GB886582A - Improvements in helicopter blade control apparatus - Google Patents

Abstract

886,582. Helicopters. BOEING AIRPLANE CO. March 11, 1960, No. 8654/60. Class 4. Centrifugally operated blade flapping control apparatus for a rotary wing aircraft has a rotor including a hub 16 and a blade mounted thereon for flapping movement, the apparatus maintaining the blade substantially at right angles to the axis of hub 16 when the rotational speed of the rotor is below a predetermined critical r.p.m., the apparatus having also a structure carried by and rotatable with the hub and including a toggle comprising three links 19, 23 and 25 arranged in an over-centre locked position interconnecting the structure and the blade, The blade is attached by a flapping hinge 14 to hub 16, on which is fixed a mast 15, to which are attached lugs 18 and 29. Pivoted to lug 18 is a link 19 and an arm 20, the other end of which is attached to weights 21 and to one end of two springs 30, which are attached at their other ends to lugs 29. Pivoted to the blade 13 at 26 is a second link 25, which incorporates a damper 28 and the counter-clockwise motion of which is limited by the roller 27 abutting against mast 15. Pivotally interconnecting links 19 and 25 is another link 23. When the angular velocity of the rotor is below a certain value, the linkage will remain in the over-centre locked position, Fig. 2, and the damper 28 will restrain the flapping motion of the blade. When, however, the centrifugal forces acting on the weights 21 exceed the tension in springs 30, link 19 will rotate anticlockwise, thus freeing the linkage. In this position, Fig. 3 (not shown), damper 28 is no longer effective, and blade flapping is limited only by the stops 31, 33.