Avro Canada VZ-9 Avrocar

Abbreviated Development Plan, (U) AVRO Vertical Take-Off Aircraft, Weapon System 606A

[Vous devez être inscrit et connecté pour voir cette image]

Design

The Avrocar was a disk-shaped aircraft with the same basic shape as a [Vous devez être inscrit et connecté pour voir ce lien], 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 [Vous devez être inscrit et connecté pour voir ce lien] 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 3,000 pounds (1,400 kg).
^{[Vous devez être inscrit et connecté pour voir ce lien]}
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.
^{[Vous devez être inscrit et connecté pour voir ce lien]}
It was discovered that the craft was inherently unstable in forward flight, as the aerodynamic [Vous devez être inscrit et connecté pour voir ce lien] was well forward of the [Vous devez être inscrit et connecté pour voir ce lien].

The Avrocar thus included a mechanical [Vous devez être inscrit et connecté pour voir ce lien] that was independent of the pilot's controls.

The turborotor had a fairly large [Vous devez être inscrit et connecté pour voir ce lien] and was intended to act as a powerful [Vous devez être inscrit et connecté pour voir ce lien], 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.

Operational history

Testing

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 [Vous devez être inscrit et connecté pour voir ce lien] 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.

^{[Vous devez être inscrit et connecté pour voir ce lien]}
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.
^{[Vous devez être inscrit et connecté pour voir ce lien]}
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 x 80 ft (24 m) wind tunnel.

The problem became clear; the ring blocked so much of the overall engine thrust that the overall power was greatly reduced.

As the craft sped up, the airflow on the underside reduced the recirculation, reducing the lift due to airflow over the upper surface.

This was somewhat unexpected; recirculation had been considered a "bad thing" due to the loss of engine thrust, and its positive effects on lift do not appear to have been appreciated.

In the end, in order to maintain lift at higher forward speeds the craft had to be pitched to the end of its control capability.

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 (190 km/h), a great improvement over the 30 knots (56 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 [Vous devez être inscrit et connecté pour voir ce lien], 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 2,700 lbf (12 kN) thrust [Vous devez être inscrit et connecté pour voir ce lien] turbojets and increased the turborotor diameter from five to six ft.
^{[Vous devez être inscrit et connecté pour voir ce lien]}
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 (37 km/h) and showed the ability to traverse a ditch six feet across and 18 inches (460 mm) deep.

Flight above the critical altitude proved dangerous if not nearly impossible due to inherent instability.

^{[Vous devez être inscrit et connecté pour voir ce lien]} The flight test report further identified a range of control problems.[Vous devez être inscrit et connecté pour voir ce lien]

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 [Vous devez être inscrit et connecté pour voir ce lien], 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.

The second Avrocar had logged about 75 flight hours at the end of the flight testing.

Judged by its performance, the Avrocar was an abject failure: it couldn't lift itself safely more than a few feet off the
ground, and its bulbous design limiting high-speed performance accompanied by unbearable heat and screaming exhaust noise, made it impractical for the military.

Although considered a technical failure, its design would be prophetic: it was a rubber skirt shy of being one of the world's first [Vous devez être inscrit et connecté pour voir ce lien], the [Vous devez être inscrit et connecté pour voir ce lien] 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.[Vous devez être inscrit et connecté pour voir ce lien]

Latest developments


The Avro VZ-9 Avrocar was a "dead end" in VTOL design, according to Russell Lee, curator at the [Vous devez être inscrit et connecté pour voir ce lien], 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 [Vous devez être inscrit et connecté pour voir ce lien], 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 [Vous devez être inscrit et connecté pour voir ce lien] 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 [Vous devez être inscrit et connecté pour voir ce lien], in [Vous devez être inscrit et connecté pour voir ce lien].

There it continued gathering dust for the next forty years. The Museum finally scheduled it for restoration and display at their newly constructed [Vous devez être inscrit et connecté pour voir ce lien].

Instead the Avrocar has been loaned to the [Vous devez être inscrit et connecté pour voir ce lien] in [Vous devez être inscrit et connecté pour voir ce lien], 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.