A folding propeller is a type of propeller whose blades automatically fold out when the engine is turning, and then fold back (or "feather") when the engine stops. Folding propellers are found on

sailing yacht A sailing yacht (US ship prefixes SY or S/Y), is a leisure craft that uses sails as its primary means of propulsion. A yacht may be a sail or power vessel used for pleasure, cruising, or racing. There is no standard definition, so the term applie ...

s, on model airplanes, and increasingly on self-launching gliders and small

motor glider A motor glider is a fixed-wing aircraft that can be flown with or without engine power. The FAI Gliding Commission Sporting Code definition is: a fixed-wing aerodyne equipped with a means of propulsion (MoP), capable of sustained soaring flight ...

s, such as the Aériane Swift PAS. Their purpose of folding propellers is to reduce drag when sailing or soaring, respectively. Folding propellers are spun outwards by

centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is parall ...

when the engine is turning, but when the engine stops, the pressure of airflow or waterflow forces the blades back. Typically, the blades are geared together so that they open and close in unison. Folding propellers used mainly to be two-bladed, but 3-bladed and 4-bladed versions are now available. The arguments for and against folding propellers are: Self-actuating variable pitch propellers A self-feathering propeller is not more efficient than a fixed bladed prop, as neither type can adopt an optimal blade angle. Exceptions are the Brunton Autoprop, Darglow FeatherStream, and the V-Prop, all of which are not merely folding propellers, but are self-actuating variable-pitch propellers. On a boat, most propellers are much less effective in astern, and this is particularly true of folding propellers; whereas the Brunton AutoProp and Darglow FeatherStream are as effective astern as ahead. Further, the Brunton Autoprop automatically and the V-Prop set their blades to the optimum pitch.

References

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External links

FlexofoldMartecGoriDarglow
Propellers