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Export restricted (ITAR), sale only to US Citizens and Organizations. Complete Reaction Motors XLR11-RM-13 rocket engine (Serial No. 52), manufactured circa 1958–1959, the very type used as the interim power plant for the initial flights of the legendary X-15 research aircraft, which served as a critical transitional propulsion system during the early phase of the program while the far more powerful XLR99 engine was still under development.
Manufactured by Reaction Motors Inc. of Rockaway, New Jersey, under U.S. Air Force contract (Order No. W33-038-AC), the engine is designated XLR11-RM-13 (Contractor Part No. A1955) and retains its original identification as Serial No. 52. The complete assembly measures approximately 24˝ wide x 56.5˝ long and weighs roughly 345 pounds. Its configuration consists of four individual thrust chambers—each approximately 21.75˝ in length and 6˝ in diameter—along with the associated propellant valves, turbopump plumbing, and related hardware, all present and intact. Housed in its original U.S. Air Force military shipping and storage container, which bears affixed "Reaction Motors Inc. / U.S. Property" data plates, and is stenciled, “XLR-11-RM-13 ROCKET ENGINE / SERIAL NUMBER 52.” The engine and container are in impressive original condition commensurate with their age and history as working aerospace hardware. The exterior of the shipping container retains its original dark paint finish with clearly legible stenciling; some surface oxidation, paint loss, and wear consistent with storage and service life are present.
The XLR-11 was originally developed by Reaction Motors in the mid-1940s as the rocket power plant for the Bell X-1 research aircraft. Burning a mixture of liquid oxygen and a water-diluted ethyl alcohol fuel (with later experimental demonstrations using ammonia), the engine employed four independently ignitable combustion chambers, allowing pilots to control thrust by firing the chambers individually or in combination. On October 14, 1947, an engine of this same family propelled Capt. Chuck Yeager through Mach 1 aboard the Bell X-1, marking the first controlled supersonic flight and inaugurating a new era in aviation.
The XLR-11 subsequently powered the entire X-1 series through its supersonic research program and was also used in the Douglas D-558-II Skyrocket. In the specific XLR11-RM-13 configuration represented here, the engine served as the interim propulsion system for the earliest powered flights of the North American X-15 in 1959, enabling engineers and pilots to begin flight testing while the far more powerful XLR99 engine was still in development. These early flights proved the X-15’s aerodynamics and control systems and helped pave the way for the aircraft’s later record-setting performance as the most advanced rocket-powered research aircraft ever flown.
This engine originates from the collection of William ‘Bill’ Bernard Arnold (b. 1928), who spent 45 years at the center of the nation’s rocket-powered aircraft programs as a Field Service Engineer for Reaction Motors, Inc. Assigned continuously to Edwards Air Force Base from 1946 to 1976, Arnold personally supported the X-1, D-558, and X-15 flight programs during their historic research flights. After Reaction Motors ceased operations, he remained the last active employee of the company, still working with its engines, continuing to support them under Thiokol and later Aerojet. In that capacity, he remained involved with these propulsion systems through the Lifting Body programs and the proposed X-24C hypersonic vehicle project, ultimately retiring from Aerojet in 1990.
Accompanying the XLR11-RM-13 is the personal archive assembled by William “Bill” Bernard Arnold during his career supporting Reaction Motors engines at Edwards Air Force Base. Technical materials include confidential pilot handbooks for the XLR-11 series, a final report on XLR-11 field engine overhaul signed by Arnold, and the official AFFTC Technical Documentary Report No. 63-3, The Rocket Research Aircraft Program 1946–1962.
Personal records include Arnold’s handwritten flight-line notebook with engine data recorded during operations at Edwards, his pocket notebook, and an original X-15 flight log. The photographic archive features large-format Thiokol / Reaction Motors Division press photographs of XLR-11 static-fire tests, additional color and black-and-white engine test photographs, a mounted color image of the X-15 in powered flight, and personal snapshots of Arnold with colleagues beside the aircraft.
Program publications include the North American Aviation X-15 press kit, NASA’s ‘Research at the Edge of Space’ booklet, the Reaction Motors brochure ‘Power…for the X-15,’ the X-15 Flight Record booklet, and a period issue of North American’s Skyline magazine featuring the X-15 on the cover.
