Early Helicopters

The first working helicopters of the late 1930s and early 1940s, which proved that a rotor-driven aircraft could be controlled and put into production. An entry belongs here when the cited article calls the craft the first practical helicopter or an early single-rotor helicopter. It excludes later military and commercial helicopters. Entries are placed by what their own cited article says, so each one sits in the narrowest group its source supports, and the group page lists it beside the other members.