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. Operational history Testing 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 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 ( longer) and more powerful engines (boosted by ). 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