A 'single-blade propeller' is a notable configuration of a propulsion system used on
aerodynes to generate
thrust. Normally
propellers are multiblades. The simplicity of a single-blade propeller fits very well on
motorized gliders, because it permits the design of a smaller aperture of the glider fuselage for retraction of the powerplant, the counter-balanced
teetering mono-blade propeller generates less vibrations than all the other conventional multiblade configurations.

Single-blade propeller drawing.

Single-blade propeller and glider drawing.
Sources
★ http://www.glidingmagazine.com/FeatureArticle.asp?id=368
★ http://www.alisport.com/eu/images/img_news/Volaresett04/VOLARE_SETT04.htm