Doak 16 VZ-4DA

Doak 16 VZ-4DA. . , The Doak Model 16 was the first Vertical Take Off and Landing (VTOL) aircraft to demonstrate the 'tilt duct' concept. The concept was proposed to the military in the early 1950s by Doak Aircraft Company. It would meet the Army's desire for a utility and observation vehicle with the VTOL capabilities of a helicopter, with the maneuverability of a higher speed fixed-wing aircraft. In 1956, the Transportation Research and Engineering Command purchased one Doak 16 and designated it VZ-4DA. The Doak made its first flight in February 1958.

The research aircraft had ducted propellers on each wing tip which rotated 90 degrees to shift from vertical take-off and hovering to horizontal flight. The Doak 16 demonstrated conventional and vertical flight in addition to 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 those were easily solvable.

The VZ-4 was the end product of Doak's many years of research and development in the VTOL field, and the aircraft proved reasonably useful in exploring the military potential of non-helicopter VTOL vehicles. After three years of joint testing by the Army and NASA, the sole VZ-4, Number 56-9642, was withdrawn from Army inventory. It was subsequently used solely by NASA before being turned over to the Transportation Museum in 1973.