Folding propeller

Folding propellers are found on sailing yachts, on model airplanes, and increasingly on self-launching gliders and small motor gliders, such as the Aériane Swift PAS.

Their purpose of folding propellers is to reduce drag when sailing or soaring, respectively.

[1][2] Folding propellers are spun outwards by centrifugal force when the engine is turning, but when the engine stops, the pressure of airflow or waterflow forces the blades back.

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 equally effective astern as ahead.

Further, the Brunton Autoprop automatically and the V-Prop set their blades to the optimum pitch.