Airpower Magazine, Volume 7 No. 3 May, 1977
The engineering side -- pros and cons, continued.
The Con Side: Those who take a negative view of the Custer Channel Wing do so persuasively and authoritatively. Their initial reaction is usually: "Oh no, not the channel wing again," followed by a measured explanation that there is not and never has been any emotional or economic prejudice against Custer's ideas. If, they say, the Channel Wing had shown merit, it would have been in the national interest to develop it, and it would have been so developed.
In more specific terms, the opponents of the Channel Wing say that it has less potential now than when it was first evaluated and found to be inferior to other approaches to STOL performance. The anti-Custer group concedes that the channel wing's lack of flaps results in a simpler, more economic system, and that the generation of high lift by the configuration is accompanied by a low pitching moment compared to conventional wing/flap arrangements.
The virtually viceless stall of the CCW is also acknowledged, as is the fact that ground personnel are exposed to less hazard by the propellers shielded by channels than by conventional propellers.
These are about the only advantages, however, and there are more than off-setting drawbacks, which the anti-CCW view lists as follows:
(a) Higher aerodynamic drag due to the increased wetted area resulting from the channels and, particularly, from the juncture of the channel to the fuselage.
(b) The very simplicity of the CCW arrangement prevents changing the wing aerodynamic characteristics to different modes of flight. In other words, the thicker CCW is optimized for one mode, while a wing with a well designed flap can be optimized for both slow flight, cruise and higher speeds.
(c) The requirement for cross shafting of the engines to avoid uncontrollable assymetric forces in the event of an engine failure when at a low airspeed, high angle of attack flight condition. (Custer concedes that production aircraft will be cross shafted.) This requirement of course dilutes the CCW claim for simplicity.
(d) A substantially lower power-off lift coefficient compared to a conventional wing/flap arrangement. This means a higher landing speed is required for a power-off landing. (Custer counters this with statistics on the relative infrequency of power off landings in any multi-engine aircraft.)
(e) Increased structural complexity of the wing.
(f) A lack of engineering investigation into the problems of stability and control, and the use of rather simplified engineering theory to explain the complex CCW aerodynamics. (This, as noted above, is a two-edged sword.)
So there you have it. Two points of view, both basically honest, and both vulnerable to the assertion that the CCW has not been amenable to really valid testing.
What is the answer? Perhaps the future will tell, for more testing, presumably this time with more sophisticated techniques, is in the offing. It will be interesting to see, after all these years, who is really right. pictures...
Special Thanks to Mr. Willard R. Custer, Harold R. Custer, and the helpful but anonymous engineers who contributed so much effort.