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A combination of analysis and testing has been utilized to develop a theory of jet-flap thrust recovery at the low speeds and high deflection angles characteristic of V/STOL lift systems. The contribution of jet mixing to the loss of thrust recovery has been computed with a viscid/inviscid interaction analysis. The results of this computation are compared to surface pressure and wake survey measurements made with a two-dimensional jet-flapped airfoil model. It is concluded that the jet-mixing drag causes a small loss of recovery at small values of the jet-thrust coefficient and deflect, an angle. However, at larger values of either jet parameter, the mainstream separates from the airfoil, producing a large loss of recovery. The loss increases suddenly, since it is due to bursting of the leading-edge separation bubble.