Patent GB-692664-A (GB)
Title: Improvements in or relating to helicopters
IPC: B64C27/54
Filed: 1951-04-09
Abstract: 692,664. Helicopters. BORDONI, F. April 9, 1951. [April 8, 1950] No. 8209/51. Class 4. A helicopter with two coaxial propellers rotating in opposite'directions is characterised in that the power drive from the motor to the two coaxial propellers is by means of a shaft contained in a stationarv tube fixed to the body and around which the two propellers revolve, the drive from the shaft to the propellers being obtained by means of two speed reducing mechanisms, one for each propeller, placed on the stationary tube. The motor 1 and tubular elements 2. 3 are connected to the aircraft body and the motor drives a shaft 4 which is enclosed bv the tubes 2, 3 and carries intermediate its ends a gear 11 and at its upper end a gear 5 forming the primary elements of speed reducing mechanisms. The gear 11 drives a crown wheel 14 through three pairs of satellite pinions 12 and 13 whereas the gear 5 drives a similar crown wheel 7 through three pinions 6 only. The crown wheels 14 and 7 are respectively fast with casings 15 and 8 mounted on the tubes 3 and 2 by bearings 16 and 9 and each carrying horizontal trunnions upon which are pivotally mounted stirrups 27. Each stirrup carries bearings 37, 38 having pivotally mounted thereon a tubular member 35 provided with a pivot 26 which carries a rotor blade 25 with freedom for flapping movement, within the limits permitted bystops 33. Each stirrup 27 and the attached blades 25 are free to tilt about the trunnions on the casings 15 and 8 and to prevent the blades of the two rotors from coming into contact at low speeds of rotation, spring urged wedges 29 are slidably or pivotally mounted between the respective members 15 or 8 and 27 and are free to be withdrawn by centrifugal force when the rotor speed increases. Each member 35 carries a pitch control arm 39 connected by a link 40 to the rotating element of a swash plate 41 of which the inner element is connected to three vertical rods 22 so positioned that the rods attached to the upper swash plate pass between the pinions 6 and the crown wheel 7 and apertures 20 in the plates 18 of the lower reduction gear and the rods connected to the lower swash plate pass through the apertured pivot pins 21 of the pinions 12. The lower end of each rod 22 is in threaded engagement with a series of right and left hand threaded elements 46, 47, 48 each carrying a pinion in engagement with toothed rings 49, 50, 51 formed interiorly on rotatable operating drums. Threaded sleeves 59 and 60 which engage the elements 46, 47, 48 are prevented from rotation by fingers 62 engaging the tube 2. The tubes 2 and 3 are connected by a right and left hand threaded sleeve 53, rotation of which raises or lowers the last-mentioned mechanism and all the rods 22 to effect collective pitch control of the rotor blades. The pitch and direction of the various threaded elements are so arranged that rotation of the drums attached to the respective rings 49, 50, 51 will adjust the rods 22 and cause appropriate cyclical pitch change of the rotor blades. In order to steer the helicopter a differential collective pitch change of the blades is effected in order to produce a torque reaction between the two rotors.