The Canadair CL-84 "Dynavert", designated by the Canadian Forces as the CX-131, was a V/STOL turbine tiltwing monoplane designed and manufactured by Canadair between 1964 and 1972. Only four of these experimental aircraft were built, with three entering flight testing. Two of the CL-84s crashed due to mechanical failures, with no fatalities in either accident. Despite the CL-84 being successful in the experimental and operational trials carried out between 1972 and 1974, none of the prospective customers placed any orders for the type.
Between 1957 and 1963, Canadair carried out research in VTOL (vertical takeoff and landing) technology with the assistance of the National Research Board (NRB) and the Defense Research Board (DRB) of Canada.[1] The studies pointed the way to a unique tilt-wing design. The wing and the powerplants of the aircraft could be tilted hydro-mechanically (recirculating ball actuator) so that the wing incidence changed through 100 degrees from a normal flight angle to those for STOL and VTOL. The incidence of the tailplane (or stabilizer) was automatically altered to deal with trim changes as the wing-incidence varied. The two sets of tail rotor blades were locked in a fore and aft position in conventional flight.
The design team included Canadair's chief designer, Frederick Phillips, and Latvian aircraft designer Karlis Irbitis, among several others.[2]
At the time of the CL-84 project, Canadair was a subsidiary of General Dynamics and the parent company christened the new aircraft, the "Dynavert."[3] Canadair project personnel typically referred to it simply as the "84".[4][5]
Contra-rotating rotors on a vertical axis in the tail provided fore-and-aft (pitch) control during hovering and transitional flight. The propulsion and lifting propellers were handed (i.e. revolved in opposite directions) and were interconnected by shafts through a central gearbox from which the tail rotors and accessories were also driven. The thrust from the propellers was matched automatically except when over-ridden by the pilot for lateral (roll) control in slow or hovering flight. A mechanical "mixing" unit was used to adjust the functions of the various controls in the different modes of flight. The flap/ailerons gave yaw control when hovering. In the cockpit fore and aft stick was always pitch, side to side was always roll and the rudder pedals were always yaw, irrespective of the wing position through its full range.
Two 1,500shp (1,100kW)Lycoming T53 shaft-turbines were used to drive the two 14ft (4.3m) four-bladed propellers. The engines were interconnected by cross shafts, so that in the event of the failure of one engine, it would automatically disconnect through torque spring clutches and both propellers would be driven by the remaining engine.
There were two main reasons for the technical success of the CL-84 design. Aerodynamic considerations were given a very high priority, and the controlling of power was kept as simple and direct as possible.
The propeller disks extended slightly beyond the wingtips, so the whole of the wing (except for the portion above the fuselage) was immersed in the propeller slipstream. This, together with full-span leading edge and trailing edge flaps which were programmed with wing tilt angle, ensured that the wing was never stalled. Trim changes were minimized by programmed tilting of the tailplane. All programming was based on extensive testing in the wind tunnel and on an outdoor mobile test rig.
The power of both engines was controlled by a single "power lever" in all flight regimes. To provide crisp thrust control during hover, movement of the power lever caused a direct adjustment of blade angle, analogous to the collective pitch control of a helicopter, with the propeller CPU governor making a follow-up adjustment of blade angle to maintain the selected rpm. The direct adjustment of blade angle was faded out automatically as the blade angle increased with increasing forward speed.
The only unfamiliar control function the pilot had to deal with was the wing-tilt control, which was a switch on the power lever (and took the place of controlling the flaps). The combination of smooth aerodynamics and simple power control made it easy for fixed-wing pilots to perform transitions between hover and wing-down modes on their first flight in the CL-84.[6]
Operational history
Testing
CL-84 CF-VTO-X during testingCL-84-1 landing on USSGuam in 1973.
CF-VTO-X, the CL-84 prototype first flew in hover on 7 May 1965, flown by Canadair Chief Pilot Bill Longhurst. On 12 September 1967, after 305 relatively uneventful flights, CF-VTO-X was at 3,000ft (910m) when a bearing in the propeller control system failed. Both pilot and observer successfully ejected but the prototype was lost. Canadair redesigned its replacement, the CL-84-1 incorporating over 150 engineering changes including the addition of dual controls, upgraded avionics, an airframe stretch (5ft 3in (1.60m) longer) and more powerful engines (boosted by 100hp (75kW)).
The first newly designed CL-84-1 (CX8401) flew on 19 February 1970 with Bill Longhurst at the controls. He continued with the CL-84 program until his retirement from active flying in January 1971. Doug Atkins then assumed the role of chief test pilot.[7] At about the same time, at the height of the Vietnam War, the US Navy expressed interest in the concept. Atkins was dispatched on a cross-country tour that took a CL-84-1 to Washington DC where he landed on the White House lawn, Norfolk, Virginia, Edwards Air Force Base and eventually full trials on USSGuam. The CL-84-1 performed flawlessly, demonstrating versatility in a wide range of onboard roles, including troop deployment, radar surveillance and anti-submarine warfare. It could perform wing transition from zero airspeed and accelerate to 100 knots (190km/h) in 8 seconds.[8]
The potency of the CL-84-1 as a gun platform was dramatically illustrated in a Canadair promotional film. Fitted with a General Electric SUU 11A/A pod with a 7.62mm minigun, Adkins maintained a rock-steady position as he sprayed a ground target. The rotating six-barrel "Gatling" gun delivered 3,000 rounds per minute.[9]
Continuing Tripartite trials by Canadian, US (Navy/Marine) and RAF evaluation pilots at the US Navy's Patuxent River Experimental Test Center showed that the CL-84-1 was a suitable multi-mission aircraft. RAF Flight Lieutenant Ron Ledwidge became the first to make a descending transition from hovering to conventional flight and back to hovering while on instruments.
On 8 August 1973, the first CL-84-1 was lost when a catastrophic failure occurred in the left propeller gearbox in a maximum power climb. The US Navy and US Marine pilots aboard ejected safely. Canadair representatives investigated and recorded that the entire propeller and supporting structure of the gearbox had broken away during the climb. The second CL-84-1 (CX8402) was rushed stateside to complete the Phase 2 trials on board USSGuadalcanal. In the face of gale storm conditions, the "84" performed tasks such as ferrying troops and "blind-flight." Phase 3 and 4 trials proceeded immediately after, but, despite positive reviews from over 40 pilots, the CL-84-1 did not win any production contracts.[10]
Cancellation
The end of the Vietnam War meant a scaling back on military requirements, but Canadair designer Fred Phillips had been cognizant of other factors gravitating against the "84." The first and most crucial was the "NBH" (not built here) factor; Canada had overcome it with other sales to the US military but the de Havilland Canada Beaver, Otter and Caribou loomed as exceptions to the rule.
A prototype and three evaluation aircraft had been built. The three CL-84s that flew made a total of over 700 flights and were flown (besides Canadair test pilots) by 36 pilots from Canadian, UK and US civil and military agencies.
Phillips, F.C. "The Canadair CL-84 Experimental Aircraft - Lessons Learned". AIAA-1990-3205, AHS, and ASEE, Aircraft Design, Systems and Operations Conference, Dayton, OH, 17–19 September 1990.
Phillips, F.C. "The Canadair CL-84 Tilt-Wing V/STOL Programme". The Aeronautical Journal of the Royal Aeronautical Society, Vol. 73, No. 704, August 1969.
Phillips, Frederick C. "Lessons Learned: The Development of the Canadair CL-84 Dynavert, Experimental V/STOL Research Aircraft." CAHS Journal, Volume 30, No. 3, Fall 1992.
A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-wing aircraft and other hybrid aircraft with powered rotors such as cyclogyros/cyclocopters and gyrodynes.
A tiltrotor is an aircraft that generates lift and propulsion by way of one or more powered rotors mounted on rotating shafts or nacelles usually at the ends of a fixed wing. Almost all tiltrotors use a transverse rotor design, with a few exceptions that use other multirotor layouts.
For fixed-wing aircraft, ground effect is the reduced aerodynamic drag that an aircraft's wings generate when they are close to a fixed surface. During takeoff, ground effect can cause the aircraft to "float" while below the recommended climb speed. The pilot can then fly just above the runway while the aircraft accelerates in ground effect until a safe climb speed is reached.
A vertical and/or short take-off and landing (V/STOL) aircraft is an airplane able to take-off or land vertically or on short runways. Vertical takeoff and landing (VTOL) aircraft are a subset of V/STOL craft that do not require runways at all. Generally, a V/STOL aircraft needs to be able to hover. Helicopters are not considered under the V/STOL classification as the classification is only used for aeroplanes, aircraft that achieve lift (force) in forward flight by planing the air, thereby achieving speed and fuel efficiency that is typically greater than the capability of helicopters.
The CarterCopter is an experimental compound autogyro developed by Carter Aviation Technologies in the United States to demonstrate slowed rotor technology. On 17 June 2005, the CarterCopter became the first rotorcraft to achieve mu-1 (μ=1), an equal ratio of airspeed to rotor tip speed, but crashed on the next flight and has been inoperable since. It is being replaced by the Carter Personal Air Vehicle.
The Bell XV-15 is an American tiltrotor VTOL aircraft. It was the second successful experimental tiltrotor aircraft and the first to demonstrate the concept's high speed performance relative to conventional helicopters.
A tiltwing aircraft features a wing that is horizontal for conventional forward flight and rotates up for vertical takeoff and landing. It is similar to the tiltrotor design where only the propeller and engine rotate. Tiltwing aircraft are typically fully capable of VTOL operations.
The Bell X-22 is an American V/STOL X-plane with four tilting ducted fans. Takeoff was to selectively occur either with the propellers tilted vertically upwards, or on a short runway with the nacelles tilted forward at approximately 45°. Additionally, the X-22 was to provide more insight into the tactical application of vertical takeoff troop transporters such as the preceding Hiller X-18 and the X-22's successor, the Bell XV-15. Another program requirement was a true airspeed in level flight of at least 525 km/h.
The Hiller X-18 was an experimental cargo transport aircraft designed to be the first testbed for tiltwing and V/STOL technology.
Cartierville Airport was an airport in Saint-Laurent, Quebec, now a borough of Montreal. The airport was decommissioned in 1988 and turned into the Bois-Franc neighbourhood. It was located next to Route 117 and the terminal buildings were accessed via Boul. Henri-Bourassa, near the present Bois-Franc Train Station on the Deux Montagnes Commuter Rail Line.
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 of the rim of the disk-shaped aircraft. In the air, it would have resembled a flying saucer.
The Canadair CP-107 Argus is a maritime patrol aircraft designed and manufactured by Canadair for the Royal Canadian Air Force (RCAF). The Argus served throughout the Cold War in the RCAF's Maritime Air Command and later the Canadian Force's Maritime Air Group and Air Command.
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A convertiplane is defined by the Fédération Aéronautique Internationale as an aircraft which uses rotor power for vertical takeoff and landing (VTOL) and converts to fixed-wing lift in normal flight. In the US it is further classified as a sub-type of powered lift. In popular usage it sometimes includes any aircraft that converts in flight to change its method of obtaining lift.
The Ling-Temco-Vought (LTV) XC-142 is a tiltwing experimental aircraft designed to investigate the operational suitability of vertical/short takeoff and landing (V/STOL) transports. An XC-142A first flew conventionally on 29 September 1964, and completed its first transitional flight on 11 January 1965 by taking off vertically, changing to forward flight, and finally landing vertically. Its service sponsors pulled out of the program one by one, and it eventually ended due to a lack of interest after demonstrating its capabilities successfully.
A powered lift aircraft takes off and lands vertically under engine power but uses a fixed wing for horizontal flight. Like helicopters, these aircraft do not need a long runway to take off and land, but they have a speed and performance similar to standard fixed-wing aircraft in combat or other situations.
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The Dornier Do 29 was an experimental aircraft developed by Dornier Flugzeugwerke and the Deutsche Versuchsanstalt für Luftfahrt in the 1950s, used to test a tilting-propeller system for short takeoff and landing (STOL) aircraft. The concept was proved successful in flight testing; however, no further development of the system or aircraft was proceeded with, and at the conclusion of its test program the Do 29 was retired.
The GL-10 Greased Lightning is a hybrid diesel-electric tiltwing unmanned aircraft.
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