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The X-1 marked a new departure in aviation development. Built by Bell Aircraft Company, the bullet-shaped research vehicle was glide-tested successfully at Pinecastle Air Force Base (now McCoy AFB), Fla., early in 1946. The X-1, like later rocket research aircraft, was dropped from the bomb bay of a "mother ship," in this case a B-29. [More]

 

 

The X-1

The X-1 marked a new departure in aviation development. Built by Bell Aircraft Company, the bullet-shaped research vehicle was glide-tested successfully at Pinecastle Air Force Base (now McCoy AFB), Fla., early in 1946. The X-1, like later rocket research aircraft, was dropped from the bomb bay of a "mother ship," in this case a B-29.

Upon completion of glide and landing tests, the X-1 was transported to Muroc, home of the embryo Air Force Flight Test Center, for the powered-flight phase of contractor testing.

The X-1's first powered flight was achieved on December 9, 1946. The Air Force took over the flight test program from the contractor on July 27, 1947. Program supervision was provided by Air Materiel Command's Aircraft Laboratory at Wright-Patterson Air Force Base, Ohio.

Although data accumulated during the first few flights indicated that the X-1 would never break the sound barrier (approximately 760 m.p.h. at sea level) the Air Force test team was convinced that it could.

Proof positive of the Air Force hypothesis came on October 14, 1947, when X-1 pilot Capt. Charles E. Yeager, on the ninth flight of the Air Force test series, exceeded the speed of sound in level flight.

Subsequent flights established the top speed of the X-1 at 967 m.p.h. Maximum altitude attained was 73,000 feet.

By 1950 the Air Force X-1 had served its purpose. On August 26, 1950, Air Force Chief of Staff General Hoyt Vandenberg formally presented the X-1 to Doctor Alexander Wetmore, secretary of the Smithsonian Institution. It is now on display in the Smithsonian's National Air Museum.

Two additional models of the X-1 were built. One went to the National Advisory Committee on Aeronautics' High Speed Flight Station at Edwards. From 1948 to 1951, NACA personnel used this X-1 to gather data on control, stability, buffeting and other aerodynamic phenomena associated with transonic and supersonic flight. On March 4, 1948, NACA test pilot Herbert Hoover became the first civilian to make a supersonic flight. The NACA X-1 was modernized in 1951 and again in 1954, and was redesignated the X-1E.

The third X-1 was delivered to Edwards in April 1951, for contractor testing. With a larger fuel capacity and a new, low-pressure fuel system, this aircraft was programmed to exceed mach 2. Unfortunately the X-1 and its B-50 carrier aircraft were destroyed by an explosion in the research craft on November 9, 1951, during defueling following a captive flight.

Specifications:
Power Plant: Reaction Motors 6,000-lb. thrust, four-chambered, liquid-fueled (LOX and alcohol) rocket engine with a burning time of 150 seconds.
Dimensions: Length 31'; height 8' 2 1/2"; wing span 28'
Top Speed: 967 m.p.h.
Maximum Altitude: 73,000 ft.

 

First powered flight: 9 Dec. 1946 Final flight: Jan. 1958 (X-1B)

 

Purpose: The Bell X-1 rocket aircraft was designed specifically for research in the transonic speed range. Aircraft of the period, including F-80 and F-84 Jets, were limited to Mach numbers near 0.8 and 0.85 and could reach these speeds only in hazardous dives. In reaching subsonic speeds, these aircraft were virtually uncontrollable making it desirable to build a research aircraft which would be slowed merely by cutting the engine. Advanced X-1 series emphasized research in such areas as aerodynamic heating, pilot reaction control systems, and problems of supersonic flight.

Description: The bullet-shaped X-1 was propelled by a four-chambered, liquid-fueled rocket engine with a burning time of 150 seconds. An improved version, the X-1A, featured turbo-driven fuel pumps, nitrogen-pressure fuel feed, increased fuel capacity, longer fuselage, and a nitrogen-pressurized cockpit modified for improved visibility.

Significant occurrences: The Air Force took over the flight test program from the contractor on 27 July 1947 and although data accumulated during the first few flights indicated that the X-1 would not break the sound barrier, Capt. Charles Yeager on 14 October 1947 exceeded the speed of sound in level flight. Later flights established the top speed of the X-1 at 967 mph and the maximum altitude attained was 73,000 feet. The second X-1 went to the NACA and after testing and modernizing in 1951 and 1954 was re-designated the X-1E. The third X-1 was destroyed by an explosion during contractor testing on a captive flight on 9 Nov. 1951. The X-1A made its first powered flight on 21 Feb. 1953; Major Yeager reached a speed of 1,650 mph in the aircraft on 12 Dec. 1953 and Major Arthur Murray attained an altitude of 90,000 feet in the craft on 4 June 1954. The plane was transferred to the NACA on 1 March 1955 but was destroyed in an explosion on 8 August 1955.

Contributions: The X-1 became the first aircraft to exceed the speed of sound in level flight and provided data on control, stability, buffeting, and other aerodynamic phenomena associated with transonic and supersonic flight. The X-1B was modified for investigation of aerodynamic heating and characteristics of reaction controls and during a three-year test program provided NACA with data on heat flow, effects of internal heat sources and sinks, and the effects of boundary-layer transition and aerodynamic interference. Research into reaction controls during the X-1B test series involved test flights at altitudes above 90,000 feet and paved the way for the hydrogen peroxide reaction system used in the X-15.

 

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X-1 Cockpit	In Boston on its way to the NASM - 25 Aug 50	Being launched from B-50 "Mother ship"
3/4 front view - S/N 46-063	In hangar - engine test S/N 46-063	Engine exhaust detail
Under construction - fuselage joined	Under Construction - fuselage in segments	Concept Wind Tunnel Model - Aft swept wings
Concept Wind Tunnel Model - forward swept wings	Concept Wind Tunnel Model - straight wings with tapered wingtips	3/4 front-top view
Front view	Side view with cockpit hatch removed - S/N 46-063	X-1 46-062 and 46-063 with mother ship
Mother ship with X-1	X-1 with Chuck Yeager - after first powered takeoff of a supersonic aircraft, 5 Jan 49	X-1 with Chuck Yeager - posed photograph taken 9 Apr 53
	In flight - S/N 46-062

Courtesy of The Air Force Museum

 

The XLR Rocket Motor

The first of the rocket-powered research aircraft, the X-1 (originally designated the XS-1), was a bullet-shaped airplane that was built by the Bell Aircraft Company for the US Air Force and the National Advisory Committee for Aeronautics (NACA).

The mission of the X-1 was to investigate the transonic speed range (speeds from just below to just above the speed of sound) and, if possible, to break the "sound barrier".

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The Bell X-1E

The XS-1 program not only proved that humans could go beyond the speed of sound, it reinforced the understanding that technological barriers could be overcome.

Many structural and aerodynamic advances were pioneered by the original XS-1s, including extremely thin, yet exceptionally strong wing sections, supersonic fuselage configurations, control system requirements, powerplant compatibility, and cockpit environment.

For the first time in a transonic-capable aircraft, an all-moving stabilizer was utilized. The flights of the XS-1's opened up a new era in aviation.

 

The X-1 :Background

The XS-1 was developed as part of a cooperative program initiated in 1944 by the National Advisory Committee for Aeronautics (NACA) and the U.S. Army Air Forces (later the U.S. Air Force) to develop special manned transonic and supersonic research aircraft.

On March 16, 1945, the Army Air Technical Service Command awarded the Bell Aircraft Corporation of Buffalo, New York, a contract to develop three transonic and supersonic research aircraft under project designation MX-653.

Initially designated the XS-1, (the S, which stood for Supersonic was dropped early in the program), the X-1 was the first aircraft given the `X' designation. 3 X-1's were built, and carried USAF serial numbers 46-062, 46-063 and 46-064.

The X-1 became the first human controlled aircraft to exceed the speed of sound in controlled level flight. This historic event occurred on October 14, 1947, while the X-1 #1 (nicknamed "Glamorous Glennis") was piloted by Captain Charles (Chuck) Yeager. Top speed achieved on this flight was 670 mph (1,078 km/h, or Mach 1.015). Altitude at the time the sound barrier was broken was approximately 45,000 ft.

The X-1 was carried under a Boeing B-29 Superfortress to an altitude of 20,000 ft, where it was drop-launched. The Reaction Motors E6000-C4 rocket engine was not throttleable, but had 4 combustion chambers which could be operated individually or simultaneously.

Though the X-1 was built with straight wings, it was able to achieve controlled flight through the "sonic barrier" due to its variable pitch horizontal stabilizer. Initially, this surface was designed to be adjusted before flight and would remain in a fixed position.

This design was changed before power flights commenced. The design change permitted the pilot to adjust the pitch of the horizontal stabilizer during flight, via an electric motor. General Chuck Yeager has often credited the success of the X-1 with the pilot adjustable variable pitch horizontal stabilizer. It was years before other nations' design teams were able to duplicate this concept (see The Tale of the Tail, below ).

 The second X-1 differed from the first and third in that it had a thicker wing (10% thickness/cord ratio vs. 8%).

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X-1E (modified X-1) on display at NASA's Dryden Flight Research Facility.

The third X-1 was over 3 years late in delivery and successfully completed only 1 drop-glide flight. Following its second flight, in which it remained attached to the B-29 for fuel system testing, the fully loaded fuel tanks were about to be emptied when an explosion destroyed the X-1. Fortunately, no one was killed as a result of this accident.

Though several significant modification were considered for the X-1 (replacing the straight wings with swept wings, and a V-tail configuration), the most significant modification was the improved windscreen on the third X-1. This windscreen was stronger than provided on the first 2 X-1's and did not require straps to hold it in place. This greatly improved visibility for the pilot.

The X-1E
After the loss of the 3rd X-1 and the X-1D. The need remained for a higher performance performance X-1 for the NACA to conduct testing in. The 2nd X-1 (46-063) was almost completely rebuilt and re-designated as the X-1E. Significant modifications include and updated canopy, ultra-thin wings (4% thickness/cord ratio) and a rocket assisted ejection seat.

 

The maximum altitude achieved by the X-1E was 75,000 ft, and the top speed was Mach 2.24 (1,450 mph). The plane was retired from service in November of 1956 after 26 flights.

The first X-1 is on permanent display at the Smithsonian Air & Space museum. The second X-1, which was reconfigured as the X-1E, is on permanent display at the NASA's Dryden Flight Research Facility.

 

The Tale of the Tail:   Click on Picture to enlarge In 1942 the British Air Ministry and the Ministry of Aviation approached Miles Aircraft with a top-secret contract for a turbojet research plane designed to reach supersonic speeds. This plane, the Miles M.52 was designed for a speed of 1000mph at 36,000 feet to be reached in 1.5 minutes. The functional model of the M.52 included a fully moveable tail surface.  Though not officially documented by British or American agencies, many believe that the X-1's moveable tail surface was "borrowed" from the M.52 design, which were initially tested on the Miles Falcon-Six racer. The M.52 program never went past the test model stage and test models were not flown until 1947, well after the X-1 had broken the "sound barrier". While it is possible that the X-1's movable tail surface was the result of the M.52's design, it was the X-1 that proved the concept in flight.

 

 

The X-1 Series

 

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Three X-1s were built, the type first being air-launched un-powered, from a Boeing B-29 Superfortress on Jan. 19, 1946. Powered flights began in Dec. of the same year. Their designations as follows: X-1-1 (46-062), X-1-2 (46-063), X-1-3 (46-064).

They were flown by eighteen pilots from 1946 to 1951.
 

The first of the three X-1s was glide-tested at Pinecastle Field, FL, in early 1946. The first powered flight of the X-1 was made on Dec. 9, 1946, at Muroc Army Air Field (later re-designated Edwards Air Force Base) with Chalmers Goodlin, a Bell test pilot, at the controls.

The second X-1 was used by the NACA for high speed flight research; the third aircraft was destroyed at Edwards AFB during fueling operations after completing only one un-powered glide flight.

The X-1A was similar to the X-1, except for having turbo-driven fuel pumps (instead of a system using nitrogen under pressure), a new cockpit canopy, longer fuselage and increased fuel capacity. In this aircraft a speed of Mach 2.435 was achieved on Dec. 12, 1953, and the following June an altitude of 90,000 ft. was reached. In Sept. 1954 the aircraft was given to the NACA and on July 20, 1955 it made its first and only flight for the NACA prior to being destroyed on Aug.8 1955.

The X-1B was similar to the X-1A except for having a slightly different wing. This aircraft was used for high speed research by the Air Force prior to being turned over to the NACA in Jan. 1955. This aircraft was flown by the NACA until Jan 1958.

Following the X-1B was the projected X-1C, which was cancelled while still in the mock-up stage and also the X-1D. The latter aircraft was destroyed in Aug. 1951 after being jettisoned from its B-50 carrier plane, following an explosion.

The last of the series was the X-1E. This was the second of the original X-1s fitted with new wings, turbo-driven fuel pumps and a knife-edge windscreen. This aircraft was modified and flown exclusively by the NACA. This aircraft made its first flight on Dec. 12, 1955 and was flown until Nov. 1958.
 

The X-1 Timeline

 

The X-1-1

The Bell X-1-1 was equipped with a 10 percent wing and 8-percent tail, (measured as the thickness divided by the chord of the airfoil), powered with an XLR-11 rocket engine and was air-launched from under a B-29A (45-21800). The X-1-1 was glide-tested at Pinecastle Army Air Field, Orlando, Florida, beginning on January 25, 1946.

The first powered flight of the X-1-1 was made on April 11, 1946, at Muroc Army Air Field with Chalmers "Slick" Goodlin, a Bell test pilot, at the controls.

On October 14, 1947, with USAF Captain Charles "Chuck" Yeager as pilot, the X-1-1 flew faster than the speed of sound for what is generally accepted as the first supersonic flight by a piloted aircraft. Captain Yeager ignited the four-chambered XLR-11 rocket engines after being air-launched from under the bomb bay of a JTB-29A (#45-21800) at 21,000 feet. The 6,000-pound thrust ethyl alcohol/liquid oxygen burning rockets, built by Reaction Motors, Inc., pushed him up to a speed of Mach 1.06 at an altitude of 45,000 feet.

On January 5, 1949, the X-1-1 aircraft with Yeager as pilot achieved the only ground takeoff of the X-1 program. He reached just over 23,000 feet before the limited propellant was exhausted.

Captain Yeager was also the pilot when the X-1-1 reached its maximum speed, Mach 1.45. Another USAF pilot. Lt. Col. Frank Everest, Jr., was credited with taking the X-1-1 to its maximum altitude of 71,902 feet.

The X-1-1 retired on May 12, 1950 after making eighty-two glide and powered flights with ten different pilots. On August 26, 1950 the aircraft became a permanent resident of the National Air Museum, In Washington, D.C.

 

The X-1-2

 

The X-1-2 was also equipped with the 10-percent wing and 8-percent tail, powered with an XLR-11 rocket engine and was air-launched from under a B-29A (45-21800). The aircraft made its first powered flight on December 9, 1946 with Chalmers "Slick" Goodlin at the controls. As with the X-1-1 the X-1-2 continued to investigate transonic/supersonic flight regime. NACA pilot Herbert Hoover became the first civilian to fly Mach 1, March 10, 1948.

X-1-2 flew until October 23, 1951, completing 74 glide and powered flights with nine different pilots, when it was retired to be rebuilt as X-1E.

 

 

The X-1-3

 

The X-1-3 was delayed due to a turbo pump development problem. It eventually fell three years behind the delivery date with its arrival to NACA High-Speed Flight Research Station at Edwards, California, in April 1951. The first glide flight was made on July 20, 1951. On November 9, 1951 following a "captive" flight the X-1-3 blew up under its own launch airplane, [EB-50A (46-006)] during static ground operations at Edwards Air Force Base, California. The B-50 was destroyed and the Bell pilot of the X-1-3, Joseph Cannon was severely burned.

 

 

 

The X-1A

The Bell X-1A was the first aircraft of the second generation of the X-1 variants. Longer and heavier than the original X-1 with a bubble canopy for better vision, the X-1A was powered by the same Reaction Motors XLR-11 rocket engine.

The main difference though, was in the fuel system. It had larger fuel tanks and a turbo-driven fuel pump to enable the X-1A to operate under power for much longer than the original X-1, which enabled it to fly higher farther and faster than the original X-1.

When Bell's company test pilot Jean "Skip" Ziegler flew it, Chuck flew as a chase pilot on these flights. But Ziegler got "spooked" by the aircrafts handling. When he looked out of the canopy at the wings, he saw shockwaves forming and told Yeager that his "aileron's were buzzing like mad", Yeager told him to "Press On and it will smooth on out for you" and continue with the flight, as this was an identical trait of the original X-1. Ziegler didn't "Press On" and the same thing happened on his next two flights.

Thinking that the airplane was unstable, he began to worry Bell's engineers with his concern. Bell's engineers decided to have the airplane returned to the plant at Buffalo for static ground testing.

Ziegler also went back to Buffalo and while he was there, he took part in a fueling test of the X-2, another Bell experimental rocket-powered research airplane. While flying with the X-2 mated to the B-50 motherplane, Skip was in the cockpit when the LOX (liquid oxygen) tank suddenly blew up at 20,000 feet. Ziegler and the X-2 were torn from the B-50 and fell the 20,000 feet to the bottom of Lake Ontario. Poor Ziegler had no chance. As Yeager says in his autobiography "same old story, another civilian test-pilot in over his head".

Bell asked the Air Force if they would take over the testing of the X-1A and requested that Yeager take over as test-pilot. General Boyd agreed and and brought back together Jack Ridley, Dick Frost & Jack Russell, Yeager's crew chief (the old X-1 team) to help.

Any pilot flying the original X-1 new that if they ever had to bail out they would end up both sides of the wing and had no chance of survival. The parachute they had served no other purpose than that something to sit on. The X-1A was another kettle of fish entirely. When the pilot was strapped in, the canopy was bolted down and the only way of survival was to land the airplane successfully!

Yeager flies the X-1A

Chuck Yeager first flew the X-1A on November 21st 1953, the flight was perfect and Yeager flew on out to Mach 1.3 at 45,000 feet. The airplane flew beatifully and exactly like the X-1 and Yeager felt right at home.

Two more flights on December 2nd and December 8th produced speeds of Mach 1.5 & Mach 1.9. Yeager had told his crew chief, Jack Russell, "Hey, you sumbitch, if I get a fire warning light, I'm gonna strap you in my lap on the next ride and let you deal with it." Russell and the rest of his ground crew knew Chuck's neck was on the line and kept the rocket chambers so clean that they were germ-free!

Fourth Powered Flight - December 12th 1953

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Over the years Chuck Yeager was to set many speed and altitude records in the Bell X-1 and the Bell X-1A. In fact he still holds the world airspeed record for a straight winged aircraft of Mach 2.44 or 1648 mph.

This record was set on the 12th December 1953 in the X-1A. On this flight he was strapped into the cockpit of the X-1A which was shackled to the belly of the B-50 motherplane and dropped from high altitude over Edwards Air Force Base in southern California, he lit the Four Rocket Chambers and proceeded to climb to 76000 feet, nosing the airplane over he commenced with his speed run. When he reached his maximum speed of Mach 2.44 the aircraft suffered from roll coupling and he began a wild and violent tumble towards the desert floor.

Careening all over the sky, the airplane was snapping, rolling and spinning all at once, pilots call this "going divergent on three axis", Chuck called it hell.

The X-1A had no ejection seat, so to save himself he also had to save the aircraft. After spinning and tumbling for 51000 feet in 51 seconds, the ship flipped into a normal spin at 30,000 and Chuck thought "I know how to get out of this" and began standard spin recovery.

He broke the cockpit canopy with his head and it was only due to the superb skills of the pilot that he and the aircaft survived.

Managing to be humorous in his radio message to Jack Ridley, he said "I think I can get back to base okay, Jack. Boy, I'm not gonna do that again. Those (Bell) guys were so right (warning against going faster than Mach 2.3). If I hadda (ejection) seat you wouldn't still see me sitting in here".

 

Summing up

There were no more high speed attempts in the X-1A, the Air Force concentrating on high altitude flight, Major Arthur "Kit" Murray getting up to 90,400 feet. After Chuck's last flight in the X-1A, he and the Air Force decided that he should get out of the testing business before he became another statistic (and road) at Edwards Air Force Base.

On this subject, Chuck Yeager is the only living test-pilot to have a road named after him at Edwards AFB (Yeager Boulevard), all the other roads at the base are named after pilots who augured in.

 

 

 

The Track To Survival

This article was excerpted from the Aerospace HeritageSeries,
Vol. 2, No. 1, VALOR. 1985, the Air Force Association.
Published by the Aerospace Education Foundation,
an affiliate of the Air Force Association,
 

by John L. Frisbee -

 

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Someone had to find out if a pilot could eject from an airplane at supersonic speed and live.

On Oct. 14, 1947, Capt Chuck Yeager broke the sound barrier in the experimental rocket-propelled X-1. Scientists and engineers now knew that an airplane and its pilot could safely fly faster than the speed of sound. But could a pilot bail out at such speed and survive? That was a question that had to be answered quickly, for USAF's first supersonic fighters were just over the horizon.

It was certain that the wind blast on leaving the cockpit could dislocate limbs and break bones. There also would be rapid--almost instantaneous--deceleration, subjecting the pilot to very high G loads. Some scientists thought the human body could endure no more than eighteen Gs, or eighteen times the force of gravity – -far less than a pilot would experience in a supersonic bailout.

Two approaches to the problem were evident: first, build a complex, heavy, expensive ejection capsule for the pilot; second, find out what stresses an unprotected human could survive. The Air Force assigned the second approach to flight surgeon Lt. Col. John Lt. Col. John Paul Stapp , a bachelor with a philosophical bent, a quiet sense of humor, a love of classical music, and unquenchable curiosity.

Under Colonel Stapp's direction, Northrop Aircraft Co. built at Edwards (then Muroc) Air Force Base, Calif., a 2,000-foot rail track for a rocket-driven "sled" that could accelerate to nearly 1,000 mph. Toward the end of the track, scoops beneath the sled would dig into a pool of water, jerking the sled from several hundred miles an hour to a stop in just over a second, simulating the deceleration of a high-speed ejection. Early passengers were dummies. At the end of one run, the safety harness broke and the dummy plunged through a one-inch wood windscreen, sailing 700 feet across the desert. A few more rides, a few improvements, and it was time for the first human passenger. 

Stapp decelerating in the   G-Whiz sled. This five frame 'movie' shows the stress he experienced. Courtesy EAFB History Office

In December 1947, Paul Stapp began riding the sled at increasing speeds. By May of the following year, he had rocketed down the track sixteen times and withstood a force of thirty-five Gs during deceleration. So much for the eighteen-G limit of human endurance.

What was the sudden stop like? Col. Stapp reported: "It felt as though my eyes were being pulled out of my head . . .I lifted my eyelids with my fingers, but I couldn't see a thing . . ..They put me on a stretcher, and in a minute or two I saw some blue specks . . . In about eight minutes . . . I saw one of the surgeons wiggle his fingers at me, and I was able to count them. Then I knew my retinas had not been detached, and that I wasn't going to be blind."

Col. Stapp continued to ride the sled at Edwards until 1953, when he was sent to Holloman Air Force Base, N.M., to work with a longer track and an improved sled called Sonic Wind. There, on December 10, 1954, the forty-four-year-old Stapp rode the sled to a record 632 miles an hour, decelerating to zero in a second and a quarter with a force of more than 40 Gs. Momentarily his body weight was about 6,800 pounds. Wind blast and deceleration were equivalent to a high-altitude ejection at supersonic speed.

Out of these wild rides came improved helmets, arm and leg restraints, better aircraft seats, stronger safety harnesses, and techniques for positioning the body to help absorb unearthly forces. And for Paul Stapp? During his twenty-nine rides came several retinal hemorrhages, cracked ribs, and two broken wrists. The second (broken wrist) he set himself while walking back to the Aero Medical Field Laboratory that he headed.

Col. Stapp was named winner of the Cheney Award for 1954. That award recognizes acts of "valor, extreme fortitude, or self-sacrifice in a humanitarian interest performed in connection with aircraft." That same year, he also won AFA's Theodore von Karman Trophy for distinguished service in the field of aerospace science. But for unassuming Paul Stapp, the greatest reward was the knowledge that he had helped make a dangerous profession a little less hazardous – that many jet pilots who had to abandon their planes were still alive and flying.

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The XLR-11 rocket engine

War is the breeding ground of heroes. In times of peace, few have the opportunity or the dedication and courage to risk permanent injury or death, as Lt. Col. John Paul Stapp did repeatedly, so that others may live. He exemplified in extraordinary measure "the noble quality we call valor."

The X-1 was powered by a four-chamber, XLR-11 rocket engine, fueled by a mixture of liquid oxygen and diluted ethyl alcohol.

Although not throttleable, the chambers could be fired individually or in groups to produce a maximum rated thrust of 6000 lbs. at sea level.

Fuel capacity limited full-power of the engine to about five minutes.

 

 

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