I mentioned the Avrocar before, but I didn't mention the number of variations of design.
The most commonly recognized iteration is the
VZ-9.
The general shape is that of a standard "flying saucer." Design for this craft started in 1953, as Project Y-2, under J.C.M "Jack" Frost of Avro
Aircraft, Canada, and the goal was to create a supersonic VTOL aircraft using a circular wing design.
According to Bernard Lindenbaum and William Blake, "VTOL capability was to be achieved by ducting fan air and engine exhaust to the periphery of the
planform and deflecting the air flow downwards. Close to the ground, this provides a cushion effect where the lift exceeds the thrust due to increased
pressure on the underside of the aircraft."
The Canadian government scratched the project in 1954, but the USAF contracted Avrocar in 1955 for further study. A prototype was made and at least
semi-operational by 1956 resulting in additional funding. In March 1957, additional AF funding was provided and the aircraft became "Weapons System
606A." The project remained classified until July 1960.
It was in 1958 that Avro, after getting USAF & Army sign-off, started working on the VZ-9. The VZ-9 was 18' in diameter and 3 feet thick. According
to Bernard Lindenbaum and William Blake, "At rollout, projected performance was far in excess of the requirement, with a 225 Kt maximum speed, 10,000
ft ceiling, 130 mile range with 1,000 lb payload, and hover out of ground effect with 2,428 lb payload. Maximum takeoff weight with transition to
forward flight out of ground effect was calculated to be 5,650 lb, maximum weight with a transition in ground effect (GETOL) was 6,970 lb."
The 2nd manufactured Avrocar rolled out August 1959 and its hover capabilities were tested, while tethered to the ground, September 29, 1959.
Unfortunately this revealed a problem "hubcapping" and the problem was never fully solved.
Lindenbaum and Blake elaborate, "Hubcapping was a rapid, unpredictable oscillation in pitch and roll. It resulted from an unstable ground cushion if
the vehicle exceeded a critical height ... . The critical height was found to be about two feet from the ground. Control inputs were ineffective in
damping the oscillation. Fifty two holes were drilled in the bottom of the vehicle, located radially three feet from the center. These were to provide
a central jet to stabilize the ground cushion."
The first free flight occurred November 12, 1959, but the nozzle spoiler control system proved unacceptable. After 5 flights, testing was temporarily
halted 12/5/1959, after logging 18.5 hours of test time in both tethered and free flight. Flight tests resumed 01/1960 and a USAF flight evaluation
was held 4/4/160. During this evaluation Max airspeed was 30 kts, above this an uncontrollable oscillation in the pitch was discovered. It was also
reported to be cramped, noisy, and excessively hot in the cockpit after just 15 mins of flight.
Further tests at NASA Ames wind tunnel found, "focussing ring control system provided insufficient thrust for forward flight out of ground effect,
and large angles of attack were required to generate aerodynamic lift. This was because the flow on the underside of the vehicle diminished the wing
circulation, reducing lift."
End of 4/1960 the project was canceled and shortly thereafter declassified by HQ USAF.
Following this a new design was pitched that received funding through 7/1960 to 7/1961. A wind tunnel test conducted by NASA Amex in 04/1961 found
sufficient control to transition to about 100 kts and "trimmed flight (thrust = drag, zero net moment was possible at this speed." It was hoped that
the change in flow over the aft portion of the vehicle would increase lift due to a jet flap effect and decrease the nose-up moment, reducing the
instability." The 'T' tail that was added was completely ineffective.

June 9, 1961 the final USAF evaluation of Avrocar was conducted. It reached a maximum speed of 20 kts and could traverse a 6' wide and 18" deep
ditch. "Flight above the critical height was impossible. The flight test report summarized a litany of control problems. For example, a large
asymmetry in directional control was present. Five seconds were required to turn the aircraft 90 degrees to the left, while eleven seconds were
required for a 90 degree right turn." The project was canceled and further designs were rejected.
Two aspects of the projects managed to live on despite the scrapping of Avrocar.
The Air Cushion Landing System was proven in 8/1967 and much later tested on a DeHavilland CC-115, given the designation of XC-8A, flying with ACLS in
3/1975. Also the lift fan driven by a turbo jet engine lives on as a key component of the Lockheed X-35 Joint Strike Fighter contender.
.
.
.
Preceding the VZ-9 design, in 1952, the Canadian Defense Research board funded
Project Y
(
ATS thread), a tail-sitter type VTOL design. Also sometimes referred to as "Spade"
or "Omega."
By 1953, a wooden mock-up of Project Y was completed, of which only images remain (see above). It appears the project was considered too costly within
the military establishment, which was at the time involved in several extremely expensive air defense projects. Despite several stunts (releasing
details to the press), funding was not forthcoming.
[edit on 6-6-2009 by Xtraeme]