The development of disc shaped aircraft — or military "flying saucers" — apparently dates back to World War II. Since much of the work has been highly classified, many details are uncertain.

A number of disc-shaped aircraft have been proposed over the years, a few being built. The best documented of these was Arthur Sack's experimental Sack AS-6, a small light plane built just before the start of World War II.

During the war some research was carried out by a number of designers on circular wings. Led by design-engineer Charles Zimmerman, Chance-Vought led a series of designs that eventually resulted in the Vought Flying Flapjack, perhaps the first aircraft explicitly designed as a disc for aerodynamic reasons. Generally wings with large chord (front to back length) compared to span (side to side length), described by a wing's aspect ratio, have very poor performance due to high induced drag. One way to avoid this problem is to taper the wingtips to a point, which is why the Supermarine Spitfire used an elliptical planform. In the Flapjack this was taken to an extreme, resulting in a plane with a huge wing and very low wing loading, allowing it to take off from aircraft carriers with ease. The Flapjack's engine's were moved to the ends of the wings to further reduce the drag induced by air currents there. By the time the design was flying in the post-war era, jet engines had rendered the design obsolete and the US Navy lost interest.

After the war, German scientist Andreas Epp claimed credit for initiating the idea of a saucer shaped aircraft during the war, a development of his work on a small circular target drone. Whether his idea or not, the concept was supposedly developed in Nazi Germany although claims of flying prototypes seem unlikely. Declassified CIA files reveal that a number of reports had been gathered from scientists in Germany of disc-like aircraft designs, but these are of dubious quality.

According to Epp, several German scientists who had worked on the project, and Epp who had not, were supposedly recruited by the Soviet Union, for whom they went on to design prototype circular craft. Supporting evidence for this claim seems to be lacking. Epp claimed to have walked out of the Soviet program in 1947, taking his knowledge to work for the USA.

In the US, a number of experimental saucer shaped craft were apparently developed as black projects by Lockheed Corporation for the USAF, and by Convair for the CIA. The saucer had the advantages of being a Vertical take-off and landing design (so avoiding the need for easily damaged runways), while the shape was well suited to diffusing radar and so making the craft stealthy. These early designs were apparently powered by turbojets, which powered a horizontal rotor to provide lift using the Coanda effect.

In an apparent attempt to quell speculation about the military nature of flying saucers, a press conference was held in July 1952, at which Major John A. Sandford denied any knowledge of the craft, and retired Major Donald E. Keyhoe declared his belief that they were of alien origin. In 1957 Keyhoe became head of the civilian UFO group NICAP (National Investigations Committee on Aerial Phenomena), which is believed to have also been infiltrated by several covert members of the CIA.

Meanwhile in Canada, the Avro Canada company was also attempting to develop saucer shaped craft, funded (initially) by the Canadian government. John Frost had initiated the design while experimenting with different ways to build more efficient jet engines, eventually settling on a large disc-shaped device with the exhaust towards the outside. He then wrapped the smallest possible airframe around the engine, piping the exhausts to the rear. For VTOL the aircraft sat on its tail for takeoff and landing, generating lift in forward flight as a large delta wing.

Frost also became interested in the Coanda effect to produce lift, eventually abandoning the original delta wing design and replacing it with a true disc. In this model the exhaust was directed downward around the entire disc by a flap ringing the aircraft, allowing it to take off and land "flat". Once in flight the flap would be angled slightly, producing a small downforce while being directed to the rear. Little lift would be generated by conventional means, the engine exhaust would instead be used to build an "artificial wing" by directing the airflow around the craft. He offered a number of increasingly dramatic performance estimates, generally claiming Mach 4 performance at 80,000 ft (24,000 m), at which point the USAF took over funding under Weapon System 606A. The result was a 29 foot (8.9 m) diameter supersonic Project Y2.

Testing soon revealed that the entire concept was unworkable; the craft would be highly unstable at supersonic speeds. Avro nevertheless continued work on the project as a subsonic design known as Project Silver Bug. Silver Bug was of interest to the US Army, who was looking for solutions for battlefield transport and support, and they took over most of the project funding. The final outcome of Silver Bug was the Avrocar or VZ-9AV, effectively (and unintentionally) a prototype hovercraft rather than an aircraft, which was made public in 1961. After Avro experienced financial difficulties in 1959, funding for future projects was apparently directed to the Bell Aircraft Corporation. Meanwhile the helicopter had proven to be the solution the Army was looking for.

During the 1980s, reports of triangular shaped UFOs revealed the existence of the F-117 Nighthawk — another black project — which became public in November 1988. See also black triangles.

The Sikorsky Cypher is a doughnut-shaped, experimental, prototype unmanned vertical takeoff and landing aerial vehicle. The Sikorsky Cypher II, (a.k.a. Sikorsky Mariner), followup aircraft has wings extending from the left and right sides of the aircraft

SOURCE: Wikipedia