CX-131 / CL-84 Dynavert - Program
In August 1963, Canadair was awarded a $ 12 million contract with the Ministry of Defense for the construction of the CL-84 experimental aircraft, which was developed in 1957. Only four of these experimental aircraft were built with three entering flight testing. Two of the CL-84s crashed due to mechanical failures, but no loss of life occurred as a result of these accidents. First flight was on May 7th, 1965.
By April 1966, the CL-84 had completed 70 test flights consisting of hover, conventional flight, STOL, and transition flights. 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, some with pilot hands and feet free of the controls. The CL-84 was, in fact, hovered and even landed vertically with the stability augmentation system not operating.
The National Aeronautics and Space Administration had been actively engaged in tiltwing V/STOL research since around 1950. Both wind-tunnel and flight studies had been made. NASA conducted an abbreviated flight-test evaluation of the second-generation tilt-wing V/STOL aircraft, the Canadair CL-84, to ascertain possible problem areas in the flight characteristics. The evaluation was concerned primarily with the flying qualities in the hover and transition modes of flight with less attention being given to the cruise mode.
The NASA flights were conducted at the manufacturer's facility during October 1966 by two NASA Langley Research Center pilots, who had previous experience in the operation of tilt-wing V/STOL aircraft, performed the flights at the manufacturer's facility. In addition to quantitative data, pilot opinions of the aircraft characteristics, expressed in terms of Cooper ratings, were obtained. A total of seven flights were made by the two NASA pilots.
The accelerating-conversion characteristics of the CL-84 were considered to be outstandingly good. Trim changes were considered minor and satisfactory, and the fuselage attitude could be maintained nearly level until the wing incidence was reduced to 15°. During the last 15° of wing movement, the fuselage attitude had to be increased about l0°, but trim changes were such that the aircraft attitude seemed to increase largely by itself. After take-off on the second full conversion, the pilot determined that it was reasonable to take off vertically to about 20 feet (6.1 m) and, leaving power fixed, hold the wing-tilt switch forward until a wing incidence of 15° was reached. Because of limited hydraulicsystem capacity, the conversion process had to pause temporarily at a 15° wing incidence so that the landing gear could be retracted. The wing incidence was then reduced to zero, at which time the tail rotor was stopped and alined with the fuselage axis for stowage. Acceleration to cruise or high-speed airplane flight was then continued.
Deceleration from cruise to about 125 knots was performed by slowly reducing power to flight idle. The initial deceleration of about 0.25g at 85 percent propeller speed seemed satisfactory although a higher value of deceleration would be desirable. At 125 knots and level-flight power, the tail rotor was activated with negligible trim changes. The wing was then unlocked and raised to an incidence of 15° with continuous wing-tilt switch actuation while power and controls were held fixed.
In general, based on the limited evaluation performed, most of the flying qualities in the hover, transition, and cruise modes of flight were considered good. However, at one conversion angle at least, in transition flight, low normal-velocity damping was experienced at moderate rates of descent which could make glide-path control difficult during instrument flight without augmentation.
The low damping was evidenced by an excessive length of time for rate of descent to stabilize after a power reduction. Data presented illustrate this characteristic at an indicated airspeed of about 40 knots and at power settings for indicated rates of descent in excess of about 300 ft/min (1.52 m/sec). Buffeting was not necessarily evident to the pilot until reaching an indicated rate of'descent of 700 ft/min (3.56 m/sec) or more. Examination of wind-tunnel data obtained from a model of similar configuration indicates that these characteristics may be related to operation near maximum lift where induced drag is increasing rapidly, and a nearly constant resultant force occurs as angle of attack increased.
Other tilt-wing aircraft have had higher than desirable noise and vibration levels. The noise level produced by the tilt-wing CL-84 in a hovering take-off and in hovering flight was judged by the NASA pilots to be acceptable from outside the aircraft and was comparable to the noise level produced by a C-47 airplane during take-off. In transition flight and in cruise flight, the noise levels were considered to be at satisfactorily low levels. The vibration levels in all modes of flight were also considered to be satisfactorily low.
The STOL take-off was very easy and the take-off distance was short. During STOL landings, the aircraft could be easily held in the level attitude through touchdown. But it was the pilot's impression that the available descent limits were not adequate for an operational aircraft, particularly for steep gradient instrument flight.
However, an indicated rate-of-descent limit of 700 ft/min (3.56 m/sec), defined by loss of control due to stalling, at a typical STOL airspeed of 42 knots, did not appear to provide enough margin for ultimate operational use. This characteristic appeared as a prolonged increase in rate of descent following a small power reduction, and was thought to be significant for instrument flight. This characteristic occurred with power settings for initial indicated rates of descent as low as 300 ft/min (1.52 m/sec). Buffeting was not always apparent to the pilot as excessive sink rates developed and, in several descents at altitude, the first indications of approach to limiting stalling were pitch-down and roll-off.
During the flight tests on September 12, 1967, the experimental takeoff and landing plane CL-84 crashed, the crew ejected. The plane lost control during a maneuver in horizontal flight at a speed of 275 km / h at an altitude of 900 m. Before the accident, the aircraft made 305 flights and flew 405 h.
In 1967, the Government of Canada issued an order worth $ 13 million to build three experimental Canadair CL-84 for evaluation tests in the Canadian army. The first of the three CL-84-1 aircraft under construction was transferred to the Canadian Army on March 31, 1969. This aircraft was developed in accordance with the Canadian Army's program for determining the effectiveness of combat employment of a rotary wing aircraft and was not intended for batch production. It was assumed that the evaluation trials would be completed in 1970 and cover a wide range of operating conditions from use from ground bases to operations from destroyers and aircraft carriers.
Starting in Canada, testing moved in December 1972 to the U.S. Navy Test Center at Patuxent River, Maryland, where the aircraft remained for most of the next eighteen months. Test exercises included the first convertiplane transition from conventional to hovering flight under blind flying conditions, which took place on April 5, 1973. Most significant was a flying demonstration that took place off a hundred-square-foot pad at the Pentagon. Trials were also carried out from helicopter carriers USS Guam and USS Guadalcanal. The USS "Guam" hosted a number of both CL-84 STOL and VTOL flights from its deck. In all, 196 test flights were completed, totalling over 169 flying hours.
The second prototype CL-84-1 crashed in July 1973 during tests under the program providing for operation from the ships of control of the seas at the aviation center of the US Navy. The accident occurred on a mode of horizontal flight, the crew of two people catapulted. As a result of the accidents of the three CL-84 aircraft built, only one remained, which was used for VTOL tests in instrument flight.
Without a market for the aircraft, the program was abandoned in 1974.
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