Patent GB-647744-A (GB)
Title: Improved pitch controlling means for rotor blades of helicopters
IPC: B64C27/54
Filed: 1947-12-22
Abstract: 647,744. Helicopters. PENNINE AIRCRAFT, Ltd., and NEALE, J. S. Dec. 22, 1947, No. 33825. [Class 4] A hydraulically-operated blade pitch control system for helicopters comprises blades mounted for restricted flapping action about axes substantially normal to the blade root axes and also transverse and fixed relative to the axis of rotation of the rotor head, the blades being journalled at their root ends for pitch change about their root axes, the flapping axes being between the said journalled root ends and the rotor axis, and a constant volume hydraulic system responsive to aerodynamic forces to effect pitch changes of the blades independently of and relative to the said flapping axis. Each blade 1 is secured at its root end by a ring of bolts 7 to a housing 8 rotatably mounted by needle roller bearings 9 and thrust bearings 12 on a fitting 4 capable of flapping movement about a pin 5 which is supported by a lug 6 on the rotor head. Flapping movement of each blade 1 about its pivot 5 is damped by a rod 14 pivotally connected at one end to a fitting 15 attached to the bracket 4, the opposite end of the rod being provided with rubber buffers 161 adapted to engage at the limits of blade flapping movement, with a lug 16 formed on the rotor head. To enable the rods 14 to cross each other as shown in Fig. 1, they are successively apertured as shown in Fig. 2. In an alternative arrangement (Figs. 5 and 6, not shown), the fitting 4 may be extended to provide a drag pivot and damping of the blade movement about the flapping and drag pivots may be effected by means of hydraulic dashpots which, in the case of drag damping, interconnect adjacent blades. Diametrically-opposed arms 24 are formed on each housing 8 to support a U-shaped fitting 25 connected at its extremities to the ends of a piston rod 26 having intermediate its ends a piston 27 capable of sliding movement within the respective cylinder of each pair of cylinders A<SP>1</SP>, A<SP>2</SP> ; B<SP>1</SP>, B<SP>2</SP> ; C<SP>1</SP>, C2, Fig. 3. The opposed ends of one cylinder of each pair, i.e. A<SP>1</SP>, B<SP>1</SP>, C<SP>1</SP> are respectively connected by means of pipes 1A, 1B, 1C and 1a, 1b and 1c to annular pipes 28 and 29 fast with the rotor head while the other cylinder of each pair is similarly connected to pipes 30 and 31. The pipes 28, 29, 30 and 31 are connected by pipes 281, 291, 301 and 31<SP>1</SP> respectively to a junction box 32 incorporating oil-tight rotary seals, further pipes 28a, 29a, 30a and 31a leading to a pair of cylinders 33, 34, the pistons of which are coupled to a manual control lever 35. The axis of the centre of pressure of each blade 1 is offset rearwardly from the axis for pitch change and since the pairs of cylinders A<SP>1</SP>, A2, B<SP>1</SP>, B2, &c. are interconnected hydraulically variation of the pitch of one blade, caused by airflow conditions in the rotor disc, will produce complementary change of pitch on the remaining blades, collective pitch change being effected by movement of the manual control 35. Specification 605,561 is referred to.