With a research and development period from 1958 to 1963 before the first prototype was constructed, the design incorporated a number of innovations including a large chord wing which was to be covered by the propeller slipstream, all engines, rotors, and the tail rotor which were connected together by intricate shafts and gear boxes, and a stability augmentation system for reduction of pilot workload in low-speed flight conditions. There was considerable scale model testing in Canadian wind tunnels to ensure the design.
The CL-84 had a maximum height of 14 feet, seven inches, and a rotor tip-to-tip length of over 4.2m. The wings had a total area of 21.6sq.m with the trailing and leading edge flaps having of 4.7sq.m. The empty weight of the plane was 3380kg. In a maximum payload configuration, the plane could be loaded to 675kg for a pure VTOL mission, with 1620kg of payload available in a STOL or conventional mission.
The prototypes weighed about 3600kg, and the wings were 10m in length Mounted on the underside were a pair of Lycoming T53-LTCIK-4A turboprop engines with 4.3m-diameter propellers.
The horizontal tail was relatively low so that it was below the wing wake during cruising flight and always within the slipstream of the wing-tilt angle. The placement within the slipstream was to prevent abrupt changes in pitching moment as a function of wing-tilt angle.
Pitch control was provided by a pair of horizontally-mounted two-bladed propellers mounted on the rear of the aircraft. When in conventional flight, the props were stopped to minimize drag.
Roll control was maintained by differential thrust from the main engines while ailerons accomplished yaw control. A so-called mixing box brought all the control forces together to act as one as it linked the elevators, rudder, ailerons, and propeller blade angles together.
The first of four prototypes was built in two years, with the first vertical flight achieved in May 1965, followed by its first conventional flight seven months later.
The first total transition flight was accomplished on January 17, 1966, at the company’s Montreal facility. Transition was made from hover to forward flight and back. Flights were made in light snow with wind gusting to 25 miles per hour. The flight, with company pilot W.S.Longhurst at the controls, came seven months ahead of schedule.
The CL-84 was able to lift 2930kg of fuel and payload in a STOL take-off, or 1850kg of fuel and payload in a VTOL mode. It was found a 65km/h wind could double the VTOL payload capability.
An advantage of the CL-84 came from the pilot’s seat where it was piloted pretty much like a conventional aircraft. The pilot sat in the left seat, but dual controls were fitted. Even with its complex control mechanisms, the control stick and rudder pedals produced the desired control functions. A new flying technique wasn’t necessary. The pilot could fly the plane without knowing the wing angle.
Significant flying maneuvers were accomplished during the test program, including forward flight from hover (wing tilt 88 degrees) to 60km/h (wing tilt 48 degrees) and return to hover mode, demonstration of adequate control in winds gusting to 45km/h, rearward, sideward, and turning flight in and out of ground effect, and sustained flight with hands free of the controls.
By April 1966, the CL-84 began investigation into the high-speed regime followed undercarriage retraction tests, with speeds up to 370km/h in 60-degree banked turns being achieved. Other significant test accomplishments occurred during low-speed maneuvers. For example, the CL-84 easily completed 2G turns at only 165km/h, followed by 60m radius turns at 90km/h.
The plane also demonstrated exceptionally stable hovering flights, including hands free flight, and the CL-84 was hovered and landed vertically with the stability augmentation system not operating.
The first prototype was flown for two years by 16 pilots for a total of 145 flying hours. A number of military applications were tested, including dropping of external stores, mini-gun firing, simulated rescues from hover, use of a cargo sling, joint operations with a helicopter at seas, and hover downwash tests. A number of United States teams also evaluated the plane.
The first prototype was lost in a reliability test accident in September 1967, both pilots ejecting safely from the plane. The aircraft was flying at 980m at 280km/h in a forward velocity mode when the plane yawed to the left and quickly pitched downward. The investigation that followed identified the probable cause as a propeller failure. The plane was on its 306th test flight when the incident occurred.
The program continued with the construction of the three additional versions which incorporated a number of design changes from the original. Only two of them would actually fly. Two of the planes would be involved in non-fatal accidents due to mechanical problems.
The additional prototypes were built between February 1968 and February 1970. The testing of them would continue until 1974, over 20 years since the design work had started.
The CL-84 was demonstrated to the US Navy and the USS Guam also hosted a number of both STOL and VTOL flights from its deck. A flying demonstration took place off a hundred-square-foot pad at the Pentagon.
Neither the United States or the Canadian government showed enough interest to bring the program into production.
The second of the three prototypes produced is on permanent display at the National Aviation Museum of Canada in Ottawa. This particular plane made 196 flights with almost 170 flight hours. The plane was donated to the museum by Canadair in 1984.
Canadair CL-84
Engine: 2 x Lycoming LTC1K-4C turboshaft, 1119kW
Wingspan: 10.16m
Length: 14.41m
Height with wing in horizontal position: 4.34m
Height with a wing in 90deg position: 5.22m
Take-off weight vertical start: 5715kg
Take-off weight with a shortened run: 6577kg
Empty weight: 3827kg
Max speed: 517km/h
Cruising speed: 497km/h
Range: 547km
