A folding propeller is a type of

propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

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 Aircraft#Heavier-than-air – aerodynes, aerodyne equipped with a means of propulsion (Mo ...

s, such as the Aériane Swift PAS. Their purpose of folding propellers is to reduce

drag Drag or The Drag may refer to: Places * Drag, Norway, a village in Tysfjord municipality, Nordland, Norway * ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania * Drag (Austin, Texas), the portion of Guadalupe Street adj ...

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 parallel ...

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 Brunton may refer to: Places * Brunton, Northumberland, England (near Alnwick) * Low Brunton, Northumberland, England (near Hexham) *Brunton, Wiltshire, England *Brunton Memorial Ground, Radlett, Hertfordshire, England * Brunton, Fife, Scotland; a ...

, 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