Abstract: The mean line (F) of each blade (1) is formed by a flat continuous curve contained in a plane OZ-OY.sub.o forming with the plane of rotation of the propeller an angle .phi..sub.o between 35.degree. and 55.degree. and preferably between 40.degree. and 50.degree., said curve having a first part of negative Y.sub.o and positive Z coordinates, and a second part of positive Y.sub.o and positive Z coordinates, the coordinate point Y.sub.o =0 being situated between the values of Z included between 0.75 and 0.85 R (R designating the radius of the propeller), the tangent to this curve has its end corresponding to the end of the blade forming with the axis Oz an angle between 30.degree. and 50.degree. and preferably between 35.degree. and 45.degree..

Abstract: The present invention relates to a blade profile for rotary wing of an aircraft, comprising, between the leading edge and the trailing edge, a convex upper surface and a non-concave lower surface, wherein, at the point of maximum curvature of the leading edge, the radius of curvature Ro is approximately defined by the expression Ro=1.7 C. e.sub.max.sup.2, in which C represents the chord and e.sub.max the relative thickness of said profile and the portion of lower surface adjacent the leading edge extends to about 20% of the chord from said leading edge and presents a very small general curvature decreasing continuously in the direction of the trailing edge up to the point of minimum curvature of the lower surface. The invention is more particularly applicable to obtaining rotary wings, for example for helicopters, capable of very high performances both when hovering, and in high speed flight, as well as during manoeuvres.