The strange-looking Vought V-173, nicknamed Flying Pancake, was a proof-of-concept aircraft from the U.S. dating back to World War II. The plane was designed by Charles H. Zimmerman, who in his patent wrote that an object of this invention was "to provide an aircraft capable of high speed in normal flight, of ascending and descending vertically, and of hovering without substantial horizontal motion."
The V-173 was a revolutionary aircraft. It was built as an experimental fighter, and unlike a conventional plane, with an all-wing design - a flying wing, but some people prefer to call it a lifting body: the flat disk-shaped body generates the lift to keep the plane up in the air. The frame was made of wood, covered with fabric skin and it had two large, wooden propellers up front, at the wingtips.
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A restored Flying Pancake currently in the Frontiers of Flight Museum, Dallas
--- via Smithsonian National Air and Space Museum Blog |
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| --- via Warbird Information Exchange |
The Flying Pancake was built on Zimmerman's theories about extremely low aspect ratio wing design that allowed the aircraft to fly at very slow speeds.
What does this mean?
Low aspect ratio translates to good maneuverability, and is more difficult to stall. However, there is a problem with short and stubby wings: they generate more induced drag than long and narrow wings.
Induced drag? Read on...
| The aspect ratio (simplified, for a rectangular wing) is the ratio of the wing's length to its width. Usually, low aspect ratio wings are short and wide and high aspect ratio wings are long and narrow. Wing shape is important, because it determines how the aircraft performs. Generally, low aspect ratio wings give less stability to the aircraft, thus they are easier to maneuver, while high aspect ratio wings give more stability and are preferred for long range and endurance. Think of the difference between a sleek fighter jet -- lower aspect ratio, and an airliner -- higher aspect ratio. |
As the aircraft moves through the air, it has resistance to its forward motion, which is called drag. Induced drag is the resistance created by the wings. Lift is generated due to the pressure differential between the upper and lower surfaces of the wing: the pressure on top is lower than on the bottom. Near the wingtips there is still pressure differential, but there's no more wing to block the flow, so the air is free to flow around the wingtip from the higher pressure region on the bottom, to the lower pressure region at the top. Thus, a wingtip vortex is created: air spinning around and trailing behind the wingtip. A pair of counter-rotating vortices form at the tips of the two wings. Essentially, these wingtip vortices induce the drag. And now back to the Flying Pancake. It is an all-wing, so it is pretty much all wingtips, there is gonna be vortices and induced drag - plenty.
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| Pressure on the top of the wing is lower than on the bottom. Air flows from high pressure to low pressure [top left], thus at the wingtips vortices start to form [bottom left]. Air spirals about the wingtips and trails behind [right]. |
We established that the Flying Pancake is highly maneuverable, but it has high induced drag as well. Zimmerman had an innovative solution to reduce drag "by neutralizing wingtip vortices”. And indeed: the propellers outboard, near the wingtips rotate in opposite directions of the vortices, thus reducing their effects somewhat. This solution helped to maintain wing lift at the slowest speed possible.
Flipping Pancake - Pancake test flights
The V-173 had over 190 flights through a 132-hour test program in 1942 and 1943. During this time it managed to surprise a lot of people with its very unusual shape. Once, the aircraft was forced to make an emergency landing on a beach. The pilot was about to land the plane when he noticed two bathers in his way. He tried to avoid crashing into them, and the aircraft flipped over onto its back. No one got injured though, and not even the aircraft was damaged.
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| --- via Warbird Information Exchange |
Zimmerman's theories worked out in practice. The aircraft was capable of short, low-speed takeoffs and landings, otherwise reached relatively high speeds, and it was nearly impossible to stall.
The end of the Pancake project
Since the aircraft was able to take off and land in tight spaces, while still a high performance fighter, it got the U.S. Navy interested - an ideal carrier aircraft, isn't it?
Working with the Navy led to a more advanced version: the Vought XF5U Flying Flapjack. This was very similar to the V-173, but the Flapjack was an all metal construction. Unfortunately, the Flying Flapjack never actually flew. There were some technical issues to solve and no more money from the Navy; the project was scrapped in 1947. In the meantime, the jet age took off and the propeller driven Flying Pancake was forgotten.
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| --- via Warbird Information Exchange |
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| --- via Warbird Information Exchange |
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| --- via Warbird Information Exchange |
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| --- via Warbird Information Exchange |
Oh yeah, my pancakes (Hungarian style) - ready for flight and grounded:
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