Oldies and Oddities: Blown Away
- By Ken Scott
- Air & Space magazine, November 2009
Tufts on the Jetwing fuselage and vertical stabilizer would reveal airflow patterns. NASM (SI-2007-1636~A)
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.
Related topics: Aerodynamics Jet Engines Jet Aircraft Aerospace Scientists and Engineers
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Comments (2)
A great friend of mine, Everett Simmons and I were flying around to different airfields back in the early 90's (back when you could walk around hangers and see what was stowed away), and down at Tullahoma Tn we found this plane pushed up in a corner. Words cannot describe how small the cockpit was and the sheet metal work was ART. The fact that it was a taildragger jet was strange enough, but to walk up to a "exhaust over the wing with no exhaust in the tail" where you would normally see vintage taildraggers was strange. I took pictures of it, drew it a few times for people, was even accused of finding a movie set jet incapable of flying, tried to find information and now thanks to the internet - BINGO, the Ball Bartoe jetwing! Thanks A&S Smithsonian - another of my aircraft mysteries solved! Next: Where is it now? is there any more history that didn't make it to print. email back if you have interesting news-Thanks again!
Jack Woerner Jr.
Murfreesboro, TN
Posted by Jack Woerner Jr. on May 30,2010 | 05:32 PM
This was one of my first projects after starting with Ball Aerospace so many years ago. I met Bob Hoover when he came to vist the project. My job was electrical but being with such talent inspired me to get my pilots license. I would listen to the hangar stories never realizing I was with so much history. Always had great memories of that program.
Posted by Warren A Cash on January 21,2011 | 05:03 PM