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DOAK 16 VZ-4DA

    The DOAK Model 16 was the first vertical take-off and landing (VTOL) aircraft to demonstrate the tilt duct concept successfully.

   It was first proposed in the early 1950s by Doak Aircraft Company of Torrance, California, and in 1956, the US Army Transportation Research and Engineering Command purchased one, and designated it the VZ-4DA.

 DOAK hovering at Ft Belvoir

Above, at Fort Belvoir, VA in 1958, the Army’s VZ-4DA hovers in flight during a press demonstration.

   The DOAK had ducted propellers on the wing tips which rotated 90 degrees.  The pilot rotated the propeller ducts to a vertical position for take-off and then returned them to horizontal position for forward flight.  To land the DOAK, the propellers were again turned vertically.  Deceleration and descent were carefully controlled to prevent the lip of the duct from stalling.

   The DOAK 16 demonstrated conventional, vertical, and short take-offs and landings.  Although the aircraft exhibited some undesirable flight characteristics, only a few were considered fundamental to the tilt-duct system, and were solvable.

   One of the most undesirable characteristics was a nose-up tendency during transition from hovering to forward flight caused by the ducts.

DOAK on tarmac in California

   The VZ-4 was the final product of Doak's many years of research in the VTOL field, and was useful in exploring the military potential of non-helicopter VTOL vehicles.

 DOAK transitioning from vertical to horizontal flight

Transitioning from vertical to forward flight.

 
DOAK undergoing tethered testing

  Above, the DOAK 16 is shown in tethered test flight.  After three years of joint testing by the Army and NASA, the sole VZ-4 was withdrawn from the Army inventory and tested further by NASA.  When NASA ceased testing, the VZ-4 was transferred to the Army Transportation Museum at Fort Eustis.

 series of photos showing DOAK transitioning from vertical to forward flight

Above, the six positions of the tilted ducts from take-off to forward flight.  Below, the DOAK is in full forward flight.

 

DOAK in forward flight

 

 

 

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