I don't think there is one. The entire notion of saucer-shaped UFOs is based on an error by a reporter. When pilot Kenneth Arnold first reported strange objects flying over Mt. Rainier back in June, 1947, he described an entirely different shape "that flew erratic, like a saucer if you skip it across the water." He said they were not round. But the United Press article implanted the notion of "flying saucers" and within days people betgan "seeing" them all over the world. Never underestimate the power of suggestion!
For a review of what really happened check this out: FLYING SAUCERS?
Au contraire: Flying Flapjack
Granted, it was WWII, and superseded by the jet age. However, the big advantage was that it only required something around 8 feet of "runway" to take off.