ClipArt ETC
An illustration of a elastic aerial screw with twisted blades. "X, End of driving shaft; v,w, Sockets in which the roots of the blades of the screw rotate, the degree of rotation being limited by steel springs (z, s); ab, ef, Tapering elastic rods forming anterior or thick margins of blades of screw; d c, h g, Posterior or thin elastic margins of blades of screw. The arrows m, n, o, p, q, r, indicate the direction of travel." -Britannica, 1910

Elastic Aerial Screw with Twisted Blades Resembling Wings

An illustration of a elastic aerial screw with twisted blades. "X, End of driving shaft; v,w, Sockets…