Patent GB-464835-A (GB)
Title: Improvements in or relating to air-screws
IPC: B64C11/36
Filed: 1935-10-25
Abstract: 464,835. Screw propellers. FORGE ET USINAGE DE METAUX LEGERS (HELICES METALLIQUES CHAUVIERE). Oct. 25, 1935, No. 29520. Convention date, June 20. [Class 114] In a variable-pitch airscrew wherein epicyclic reduction gears driven off the engine shaft are connected by worm gearing at the blade roots and wherein effective actuation is produced by braking the epicyclic train, there are disposed means for rendering the action inoperative at predetermined limiting angular positions of the blades. The roots 1 of the blades have secured thereto worm wheels 4 engaging worms 5 on shafts which at the ends are serrated to carry pinions 8 and are journalled in a rigid member 7 which constitutes a casing for the gears and is secured rigidly to the driving shaft 2<a>. The pinions 8 for the separate blades are in constant mesh with a pinion 10 and on this wheel are pawls 12 set in reverse directions, the noses of which engage teeth 13<a> on a pinion 13 loosely mounted on a sleeve 13<c> surrounding the hub of the casing 7. The pawls 12 can be rocked for disengagement from the teeth 13<a> by their contact with abutments 29, 31 which take the form of cams. These abutments 29, 31 may be adjusted in position in arcuate slides 29<a>, 31<a> for determining the extreme positions of the blades. If desired the abutments 31 can be retracted out of use by means of a roller 32 on a lever 32<a> which has an outer counterweight 32b adapted to balance centrifugal force. The lever 32<a> is rigid with a stud 33<a> on the casing 7 and this is provided with an abutment surface over a spring control pin 35. On the stud 33<a> is also secured a lever 33 the nose of which engages a lever 34 forming part of a locking device for the cam 31a. The teeth 13a are constantly in mesh with double planet pinions 15 journaled in a tooth crown wheel 17 loosely mounted on a sleeve. The planet pinions 15 also mesh with a tooth wheel 14 rigidly connected with the shaft 2<a>. Crown wheel 17 is in driving connection with the coaxial crown wheel or drum 21 equally through the medium of bevel pinions 24 or planet pinions 37. To obtain small variations of pitch, two other pawls 19<c> can be made to act on teeth 17<a>, 17<c>, provided on the crown wheel 17. These pawls are pivoted on pins and can be adjusted from the outside by means of a movable cam 30. To limit the amplitude of motion imparted by these pawls further cams 28 are fitted to the wheel 10 in adjustable positions whereby they may act on a projection 19<d> of the pawl 19<c> for removing the nose of the pawl from the corresponding teeth. A braking device 26 is interposed between the casing 7 and the crown wheel 17 and consists of a friction bevel 26<a> and springs 26b. The crown wheels or the drums 17 and 21 can be held stationary by a brake 18 controlled by the lever 27, the latter being operated by means of Bowden cables or alternatively by a pneumatic transmission system. When blades of wood are employed the roots 100 are screwed externally, and two flat cheeks are placed on the wooden roots and held by means of hollow rivets. The screwed part of the root 100 carries a sleeve 105 which is integral with the worm 4 and has a flange adapted to contact the thrust race of.the bearing 106. The inner end of the root of the blade is mounted on a conical roller journal bearing and at the outer end is supported by needle bearings 107 in an extension 2 of the hub socket.