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 2 of 4)
In 1959, Custer tested CCW-5 for the Marine Corps, and despite the aircraft’s unique aerodynamic performances, it too was rebuffed. Part of the reason for these failures was that Custer was unable to adequately explain to the military the advantages his channel wing seemed to bestow.
But science may have caught up with the inventor. In 1995, Bushnell became the new research chief of the Langley center. Among the bundles of correspondence he inherited from his predecessor was a letter setting forth “technical quibbles” related to the testing of the Custer Channel Wing done in Langley’s 30- by 60- foot wind tunnel in 1950s. Inspired by the letter, Bushnell “went to school” on the design, and grew impressed by the potential.
Years later, while driving home from his office, Bushnell was mulling over the growing demand for ways to get aircraft in tight spaces off the ground. The accepted methods, rotary wing and direct thrust, weren’t enough. Then it hit him. If combined with “circulation control,” a method of generating lift by using jets of air to improve the aerodynamic efficiency of wings the forgotten design could provide another option. “The channel wing couldn’t do it, circulation control couldn’t do it, but maybe they’d be able to do it together,” Bushnell says.
Bushnell directed some money from his discretionary funds, reserved for high-risk, high-payoff projects, and “got back into it” with a program that lasted from 1999 to 2004. The grant money funded Englar’s laboratory work at Georgia Tech. Since then, Bushnell and Englar have co-patented their marriage of circulation control and the channel wing, and Englar continues his work under the auspices of Georgia Tech.
Circulation control is based on the Coanda Effect, named for Romanian aviation researcher Henri Coanda, who in 1910 found that hot gas exiting a jet followed the contour of plates he had installed to deflect the exhaust. Coanda had inadvertently discovered the tendency of a pressurized gas to adhere to an adjacent curved surface. That tendency can be used to increase the lift created by an airplane wing if the exhaust is deflected downward by the wing’s trailing edge.
Circulation control technology works by blowing compressed air—rather than Coanda’s exhaust—over curved trailing or leading edges to achieve very high lift, where and when needed. Researchers believe that circulation control can one day make moving surfaces on aircraft obsolete. By replacing flaps and other mechanical lift maximizers with pneumatic air hoses, engineers can make airplanes lighter, quieter, and easier to maintain.
To find the ideal way to combine circulation control with Custer’s design, Englar used the modern methods of computational fluid dynamics, including data from wind tunnel tests of sensor-studded models. One early goal was to prove that a channel wing with enhanced circulation control could turn a generic twin-engine transport into a super-STOL