If Bob Englar is correct, he may be well positioned to breathe new life into an airplane design long abandoned as dead. “Good aero ideas recycle,” says the engineer from his laboratory at the Georgia Institute of Technology Research Institute in Atlanta.
Englar is applying decades of his own research to an aeronautical oddity that hasn’t always been recognized as a good idea: the Custer Channel Wing. The channel wing, which takes its name from the semicircular trough each wing forms below the engine, is a 1940s design that didn’t get past a prototype. But the channels, which seem out of place, if not freakish, in an airplane’s wing, generate high levels of lift, and that opens up all sorts of design possibilities.
Englar is combining the concept with other techniques to generate the extreme lift needed to raise a C-130-size transport off a 60-foot runway, or keep a futuristic personal air vehicle hovering above a suburban driveway. NASA funded his studies from a small program investigating novel ways to make aircraft more efficient.
Building deep channels into the wings of aircraft, dropping like twin smiles under the propellers, was the idea of Maryland inventor Willard Custer. Custer’s insight was that the amount of lift generated can depend on the speed of air over the wing, not, as had been thought, solely the speed of the wing moving through the air.
“The beauty of the Custer Channel Wing is that we can generate lift at zero forward speed by using the engines to provide airflow,” says Dennis Bushnell of NASA’s Langley Research Center in Virginia, who is the primary force behind the research. “What you need is relative motion.”
In addition, the shape of the channel deflects propeller thrust downward, as much as 26 degrees. With this extra lift, an aircraft with a channel wing is quickly airborne once it begins rolling and is able to maintain control at very slow speeds. Custer envisioned airplanes that could take off or land almost vertically, making him an early prophet of short-takeoff-and-landing aircraft.
The trouble with being a prophet is that people don’t always listen. In 1943, Custer’s first aircraft, the CCW-1, demonstrated STOL ability to the U.S. Army with a flight in Maryland. Despite interest by the media and some aircraft manufacturers, the CCW-1 was ultimately deemed impractical because it couldn’t maintain control if it were to lose one engine and because it required an extreme nose-up attitude to land
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.