Screw propellers arranged in tandem and oppositely rotated are adapted to be varied in pitch by a double sun and planet control of one propeller by an operating gear passing through the hollow propeller shaft whilst the first propeller through a second set of double sun and planet gears adjusts the second propeller. An electric motor 29, or a hydraulic motor, is employed to actuate the shaft 25 carrying at its lower end a bevel wheel 24 which meshes with a bevel wheel 23 on a tubular shaft 20 which passes through the hollow hub and at its forward end carries a spur‐wheel 30. Within this shaft 20 is a second shaft 19 which is fixed at its inner end to the engine casing 21, and at its other end carries a gear wheel 22. These wheels 22 and 30 constitute twin sun wheels and between them is a spider 31 carrying planet wheels 32, 33 of which the wheels 32 which mesh with the fixed sun wheel 22 also coact with an internally toothed ring 34 mounted to rotate as one with the front propeller 11, while the planet wheels 33 which mesh with the adjustable sun wheel 30 also coact with an internally toothed ring 35 which is freely mounted on the propeller and which by reason of the outer ring of teeth 36 and the pinions 37 provide for the actuation of the shaft 38 whereby the pitch of the blades is adjusted. The shaft 38 is continued to carry a pinion 41 which meshes with the second pinion 42 freely mounted on the hub and continued to drive a similar double sun and planet wheel layout which in turn actuates the adjusting shaft 52 of the second propeller 12. The arrangement for actuating the pitch adjusting gear is also utilized to actuate a pitch indicator and for this purpose the spindle 25 carries an extension which through suitable gearing is conveyed to the indicator. Specification 398,993 is referred to.
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