An axial impeller has a tubular housing mounted on bearings for rotation. The housing is capable of engaging a motor or generator directly or through a drive belt. Interior turbine blades are mounted on the housing wall. The blades may be hinged so they can rotate between a retracted position adjacent to the wall and an extended radial position. Rods penetrate the wall to position the blades between retracted and extended positions. When extended, the blades may be rotated to propel a fluid through the housing; and when retracted natural fluid flow is less restricted.