Abstract: An air turbine including a plurality of elongated rotor blades extending from a hub, first and second airfoils interconnecting the blades, and a vane element positioned between the airfoils, said airfoils and vane element being concentrically disposed about the hub.

Abstract: A blast wave choke to be disposed at the above ground entrances of a ventilation system for a underground personnel shelter wherein a plurality of annular choke elements of progressively smaller inside diameter are aligned along a common axis and spaced one from the other by annular interposed spacer elements wherein each spacer element has an inside diameter that is greater than the adjacent choke elements wherein a blast wave entering the ventilation system will encounter a series of rings and set up an interference pattern which will dissipate the energy of the blast wave before it can enter the underground shelter and cause injury to persons or damage to property therein.

Abstract: A wind powered turbine augmented by a superstructure which forms a low pressure chamber for receiving turbine exhaust air and which is maintained at below atmospheric pressure by the action of wind directed to flow over adjustable inverted airfoils mounted on the superstructure adjacent exhaust ports from the low pressure chamber.