page_title: Avro Canada VZ-9 Avrocar
section_title: Testing
hierarchical_section_title: Avro Canada VZ-9 Avrocar / Operational history / Testing
caption_attribution_description: Avrocar flying
context_page_description: The Avro Canada VZ-9 Avrocar was a VTOL aircraft developed by Avro Canada as part of a secret U.S. military project carried out in the early years of the Cold War. The Avrocar intended to exploit the Coandă effect to provide lift and thrust from a single "turborotor" blowing exhaust out the rim of the disk-shaped aircraft. In the air, it would have resembled a flying saucer.
  Originally designed as a fighter-like aircraft capable of very high speeds and altitudes, the project was repeatedly scaled back over time and the U.S. Air Force eventually abandoned it. Development was then taken up by the U.S. Army for a tactical combat aircraft requirement, a sort of high-performance helicopter. In flight testing, the Avrocar proved to have unresolved thrust and stability problems that limited it to a degraded, low-performance flight envelope; subsequently, the project was cancelled in September 1961.
  Through the history of the program, the project was referred to by a number of different names. Avro referred to the efforts as Project Y, with individual vehicles known as Spade and Omega. Project Y-2 was later funded by the U.S.
context_section_description: The first Avrocar, #58-7055, rolled out of the Avro Malton factory in May 1959. From 9 June to 7 October 1959, it was tested in a static hover rig. Unfortunately, hot gas from the exhaust was found to mix back into the intakes in hover, reducing engine thrust. In addition, the fan generated lift only from a small area of its surface, lowering overall thrust available. The ducts also proved to have higher losses than expected, and a series of modifications were not able to solve this problem to any large degree. These problems reduced maximum lift at higher altitudes out of the ground effect to 3,150 lb (1,430 kg), less than the empty weight of the aircraft at 4,285 lb (1,944 kg). This meant the aircraft would be incapable of hovering out of the ground effect. Following these tests, the vehicle was sent to NASA Ames for a wind tunnel testing.
  The second, #59-4975, was completed August 1959. On 29 September, the first attempt to hover was made with the Avrocar tethered to the ground. After the vehicle became airborne, an uncontrollable roll and pitch-coupled oscillation started that forced each of the three wheels into the ground in turn. The pilot, W. D. "Spud" Potocki, immediately shut down all engines. Changes were made to the stability system to provide more control authority, while new tethers were investigated to improve the ability to control these sorts of problems. As testing continued it became clear that the problem was inherent to the design, and the engineers started referring to the effect as "hubcapping," so-named as it appeared similar to a hubcap spun on the ground.
  Investigations into the effect revealed what was causing the problem. While in the ground effect, the high-pressure air under the craft was trapped, filling the entire area and thus providing a stable base. When the craft rose out of the ground effect, the air formed itself into a single narrow column, described by Frost as "tree trunking". At intermediate altitudes the craft would momentarily transition from one regime to the other, during which time one side of the vehicle would be entirely supported while the support was disappearing under the other. This led to a strong pitching motion towards the unsupported side. As soon as this occurred that side would approach the ground and re-establish the supporting air, while the other side would then be raised above this limit. This process would repeat itself, with the craft rolling from side to side. Modifications were carried out in order to try to solve the problem. Eventually a series of 52 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.
  With these modifications complete and apparently working, the first completely free flight occurred on 12 November 1959. This test proved the nozzle control system unacceptable. The spoilers were intended to direct the air out over the top or bottom of the annular flap, out the bottom only during hover, but over the top and bottom during forward flight. The idea was that when the flap was positioned in order to provide control, the lift would be lowered on one side and raised on the other. Lift was indeed lowered on one side, but sadly the lift did not improve on the other, so every control input resulted in a loss of altitude. After five flights, testing was temporarily halted on 5 December 1959, by which time the Avrocar had logged 18.5 hours of test time in total.
  A completely new design was installed over the winter. The original spoilers were removed and replaced by a single ring below the annular flap. The ring shifted in relation to the craft under control input, "sealing off" the gap on one side while opening it on the other. Tests continued in January 1960, and appeared to work much better. However, while the new control system improved the hovering qualities, the craft now became unstable at higher speeds above 30 knots (56 km/h). The first Avrocar at Ames was similarly modified, and, in April 1960, it was tested in their 40 ft × 80 ft (
caption: Avrocar 59-4975 after modifications, was tested without the canopies and incorporating the perimeter "focusing" ring c. 1961. Tests showed that the heat was so oppressive that all instruments were baked brown after only a few flights.
exif: {}