The principles of regenerative soaring with a dual-role propeller and windmill, or “windprop,” are described. Emphasizing the aerodynamic design and performance of the vehicle and windprop, principles of regenerative flight are derived. Approximate models of atmospheric updraft velocity are suggested. Regenerative aircraft total energy is defined, and the rate of change thereof is studied. We find that regenerative soaring appears both feasible and attractive in relation to classical soaring. In addition, the study reveals good efficiency for both propeller and windmill modes.