NASA-Army-Bell XV-15 tiltrotor research aircraft hovered (1976) and then demonstrated conversion and forward flight (1978)
NASA
2018-02-16
<a href="//commons.wikimedia.org/wiki/File:Tiltrotor_research_aircraft_hovering_-_GPN-2002-000192.jpg" title="File:Tiltrotor research aircraft hovering - GPN-2002-000192.jpg">commons file</a>