Found and Explained Official on MSN

The VTOL plane that was easier than a jet - Bell X-22

Bell and Lockheed built the X-22A around four tilting ducted fans, aiming for a compact transport that could lift off ...
DARPA has assigned the designation X-76 to the Speed and Runway Independent Technologies (SPRINT) project, a Bell proof-of-concept technology demonstrator for a high-speed tiltrotor. DARPA (Defense ...