Test pilot Robert C. Chilton with the North American Aviation prototype NA-73X, NX19998. (North American Aviation, Inc.)
3 April 1941: North American Aviation test pilot Robert Creed Chilton takes his first flight—a one hour familiarization—in the company’s prototype of a new fighter for the Royal Air Force, the NA-73X, NX19998, at Mines Field. (Mines would later become Los Angeles International Airport, LAX.)
The airplane had first been flown by free-lance test pilot Vance Breese, 26 October 1940, and he had flown it several times. North American’s Chief Test Pilot, Paul Baird Balfour, on his first flight in NX19998, ran out of fuel and crash landed in a plowed field 150 yards (137 meters) west of the airfield, 20 November 1940. The prototype had flown just 3 hours, 20 minutes.
The NA-73X was repaired and Bob Chilton was assigned to complete the testing program. The airplane would become the legendary P-51 Mustang, and Chilton would continue to conduct the majority of flight testing on its improvements and modifications.
Test pilot Robert C. Chilton stands on the wing of a North American Aviation P-51B Mustang. (North American Aviation, Inc.)
Robert Creed Chilton was born 6 February 1912 at Eugene, Oregon, the third of five children of Leo Wesley Chilton, a physician, and Edith Gertrude Gray. He attended Boise High School in Idaho, graduating in 1931. Chilton participated in football, track and basketball, and also competed in the state music contest. After high school, Chilton attended the University of Oregon where he was a member of the Sigma Chi fraternity (ΣΧ). He was also a member of the Reserve Officers Training Corps (ROTC).
Bob Chilton enlisted as an Aviation Cadet in the U.S. Army Air Corps, 25 June 1937. He was trained as a fighter pilot at Randolph Field and Kelly Field in Texas, and was commissioned as a Second Lieutenant in 1938. Lieutenant Chilton was assigned to fly the Curtiss P-36 Hawk with the 79th Pursuit Squadron, 20th Pursuit Group, at Barksdale Field, Louisiana. Because of a medical condition, he was released from active duty, 1 April 1939.
At some time prior to 1940, Bob Chilton, married his first wife, Catherine. They lived in Santa Maria, California, where he worked as a pilot at the local airport.
In January 1941, Chilton went to work as a production test pilot for North American Aviation, Inc., Inglewood, California. After just a few months, he was assigned to the NA-73X.
Chilton married his second wife, Betty W. Shoemaker, 15 November 1951.
On 10 April 1952, Bob Chilton returned to active duty with the U.S. Air Force, with the rank of lieutenant colonel. He served as Chief of the Repulic F-84 and F-105 Weapons System Project Office, Air Material Command, at Wright-Patterson Air Force Base, Dayton, Ohio, until 9 March 1957.
From 1958, Chilton was a vice president for Horkey-Moore Associates, an engineering research and development company in Torrance, California, founded by former North American aerodynamacist Edward J. Horkey. In 1961, he followed Horkey to the Space Equipment Corporation, parent company of Thompson Industries and Kerr Products, also located in Torrance. Chilton served as corporate secretary and contracts administrator.
Chilton married his third wife, Wilhelmina E. Redding (Billie E. Johnson) at Los Angeles, 26 July 1964. They divorced in 1972.
In 1965, Bob Chilton returned to North American Aviation as a flight test program manager. He retired in 1977.
Robert Creed Chilton died at Eugene, Oregon, 31 December 1994, at the age of 82 years.
North American Aviation B-25B Mitchell 40-2291 at Eglin Field, Florida, March 1942. (U.S. Air Force)
27 March 1942: After three weeks of intensive training at Eglin Field, Florida, twenty-two North American Aviation B-25B Mitchell twin-engine medium bombers of the 34th Bombardment Squadron (Medium), 17th Bombardment Group (Medium), U.S. Army Air Force, under the command of Lieutenant Colonel James Harold Doolittle, completed a two-day, low-level, transcontinental flight, and arrived at the Sacramento Air Depot, McClellan Field, California, for final modifications, repairs and maintenance before an upcoming secret mission: The Halsey-Doolittle Raid.
The B-25 had made its first flight 19 October 1940 with test pilot Vance Breese and engineer Roy Ferren in the cockpit. It was a mid-wing airplane with twin vertical tails and retractable tricycle landing gear. The first 8–10 production airplanes were built with a constant dihedral wing. Testing at Wright Field showed that the airplane had a slight tendency to “Dutch roll” so all B-25s after those were built with a “cranked” wing, using dihedral for the inner wing and anhedral in the wing outboard of the engines. This gave it the bomber’s characteristic “gull wing” appearance. The two vertical stabilizers were also increased in size.
A 34th Bombardment Squadron B-25B Mitchell bomber at Mid-Continent Airlines, Minneapolis, Minnesota, for modifications, January–February 1942. (U.S. Air Force)
The B-25B Mitchell was operated by a crew of five: two pilots, a navigator, bombardier and radio operator/gunner. It was 53 feet, 0 inch (16.154 meters) long with a wingspan of 67 feet, 7.7 inches (20.617 meters) and overall height of 15 feet, 9 inches (4.801 meters). The The B-25B had an empty weight of 20,000 pounds (9,072 kilograms) and the maximum gross weight was 28,460 pounds (12,909 kilograms).
The B-25B was powered by two air-cooled, supercharged, 2,603.737-cubic-inch-displacement (42.668 liter) Wright Aeronautical Division Cyclone 14 GR2600B665 (R-2600-9) two-row 14-cylinder radial engines with a compression ratio of 6.9:1. The engines had a Normal Power rating of 1,500 horsepower at 2,400 r.p.m., and 1,700 horsepower at 2,600 r.p.m. for takeoff, burning 100-octane gasoline. These engines (also commonly called “Twin Cyclone”) drove three-bladed Hamilton Standard Hydromatic variable-pitch propellers through 16:9 gear reduction. The R-2600-9 was 5 feet, 3.1 inches (1.603 meters) long and 4 feet, 6.26 inches (1.378 meters) in diameter. It weighed 1,980 pounds (898 kilograms).
“On a low level training mission early in 1942 B-25 40-2297 would be airplane number 14 for the Doolittle Raid on Tokyo — This image was taken before the modification to the troublesome ventral turret. Pilot Major J.A. Hilger, Co-Pilot 2nd Lt. Jack A. Sims, Navigator 2nd Lt. James H. Macie, Jr., Bombardier S/Sgt. Jacob Eierman, Engineer/Gunner S/Sgt. Edwin V. Bain” —HISTORYNET
The medium bomber had a maximum speed of 322 miles per hour (518 kilometers per hour) at 15,000 feet (4,572 meters) and a service ceiling of 30,000 feet (9,144 meters).
It could carry a 3,000 pound (1,361 kilograms) bomb load 2,000 miles (3,219 kilometers). Defensive armament consisted of a single Browning M2 .30-caliber machine gun mounted in the nose, two Browning M2 .50-caliber machine guns in a power dorsal turret, and two more .50s in a retractable ventral turret. (The lower turrets were removed from all of the Doolittle B-25s.)
North American Aviation, Inc., built 9,816 B-25s at Inglewood, California, and Kansas City, Kansas. 120 of these were B-25Bs.
North American Aviation B-25 Mitchell medium bombers being assembled at the Kansas City bomber plant, October 1942. (Alfred T. Palmer, Office of War Information)
Joseph Albert Walker in the cockpit of North American Aviation X-15A 56-6670, after a flight, 1960. (NASA)
24 March 1960: After North American Aviation’s Chief Engineering Test Pilot, Albert Scott Crossfield, had made the first flights in the new X-15 hypersonic research rocketplane (one gliding, eight powered), NASA Chief Test Pilot Joseph Albert Walker made his first familiarization flight.
The X-15, 56-6670, the first of three built by North American Aviation, Inc., was carried aloft under the right wing of a Boeing NB-52A Stratofortress, 52-003, flown by John E. Allavie and Fitzhugh L. Fulton.
Fitz Fulton and and Jack Allavie with a Boeing NB-52 drop ship. (Jet Pilot Overseas)
The rocketplane was dropped from the mothership over Rosamond Dry Lake at 15:43:23.0 local time, and Joe Walker ignited the Reaction Motors XLR-11 rocket engine. The engine burned for 272.0 seconds, accelerating Walker and the X-15 to Mach 2.0 (1,320 miles per hour/2,124.3 kilometers per hour) and a peak altitude of 48,630 feet (14,822.4 meters). Walker landed on Rogers Dry Lake at Edwards Air Force Base after a flight of 9 minutes, 8.0 seconds.
Joe Walker made 25 flights in the three X-15 rocket planes from 24 March 1960 to 22 August 1963. He achieved a maximum Mach number of 5.92, maximum speed of 4,104 miles per hour (6,605 kilometers per hour) and maximum altitude of 354,200 feet (107,960 meters).
Joe Walker with the Number 2 North American Aviation X-15, 56-6671, on Rogers Dry Lake. (NASA)
Joe Walker was killed in a mid-air collision between his Lockheed F-104N Starfighter and a North American Aviation XB-70A Valkyrie near Barstow, California, 1 June 1966.
The number one ship, 56-6670, made 81 of the 199 flights of the X-15 Program. It was the first to fly, and also the last, 24 October 1968. Today, it is in the collection of the Smithsonian Institution National Air and Space Museum.
North American Aviation, Inc. X-15A 56-6670 on Rogers Dry Lake, Edwards Air Force Base, California. (NASA)
North American Aviation XB-45 45-59479 in flight. (U.S. Air Force)
17 March 1947: The prototype of the United States’ first jet-powered bomber, the North American Aviation XB-45 Tornado, 45-59479, made a one-hour first flight at Muroc Army Air Field (later known as Edwards Air Force Base) with company test pilot George William Krebs at the controls.
The photographs below show the XB-45 parked on Muroc Dry Lake. Notice that the windows over the bombardier’s compartment in the nose are painted on.
The North American Aviation XB-45 Tornado was a four-engine prototype bomber. It had a high-mounted straight wing and tricycle landing gear. It was 74 feet, 0 inches (22.555 meters) long with a wingspan of 89 feet, 6 inches (27.279 meters) and overall height of 25 feet, 2 inches (7.671 meters). It had an empty weight of 41,876 pounds (18,995kilograms) and maximum takeoff weight of 82,600 pounds (37,467 kilograms).
North American Aviation XB-45 Tornado 45-59479 parked on the dry lake bed at Muroc Army Airfield, California. (U.S. Air Force)
North American Aviation XB-45 Tornado 45-59479 parked on Muroc Dry Lake. (U.S. Air Force)North American Aviation XB-45 45-59479 makes a low pass over the runway. (U.S. Air Force)
The three prototypes were powered by four Allison-built General Electric J35-A-4 turbojet engines, installed in nacelles which were flush with the bottom of the wings. The J35 was a single-shaft engine with an 11-stage axial-flow compressor section and a single-stage turbine. The J35-A-4 was rated at 4,000 pounds of thrust (14.79 kilonewtons). The engine’s maximum speed was 8,000 r.p.m. The J35 was 14 feet, 0 inches (4.267 meters) long, 3 feet, 4.0 inches (1.016 meters) in diameter, and weighed 2,400 pounds (1,089 kilograms).
The maximum speed of the XB-45 was 494 miles per hour (795 kilometers per hour) at Sea Level and 516 miles per hour (830 kilometers per hour) at 14,000 feet (4,267 meters). The service ceiling was 37,600 feet (11,461 meters).
North American Aviation XB-45 45-59479 as a test bed for rocket assisted take-off, 24 September 1958. (U.S. Air Force)
The production B-45A Tornado was heavier and had better performance. It was operated by two pilots and carried a bombardier/navigator and a tail gunner. It was 75 feet, 4 inches (22.962 meters) long with a wingspan of 89 feet, 0 inches (27.127 meters) and overall height of 25 feet, 2 inches (7.671 meters).
The B-45A had a total wing area of 1,175 square feet (109.2 square meters). The leading edges were swept aft 3° 30′. Their angle of incidence was 3° with -3° 30′ twist and 1° dihedral.
The bomber’s empty weight was 45,694 pounds (20,726 kilograms) and maximum takeoff weight was 91,775 pounds (41,628 kilograms).
Cutaway illustration of the North American Aviation B-45 Tornado showing internal structure and arrangement. (U.S. Air Force)
The B-45A was powered by four General Electric J47-GE-13 turbojet engines. The J47 was an axial-flow turbojet with a 12-stage compressor and single stage turbine. It had a normal power rating of 4,320 pounds of thrust (19.216 kilonewtons) at 7,370 r.p.m.; military power, 5,200 pounds (23.131 kilonewtons) at 7,950 r.p.m. (30-minute limit); and maximum power rating of 6,000 pounds(26.689 kilonewtons) at 7,950 r.p.m., with water/alcohol injection (5-minute limit). The engine was 12 feet, 0.0 inches (3.658 meters) long, 3 feet, 3.0 inches (0.991 meters) in diameter and weighed 2,525 pounds (1,145 kilograms).
The B-45A Tornado had a cruise speed of 393 knots (452 miles per hour/728 kilometers per hour), and maximum speed of 492 knots (566 miles per hour (911 kilometers per hour) at 4,000 feet (1,219 meters). Its service ceiling was 46,800 feet (14,265 meters) and it had a maximum range of 1,886 nautical miles (2,170 statute miles/3,493 kilometers).
The bomb load was 22,000 pounds (9,979 kilograms). (It was capable of carrying the Grand Slam bomb.) Two Browning .50-caliber AN-M3 machine guns were mounted in the tail for defense, with 600 rounds of ammunition per gun.
41 B-45As were modified the the “Back Breaker” configuration, which enabled them to be armed with nuclear weapons.
The B-45 served with both the United States Air Force and the Royal Air Force. 143 were built, including the three XB-45 prototypes.
On 20 September 1948, the first production B-45A-1-NA Tornado, 47-001, was put into a dive to test the airplane’s design load factor. During the dive, an engine exploded, which tore off several cowling panels. These hit the horizontal stabilizer, damaging it. The B-45 pitched up, and both wings failed due to the g load. The prototype had no ejection seats and test pilots George Krebs and Nicholas Gibbs Pickard, unable to escape, were both killed.
George William Krebs
George William Krebs was born in Kansas City, Missouri, 5 March 1918. He was the first of three children of William J. Krebs, an advertising executive, and Betty Schmitz Krebs. He attended Southwest High School, graduating in 1935.
Krebs studied at the Massachussetts Instititute of Technology (M.I.T.) at Cambridge, Massachussetts. He was a member of the Sigma Chi fraternity.
In 1940, Krebs was the owner of a Luscombe airplane distributorship in Kansas City. He had brown hair, blue eyes and a ruddy complexion. He was 5 feet, 9 inches tall (1.75 meters) and weighed 135 pounds (61 kilograms).
George Krebs married Miss Alice Bodman Neal at Kansas City, Missouri, 26 December 1942. They had one son, William John Krebs II, born 1944.
During World War II, Krebs was employed as a test pilot at the North American Aviation, Inc., B-25 Mitchell medium bomber assembly plant at Kansas City, Kansas. Prior to taking over the XB-45 project, he was the chief test pilot at K.C.
North American Aviation B-25 Mitchell medium bombers near completion at the Kansas City, Kansas, bomber plant. (Alfred T. Palmer)Nicholas Gibbs Pickard
Nicholas Gibbs Pickard was born at Brooklyn, New York, 5 November 1916. He was the second of three children of Ward Wilson Pickard, a lawyer, and Alice Rossington Pickard.
During World War II, Pickard served as a ferry pilot for the Royal Air Force Transport Command.
On 21 January 1944, Captain Pickard married Miss Kathleen Baranovsky at Montreal, Quebec, Canada. They had two daughters, Sandra and Manya.
Following the war, Pickard was employed as a test pilot by North American Aviation.
Nicholas Gibbs Pickard was buried at the Pacific Crest Cemetery, Redondo Beach, California.
The tenth production North American Aviation B-45A-1-NA Tornado, 47-011, in flight. (U.S. Air Force)
North American Aviation X-15A 56-6670 carried aloft by Boeing NB-52A Stratofortress 52-003. The absence of frost on the fuselage of the X-15 shows that no cryogenic propellants are aboard for this captive flight. The chase plane is a Lockheed F-104A-15-LO Starfighter, 56-0768. This Starfighter suffered an engine failure on take off at Edwards AFB, crashed and was destroyed, 30 June 1959. (NASA)
10 March 1959: With North American Aviation’s Chief Engineering Test Pilot Albert Scott Crossfield in its cockpit, the X-15 hypersonic research rocket plane was airborne for the first time. X-15A 56-6670 was carried aloft under the wing of the Boeing NB-52A Stratofortress drop ship, 52-003, for a series of captive flights. The purpose was to verify that all the systems on both the X-15 and the B-52 were properly functioning up to the point that the drop would occur.
The NB-52A Stratofortress flight crew, left to right: Harry W. (“Bill”) Berkowitz, NAA, Launch Panel Operator; Captain John E. (“Jack”) Allavie, USAF, Pilot; Captain Charles C. Bock, Jr., USAF, Aircraft Commander, at Edwards AFB, 7 February 1959. (U.S. Air Force via Jet Pilot Overseas)North American Aviation X-15A 56-6670 carried aloft by Boeing NB-52A Stratofortress 52-003. The absence of frost on the fuselage of the X-15 shows that no cryogenic propellants are aboard for this captive flight. (NASA)
Fully settled in my tiny flight office, I could speak by radio to the B-52 pilot, Charlie Bock, who was about thirty feet away in the nose of the mother plane, out of sight. . .
As we sat, waiting at the end of the long runway while chase planes took off and circled, the clock on the instrument panel of the X-15 showed 0955. . . On signal, B-52 pilot Charlie Bock cobbed the eight engines, standing hard on the brake pedal. As the engines wound up to full military power, the X-15 trembled and the noise was tremendous. Through my radio earphones I heard Bock call a countdown for the benefit of the official movie cameramen who would record every inch of the takeoff:
“Five . . . four . . . three . . . two . . . one. BRAKE RELEASE.”
One hundred thirty tons of aluminum, fuel, Inconel X, five men and the hope of a nation began rolling down the long runway. . .
As we rolled, the huge runway distance markers flashed by, clocking our path: 14,000 . . . 13,000 . . . 12,000 . . . 8,000. When the X-15 air-speed indicator reached 170 knots, I noted only a minor vibration. We would continue the takeoff. 6,000 . . . 5,000 . . . 4,000, and we broke ground. It was smooth and gentle, like the take-off of an airliner. The air-speed indicator crept up to 260 knots. The parched brown desert fell away. . . .
—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, Chapters 34 and 35 at Pages 316–321.
X-15A 56-6670 under the wing of NB-52A 52-003 at high altitude. Scott Crossfield is in the cockpit of the rocketplane. (Air Force Flight Test Center History Office, U.S. Air Force)
The gross weight of the combined aircraft was 258,000 pounds (117,000 kilograms). After a takeoff roll of 6,200 feet (1,890 meters) the B-52/X-15 lifted of at 168 knots (193 miles per hour/311 kilometers per hour). During the 1 hour, 8 minute flight the the B-52 climbed to 45,000 feet (13,716 meters) and reached a speed of 0.83 Mach (548 miles per hour/881 kilometers per hour).
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.
Test pilot Albert Scott Crossfield with X-15 56-6670 attached to the right wing pylon of NB-52A 52-003 at Edwards Air Force Base. (North American Aviation Inc.)
The first flight took place 8 June 1959, again, with Scott Crossfield in the cockpit of the Number 1 ship, 56-6670.
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 planned 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. 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.
Scott Crossfield prepares for a flight in the North American Aviation X-15A. Crossfield is wearing a David Clark Co. MC-2 full-pressure suit and MA-3 helmet, which he helped to develop. (NASA)
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 dihedral, 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.
X-15A cockpit with original Lear Siegler instrument panel. (NASA)
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.
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).
North American Aviation, Inc. X-15A 56-6670 on Rogers Dry Lake, Edwards Air Force Base, California. (NASA)
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.
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): was 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.
Two Reaction Motors Division XLR11-RM-5 four-chamber rocket engines installed on an X-15. (NASA)
Delays in the production of the planned Reaction Motors XLR99 rocket engine forced engineers to adapt two vertically-stacked Reaction Motors XLR11-RM-5 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’ four chambers could be ignited individually. Each engine was rated at 11,800 pounds of thrust (58.49 kilonewtons) at Sea Level.
The Reaction Motors XLR99-RM-1 rocket engine was throttleable by the pilot from 28,500 to 60,000 pounds of thrust. 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 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/ 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.
North American Aviation Inc./U.S. Air Force/NASA X-15A 56-6670 hypersonic research rocketplane on display at the National Air and Space Museum. (NASM)
3 April 1941: North American Aviation test pilot Robert Creed Chilton takes his first flight—a one hour familiarization—in the company’s prototype of a new fighter for the Royal Air Force, the NA-73X, NX19998, at Mines Field. (Mines would later become Los Angeles International Airport, LAX.)
