Tag Archives: Joseph Albert Walker

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.

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. 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/ 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)

© 2016, Bryan R. Swopes

Facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

20 December 1962

Milton O. Thompson with a Lockheed JF-104A Starfighter at Edwards Air Force Base, 20 December 1962. [This aircraft has reaction control jets, which identify it as 55-2961. It was later designated as NASA 818 and is currently on display at the National Air and Space Museum.] (NASA)
Milton O. Thompson with a Lockheed JF-104A Starfighter at Edwards Air Force Base, 20 December 1962. (NASA photograph via Jet Pilot Overseas)
20 December 1962: Milton Orville Thompson, a NASA test pilot assigned to the X-15 hypersonic research program, was conducting a weather check along the X-15’s planned flight path from Mud Lake, Nevada, to Edwards Air Force Base in California, scheduled for later in the day. Thompson was flying a Lockheed F-104A-10-LO Starfighter, Air Force serial number 56-749, call sign NASA 749.

NASA 749, a Lockheed JF-104A Starfighter, 56-749, with an ALSOR sounding rocket on a centerline mount, at Edwards Air Force Base. Right front quarter view. (NASA)
NASA 749, a Lockheed JF-104A Starfighter, 56-749, with an ALSOR sounding rocket on a centerline mount, at Edwards Air Force Base. (NASA)

In his autobiography, At the Edge of Space, Thompson described the day:

“The morning of my weather flight was a classic desert winter morning. It was cold, freezing in fact, but  the sky was crystal clear and there was not a hint of a breeze—a beautiful morning for a flight.”

Completing the weather reconnaissance mission, and with fuel remaining in the Starfighter’s tanks, Milt Thompson began practicing simulated X-15 approaches to the dry lake bed.

X-15 pilots used the F-104 to practice landing approaches. The two aircraft were almost the same size, and with speed brakes extended and the flaps lowered, an F-104 had almost the same lift-over-drag ratio as the X-15 in subsonic flight. Thompson’s first approach went fine and he climbed back to altitude for another practice landing.

Lockheed F-104A-10-LO Starfighter 56-749 (NASA 749) carrying a sounding rocket on a centerline mount. (NASA)
Lockheed F-104A-10-LO Starfighter 56-749 (NASA 749) carrying an ALSOR sounding rocket on a centerline mount. (NASA)

When Milt Thompson extended the F-104’s flaps for the second simulated X-15 approach, he was at the “high key”— over Rogers Dry Lake at 35,000 feet (10,668 meters) — and supersonic. As he extended the speed brakes and lowered the flaps, NASA 749 began to roll to the left. With full aileron and rudder input, he was unable to stop the roll. Adding throttle to increase the airplane’s airspeed, he was just able to stop the roll with full opposite aileron.

Thompson found that he could maintain control as long as he stayed above 350 knots (402 miles per hour/648 kilometers per hour) but that was far too high a speed to land the airplane. He experimented with different control positions and throttle settings. He recycled the brake and flaps switches to see if he could get a response, but there was no change. He could see that the leading edge flaps were up and locked, but was unable to determine the position of the trailing edge flaps. He came to the conclusion that the trailing edge flaps were lowered to different angles.

Thompson called Joe Walker, NASA’s chief test pilot, on the radio and explained the situation:

I told him the symptoms of my problem and he decided that I had a split trailing edge flap situation with one down and one up.

“He suggested I recycle the flap lever to the up position to attempt to get both flaps up and locked. I had already tried that, but I gave it another try. Joe asked if I had cycled the flap lever from the up to the takeoff position and then back again. I said no. I had only cycled the flap lever from the up position to a position just below it and then back to the up position. Joe suggested we try it his way. I moved the flap lever from the up position all the way to the takeoff position and then back to the up position. As soon as I moved the lever to the takeoff position, I knew I had done the wrong thing.

“The airplane started rolling again, but this time I could not stop it. The roll rate quickly built up to the point that I was almost doing snap rolls. Simultaneously, the nose of the airplane started down. I was soon doing vertical rolls as the airspeed began rapidly increasing. I knew I had to get out quick because I did not want to eject supersonic and I was already passing through 0.9 Mach. I let go of the stick and reached for the ejection handle. I bent my head forward to see the handle and then I pulled it. Things were a blur from that point on.”

At the Edge of Space: The X-15 Flight Program, by Milton O. Thompson, Smithsonian Institution Press, Washington and London, 1992. Chapter 5 at Pages 119–120.

Impact crater caused by crash of Milt Thompson's Lockheed F-104 Starfighter, 20 Decemver 1962. NASA)
Impact crater caused by the crash and explosion of Milt Thompson’s Lockheed JF-104A Starfighter, 20 December 1962. (NASA)

As Thompson descended by parachute he watched the F-104 hit the ground and explode in the bombing range on the east side of Rogers Dry Lake. He wrote, “It was only 7:30 a.m. and still a beautiful morning.”

© 2016, Bryan R. Swopes

Facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

6 November 1958

Bell X-1E 46-063 on Rogers Dry Lake. (NASA)
Bell X-1E 46-063 on Rogers Dry Lake, 1955. (NASA)

6 November 1958: NASA Research Test Pilot John B. (Jack) McKay made the final flight of the X-1 rocketplane program, which had begun twelve years earlier.

Bell X-1E 46-063 made its 26th and final flight after being dropped from a Boeing B-29 Superfortress over Edwards Air Force Base on a flight to test a new rocket fuel.

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

When the aircraft was inspected after the flight, a crack was found in a structural bulkhead. A decision was made to retire the X-1E and the flight test program was ended.

The X-1E had been modified from the third XS-1, 46-063. It used a thinner wing and had an improved fuel system. The most obvious visible difference is the cockpit, which was changed to provide for an ejection seat. Hundreds of sensors were built into the aircraft’s surfaces to measure air pressure and temperature.

The Bell X-1E was 31 feet (9.449 meters) long, with a wingspan of 22 feet, 10 inches (6.960 meters). The rocketplane’s empty weight was 6,850 pounds (3,107 kilograms) and fully loaded, it weighed 14,750 pounds (6,690 kilograms). The rocketplane was powered by a Reaction Motors XLR11-RM-5 rocket engine which produced 6,000 pounds of thrust (26.689 kilonewtons). The engine burned ethyl alcohol and liquid oxygen. The X-1E carried enough propellants for 4 minutes, 45 seconds burn.

The Bell X-1E rocketplane being loaded into a Boeing B-29 Superfortress mothership for another test flight. (NASA)
The Bell X-1E rocketplane being loaded into NACA 800, a Boeing B-29-96-BW Superfortress mothership, 45-21800, for another test flight. (NASA)

The early aircraft, the XS-1 (later redesignated X-1), which U.S. Air Force test pilot Charles E. (“Chuck”) Yeager flew faster than sound on 1 October 1947, were intended to explore flight in the high subsonic and low supersonic range. There were three X-1 rocketplanes. Yeager’s Glamorous Glennis was 46-062. The X-1D (which was destroyed in an accidental explosion after a single glide flight) and the X-1E were built to investigate the effects of frictional aerodynamic heating in the higher supersonic ranges from Mach 1 to Mach 2.

Bell X-1E loaded aboard Boeing B-29 Superfortress, circa 1955. (NASA)
Bell X-1E 46-063 loaded aboard NACA 800, a Boeing B-29-96-BW Superfortress, 45-21800, circa 1955. (NASA)

The X-1E reached its fastest speed with NASA test pilot Joseph Albert Walker, at Mach 2.24 (1,450 miles per hour/2,334 kilometers per hour), 8 October 1957. Walker also flew it to its peak altitude, 70,046 feet (21,350 meters) on 14 May 1958.

NACA test pilot Joseph Albert Walker made 21 of the X-1E's 26 flights. In this photograph, Joe Walker is wearing a David Clark Co. T-1 capstan-type partial-pressure suit with a K-1 helmet for protection at high altitudes. (NASA)
NACA test pilot Joseph Albert Walker made 21 of the X-1E’s 26 flights. In this photograph, Joe Walker is wearing a David Clark Co. T-1 capstan-type partial-pressure suit with a K-1 helmet for protection at high altitudes. (NASA)

There were a total of 236 flights made by the X-1, X-1A, X-1B, X-1D and X-1E. The X-1 program was sponsored by the National Advisory Committee on Aeronautics, NACA, which became the National Aeronautics and Space Administration, NASA, on 29 June 1958.

The X-1E is on display in front of the NASA administration building at the Dryden Flight Research Center, Edwards Air Force Base, California.Bell X-1E 46-063 on display at Dryden Flight Research Center© 2016, Bryan R. Swopes

Facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

27 October 1954

NACA's chief project test pilot for the Douglas X-3, in the cockpit of the research aircraft, circa 1954-1956. (LIFE Magazine via Jet Pilot Overseas)
NACA’s chief project test pilot for the Douglas X-3, Joe Walker, in the cockpit of the research aircraft, circa 1954-1956. (LIFE Magazine via Jet Pilot Overseas)

October 27, 1954: between August 1954 and May 1956, Joseph A. Walker, the National Advisory Committee for Aeronautics’ chief project test pilot for the Douglas X-3 supersonic research aircraft, made twenty research flights in the “Stiletto.”

On the tenth flight, 27 October, Walker took the X-3 to an altitude of 30,000 feet (9,144 meters). With the rudder centered, he put the X-3 into abrupt left aileron rolls, first at 0.92 Mach and then at Mach 1.05. Both times, the aircraft violently yawed to the right and then pitched down. Walker was able to recover before the X-3 was completely out of control.

Screen Shot 2015-10-20 at 12.08.52
The Douglas X-3 during NACA flight testing, 1954-1956. (LIFE Magazine via Jet Pilot Overseas)

This was a new and little understood condition called inertial roll coupling. It was a result of the aircraft’s mass being concentrated within its fuselage, the gyroscopic effect of the turbojet engines and the inability of the wings and control surfaces to stabilize the airplane and overcome its rolling tendency. (Just two weeks earlier, North American Aviation’s Chief Test Pilot George S. Welch had been killed when the F-100A Super Sabre that he was testing also encountered inertial roll coupling and disintegrated.)

A post-flight inspection found that the X-3 had reached its maximum design load. The airplane was grounded for the next 11 months.

Unlike its predecessors, the Bell Aircraft Corporation's X1 and and X-2 rocketplanes, teh turbojet-powered Douglas X-3 took off under its own power. here, its two Westinghouse J37 engines are stirring up teh sand on Runway 35 at Rogers Dry Lake. (LIFE Magazine via jet Pilot Overseas)
Unlike its predecessors, the Bell Aircraft Corporation’s X1 and and X-2 rocketplanes, the turbojet-powered Douglas X-3 took off under its own power. Here, its two Westinghouse J37 engines are stirring up the sand on Runway 35 at Rogers Dry Lake. (LIFE Magazine via jet Pilot Overseas)

The Douglas X-3, serial number 49-2892, was built for the Air Force and NACA to explore flight in the Mach 1 to Mach 2 range. It was radically shaped, with a needle-sharp nose, very long thin fuselage and small straight wings. Two X-3 aircraft had been ordered from Douglas, but only one completed.

The X-3 was 66 feet, 9 inches (20.345 meters) long, with a wing span of just 22 feet, 8.25 inches (6.915 meters). The overall height was 12 feet, 6.3 inches (3.818 meters). The X-3 had an empty weight of 16,120 pounds (7,312 kilograms) and maximum takeoff weight of 23,840 pounds (10,814 kilograms).

It was to have been powered by two Westinghouse J46 engines, but when those were unsatisfactory, two Westinghouse XJ34-WE-17 engines were substituted. This was an axial flow turbojet with an 11-stage compressor and 2-stage turbine. It was rated at 3,370 pounds (14.99 kilonewtons) of thrust, and 4,900 pounds (21.80 kilonewtons) with afterburner. The XJ34-WE-17 was 14 feet, 9.0 inches (4.496 meters) long, 2 feet, 1.0 inch (0.635 meters) in diameter and weighed 1,698 pounds (770 kilograms).

The X-3 had a maximum speed of 706 miles per hour (1,136 kilometers per hour) and a service ceiling of 38,000 feet (11,582 meters).

The X-3 was very underpowered with the J37 engines, and could just reach Mach 1 in a shallow dive. The X-3′s highest speed, Mach 1.208, required a 30° dive. It was therefore never able to be used in flight testing the supersonic speed range for which it was designed. Because of its design characteristics it was very useful in exploring stability and control in the transonic range.

At one point, replacing the X-3’s turbojet engines with two Reaction Motors XLR-11 rocket engines was considered. Predictions were that a rocket-powered X-3 could reach Mach 4.2. However, with Mach 2 Lockheed F-104 becoming operational and North American Aviation’s X-15 hypersonic research rocketplane under construction, the idea was dropped. Technology had passed the X-3 by.

In addition to Douglas Aircraft test pilot Bill Bridgeman, the Douglas X-3 was flown by Air Force test pilots Lieutenant Colonel Frank Everest and Major Chuck Yeager and  NACA pilot Joe Walker.

Joe Walker resumed flight testing the X-3 in 1955. It’s last flight was 23 May 1956. After the flight test program came to an end, the X-3 was turned over to the National Museum of the United States Air Force, Wright-Patterson Air Force Base, Ohio.

NACA test pilot Joe Walker with the Douglas X-3. (LIFE Magazine via Jet Pilot Overseas)
NACA test pilot Joe Walker with the Douglas X-3. (LIFE Magazine via Jet Pilot Overseas)

© 2017, Bryan R. Swopes

Facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

22 August 1963

Joe Walker and the X-15 on Rogers Dry Lake at the end of a flight. Walker is wearing a David Clark Co. MC-2 full-pressure suit. (U.S. Air Force)

22 August 1963: On his twenty-fifth and last flight with the X-15 program, NASA Chief Research Test Pilot Joseph Albert Walker would attempt a flight to Maximum Altitude. Engineers had predicted that the X-15 was capable of reaching 400,000 feet (121,920 meters) but simulations had shown that a safe reentry from that altitude was risky. For this flight, Flight 91, the flight plan called for 360,000 feet (109,728 meters) to give Walker a safety margin. Experience had shown that slight variations in engine thrust and climb angle could cause large overshoots in peak altitude, so this was not considered an excessive safety margin.

For this flight, Joe Walker flew the Number 3 X-15, 56-6672. It was the only one of the three North American Aviation X-15s equipped with the Honeywell MH-96 flight control system, which had been developed to improve control of the rocketplane outside Earth’s atmosphere. This flight was the twenty-second for Number 3.

North American Aviation X-15 56-6672 immediately after being dropped by the Boeing NB-52 Stratofortress. (NASA)
North American Aviation X-15A 56-6672 immediately after being dropped by the Boeing NB-52 Stratofortress. (NASA)

Walker and the X-15 were airdropped from the Boeing NB-52A Stratofortress 52-003, The High and Mighty One, at 45,000 feet (13,716 meters) above Smith Ranch Dry Lake, Nevada, about half-way between the city of Reno and the NASA High Range Tracking Station at Ely. Launch time was 10:05:57.0 a.m., PDT. Walker ignited the Reaction Motors XLR99-RM-1 rocket engine. This engine was rated at 57,000 pounds of thrust. Experience had shown that different engines varied from flight to flight and that atmospheric conditions were a factor. Thrust beyond 60,000 pounds was often seen, but this could not be predicted in advance. The flight plan called for the duration of burn to be 84.5 seconds on this flight. The X-15 climbed at a 45° angle.

As Walker was about to shut down the engine according to plan, it ran out of fuel. The total burn time was 85.8 seconds, just slightly longer than planned.

“At burnout, Joe was passing 176,000 feet [53,645 meters] and traveling at 5,600 feet per second [1,707 meters per second]. He then began the long coast to peak altitude. It would take almost 2 minutes to reach peak altitude after burn out. Two minutes does not seem like a lot of time, but try timing it. Just sit back in your easy chair and count off the seconds. It is almost impossible to believe that you can continue to coast up in altitude for that length of time after the engine burns out. It gives you some feel for how much energy is involved at those speeds. For comparison, when you throw a ball up in the air as hard as you can, it only coasts upward a maximum of 4 or 5 seconds. The X-15 coasted up for 120 seconds.

“The airplane would coast up another 178,000 feet during that time to peak out at 354,200 feet. . . .”

At The Edge of Space: The X-15 Flight Program, by Milton O. Thompson, Smithsonian Institution Press, Washington, 1992, Chapter 5 at Page 125.

Joe Walker and the X-15 reached the peak of their ballistic trajectory at 354,200 feet (67.083 miles, 107,960 meters). Walker pitched the nose down to be in the proper attitude for atmospheric reentry. The X-15 decelerated as it hit the atmosphere and Walker experienced as much as 7 Gs. The rocketplane’s aerodynamic control surfaces again became operational as it descended through 95,000 feet (28,956 meters) and Walker leveled at 70,000 feet (21,336 meters). He then glided to a landing on Rogers Dry Lake at Edwards Air Force Base, California, after 11 minutes, 8.6 seconds of flight.

Flight 91 was the highest flight achieved by any of the X-15s. It was Joe Walker’s second flight into space. His record would stand for the next 41 years.

© 2016, Bryan R. Swopes

Facebooktwittergoogle_plusredditpinterestlinkedinmailby feather