Abstract: A propeller for fluid propulsion comprises a pair of substantially rigid blades which rotate about their longest dimension in opposite directions, the blades each being oppositely helically twisted along the longest blade dimension and positioned together in synchronously opposite, rotatable condition, with the rotating blades passing by each other in closely spaced relation substantially without physical contact. The blades occupy a tubular housing enclosing the rotating blades in closely-spaced relation between the housing and blades. Further sealing is provided by each blade side carrying a hemicylindrical wall with a concave side facing outwardly, each hemicylindrical wall being helically twisted in a manner identical to the helical twist of the blade. The hemicylindrical walls have a cross-sectional diameter that permits, upon blade rotation, an edge of the other blade to sweep across the concave side of each hemicylindrical wall in closely spaced relation for sealing purposes.

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.