The X-15 Aircraft and the RMD XLR-99 Engines

I am in the process of building this list and locating new information.
I have been told that there were 10 engines delivered, Serial Number 101 thru 110
Many of the engine serial numbers have not been verified and any help would be appreciated.


Link: Goleta Air & Space Museum

Where in the world are the engines?
Serial Number UNKNOWN
One engine blew due to a valve malfunction during a tie down engine test at Edwards but I have been told that it might have been just a test engine.

Link: Accident Report June 8th, 1960, a ground test of final engine XLR99 finished the destruction of all the back of X-15 number 3 following an explosion.

Serial Number UNKNOWN - The Loss of Maj. Michael Adams in X-15A-3 #66672

Link: The Crash of the X-15A-3

Serial Number UNKNOWN - Bad landing, more info to follow

Serial Number UNKNOWN, Washington, Smithsonian

X15 now residing in the Smithsonian in Washington DC

Rear view complete with engine. The Bell X-1 is in the upper right

Serial Number UNKNOWN, Aviation Hall of Fame. Teterboro, New Jersey -
This unit was donated by Reaction Motors and appears to be one of the early test engines.
This would indicate that it did not have an official serial number and I could not find a nameplate.
Also notice that all the additional access plumbing to the shroud arround the exhaust is not present.
The engine is mounted on a work stand and is rotated 90 degrees. The pump is vertical and the turbine exhaust is on the bottom.
This engine has never been fired or the chamber has been replaced as the exhaust cone shows no burn marks.
See the next or previous pictures for typical burn marks.

Serial Number UNKNOWN, Pima Air and Space Museum in Tucson Arizona

April 18, 2005
While on vacation I visited the Pima Air and Space Museum in Tucson Arizona and there next to a mockup of the X-15 was an XLR-99 engine.
It had been donated with only the information on the plaque so I was able to enjoy going back about 50 years and explain to the tour guides how it worked.
I don't know who donated it or what the serial number is.

Serial Number 106 and 107, Edwards Air Force Base

February 2006, E-Mail from the Director of the Museum at Edwards Air Force Base

Stumbled on your site while Googling some X-15 stuff. Very interesting and nicely done.
Wasn't sure if you knew that we have two complete XLR-99s (Ser Nos 106 and 107) and a number of thrust chambers in our collection here at the Air Force Flight Test Center Museum at Edwards AFB, CA. We were fortunate enough to get the maintenance and inspection logs on each engine so we could match up which flights each was used on. We had three complete engines at one time but sent one to the Smithsonian.
S/N 107 was used on Joe Engle's and Milt Thompson's first flights, Engle's astronaut wings flight, and it set an unofficial world speed record of Mach 5.92 on 27 Jan 62. We have 107 mounted on a trailer so we can haul it around to airshows and other aerospace events.
S/N 106 had a very distinguished career on the X-15 program from its acceptance in Jan 61 to its last flight in Nov 66. It was used on the first flight of X-15 #3 in Dec 61; on the first powered flight of the #2 X-15 modified to the the X-15A-2 configuration in June 1964; on the first X-15A-2 flight with full external fuel tanks in Jul 66; and-during its last flight on 18 Nov 66-it was used to set an unofficial world's absolute speed record of Mach 6.33 (4250 mph) with William J. "Pete" Knight at the controls. It reached a maximum altitude of 249,000 feet. This engine is on display in our museum.
For more information see the Edwards AFB public site at Click on "About Edwards" then "Museum" and select the "XLR99 Exhibit."

    Best Regards, DOUG NELSON, Director, AFFTC Museum
    (661) 277-8050 * DSN 527-8050 - "Keepers of the Right Stuff"

Serial Number 108, 109, 110 - National Museum of the USAF

Thank you for contacting the National Museum of the United States Air Force. Per your request, we have reviewed our museum collection and can verify the location and exhibit status of the following Reaction Motors LR-99 rocket engines:

XLR-99-RM1 s/n 106 Location: On Loan to Air Force Flight Test Center (AFFTC) Museum, Edwards AFB, CA
XLR-99-RM1 s/n 107 Location: On Loan to Air Force Flight Test Center (AFFTC) Museum, Edwards AFB, CA
YLR-99-RM1 s/n 108 See Below
YLR-99-RM1 s/n 109 Location: On exhibit in Hall of Missiles, Ntl Museum of US Air Force, WPAFB, OH
YLR-99-RM1 s/n 110 Location: Installed in X-15A-2 s/n 56-6671, Ntl Museum of US Air Force, WPAFB, OH

We maintain one additional example of the YRL-99-RM1 on exhibit in our Research & Development Gallery. This motor is unidentified as the serial plate has been removed, though it likely once carried Serial No. 108.

Serial Number 108

Serial Number 109

Serial Number 110, in aircraft

    Received this update from "Rick" and I have not had a chance to compair it yet.

    Ground test engines:
  • 006 The NASA DFRC gave this engine to the Pima Air & Space Museum in October 1983.
  • 011, 012, and 014 These engines were used in the preliminary flight rating tests and have yet to be accounted for.

    Flight engines used only for ground tests:
  • 101 This engine exploded during a ground test on November 16, 1962 at Edwards AFB.
  • 102 This engine was also used in the preliminary flight rating tests and has yet to be accounted for.

    Flight engines:
  • 103 This engine is in the X-15 # 1 at the NASM. Used for John McKay's short November 9, 1962 flight.
  • 104 This engine is in storage at the NASA DFRC. XLR-8 S/N 2 and XLR-11 S/N 50 are also in storage.
  • 105 This engine was damaged beyond economical repair on June 8, 1960 in the X-15 # 3.
  • 106 This engine is on display at the AFFTC Museum.
  • 107 This engine is displayed on a trailer at the AFFTC Museum.
  • 108 This engine is in storage at the NASM.
  • 109 This engine is on display in the Hall of Missiles at the USAF Museum.
  • 110 This engine is in the X-15 # 2 at the USAF Museum. Used for the Mach 6.70 flight.
  • 111 This engine was destroyed in the crash of X-15 # 3 on November 15, 1967. Used for the 354,200 feet flight.

    Miscellaneous XLR-99's:
  • 1 early engine destroyed itself on a test stand (at Lake Denmark?) on October 24, 1958.
  • 1 engine is on display in the R & D Gallery at the USAF Museum (missing data plate).
  • 1 engine is on display at the Aviation Hall of Fame and Museum of New Jersey (no flame pattern).
  • 1 engine, S/N 49, has been on loan from Ken Mason to the Vernon Saxon Museum of Boron, CA since July, 2004.
  • 1 or more engine bodies are at Norton Sales, Inc of North Hollywood, CA (no flame pattern).
  • 1 engine body that Brian Lockett of the "Goleta Air & Space Museum" sold on Ebay (no flame pattern).
  • 2 or more engine bodies are owned by Ken Mason (no flame pattern).
  • 1 engine body owned by Ken Mason was retrieved by Waldo Stakes from the Space Murals Museum outside of Las Cruces, NM in October/November 2007. It had been on loan to the museum for about 10 years.