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Avrocar (aircraft)
Encyclopedia
The Avro Canada VZ-9 Avrocar was a VTOL aircraft developed by Avro Aircraft Ltd. (Canada)
Avro Canada
Commonly known as Avro Canada, this company started in 1945 as an aircraft plant and became within thirteen years the third-largest company in Canada, one of the largest 100 companies in the world, and directly employing over 50,000...
as part of a secret U.S. military project carried out in the early years of the Cold War
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
. The Avrocar intended to exploit the Coandă effect
Coanda effect
The Coandă effect is the tendency of a fluid jet to be attracted to a nearby surface. The principle was named after Romanian aerodynamics pioneer Henri Coandă, who was the first to recognize the practical application of the phenomenon in aircraft development....
to provide lift and thrust from a single "turborotor" blowing exhaust out the rim of the disk-shaped aircraft to provide anticipated VTOL
VTOL
A vertical take-off and landing aircraft is one that can hover, take off and land vertically. This classification includes fixed-wing aircraft as well as helicopters and other aircraft with powered rotors, such as cyclogyros/cyclocopters and tiltrotors...
-like performance. In the air, it would have resembled a flying saucer
Flying saucer
A flying saucer is a type of unidentified flying object sometimes believed to be of alien origin with a disc or saucer-shaped body, usually described as silver or metallic, occasionally reported as covered with running lights or surrounded with a glowing light, hovering or moving rapidly either...
. Two prototypes were built as "proof-of-concept" test vehicles for a more advanced USAF fighter and also for a U.S. Army tactical combat aircraft requirement. In flight testing, the Avrocar proved to have unresolved thrust and stability problems that limited it to a degraded, low-performance flight envelope
Flight envelope
In aerodynamics, the flight envelope or performance envelope of an aircraft refers to the capabilities of a design in terms of airspeed and load factor or altitude. The term is somewhat loosely applied, and can also refer to other measurements such as maneuverability...
; 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 US Air Force, who referred to it as WS-606A, Project 1794 and Project Silver Bug. When the US Army joined the efforts it took on its final name "Avrocar", and the designation "VZ-9", part of the US Army's VTOL projects in the VZ series.
Design and development
The Avrocar was the ultimate result of a series of blue skies researchBlue skies research
Blue skies research is scientific research in domains where "real-world" applications are not immediately apparent...
projects by designer "Jack" Frost
John Carver Meadows Frost
John Carver Meadows Frost known as "Jack" was a British aircraft designer. His primary contributions centred on pioneering supersonic British experimental aircraft and as the chief designer who shepherded Canada's first jet fighter project, the Avro Canada CF-100, to completion...
, who had joined Avro Canada in June 1947 after working for several British firms. He had been with de Havilland
De Havilland
The de Havilland Aircraft Company was a British aviation manufacturer founded in 1920 when Airco, of which Geoffrey de Havilland had been chief designer, was sold to BSA by the owner George Holt Thomas. De Havilland then set up a company under his name in September of that year at Stag Lane...
from 1942 and had worked on the de Havilland Hornet
De Havilland Hornet
The de Havilland DH.103 Hornet was a piston engine fighter that further exploited the wooden construction techniques pioneered by de Havilland's classic Mosquito. Entering service at the end of the Second World War, the Hornet equipped postwar RAF Fighter Command day fighter units in the UK and was...
, de Havilland Vampire
De Havilland Vampire
The de Havilland DH.100 Vampire was a British jet-engine fighter commissioned by the Royal Air Force during the Second World War. Following the Gloster Meteor, it was the second jet fighter to enter service with the RAF. Although it arrived too late to see combat during the war, the Vampire served...
jet fighter and the de Havilland Swallow
De Havilland Swallow
The de Havilland DH 108 "Swallow" was a British experimental aircraft designed by John Carver Meadows Frost in October 1945. The DH 108 featured a tailless, swept wing with a single vertical stabilizer, similar to the layout of the wartime German Messerschmitt Me 163 Komet rocket-powered...
aircraft, where he had been the chief designer on the supersonic research project. At Avro Canada, he had worked on the Avro CF-100
Avro CF-100
The Avro Canada CF-100 Canuck was a Canadian jet interceptor/fighter serving during the Cold War both in NATO bases in Europe and as part of NORAD. The CF-100 was the only Canadian-designed fighter to enter mass production, serving primarily with the RCAF/CAF and in small numbers in Belgium...
before creating a research team known as the "Special Projects Group" (more commonly known as SPG). Frost first surrounded himself with a collection of like-minded "maverick" engineers, then arranged for a work site. Initially ensconced in the "Penthouse" (the derisive company nickname for the executive wing) of the Administration Building, the SPG was subsequently relocated to a Second World War
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
-era structure across from the company headquarters, the Schaeffer Building, that was secured with security guards, locked doors and special pass cards. At times, the SPG also operated out of the Experimental Hangar where it shared space with other esoteric Avro project teams.
At the time, Frost was particularly interested in jet engine design and ways to improve the efficiency of the compressor without sacrificing the simplicity of the turbine engine. He found Frank Whittle
Frank Whittle
Air Commodore Sir Frank Whittle, OM, KBE, CB, FRS, Hon FRAeS was a British Royal Air Force engineer officer. He is credited with independently inventing the turbojet engine Air Commodore Sir Frank Whittle, OM, KBE, CB, FRS, Hon FRAeS (1 June 1907 – 9 August 1996) was a British Royal Air...
's "reverse flow" design too complex and was interested in ways to "clean up" the layout. This led him to design a new type of engine layout with the flame cans lying directly outside the outer rim of the centrifugal compressor
Centrifugal compressor
Centrifugal compressors, sometimes termed radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.The idealized compressive dynamic turbo-machine achieves a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller...
, pointed outwards like the spokes on a wheel. Power for the compressor was drawn from a new type of turbine similar to a centrifugal fan
Centrifugal fan
A centrifugal fan is a mechanical device for moving air or other gases. It has a fan wheel composed of a number of fan blades, or ribs, mounted around a hub. As shown in Figure 1, the hub turns on a driveshaft that passes through the fan housing...
, as opposed to the more typical propeller-like turbine, driving the compressor using gearing rather than a shaft. The resulting engine had no conventional thrust axis, and was arranged in the form of a large disk, which he referred to as a "pancake engine." The jet thrust exited from around the entire rim of the engine, and this presented problems trying to adapt the design to a typical aircraft.
Project Y
VTOL
A vertical take-off and landing aircraft is one that can hover, take off and land vertically. This classification includes fixed-wing aircraft as well as helicopters and other aircraft with powered rotors, such as cyclogyros/cyclocopters and tiltrotors...
aircraft. It was expected that any future European war would start with a nuclear exchange that would destroy most airbases, so aircraft would need to operate from limited airbases, roads or even unprepared fields. Considerable research effort was put into various solutions to securing a second-strike capability. Some of these solutions included rocket-launched aircraft like the zero-length launch concept, while many companies started work on VTOL aircraft as a more appropriate long-term solution.
Frost felt the excellent performance of his new engine would be a natural fit for a VTOL aircraft due to its high expected power-to-weight ratio
Power-to-weight ratio
Power-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources...
. The problem was how to use the annular thrust to drive the aircraft forward, as well as the problem of fitting the very large engine into a suitable airframe. Frost suggested using a series of vents to redirect the thrust flowing out of the "front" of the engine towards the rear, although it was well known that long channeling leads to a loss of thrust. In order to keep the "piping" as short as possible, the design ported the thrust out along the leading edge of what was essentially a very large delta wing
Delta wing
The delta wing is a wing planform in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta .-Delta-shaped stabilizers:...
. As the engine was disk-shaped, the triangular shape was "pushed out" near the front, producing a planform
Planform
In aviation, a planform is the shape and layout of a fixed-wing aircraft's fuselage and wing. Of all the myriad planforms used, they can typically be grouped into those used for low-speed flight, found on general aviation aircraft, and those used for high-speed flight, found on many military...
shaped roughly like a spade
Spade
A spade is a tool designed primarily for the purpose of digging or removing earth. Early spades were made of riven wood. After the art of metalworking was discovered, spades were made with sharper tips of metal. Before the advent of metal spades manual labor was less efficient at moving earth,...
. For this reason the design was also referred to as the "Avro Ace," a likely reference to the Ace of Spades. The compressor inlet was located at the middle of the engine, so the engine air intakes were located just to the front of the centre on the top and bottom of the aircraft. The cockpit was positioned over the main bearing, behind the intakes. A "spine" on the top and bottom ran from the cockpit area to the rear edge of the aircraft. Several other versions of the basic layout were also studied, including the "Omega" which was more disk-like as it cut away the rear portions of the delta wing as well.
For VTOL operations the aircraft was expected to sit pointed up, supported by long landing legs that extended out of the spine. Landing would be accomplished at a very high angle, making visibility during the approach very difficult. A number of other VTOL experiments of the era attempted various solutions to this problem, including rotating pilots seats and cockpits, but none proved very effective. Another problem with various VTOL experiments was that stability in a hover was difficult to arrange, although not entirely unexpected. A solution to this problem would require the thrust to be directed downward from a larger area, as it is in a helicopter, where the lift is supplied over the entire area of the rotor disk. Most designers turned to bleeding off air from the engine's compressor, and directing that through pipes arranged around the aircraft. Frost's engine design used such a large number of nozzles that such an arrangement would not be to easy to build.
In 1952, the design was advanced enough that the Canadian Defense Research Board funded the effort with a $400,000 contract. By 1953, a wooden mock-up of Project Y was completed, of which only images remain. 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. On 11 February 1953, a story on the project was leaked to the Toronto Star
Toronto Star
The Toronto Star is Canada's highest-circulation newspaper, based in Toronto, Ontario, Canada. Its print edition is distributed almost entirely within the province of Ontario...
along with images of the Omega design, apparently in order to gain further funding (a strategy widely employed in the U.S. at the time, known as policy by press release
Policy by press release
Policy by press release refers to the act of attempting to influence public policy through press releases intended to alarm the public into demanding action from their elected officials. The practice is frowned upon, but remains effective and widely used...
). Five days later, the Minister for Defense Production informed the House of Commons that Avro was indeed working on a "mock-up model" of a flying saucer, capable of flying at 1500 miles per hour (2,414 km/h) and climbing vertically. Nevertheless, further funding was not forthcoming.
Project Y-2: the "flat-riser"
Coanda effect
The Coandă effect is the tendency of a fluid jet to be attracted to a nearby surface. The principle was named after Romanian aerodynamics pioneer Henri Coandă, who was the first to recognize the practical application of the phenomenon in aircraft development....
, where fluid flows will follow strongly convex shapes, something that might be unexpected at first glance. Frost felt the effect could be used with his engine design to produce a more practical VTOL aircraft, the exhaust flowing outward over the upper surface of the aircraft and then being directed downward over a flap-like arrangement. This would produce a lift force around the entire edge of the aircraft, allowing it to land "flat". He produced a number of small experimental designs using compressed air in place of an engine in order to select a suitable planform
Planform
In aviation, a planform is the shape and layout of a fixed-wing aircraft's fuselage and wing. Of all the myriad planforms used, they can typically be grouped into those used for low-speed flight, found on general aviation aircraft, and those used for high-speed flight, found on many military...
shape, and eventually decided that a disk was the best solution.
As he continued these experiments, he found that the same thrust-direction system he intended for VTOL operations worked just as well for forward flight. In this case the disk shape was not of itself a good lifting surface, as it was neutral in terms of lift direction – that is, it would fly sideways as readily as it would fly forward. However, by modifying the airflow with the application of a small amount of jet thrust, the overall airflow over the craft could be dramatically altered, creating a sort of "virtual airfoil" of any needed configuration. For instance, by directing even a small amount of jet thrust down, a large mass of air would be pulled over the upper surface of the wing and dramatically augment the flow over the wing, creating lift.
This appeared to offer a solution to one of the most vexing problems of the era, designing an aircraft that was effective at subsonic and supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
speeds. Subsonic lift is created by the airflow around the wing following streamline
Streamliner
A streamliner is a vehicle incorporating streamlining in a shape providing reduced air resistance. The term is applied to high-speed railway trainsets of the 1930s to 1950s, and to their successor "bullet trains". Less commonly, the term is applied to fully faired recumbent bicycles...
s, but supersonic lift is generated by shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
s at points of critical curvature. No single design could offer high performance for both regimes. The blown disk could attack this problem by being laid out for supersonic performance only, and then using jet thrust to modify subsonic airflow into a semblance of a normal wing. The resulting design would be tuned for high supersonic performance, have reasonable subsonic performance, and would also offer VTOL, all in a single design.
U.S. Involvement: Project 1794/WS 606A
A wide variety of designs were studied for a VTOL fighter aircraft, all revolved around the disk shape, leading to the Project 1794 involving a supersonic large disk fighter aircraft. The concept proceeded to wind tunnel testing with a variety of scale models. It featured a raised section in the middle over the engine, the intake covered with a series of louvers that would be closed in forward flight. Frost's performance estimates for the concept were for a potential of Mach 3.5 at 100000 ft (30,480 m) altitudes.
There was some debate about the concept within the USAF, as many groups were attempting to gain funding for their own pet projects, like nuclear powered bombers
Nuclear aircraft
A nuclear aircraft is an aircraft powered by nuclear energy. Research into them was pursued during the Cold War by the United States and the Soviet Union as they would presumably allow a country to keep nuclear bombers in the air for extremely long periods of time, a useful tactic for nuclear...
. In a repeat of the earlier Toronto Star release, in 1955 an extensive article appeared in Look Magazine
Look (American magazine)
Look was a bi-weekly, general-interest magazine published in Des Moines, Iowa from 1937 to 1971, with more of an emphasis on photographs than articles...
that, among other claims, speculated that current UFO sightings were Soviet-built saucers. The article went on to describe such an aircraft with diagrams that were clearly influenced by the Avro design.
A new impeller-driven engine design was proposed as Avro PV-704 (PV stood for Private Venture), powered by six Armstrong Siddeley Viper jet engines blowing across the outer rim of a central rotor. The PV-704 was a "stop-gap" design built into a bunker-like building behind the Avro Experimental Test facility. It was intended to test various Project 1794 concepts and provide the USAF with test data to show the viability of the concept. The original plan to initially test the "Viper Engine Rig" was to have continued into "free flight" testing. Unfortunately, testing was anything but smooth; the test model suffered from hazardous oil leaks, resulting in three fires. It eventually got to the point that staff were afraid of the machine, even when safely ensconced in a booth constructed of bullet-proof glass and quarter-inch-thick steel. A final, disastrous and nearly lethal engine test in 1956 which involved a Viper jet engine "running wild" convinced Frost that a less dangerous test vehicle was necessary.
Genesis of the Avrocar
To gather flight data on the basic concept while the engine development continued, in 1958 Frost proposed building a smaller "proof-of-concept" test vehicle he called the Avrocar. By this point, the US Army was involved in a wide variety of experiments on smaller VTOL aircraft that would act as a "flying Jeep," and they became interested in Avro's concept as well. Frost pitched his smaller design both as a prototype of a vehicle suitable for the Army's needs, as well as an aerodynamic testbed for the WS-606. Initial performance requirements for the Avrocar were a ten-minute hover capability in ground effect and 25 miles (40 km) range with a 1000 lb (453.6 kg) payload.
UH-1 Iroquois
The Bell UH-1 Iroquois is a military helicopter powered by a single, turboshaft engine, with a two-bladed main rotor and tail rotor. The helicopter was developed by Bell Helicopter to meet the United States Army's requirement for a medical evacuation and utility helicopter in 1952, and first flew...
would be the last helicopter the Army would buy since the helicopter would be replaced by the Avrocar.
Additional Air Force funding of approximately $700,000 (unexpended from the 606A program) was also moved to the Avrocar project. In March 1959, an additional $1.77 million contract was received for a second prototype. At rollout, projected performance was far in excess of the requirement, with a 225 knots (441 km/h) maximum speed, 10000 feet (3,048 m) ceiling, 130 miles (209 km) range with 1000 lb (453.6 kg) payload, and hover out of ground effect with 2428 lb (1,101.3 kg) payload. Maximum takeoff weight with transition to forward flight out of ground effect was calculated to be 5650 lb (2,562.8 kg), maximum weight with a transition in ground effect (GETOL) was 6970 lb (3,161.5 kg).
Just as the first working test models were being manufactured, disaster struck. The Canadian government cancelled the Avro CF-105 Arrow
CF-105 Arrow
The Avro Canada CF-105 Arrow was a delta-winged interceptor aircraft, designed and built by Avro Aircraft Limited in Malton, Ontario, Canada, as the culmination of a design study that began in 1953...
program on "Black Friday," 20 February 1959. The ensuing result was the lay-off of almost all Avro Canada employees, including those with the Special Projects Group. However, three days following the announcement of the Arrow cancellation, many of the Special Projects employees were rehired. But it wasn't quite business as usual. The team now included people from the CF-100 and CF-105 teams and the Special Projects Group was moved into the main building, which was nearly empty. As well, company "brass" became more involved in the group’s operations.
The USAF Project Office devoted to the Avro projects, recommended that the WS-606A and all related work (including the Avrocar) be cancelled. A "stop/go" work order came down and Frost was forced once more to try and rescue the project. In an elaborate effort, Frost made a resounding case for continuation of US military funding. Late in May 1959, the USAF authorized Avro to continue the "flying saucer" programs.
Design
Frisbee
A flying disc is a disc-shaped glider that is generally plastic and roughly in diameter, with a lip. The shape of the disc, an airfoil in cross-section, allows it to fly by generating lift as it moves through the air while rotating....
, the upper surface of the disk being fairly curved, and the bottom much less so. The disk was 18 feet (5.5 m) in diameter and 3.5 feet (1.1 m) thick. The main structural truss was a large equilateral triangle, to which the various components were attached. The 124-blade "turborotor" sat in the center of the triangle, with most of the rotor's thrust directed straight down through an opening in the lower surface, but some was bled off to power the control system running along the outer rim of the disk. Power for the rotor was provided by three Continental J69-T-9
Teledyne CAE J69
|-See also:-External links:*...
jet engines attached to the truss. Each engine had its own fuel and oil tanks and other support systems, although it was expected these would be interconnected in future models. The majority of the airframe was made of aluminum with an empty weight of 3000 pounds (1,360.8 kg).
Pilot control was entirely through a single side-mounted control stick. Pitch and roll were controlled through conventional fore-aft and side-to-side motions, while yaw could be controlled by twisting the stick. No mechanical linkages were used, the stick instead controlled the flow of high pressure air around the craft, which either directly attached to various control surfaces, or indirectly through local cable linkages to replace controls that were intended to be cable-actuated (like throttle controls on the engines).
The attitude/thrust control system consisted of a large ring situated outside of the main disk, shaped roughly like a rounded triangle with the flat surface on the "inside." Viewing the craft from the side, the control flap is almost invisible, appearing in its neutral position to blend into the profile. The pilot's controls moved the ring in relation to the rest of the craft, affecting the airflow moving outward from the center of the craft. Vertical lift could be increased by moving the entire ring down, which would produce more airflow over its upper surface, which would then bend down over this surface toward the ground. Tilting the ring resulted in asymmetric thrust for directional control.
It was discovered that the craft was inherently unstable in forward flight, as the aerodynamic center of pressure
Center of pressure
The center of pressure is the point on a body where the total sum of a pressure field acts, causing a force and no moment about that point. The total force vector acting at the center of pressure is the value of the integrated vectorial pressure field. The resultant force and center of pressure...
was well forward of the center of gravity
Center of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
. The Avrocar thus included a mechanical stability control system that was independent of the pilot's controls. The turborotor had a fairly large angular momentum
Angular momentum
In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...
and was intended to act as a powerful gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...
, providing a "normal" direction of flight. Control cables attached to the base of the rotor would be pulled when the craft moved in relation to the rotor, actuating the control surfaces to counteract the motion.
The vehicle was manned by a crew of two, positioned in separate cockpits squeezed into empty areas in the airframe. In practice, only one pilot was usually on board during testing; a number of flights were made with an observer in the second cockpit. Until control problems were completely solved, the Avro test pilots acquired a "touch" for the extremely sensitive control inputs and Avro Aircraft Chief Development Test Pilot Potocki was eventually able to demonstrate a "hands-off" flight. Nonetheless, Avro test pilot Peter Cope, USAF project pilot Walter J. Hodgson and NASA Ames Chief Test Pilot Fred J. Drinkwater III, who all flew the Avrocar, considered it still a tricky vehicle to fly. Drinkwater likened a flight in it to "balancing on a beach ball."
The undercarriage of the Avrocar was rudimentary with three small castoring wheels mounted on "stub" shafts; a set of skids was substituted later in testing although they were not normally fitted.
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.
Avro was convinced that the concept was still workable, and proposed a new program for major rework of the propulsion and control system. Instead of the single annular triangular flap and spoilers, or the later ring control, the new system included two separate control systems for hover and forward flight, combined into a single nozzle. For hover, a series of "transition doors" were opened into the nozzles, blocking them off and re-directing the flow downward under the aircraft. Control during this regime was provided by moving the outer portion of the flap to "focus" the flow. At higher speeds, the doors were closed, allowing the air to flow out from the edge of the aircraft, where a series of simple flap-like controls were located. The new control system covered the rear 3/4's of the aircraft's outer circumference; the front section featured the hovering controls only.
Modifications were completed on the Ames model and testing resumed in April 1961. The new design demonstrated much better control in hover and considerably improved lift. The vehicle was now able to travel at up to 100 knots (196 km/h), a great improvement over the 30 knots (59 km/h) previously reached. However, it remained unstable in pitch, and exhibited a strong nose-up trim. NASA engineers attempted to modify this with a T-tail
T-tail
thumb|right|Grob motor gliderA T-tail is an aircraft tail stabilizer configuration in which the horizontal surfaces are mounted to the top of the vertical stabilizer. Traditionally, the horizontal control surfaces are mounted to the fuselage at the base of the vertical stabilizer...
, but this proved to sit within the airflow of the turborotor and it simply didn't help the situation. Frost's team considered two new designs, one with a large vertical tail and one with a wing with tip mounted verticals —"winglets." Both designs used two 2700 lbf (12 kN) thrust General Electric J85
General Electric J85
-External links:**...
turbojets and increased the turborotor diameter from five to six ft.
On 9 June 1961, a second USAF/NASA flight evaluation of the Avrocar was conducted on the similarly modified second prototype at the Avro facility. During these tests, the vehicle reached a maximum speed of 20 knots (39 km/h) and showed the ability to traverse a ditch six feet across and 18 inches (457.2 mm) deep. Flight above the critical altitude proved dangerous if not nearly impossible due to inherent instability. The flight test report further identified a range of control problems.
Cancellation
Before modifications could be achieved, funding ran out in March 1961. Frost's proposals for a modified design were not accepted, and the Avrocar and related WS-606A supersonic VTOL programs were officially cancelled in December 1961 by the U.S. military. Avro company executives encouraged additional VTOL research projects, exploring new configurations married to a disk platform and even a "lift jet" version, but no further interest resulted from Canadian or other sources, to cap the end of this Special Projects Group program. In 1961, a number of later proposals, including the Avro P470 VTOL fighter concept derived from the Special Projects Group, were submitted to fulfill a NATO competition for a tactical strike fighter. These needs were filled by the Hawker Siddeley Harrier, but in more general terms, interest in VTOL faded as it became widely believed a nuclear first strike would not be used at the start of a European war..jpg)
Hovercraft
A hovercraft is a craft capable of traveling over surfaces while supported by a cushion of slow moving, high-pressure air which is ejected against the surface below and contained within a "skirt." Although supported by air, a hovercraft is not considered an aircraft.Hovercraft are used throughout...
, the Saunders Roe SR.N1 also taking off in 1959. Nevertheless, company designer, John Frost applied for a number of patents in Canada, the UK and the US that established the pivotal role that the Avrocar and related Avro experimental vehicles, made in the VTOL world.
Latest developments
The Avro VZ-9 Avrocar was a "dead end" in VTOL design, according to Russell Lee, curator at the National Air and Space MuseumNational Air and Space Museum
The National Air and Space Museum of the Smithsonian Institution holds the largest collection of historic aircraft and spacecraft in the world. It was established in 1976. Located in Washington, D.C., United States, it is a center for research into the history and science of aviation and...
, yet its technological innovations have intrigued other designers. One of the design elements it embodied, the use of ducted fans led to other experimental programs. Dr. Paul Moller, a Canadian expatriate who had worked at Avro Canada as a young engineer, based an initial series of experimental VTOL vehicles on "saucer" technology utilizing the buried ducted fan à la-Avrocar. The XM-2, the first of the series looked remarkably like a miniature flying saucer. After successful tether tests, the saucer designs also at one time publicized as "discojet" were abandoned and their latest project, the Moller Skycar
Moller Skycar
-Criticism:The only flight demonstrations have been hover tests performed in 2003 by a Skycar prototype that for insurance reasons was tethered to a crane...
, has a flying-car appearance.
The Avrocar story did not end with the termination of the program. Only two Avrocars were ever produced and because the U.S. military had paid for the work, they reverted to U.S. ownership at the end of the program. The second example, S/N 59-4975, utilized for "flight" testing, returned to Canada briefly for display in Montreal at the Man and His World Exhibition (1968); after a lengthy period of outdoor display, it is now under restoration at the U.S. Army Transportation Museum
U.S. Army Transportation Museum
The U.S. Army Transportation Museum is a United States Army museum of vehicles and other transportation-related equipment and memorabilia. It is located on the grounds of Fort Eustis, Virginia, in Newport News, on the Virginia Peninsula.-History:...
in Fort Eustis, Virginia.
The first Avrocar, S/N 58-7055 (marked AV-7055), after tethered testing, became the "wind tunnel" test model at NASA Ames, where it remained in storage from 1961 until 1966, when it was donated to the National Air and Space Museum
National Air and Space Museum
The National Air and Space Museum of the Smithsonian Institution holds the largest collection of historic aircraft and spacecraft in the world. It was established in 1976. Located in Washington, D.C., United States, it is a center for research into the history and science of aviation and...
, in Suitland, Maryland. There it continued gathering dust for the next forty years. The Museum finally scheduled it for restoration and display at their newly constructed Steven F. Udvar-Hazy Center
Steven F. Udvar-Hazy Center
The Steven F. Udvar-Hazy Center is the Smithsonian National Air and Space Museum 's annex at Washington Dulles International Airport in the Chantilly area of Fairfax County, Virginia, United States....
. Instead the Avrocar has been loaned to the National Museum of the United States Air Force
National Museum of the United States Air Force
The National Museum of the United States Air Force is the official museum of the United States Air Force located at Wright-Patterson Air Force Base northeast of Dayton, Ohio. The NMUSAF is the world's largest and oldest military aviation museum with more than 360 aircraft and missiles on display...
in Dayton, Ohio
Dayton, Ohio
Dayton is the 6th largest city in the U.S. state of Ohio and the county seat of Montgomery County, the fifth most populous county in the state. The population was 141,527 at the 2010 census. The Dayton Metropolitan Statistical Area had a population of 841,502 in the 2010 census...
, arriving in November, 2007. After a full restoration, which included fabrication of both missing plexiglass bubbles, it was put on display in June 2008 in the Museum's Cold War Gallery. It has since been moved to the Presidential Aircraft Gallery.
A full-scale replica of the Avrocar was prepared for the 2002 production, Avrocar: Saucer Secrets from the Past. It now resides as an exhibit at the Western Canada Aviation Museum
Western Canada Aviation Museum
The Western Canada Aviation Museum is a museum in Winnipeg, Manitoba, Canada. It is the second largest aviation museum in Canada. The collection is housed in an original Trans-Canada Air Lines hangar dating from the 1930s....
, Winnipeg
Winnipeg
Winnipeg is the capital and largest city of Manitoba, Canada, and is the primary municipality of the Winnipeg Capital Region, with more than half of Manitoba's population. It is located near the longitudinal centre of North America, at the confluence of the Red and Assiniboine Rivers .The name...
, Manitoba
Manitoba
Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...
, Canada.
Specifications (VZ-9-AV)
