Oldies and Oddities: Blown Away
- By Ken Scott
- Air & Space magazine, November 2009
When jet engines came into widespread use, in the 1950s, engineers pondered the high-energy exhaust they produced. If it could be ducted and blown over the wing, the increased airflow would increase lift. With more lift, wings could be smaller, which enabled higher speeds, and with a blown wing there would be enough lift to support the slow speeds military aircraft needed to land on unimproved runways and aircraft carriers.
Employed since 1956 by the Ball Corporation, manufacturer of glass canning jars, Otto E. “Pete” Bartoe was named company president in 1969. A gifted engineer with a practical bent, he convinced Ball to finance a spinoff company to explore his ideas about a blown wing. In 1973, the Ball-Bartoe Aircraft Corporation was formed in Boulder, Colorado. Over the next four years, Bartoe produced more than 200 engineering drawings, which Brad Davenport (“a master mechanic and an amazingly productive worker,” says Bartoe) and Sig Williams turned into the experimental Ball-Bartoe Jetwing.
A Pratt & Whitney JT15D-1 turbofan was mounted in the nose, well ahead of the cockpit and wing. The hot airstream exited the engine core, entered a bifurcated duct, and exhausted just outside the fuselage through slots in the top skins of both wings. Air from the fan was directed aft by vanes in the duct and ducted farther out through slots on the leading edges. About 70 percent of the wingspan was bathed in the exhaust stream.
Mounted inches above the main wing was an “augmentor,” a small wing; exhaust gases passed through a slot between the two. A phenomenon Bartoe calls “supercirculation” caused the lower pressure in the slot to draw in more air and increase lift. At the trailing edge, large flaps rotated and extended up to 52 degrees. They remained in contact with the top skin and made use of the Coanda effect, in which airflow bends to follow a curved surface. With the flaps down, the “bend” in the airstream provided downward thrust and enabled the Jetwing to fly as slow as 40 mph.
The Jetwing first flew in 1977, at Mojave, California, with Lockheed test pilot Harold “Fish” Salmon at the controls. The blown-wing configuration generated more than twice the lift of a conventional wing of the same area. The Jetwing flew slowly enough that Bartoe could use his Super Cub as a chase plane.
After Salmon completed the initial testing, Bartoe flew the Jetwing back to Boulder. The 106-gallon fuel tank allowed only 40-minute flights, so the trip required 11 refueling stops. Because many of the airports Bartoe used carried only gasoline, a pickup truck carrying jet fuel followed him.
“It was fun to fly,” Bartoe recalls. “It was extremely quiet. As long as the engine was running, you couldn’t stall it. Landings were interesting: The jet blast came off the deployed flap, bounced off the ground, and forced the tail up. If you reduced power, the tail would come down suddenly, just as the wing was losing lift. But everything happened at such a slow forward speed that it was manageable.”
In a Navy program, the Jetwing landed in a mere 300 feet—this from an airplane that could reach 350 mph.
The Jetwing was the only aircraft that used the blown wing for propulsion as well as lift, but in the 1950s and ’60s many designers experimented with blown flaps. Currently displayed at the Wings Over the Rockies Air and Space Museum in Denver, Colorado, the Jetwing remains the world’s only blown-wing tailwheel jet aircraft.