An Unusual Sight in the Sky

By Robert Stinson

 

Dynavert 1

 

You may have seen this flying at the SEFSD field and wondered what it was.  Is it a real plane, did it really have a third motor on the tail?  The answer to both questions is yes!  The plane is the Canadair CL-84 Dynavert, developed for the Canadian Armed Forces in 1964.  Four were built, two still exist in museums.  In an age before "fly by wire" electronics, the design was truly visionary. Top speed was 321mph, certainly faster than the helicopters of its time. However, its uniqueness and the rapid pace of helicopter development kept it from being adopted operationally.

 

The model has two modes, hover and forward flight, both controlled by an onboard computer.  In hover, the two main motors provide lift and roll control while the tail motor, which rotates left and right, provides pitch and yaw control. Stability in transition to forward flight is handled by the computer. A big servo in the fuselage pivots the wing. In forward flight, the tail motor shuts down and control is by standard elevator, ailerons and rudder. The real plane did not tilt the tail motor, but achieved hover control via variable pitch propellers, and flaps and ailerons in the main propwash.

 

The Dynavert model sometimes gets mistaken for a V-22 Osprey, but the Dynavert preceded the Osprey by 40 years. One main difference is the CL-84 tilted the whole wing, while the Osprey only tilts the motor nacelles. This latter is a distinct advantage, as when the Dynavert wing is vertical it makes a great air dam! If the model is flown in a breeze, it sometimes has to tilt close to 45 degrees simply to keep stationary.

 

Dynavert 2

 

An example of the real one is on display at the Canada Aviation Museum in Ottowa.