[1] From the X-100 Curtiss-Wright developed the larger X-200, of which the United States Air Force ordered two prototypes designated the X-19A.

Each wing mounted two 13 ft (4.0 m) propellers that could be rotated through 90 degrees, allowing the aircraft to take off and land like a helicopter.

[3] The second X-19 prototype is currently being stored in the restoration facilities at the National Museum of the United States Air Force in Dayton, Ohio.

Like most pioneering tilt aircraft, the aerodynamic complexity of coupled pitch, roll, and yaw, and torque, particularly in transition from vertical takeoff to horizontal flight, made design of the X-19 extremely challenging.

Owing to design complexity, tiltrotor VTOL aircraft did not enter operational service until the Bell-Boeing V-22 Osprey introduction in 2007.