but oppositely cambered. The blades may, during manufacture, be given a slight inherent upward curvature. The fuselage carries a rudder 8 and a tailplane. Flaps 10, operable by the pilot, are fitted to the fuselage. The rotor is driven, through a jointed telescopic shaft, a freewheel device, and a clutch operable by the pilot and by centrifugal force. The clutch may be arranged in accordance with Specification 447,066 and the drive may be arranged to fracture on jamming of the driving mechanism. The engine drives a fan or blower for drawing engine cooling air through the aperture 12a and discharging it through a similar aperture on the opposite side of the fuselage. The landing gear includes wheels 30 carried on structures 32 pivoted at their roots, to the fuselage, for retraction and a wheel 31 which may be freely castoring. Specification 435,818 also is referred to.