Abstract: A propeller for fluid propulsion (such as air or water) comprises a pair of substantially rigid blades. The blades are mounted for rotation about respective, separate, parallel rotation axes, with the axes being also substantially parallel to the longest dimension of the blades. The blades each define a plate that is oppositely helically twisted along the longest blade dimension compared with the other blade. The blades are positioned together in synchronously opposite, rotatable condition, with the rotating blades passing by each other in closely spaced relation without physical contact. A tubular housing encloses the rotating blades in closely-spaced relation between the housing and blades. Such a blade system can provide a high velocity jet of large mass at relatively low rotational speed.

Abstract: An aircraft having an elliptical fuselage and low skin friction drag. The aircraft includes(a) a lifting fuselage having a cross-section constituting an airfoil in a majority of vertical planes taken parallel to the flight direction, an aspect ratio (AR.sub.f) of 0.33 to 1.10, a forebody having a substantially elliptic cross-section in all planes taken normal to the flight direction, and a substantially elliptic planform leading edge;(b) wings fixed to the fuselage having an aspect ratio (AR.sub.w) of at least 5.0;(c) a mechanism controlling aircraft attitude; and(d) a mechanism propelling the aircraft;wherein the wings and fuselage produce lift in varying proportions depending upon flight conditions as follows:(i) the aircraft has a cruise design point in which the fuselage lift coefficient (C.sub.LF) is 0.08 or less, and(ii) the fuselage lift coefficient is at least 0.50 at an angle of attack (.alpha..sub.LZo) of 10.degree.