Bell XV-15 tiltrotor landing_at_Capitol
Maisel, Martin D., Demo J. Giulianetti and Daniel C. Dugan
2000
<a rel="nofollow" class="external free" href="http://history.nasa.gov/monograph17.pdf">http://history.nasa.gov/monograph17.pdf</a> NASA SP-2000-4517, "The History of the XV-15 Tilt Rotor Research Aircraft: From Concept to Flight"