Hiller X-18

Credit - U.S. Air Force Photo

Lockheed SFV-1 Salmon

Credit - Lockheed-Martin

Curtiss-Wright X-19

Credit - Curtiss-Wright Corp.

Curtiss-Wright X-100

Credit - Curtiss-Wright Corp.

Doak VZ-4 tiltrotor

Credit - U.S. Army Photo

Vertol VZ-2 VTOL aircraft

Credit - NASA

V-22 Osprey

Credit - Defense Visual Information Center

Harrier

Credit - Defense Visual Information Center

Bell XV-3

Credit - "Photographs are copyright, 1996-2000 Bell Helicopter Textron, Inc."

Bell XV-15

Credit - Courtesy of Aerofiles

Bell X-22a

Credit - Courtesy of Aerofiles

Bell Boeing V-22 Osprey

Credit - "Photographs are copyright, 1996-2000 Bell Helicopter Textron, Inc."

C-17 Globemaster

Credit - Defense Visual Information Center