Variable lift inflatable airfoil for tethered balloons

In a tethered balloon having a body and an inflatable airfoil structure mounted on said body, the improvement residing in said inflatable airfoil structure, said airfoil structure comprising at least one inflatable horizontal fin, said fin being made up of a primary and a secondary chamber, said primary chamber being defined by a pair of non-rigid, gas retaining membranes and a plurality of supporting elements mounted therein, each of said supporting elements being secured between the inner surfaces of said pair of membranes in the spanwise direction, said secondary chamber being mounted on said primary chamber, said secondary chamber being defined by the outer surface of one of said membranes of said primary chamber, another non-rigid, gas retaining membrane and a plurality of supporting elements mounted therein, each of said supporting elements of said secondary chamber being secured between the outer surface of one of said membranes of said primary chamber and the inner surface of said membrane of said secondary chamber, a pair of valves, one of said valves being located within one of said membranes of said primary chamber and the other of said valves being located within said membrane of said secondary chamber, said pair of valves regulating the flow of gas within said secondary chamber and means operatively connected to said primary chamber for providing said primary chamber with a regulated flow of gas.