That Extra Little Lift
Willard Custer's Channel Wing looked like a mistake. Turns out his critics were the ones who were wrong.
- By Tim Wright
- Air & Space magazine, May 2007
(Page 3 of 4)
The wind tunnel model has an electronic motor that drives either two or three propellers. These can be positioned at various locations to test which placement generates the most lift. In a typical test from 2002, for example, various levels of prop thrust and blowing pressure were tested while the model was kept at a constant angle of attack. In other tests, the angle was changed while the other conditions remained constant.
The research confirmed the potential aerodynamic payoffs of the design in ways that Custer simply could not have. Says Bushnell, “You couldn’t have computed it back then.”
Custer understood that the airflow to generate lift could come either from the airplane’s forward motion or from the engine. But the former auto mechanic and salesman didn’t know—and given the technology of the time, couldn’t have known, engineers now say—that his channel wing caused the air flowing over it to separate and become turbulent. At low speeds and smaller angles of attack, the flow of air detaches from the surface it is traveling across, leading to a loss of the pressure difference that causes lift. Custer could not determine when this would happen, or how to design around it. Also, he didn’t have the digital design tools that could have shown him how to place the external struts of his aircraft without interfering with its aerodynamics.
Englar’s task is to find a way to simultaneously use the channel wing’s ability to generate a lot of lift while weeding out the problems associated with the design. To land, Custer’s airplanes had to be flown at high angles of attack, a dangerous attitude because the pilot can’t see over the nose of an airplane. Also, at a high angle of attack, the failure of one of the two engines could lead to dangerous rolls or stalls, with no way to compensate.
“We were trying to avoid all those problems” by using circulation control, Englar says. The blowing air increases the already considerable lift, eliminating the need to land at those high angles of attack. The pneumatic controls enable pilots to quickly compensate for engine failure or other dangerous asymmetries.
Like Custer, Englar fervently believes in his work despite the disappointment that his circulation control systems have not been adapted for production aircraft or for other vehicles beyond prototypes.
Englar shares some of the same frustration Custer felt when he was trying to convince the world to do something new. Use the word “curse” in relation to this grim similarity and Englar won’t object. “It takes a while for people to realize the potential,” he says. “And when they believe you, they say, ‘Well then why is it not being used in any production