Prototype Doak VZ-4 VTOL research aircraft

The Doak VZ-4 (or Doak Model 16) was an American prototype VTOL aircraft built in the 1950s for service in the United States Army. It was originally powered by an 840 shp Lycoming YT53 turboprop engine. It was replaced with a 1000 shp Lycoming T53-L-1 turbine. The turbine engine is mounted in the fuselage driving two ducted fan propellers.

Only one aircraft was produced. Given serial number 56-9642, it is on display at the U.S. Army Transportation Museum located at Fort Eustis, VA.