Tag Archives: Neil Alden Armstrong

20 April 1962

E-334220 April 1962: “Neil’s Cross-Country.” NASA Research Test Pilot Neil Alden Armstrong conducts a flight to test the Minneapolis-Honeywell MH-96 flight control system installed in the third North American Aviation X-15, serial number 56-6672. The new system combined both aerodynamic and reaction thruster flight controls in one hand controller rather than the two used in X-15s -670 and -671, simplifying the tasks for the pilot.

On its fourth flight, -672 was air-dropped from the Boeing NB-52B Stratofortress drop ship, Balls 8, over Mud Lake, Nevada. Armstrong fired the Reaction Motors XLR99-RM-1 engine and let it burn for 82.4 seconds. The X-15 accelerated to Mach 5.31 (3,789 miles per hour/6,098 kilometers per hour). After the engine was shut down, the rocketplane continued to its peak altitude on a ballistic trajectory, reaching 207,500 feet (63,246 meters) before going over the top and beginning its descent back toward the atmosphere. The test of the new flight control system went well.

E63-9834Neil Armstrong began to pull out of the descent at about 100,000 feet (30,480 meters), but the X-15 “ricocheted” off the top of the atmosphere and climbed back to 115,000 feet (35,052 meters) where the aerodynamic control surfaces could not function. He used the reaction thrusters to turn toward the dry lake landing area at Edwards Air Force Base, but although the X-15 rolled into a left bank, it would not change direction and still in ballistic flight, went zooming by Edwards at Mach 3 and 100,000 feet in a 90° left bank.

As the X-15 dropped back into the atmosphere, Armstrong was finally able to get it slowed down, but he was far south of his planned landing site. By the time he got -672 turned around he was 45 miles (72.4 kilometers) to the south, over the Rose Bowl in Pasadena, and gliding through 45,000 feet (13,716 meters). There was real doubt that he would be able to make the X-15 stretch its glide to reach the dry lake.

E-7469In a masterful display of airmanship, Neil Armstrong was able to get the X-15 to reach the south end of the dry lake, 12 miles (19.3 kilometers) from the planned landing spot to the north. But it was a very close call. In debriefing, the pilots of the four F-104 chase planes were asked how much clearance Armstrong had as he crossed over the Joshua trees at the edge of the lake bed. One of them answered, “Oh, at least 100 feet—on either side.”

At 12 minutes, 28.7 seconds, this was the longest flight of the entire X-15 program. It is called “Neil’s cross-country flight.”

North American Aviation X-15 56-6670 with Neil A. Armstrong, Jr., NASA Research Test Pilot, Edwards AFB, 1960A U.S. Navy fighter pilot who flew 78 combat missions during the Korean War, Neil Armstrong became a civilian test pilot at NACA (National Advisory Committee on Aeronautics, the predecessor to NASA) in 1955. He made 7 flights in the X-15 before transferring to NASA’s Project Gemini in 1962.

Armstrong was command pilot for Gemini 8 and Gemini 11, commander of the backup flight crew of the Apollo 8 mission, and was commander of Apollo 11.

On 20 July 1969, Neil Alden Armstrong was the First Man To Stand on the Surface of The Moon.


© 2018, Bryan R. Swopes

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22 March 1956

Boeing P2B-1S, Bu. No. 84029, at Edwards AFB, 22 March 1956. (NASA)

22 March 1956: While carrying the U.S. Navy’s Douglas D-558-II Skyrocket, problems developed aboard both the research rocketplane and the “mothership.” The modified four-engine heavy bomber, a U.S. Air Force Boeing B-29-95-BW Superfortress (which had been transferred to the U.S. Navy and redesignated P2B-1S Superfortress), had a runaway propeller on the Number 4 engine, outboard on the right wing. The propeller broke apart from excessive rotational speed, slicing through the Number 3 engine, the fuselage, and striking the Number 2 engine.

Douglas D-558-II Skyrocket, Bu. No., 37974, NACA 144, is dropped from the Boeing P2B-1S Superfortress, Bu. No. 84029, NACA 137. (NASA)

NACA research test pilot John Barron (“Jack”) MacKay, in the cockpit of the Skyrocket, had called “No drop!” because of problems with the rocketplane, but he was jettisoned so that the mothership could maintain flight and make an emergency landing.

McKay dumped the Skyrocket’s propellants and glided to the lake bed.

John Barron McKay, NACA/NASA Research Test Pilot. (NASA)

“Each rocket-plane pilot had worked out, in conjunction with the pilot of the mother ship, a procedure to follow if any emergency developed in either plane. Jack McKay, who had developed into a very able test pilot, and I had agreed with Butchart that if something went wrong after either of us had entered the cockpit of the Skyrocket and had closed the canopy, he would immediately jettison the rocket plane, leaving the rocket-plane pilot to look after his own hide. As a matter of fact, McKay and Butchart later ran into such an emergency. One day something went haywire in a propeller on the B-29 mother plane. As agreed, Butchart instantly cut loose the Skyrocket. A split second later the B-29 prop tore loose and cartwheeled through the space the Skyrocket had just vacated. McKay landed without difficulty; but had Butchart not cut the parasite plane loose, the prop would have ripped into its fuel tanks, causing an explosion that would have killed everyone, including McKay.”

Always Another Dawn: The Story of a Rocket Test Pilot, by A. Scott Crossfield and Clay Blair, Jr., The World Publishing Company, Cleveland and New York, 1960, Chapter 21 at Pages 201–202.

The Superfortress pilots, Stanley Paul Butchart and Neil Alden Armstrong, landed the plane safely on the lake bed at Edwards Air Force Base.

Neil Armstrong would land on The Moon 13 years later.

The P2B1-S is jacked up inside a hangar at Edwards AFB so the the Douglas D-558-II Skyrocket can be loaded aboard.
The P2B-1S is jacked up inside a hangar at Edwards AFB so the the Douglas D-558-II Skyrocket can be loaded aboard. (NASA)

© 2017, Bryan R. Swopes

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16 March 1966, 16:41:02.389 UTC, T minus Zero

Gemini VIII lifts off from Launch Complex 19, Kennedy Space Center, 17:41:02 UTC, 16 March 1966. (NASA)
Gemini VIII lifts off from Launch Complex 19, Cape Kennedy Air Force Station, 16:41:02 UTC, 16 March 1966. (NASA)

16 March 1966: At 16:41:02.389 UTC (12:41:02 p.m. Eastern Standard Time), forty years to the day after the launch of Dr. Robert Goddard’s first liquid-fueled rocket, Gemini VIII, with command pilot Neil Alden Armstrong and pilot David Randolph Scott, lifted off from Launch Complex 19 at the Cape Kennedy Air Force Station, Cape Kennedy, Florida, aboard a Titan II GLV booster. Their mission was to rendezvous and dock with an Agena Target Vehicle launched earlier aboard an Atlas rocket.

Gemini VIII/Titan GLV-8 accelerates toward Low Earth Orbit, 16 March 1966. (NASA, MSCF-9141927)

Gemini VIII entered a 86.3  × 146.7 nautical mile (99.3 × 168.8 statute miles/160 × 271.7 kilometers) elliptical orbit. The spacecraft was traveling at 17,549 miles per hour (28,242 kilometers per hour).

The Gemini Agena Target Vehicle seen from Gemini VIII, 16 March 1966. (David R. Scott, NASA)

The docking, the first ever of two vehicles in Earth orbit, was successful, however after about 27 minutes the combined vehicles begin rolling uncontrollably. The Gemini capsule separated from the Agena, and for a few minutes all seemed normal. But the rolling started again, reaching as high as 60 r.p.m.

The astronauts were in grave danger. Armstrong succeeded in stopping the roll but the Gemini’s attitude control fuel was dangerously low.

David R. Scott and Neil A. Armstrong, flight crew of Gemini VIII. (NASA)

The pilots’ report reads:

     Shortly after sending encoder command 041 (recorder ON), roll and yaw rates were observed to be developing. No visual or audible evidence of spacecraft thruster firing was noted, and the divergence was attributed to the GATV.

     Commands were sent to de-energize the GATV ACS, geocentric rate, and horizon sensors, and the spacecraft Orbital Attitude and Maneuver System (OAMS) was activated.

     The rates were reduced to near zero, but began to increase upon release of the hand controller. The ACS was commanded on to determine if GATV thruster action would help reduce the angular rates. No improvement was noted and the ACS was again commanded off. Plumes from a GATV pitch thruster were visually observed, however, during a period when the ACS was thought to be inactivated.

     After a period of relatively stable operation, the rates once again began to increase. The spacecraft was switched to secondary bias power, secondary logics, and secondary drivers in an attempt to eliminate possible spacecraft control-system discrepancies. No improvement being observed, a conventional troubleshooting approach with the OAMS completely de-energized was attempted, but subsequently abandoned because of the existing rates.

     An undocking was performed when the rates were determined to be low enough to precluded any recontact problems. Approximately a 3 ft/sec velocity change was used to effect separation of the two vehicles.

     Angular rates continued to rise, verifying a spacecraft control-system problem. The hand controller appeared to be inactive. The Reentry Control System (RCS) was armed and, after trying ACME-DIRECT and then turning off all OAMS control switches and circuit breakers, was found to be operative in DIRECT-DIRECT. Angular rates were reduced to small values with the RCS B-ring. Inspection of the OAMS revealed that the no. 8 thruster had failed to open. Some open Attitude Control and Maneuver Electronics (ACME) circuit breakers probably accounted for the inoperative hand controller noted earlier. All yaw thrusters other than number 8 were inoperative. Pitch and roll control were maintained using the pitch thrusters. . .

      All four retrorockets fired on time. . . .

GEMINI PROGRAM MISSION REPORT, GEMINI VIII, Gemini Mission Evaluation Team, National Aeronautics and Space Administration, Manned Spacecraft Center, Houston, Texas, , MSC-G-R-66-4, Section 7 at Pages 7-21 and 7-22

The mission was aborted and the capsule returned to Earth after 10 hours, 41 minutes, 26.0 seconds, landing in the Pacific Ocean at N. 25° 12′, E. 136° 05′. U.S. Air  Force pararescue jumpers (“PJs”) parachuted from a Douglas C-54 transport and attached a flotation collar to the Gemini capsule. The astronauts were recovered by the Gearing-class destroyer USS Leonard F. Mason (DD-852), about three hours later..

The Gemini VIII spacecraft is displayed at the Neil Armstrong Air and Space Museum, Wapakoneta, Ohio.

Gemini VIII with flotation collar. (NASA)

The two-man Gemini spacecraft was built by the McDonnell Aircraft Corporation of St. Louis, Missouri, the same company that built the earlier Mercury space capsule. The spacecraft consisted of a series of cone-shaped segments forming a reentry module and an adapter section. It had an overall length of 18 feet, 9.84 inches (5.736 meters) and a maximum diameter of 10 feet, 0.00 inches (3.048 meters) at the base of the equipment section. The reentry module was 11 feet (3.353 meters) long with a maximum diameter of 7 feet, 6.00 inches (2.347 meters). The Gemini re-entry heat shield was a spherical section with a radius of 12 feet, 0.00 inches (3.658 meters). The weight of the Gemini spacecraft varied from ship to ship. Gemini VIII weighed 8,351.31 pounds (3,788.09 kilograms) at launch. Spacecraft 8 was shipped from the St. Louis factory to Cape Kennedy on 2 January 1966.

Artist’s concept of Gemini spacecraft, 3 January 1962. (NASA-S-65-893)

The Titan II GLV was a “man-rated” variant of the Martin SM-68B intercontinental ballistic missile. It was assembled at Martin’s Middle River, Maryland plant so as not to interfere with the production of the ICBM at Denver, Colorado. Twelve GLVs were ordered by the Air Force for the Gemini Program.

Titan II GLV, (NASA Mission Report, Figure 3-1, at Page 3–23)

The Titan II GLV was a two-stage, liquid-fueled rocket. The first stage was 70 feet, 2.31 inches (21.395 meters) long with a diameter of 10 feet (3.048 meters). It was powered by an Aerojet Engineering Corporation LR87-7 engine which combined two combustion chambers and exhaust nozzles with a single turbopump unit. The engine was fueled by Aerozine 50, a hypergolic 51/47/2 blend of hydrazine, unsymetrical-dimethyl hydrazine, and water. Ignition occurred spontaneously as the components were combined in the combustion chambers. The LR87-7 produced approximately 430,000 pounds of thrust (1,912.74 kilonewtons). It was not throttled and could not be shut down and restarted. Post flight analysis indicated that the first stage engine of GLV-8 had produced an average of 461,080 pounds of thrust ( kilonewtons).

The second stage was 25 feet, 6.375 inches (7.782 meters) long, with the same diameter, and used an Aerojet LR91 engine which produced approximately 100,000 pounds of thrust (444.82 kilonewtons), also burning Aerozine 50. GLV-7’s LR91 produced an average of 102,735 pounds of thrust ( kilonewtons).

The Gemini/Titan II GLV VIII combination had a total height of 107 feet, 7.33 inches (32.795 meters) and weighed 345,359 pounds (156,652 kilograms) at ignition.

The Atlas-Agena Target vehicle takes off at Launch Complex 14, 17:00:00 UTC, 16 March 1966. (NASA)
The Atlas-Agena Target Vehicle takes off at Launch Complex 14, Cape Kennedy Air Force Station, 15:00:03 UTC, 16 March 1966. (NASA)

© 2019, Bryan R. Swopes

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19–20 February 1979

Professor Neil A. Armstrong in his classroom at the Iniversity of Cincinatti College of Engineering, 1974. (Peggy Palange, UC Public Informaton Office)
Professor Neil A. Armstrong in his classroom at the University of Cincinnati College of Engineering, 1974. (Peggy Palange, UC Public Information Office)

19–20 February 1979: Professor Neil Alden Armstrong of the University of Cincinnati College of Engineering, a member of the Board of Directors of Gates Learjet Corporation, former United States Navy fighter pilot, NACA/NASA research test pilot, Gemini and Apollo astronaut, and The First Man To Set Foot On The Moon, set five Fédération Aéronautique Internationale (FAI) and National Aeronautics Association class records for time to climb to an altitude and altitude while flying the prototype Learjet 28, serial number 28-001.

Professor Neil Armstrong and co-pilot Peter Reynolds in the cockpit of the record-setting Learjet 28, March 1979.
Professor Neil Armstrong and co-pilot Peter Reynolds in the cockpit of the record-setting Learjet 28.

Armstrong, with Learjet program test pilot Peter Reynolds as co-pilot, and with NAA observer Don Berliner aboard, flew the Learjet 28 to 15,000 meters (49,212.598 feet) in 12 minutes, 27 seconds over Kittyhawk, North Carolina, on 19 February.¹

On the same day, during a flight from Wichita, Kansas, to Elizabeth City, North Carolina, Armstrong flew the Learjet to 15,584.6 meters (51,130.577 feet), setting records for altitude, and for sustained altitude in horizontal flight.²  ³

The following day, 20 February 1979, flying from Elizabeth City, North Carolina, to Florence, Kentucky, Armstrong again set altitude and sustained altitude in horizontal flight, in a different class, by taking the Learjet to 15,585 meters (51,131.89 feet).⁴ ⁵

Learjet 28, serial number 28-001
Learjet 28, serial number 28-001. (NASA)

The Learjet 28 was a development of the Learjet 25 twin-engine business jet. It is operated by two pilots and can carry 8 passengers. The Model 28 used a new wing design. It was the first civil aircraft to be certified with winglets. The prototype first flew 24 August 1977, and it received certification from the Federal Aviation Administration 29 July 1979.

The Learjet 28 is 47 feet, 7.5 inches (14.516 meters) long with a wingspan of 43 feet, 9½ inches (13.348 meters) and overall height of 12 feet, 3 inches (3.734 meters). The wing area is 264.5 square feet (24.6 square meters) It has an empty weight of 7,895 pounds (3,581 kilograms) and maximum takeoff weight of 15,000 pounds (6,804 kilograms).

Gates Learjet 28 three-view illustration. (FLIGHT International, No. 3647, Vol. 115, 10 February 1979, Page 402)

The Learjet 28 is powered by two General Electric CJ610-8A turbojet engines. This is a single-shaft axial-flow turbojet, developed from the military J85. It has an 8-stage compressor section and 2-stage turbine. The CJ610-8A is rated at 2,850 pounds of thrust (12.68 kilonewtons) at 16,500 r.p.m., and 2,950 pounds (13.12 kilonewtons) at Sea Level, for takeoff (five minute limit).

The business jet has a cruise speed of 464 knots (534 miles per hour (859 kilometers per hour) at 51,000 feet (15,544.8 meters). The Learjet 28 has a maximum range of 1,370 nautical miles (1,577 statute miles/2,537 kilometers). The airplane’s maximum operating altitude is 51,000 feet (15,545 meters), the same as the record altitude. It can reach that altitude in less than 35 minutes.

The aircraft was limited by its older technology turbojet engines, and only five Learjet 28s were built.

gates Learjet 28 N128LR. (Business Aviation Online)

The first Learjet 28, serial number 28-001, has been re-registered several times. At the time of its FAI record-setting flights, it carried FAA registration N9RS. Later it was registered as N3AS. The most recent information shows it currently registered as N128LR.

Neil Alden Armstrong, one of America’s most loved heroes, passed away 25 August 2012.

A bronze statue of Neil Alden Armstrong in front of the Hall of Engineering.
A bronze statue of Neil Alden Armstrong in front of the Hall of Engineering.

¹ FAI Record File Number 2652

² FAI Record File Number 8670

³ FAI Record File Number 8657

⁴ FAI Record File Number 2653

⁵ FAI Record File Number 2654

© 2019, Bryan R. Swopes

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North American Aviation, Inc., X-15A Hypersonic Research Rocketplane

Rollout AFFTC History Office
North American Aviation, Inc., X-15A-1, 56-6670, at Los Angeles Division, October 1958. (Air Force Flight Test Center History Office)

20 December 1968: After 199 flights, the National Aeronautics and Space Administration cancelled the X-15 Hypersonic Research Program. A 200th X-15 flight had been scheduled, but after several delays, the decision was made to end the program. (The last actual flight attempt was 12 December 1968, but snow at several of the dry lakes used as emergency landing areas resulted in the flight being cancelled.)

The X-15A rocketplane was designed and built for the U.S. Air Force and the National Advisory Committee for Aeronautics (NACA, the predecessor of NASA) by North American Aviation, Inc., to investigate the effects of hypersonic flight (Mach 5+). Design work started in 1955 and a mock-up had been completed after just 12 months. The three X-15s were built at North American’s Los Angeles Division, at the southeast corner of Los Angeles International Airport (LAX), on the shoreline of southern California.

The first flight took place 8 June 1959 with former NACA test pilot Albert Scott Crossfield in the cockpit of the Number 1 ship, 56-6670.

Scott Crossfield prepares for a flight in the North American Aviation X-15A.

While earlier rocketplanes, the Bell X-1 series, the the Douglas D-558-II, and the Bell X-2, were airplanes powered by rocket engines, the X-15 was a quantum leap in technology. It was a spacecraft.

Like the other rocketplanes, the X-15 was designed to be carried aloft by a “mothership,” rather than to takeoff and climb to the test altitude under its own power. The carrier aircraft was originally to be a Convair B-36 intercontinental bomber but this was soon changed to a Boeing B-52 Stratofortress. Two B-52s were modified to carry the X-15: NB-52A 52-003, The High and Mighty One, and NB-52B 52-008, Balls 8.

From 8 June 1959 to 24 October 1968, the three X-15s were flown by twelve test pilots, three of whom would qualify as astronauts in the X-15. Two would go on to the Apollo Program, and one, Neil Alden Armstrong, would be the first human to set foot on the surface of the Moon, 20 July 1969. Joe Engle would fly the space shuttle. Four of the test pilots, Petersen, White, Rushworth, and Knight, flew in combat during the Vietnam War, with Bob White being awarded the Air Force Cross. Petersen, Rushworth and White reached flag rank.

One pilot, John B. (“Jack”) McKay, was seriously injured during an emergency landing at Mud Lake, Nevada, 9 November 1962. Another, Michael James Adams, was killed when the Number 3 ship, 56-6672, went into a hypersonic spin and broke up on the program’s 191st flight, 15 November 1967.

North American Aviation, Inc. X-15A 56-6670 on Rogers Dry Lake, Edwards Air Force Base, California. (NASA)
North American Aviation, Inc., X-15A-1 56-6670 on Rogers Dry Lake, Edwards Air Force Base, California. (NASA Image E-5251)

Flown by a single pilot/astronaut, the X-15 is a mid-wing monoplane with dorsal and ventral fin/rudders and stabilators. The wing had no dihdral, while the stabilators had a pronounced -15° anhedral. The short wings have an area of 200 square feet (18.58 square meters) and a maximum thickness of just 5%. The leading edges are swept to 25.64°. There are two small flaps but no ailerons. The entire vertical fin/rudder pivots for yaw control.

Above 100,000 feet (30,840 meters) altitude, conventional aircraft flight control surfaces are ineffective. The X-15 is equipped with a system of reaction control jets for pitch, roll and yaw control. Hydrogen peroxide was passed through a catalyst to produce steam, which supplied the control thrusters.

The forward landing gear consists of a retractable oleo strut with steerable dual wheels and there are two strut/skids at the rear of the fuselage. The gear is retracted after the X-15 is mounted on the NB-52 and is extended for landing by its own weight.

 North American Aviation X-15A 56-6672 touches down on Rogers Dry Lake. (NASA)
North American Aviation, Inc., X-15A-3 56-6672 just before touch down on Rogers Dry Lake. (NASA Image E-7469)

The rocketplane’s cockpit featured both a conventional control stick as well as side-controllers. It was pressurized with nitrogen gas to prevent fires. The pilot wore an MC-2 full-pressure suit manufactured by the David Clark Company of Worcester, Massachusetts, with an MA-3 helmet. The suit was pressurized below the neck seal with nitrogen, while the helmet was supplied with 100% oxygen. This pressure suit was later changed to the Air Force-standardized A/P22S.

X-15A cockpit with original Lear Siegler instrument panel. (NASA)
X-15 cockpit with original Lear Siegler instrument panel. (NASA image E63-9834)

The X-15 is 50.75 feet (15.469 meters) long with a wing span of 22.36 feet (6.815 meters). The height—the distance between the tips of the dorsal and ventral fins—is 13.5 feet (4.115 meters). The stabilator span is 18.08 feet (5.511 meters). The fuselage is 4.67 feet (1.423 meters) deep and has a maximum width of 7.33 feet (2.234 meters).

Since the X-15 was built of steel rather than light-weight aluminum, as are most aircraft, it is a heavy machine, weighing approximately 14,600 pounds (6,623 kilograms) empty and 34,000 pounds (15,422 kilograms) when loaded with a pilot and propellants. The X-15s carried as much as 1,300 pounds (590 kilograms) of research instrumentation, and the equipment varied from flight to flight. The minimum flight weight (for high-speed missions): 31,292 pounds (14,194 kilograms) The maximum weight was 52,117 pounds (23,640 kilograms) at drop (modified X-15A-2 with external propellant tanks).

Initial flights were flown with a 5 foot, 11 inch (1.803 meters)-long air data boom at the nose, but this would later be replaced by the “ball nose” air sensor system. The data boom contained a standard pitot-static system along with angle-of-attack and sideslip vanes. The boom and ball nose were interchangeable.

Neil Armstrong with the first North American Aviation X-15A, 56-6670, on Rogers Dry Lake after a flight, 1960. His hand is resting on the rocketplane's ball nose sensor. (NASA)
NASA Research Test Pilot Neil A. Armstrong with the first North American Aviation X-15A, 56-6670, on Rogers Dry Lake after a flight, 1960. His right hand is resting on the rocketplane’s ball nose sensor. (NASA Image E60-6286)

The X-15s were built primarily of a nickel/chromium/iron alloy named Inconel X, along with corrosion-resistant steel, titanium and aluminum. Inconel X is both very hard and also able to maintain its strength at the very high temperatures the X-15s were subjected to by aerodynamic heating. It was extremely difficult to machine and special fabrication techniques had to be developed.

Delays in the production of the planned Reaction Motors XLR99 rocket engine forced engineers to adapt two vertically-stacked Reaction Motors XLR11-RM-13 four-chamber rocket engines to the X-15 for early flights. This was a well-known engine which was used on the previous rocketplanes. The XLR11 burned a mixture of ethyl alcohol and water with liquid oxygen. Each of the engines’ chambers could be ignited individually. Each engine was rated at 11,800 pounds of thrust (58.49 kilonewtons) at Sea Level.

Two Reaction Motors Division XLR11-RM-5 four-chamber rocket engines installed on an X-15. (NASA)
Two Reaction Motors Division XLR11-RM-13 four-chamber rocket engines installed on an X-15. The speed brakes of the ventral fin are shown in the open position. (NASA)

The Reaction Motors XLR99-RM-1 rocket engine was throttleable by the pilot from 28,500 to 60,000 pounds of thrust (126.77–266.89 kilonewtons). The engine was rated at 50,000 pounds of thrust (222.41 kilonewtons) at Sea Level; 57,000 pounds (253.55 kilonewtons) at 45,000 feet (13,716 meters), the typical drop altitude; and 57,850 pounds (257.33 kilonewtons) of thrust at 100,000 feet (30,480 meters). Individual engines varied slightly. A few produced as much as 61,000 pounds of thrust (271.34 kilonewtons).

The XLR99 burned anhydrous ammonia and liquid oxygen. The flame temperature was approximately 5,000 °F. (2,760 °C.) The engine was cooled with circulating liquid oxygen. To protect the exhaust nozzle, it was flame-sprayed with ceramic coating of zirconium dioxide. The engine is 6 feet, 10 inches (2.083 meters) long and 3 feet, 3.3 inches (0.998 meters) in diameter. It weighs 910 pounds (413 kilograms). The Time Between Overhauls (TBO) is 1 hour of operation, or 100 starts.

Thiokol Reaction Motors Division XLR-RM-1 rocket engine. (U.S. Air Force)
Thiokol Corporation Reaction Motors Division XLR99-RM-1 rocket engine. (U.S. Air Force)

The XLR99 proved to be very reliable. 169 X-15 flights were made using the XLR99. 165 of these had successful engine operation. It started on the first attempt 159 times.

The highest speed achieved during the program was with the modified number two ship, X-15A-2 56-6671, flown by Pete Knight to Mach 6.70 (6,620 feet per second/4,520 miles per hour/7,264 kilometers per hour) at 102,700 feet (31,303 meters). On this flight, the rocketplane exceeded its maximum design speed of 6,600 feet per second (2,012 meters per second).

The maximum altitude was reached by Joe Walker, 22 August 1963, when he flew 56-6672 to 354,200 feet (107,960 meters).

The longest flight was flown by Neil Armstrong, 20 April 1962, with a duration of 12 minutes, 28.7 seconds.

North American Aviation X-15A-1 56-6670 is on display at the Smithsonian Institution National Air and Space Museum. X-15A-2 56-6671 is at the National Museum of the United States Air Force.

A North American Aviation F-100 Super Sabre chase plane follows NB-52A 52-003 prior to launch of an X-15. (NASA)
A North American Aviation F-100 Super Sabre chase plane follows NB-52A 52-003 prior to launch of an X-15. (NASA)

Recommended reading:

Always Another Dawn: The Story of a Rocket Test Pilot, by A. Scott Crossfield and Clay Blair, Jr., The World Publishing Company, Cleveland and New York, 1960

At The Edge Of Space, by Milton O. Thompson, Smithsonian Institution Press, 1992

X-15 Diary: The Story of America’s First Spaceship, by Richard Tregaskis, E.F. Dutton & Company,  New York, 1961; University of Nebraska Press, 2004

X-15: Exploring the Frontiers of Flight, by David R. Jenkins, National Aeronautics and Space Administration http://www.nasa.gov/pdf/470842main_X_15_Frontier_of_Flight.pdf

The X-15 Rocket Plane: Flying the First Wings into Space, by Michelle Evans, University of Nebraska Press, Lincoln and London, 2013

Screen Shot 2016-06-07 at 21.18.14
North American Aviation, Inc., X-15A-2 56-6671 accelerates after igniting its Reaction Motors XLR99-RM-1 rocket engine (NASA)

© 2018, Bryan R. Swopes

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