Abstract: A removable wheel covering to improve the aerodynamic profile of a motor vehicle tire comprising means for fastening the wheel covering to a wheel rim, the rim having a first axis about which the rim is rotatable; means for flexibly adhering the wheel covering to a tire side wall; and an air engaging circular surface that is rotatable about the axis, that is convex with respect to the tire, and that has a diameter that is proximal to the diameter of the tire at the side wall.

Abstract: An aerodynamic shroud positionable surrounding a hub to which blades are attached is disclosed. The shroud has a textured outer surface that is configured so as to create a turbulent boundary layer for fluid flowing over the surface. The turbulent boundary layer delays flow separation from the shroud and reduces drag. The shroud may be formed from a domed shell mounted on the hub and have skirts that surround the hub. The textured surface is provided by dimples in the surface or projections from the surface. The shroud is intended to reduce main and tail rotor hub drag on helicopters but is also useful on marine propellers, aircraft propellers and jet engine fans.