The Channel Wing Revisited

In a recent publication NASA has declared the channel wing, usually referred to as the Custer channel wing after its inventor, to be an aerodynamic flow control approach with potential for expanding the performance envelope of aeronautical vehicles. This means there have been on the order of seventy years for the concept’s advocates to show that it deserves such an endorsement, and while theory, model tests and visionary airplanes incorporating it have created great enthusiasm, the performance of airplanes actually using the approach has been uniformly and severely disappointing. The reasons are many and include unconstrained optimism over a novel application of an old theory, incorporating the channel wing into conveniently available existing airplanes without adequately analyzing if those configuration could cope with the demands of the resulting unusual flight conditions, ignoring that the semi-circular beam wing configuration incurs increased profile drag and weight penalties over a conventional wing of the same lifting planform, and overlooking that the latter common straight wing could provide almost the equivalent lift enhancement when exposed to the same slipstream induced increased dynamic pressure. This last is demonstrated by theory and scale model tests, and while the relative simplicity of this approach is attractive - and without the above penalties associated with the channel wing - it is subject to the same concerns about control under conditions of low speed and large power effects. One channel wing airplane flight tested, to be offered in the general aviation market, was found incapable of meeting certification requirements and, while having a slight advantage in takeoff and landing performance, suffered overwhelmingly in climb and high speed capability compared to already certificated, traditionally designed twin engine airplanes available in the field. One airplane company evaluating this channel wing model summarized the situation well for all: the small advantage in field length performance achieved did not offset the concept’s many deficiencies in flight and in cost.