Pitcairn XO-61

The Pitcairn XO-61 was an American autogyro designed by Pitcairn Aircraft. One of the last autogyros produced, in competition with the Kellett YO-60 and the Sikorsky R-4, it fell victim to cooling problems with its rear-mounted engine and the coming of the helicopter with its ability to hover.Gregg, E. Stuart, [http://www.airspacemag.com/history-of-flight/Jump_Ship.html "Above & Beyond: Jump Ship"] {{Webarchive|url=https://web.archive.org/web/20131017213817/http://www.airspacemag.com/history-of-flight/Jump_Ship.html |date=2013-10-17 }}. Air & Space Smithsonian, March 2001Harris, Franklin D. [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080022367_2008020986.pdf An Overview of Autogyros and The McDonnell XV-1 Convertiplane], NASA/CR—2003–212799. NASA Ames Research Center, October 2003

Also known by the company model number PA-44 and the contract designation MX-157,Cully, George & Andreas Parsch: [https://www.designation-systems.net/usmilav/mx/1-499.html MX-1 to MX-499 Listing], designation-systems.net the contract for the XO-61 was taken over by G&A Aircraft upon G&A's acquisition of Pitcairn Aircraft.[http://dvhaa.org/newsletters/dvhaa-newsletter-07-08-winter.pdf Wings of Freedom Winter 2007/2008] {{Webarchive|url=https://web.archive.org/web/20080509121847/http://www.dvhaa.org/newsletters/dvhaa-newsletter-07-08-winter.pdf |date=2008-05-09 }}, Volume 22 Number 4, Delaware Valley Historical Aircraft Association.