GB856491A - Helicopter - Google Patents

Abstract

856,491. Helicopters. UNITED AIRCRAFT CORPORATION. Aug. 27, 1958 [Feb. 24, 1958], No. 27459/58. Class 4. A helicopter main rotor comprises hinge means for each blade such that as the blade advances and flaps upwardly, the blade lags, the axis of the hinge being at an acute angle to the plane of blade rotation, the hinge being located outboard from the rotor axis at a distance given by I cos<SP>2</SP>α/Mxc, where I is the moment of inertia of the blade about its hinge, α is the angle between the hinge line and the rotor axis, M is the blade weight, and xc is the distance from the hinge line to the centre of gravity of the blade, and comprises means connecting adjacent blades so that as one blade advances and lags, the other blade leads. Fig. 2 is an elevation of a two bladed rotor, the root 78 of each blade 32 being mounted by pitch change bearing 30 to a fork 28 forming a pivot with an inclined pin 34 and an arm 24 on the drive shaft 14. A pin 50 journalled in arm 24 is rigid with arms 46, 48 supporting counterweights 52, 54, which should have a natural frequency of oscillation equal to that of the blade, and should be in static balance with the blade. Pulleys 40 rigid with fork 28 and 44 rigid with the counterweights are drivingly connected by a crossed cable 42 so that leading movements of the blade result in lagging movements of the weights. Arm 48 drives a pulley connected by a crossed cable to a similar pulley associated with the other blade, so that as one blade leads, the other lags. The arms 24 of the two blades may be integral and pivoted to the drive shaft about an axis, perpendicular to that of the blades. Cyclic and collective pitch control movements are effected by reciprocating rods 16 (see also Fig .5) shown for one blade, each connected to a bell crank lever 60 pivoted to arm 24 by pivot 64. A rod 68 is connected to lever 60 and supported by a radius arm 72 pivoted to arm 24 by a pivot 70 coaxial with pivot 64. Rod 68 is connected by link 74 to a horn 76 on the blade root 78, by a pivot located on the axis of pin 34, so that lag/lead movements do not affect the pitch by interaction with the pilots' pitch control linkage system. The forward speed at which the retreating blade stalls is stated to be increased.