reactionmotors

The correct Air Force serial number for this Republic XF-91 is 46-680.

Little known that the XF-91 was the first American combat aircraft (albeit a prototype that wasn't mass produced) to go supersonic in level flight (Dec. '51), and with both its jet (J47) and rockets (XLR11) working, it reached 1126 mph (Mach 1.71). Survives today in the R&D Section of the NMUSAF in Dayton, OH. It's sister-ship 681 (with a "V" tail) burned to the ground @ Edwards. www.flickr.com/photos/sdasmarchives/16148468640/in/set-72...

This appears to be a Reaction Motors XLR-11 rocket motor. See: en.wikipedia.org/wiki/Reaction_Motors_XLR11

The Bell X-1, designated originally as XS-1, was a joint National Advisory Committee for Aeronautics-U.S. Army Air Forces-U.S. Air Force supersonic research project built by the Bell Aircraft Company. Conceived during 1944 and designed and built during 1945, it achieved a speed of nearly 1,000 miles per hour (1,600 km/h; 870 kn) during 1948. A derivative of this same design, the Bell X-1A, having greater fuel capacity and hence longer rocket burning time, exceeded 1,600 miles per hour (2,600 km/h; 1,400 kn) during 1954. The X-1 was the first manned airplane to exceed the speed of sound in level flight and was the first of the so-called X-planes, a series of American experimental rocket planes designated for testing of new technologies and often kept secret