Convertawings A Quadrotor

Lore & Background

The Model A Quadrotor was developed by Convertawings as a prototype and technology demonstrator for civilian and military quadrotors. The design is based on early quadrotor experiments by Étienne Œhmichen and George de Bothezat.

It features four rotors aligned in an "H" configuration, mounted in tandem pairs on each side on four outriggers. The four rotors are powered by two Continental C-90 reciprocating engines, with power transmitted using belts, shafts and an interconnected transition system. In case of an engine failure, a single engine is capable of powering the entire aircraft.

The rotors consisted of three 17 cm wide blades with a NACA 0015 airfoil, rotating at 549 rpm with a tip velocity of 170 m/s. The rotor surface area overlaps by around 20%. Control in pitch and roll was achieved through differential collective pitch between the rotors, eliminating the need for complex cyclic pitch control systems. Directional control (yaw) was obtained by varying rotor thrust and, in some designs, by slightly tilting the rotor axes.

The first and only prototype was completed in 1955, and the first test flight took place during March 1956. Tests were conducted on Long Island, New York by designer and test pilot David H. Kaplan. The aircraft flew successfully multiple times during 1956, proving that forward flight was possible with a four-rotor configuration for the first time. The program was cancelled shortly after its first few flights due to a lack of commercial interest and cutbacks in military spending.

Reader's Guide

The Convertawings A Quadrotor demonstrated that forward flight was achievable with a four-rotor configuration, a milestone for VTOL aircraft. It also proved that differential thrust control was practical and effective for stable quadrotor flight. These tests influenced later multi-rotor and VTOL aircraft designs.

The aircraft served successfully as a technology demonstrator, showing that quadrotor aircraft could achieve stable and effective flight using relatively simple mechanical systems. The program was cancelled shortly after its first few flights due to a lack of commercial interest and cutbacks in military spending during the time. The only known still existing model is displayed at the Classic Rotors Museum in Ramona, California.