First-Hand:The X-1 Project - Chapter 3 of the Experimental Research Airplanes and the Sound Barrier


By David L. Boslaugh, CAPT USN, Retired


General layout of the X-1. The liquid oxygen tank was placed ahead of the wing, and the alcohol tank behind the wing. The compartment above the wing would hold test instrumentation. Because the two tanks took up the entire circumference of the fuselage, tunnels were placed above and below the tanks to hold control cables, piping and wiring. NACA drawing

In the summer of 1944 Major Ezra Kotcher, on behalf ot the Army Air Force, began to look for a contractor capable of, and interested in, designing and building a ‘one-of-a-kind’ rocket propelled high speed research craft. [39, p.16] In November 1944, Robert Woods, Bell Aircraft Corporation’s chief design engineer, on a visit to the Air Technical Services Command (ATSC), happened to drop in to Kotcher’s office, and Kotcher took the opportunity to show him the preliminary design of his research airplane and asked if Bell was interested in building it. Woods was interested but was also concerned about the risk inherent in such a craft, especially if Bell was required to demonstrate it up to the speed of sound. Later, when the Air Force agreed that Bell would only have to demonstrate that the plane as safe and controllable up to Mach 0.8, Bell Aircraft agreed to take on the contract. Representatives from the Air Force, NACA, and Bell met to draft detailed specifications for the craft, and finished their deliberations in December 1944. Among other things, considering the uncertainties of supersonic flight, the team agreed the plane would be stressed to withstand loads of 18 times the force of gravity, whereas fighter planes were stressed only to 12 Gs. [39, pp.15-17]

When it came to fuselage shape the design team agreed that the standard military 50 caliber bullet had no problem traveling at supersonic speeds, and would be the pattern for forward fuselage shape. (It must be remembered, however, that bullets spin for accurate stabilization.) Little was known about swept wings at the time, so it was a foregone conclusion the wings would be straight. The contract called for three aircraft, but the Air Force initially paid only for the first two, and witheld funds for the third. NACA was also given the option of buying the third. The first of the two Air Force craft were to have thin wings, the first with a thickness to chord ratio of 8%, and the second to have a 10% ratio. The top and bottom wing surfaces would be milled out of solid aluminum blanks having a root thickness of one-half inch, tapering to 1/32 inch at the tip. [39, p.17, 22] The new aircraft was to have the Air Force designation XS-1 standing for Experimental Supersonic-1. It would later be changed to X-1. [52, p.53]

The XLR11 Rocket Engine

A small company named Reaction Motors Inc. (RMI) was formed by four members of the American Rocket Society in 1941 in quest of a navy contract for their invention of a liquid fueled rocket engine. The Navy was looking for a rocket motor to assist aircraft in making short takeoffs, and they were interested in RMI’s new technology of using the liquid propellants to cool the combustion chamber, allowing rocket burns for longer periods than had been achieved by other rocket motors. In 1942 the Navy awarded a contract for production of single-chamber rocket motors having a thrust of 1,000 pounds. [82 p.108-113, 214] Then in 1945 ATSC authorized Bell to subcontract with RMI for rocket motors for the X-1 research airplanes. [82 p.211]The motors were to be made of four 1,500 pound thrust rocket chambers bundled together, which would, in theory, provide enough thrust to achieve high transonic flight; maybe even Mach 1. The Air Force designated the four-chamber engine XLR11.

The individual XLR11 rocket chambers could not be throttled, but could be turned on or off so that thrust could be controlled in four increments, and speed could be controlled by length of burn and number of chambers used. Although the engine could produce maximum thrust of 6000 pounds, it weighed only 345 pounds with turbopump and 210 pounds without the pump. The engine would run on a combination of liquid oxygen and alcohol, and in original X-1 design the two tanks would have enough fuel and oxidizer to burn for five minutes before emptying tanks. In 1945 there were two schools of thought about how the X-1 would be launched. Bell’s chief designer Woods favored ground launching, and he reasoned a five- minute burn time would be enough to achieve maximum design speed. He also had hopes for a follow-on production contract for a number of the planes to be used as armed ground launched rocket propelled interceptors similar to the German Messerschmitt Me 163 rocket interceptor. However, other of his engineers argued that much higher speed performance could come from air launching from a modified B-29 bomber. [39, p.17, 23] [77] [78]

The XLR11 rocket engine was four navy Rocket Assisted Takeoff motors clustered together. With all four chambers firing, it could develop 6,000 pounds of thrust. U.S. Air Force photo

Another problem arose that resolved the dilemma. Initial XLR11 design called for turbopumps to transfer fuel and oxidizer to the combustion chambers, but pump development fell too far behind schedule, and another transfer method had to be found in place of the pumps. The solution was a number of spherical nitrogen tanks that would pressurize the main tanks and force propellants to the combustion chambers. The nitrogen tanks cut severely into the volume of the propellant tanks, leaving only enough for a two and one half-minute burn. There was no choice but to use air launch. Next, Reaction Motors’ whole XLR11 design effort fell considerably behind the first two X-1’s construction schedule, leaving X-1-1 complete, but without an engine in December 1945. The first X-1 test flights were to be unpowered glide flights launched from a B-29 mother plane, so ballast in the tail would take place of the engine. [77]

First Glide Flights at Pinecastle

Cockpit of the X-1-1. The special heat resistant glass canopy was fixed in place above the pilot so there could be no ejection seat. Instead of a conventional joystick for control, the pilot was given a control yoke so he could use both hands for control in case needed control forces became high. Photo by Eric Long, Smithsonian National Air and Space Museum (WEB11626 2010)

Although NACA wanted to test the X-1 at its Langley research facility's airfield, the Air Technical Service Command wanted another location offering more privacy for the classified project and a longer runway. Bell examined numerous sites nationally before recommending Pinecastle Army Air Field in Orlando, Florida. Pinecastle was chosen for its remote location and its 10,000 feet long runway. Bell's first choice, Muroc Army Air Field, in the California Mojave Desert, had its annual flood of its large flat lake bed during the proposed initial testing period, and the ATSC and Bell did not want to postpone the tests until the normally dry lakebed was again useable. [81 p.26, 41, 95] Having a mother plane gave a convenient way to transport the X-1-1, and by 19 January 1946 it was at Pinecastle. Waiting there was a group of technicians and engineers from the NACA Langley Laboratory to provide technical support for the flight testing and to set up, operate, maintain, and interpret the readings from the 500 pounds of instrumentation in the X-1-1. The first glide flight was on 25 January with Bell test pilot Jack Woolams at the controls. It was released from the B-29 at 22,600 feet. Woolams reported that the break from the mother plane was clean with no bumping or turbulence. Maximum speed during the glide was 275 mph, and Woolams reported that the craft was stable and felt “light as a feather” during maneuvers. He said required control forces were light and well balanced. During the ten-minute flight, Woolams had time to do a few stalls with flaps and landing gear both up and down. In these, he said the plane was well behaved. He did report that visibility out of the flush, streamlined canopy was not good. It is probably due to this and his misjudgement of the plane's steep glide slope that he landed short, and to one side of the runway on the grass shoulder. [39, pp.17-18] [42, p.1] [81 pp. 66-88]

The only way out of the X-1 was through the side door, of which General Chuck Yeager wrote, “But the thin wings were razor-edged...” He went on to say that if you bailed out through the side door you would be impaled by the sharp wing. [80, p.97]. The main use of the pilot’s parachute seemed to be as a seat cushion. NACA photo

Move to Muroc

It must be remembered that this phase of XS-1 testing was Bell Aircraft’s contractual responsibility and Bell had liberty to chose where they did the flight testing. Mindful of the X-1 cockpit visibility problem, its relatively high sink rate, and the fact that Florida’s frequently clouded skies made spotting the plane difficult, in March 1946 Bell made the decision to relocate the project to its first choice, Muroc Army Air Field in the Mojave desert. This was a WW II training base located on the edge of a roughly six-by-12 mile dry lake bed suitable as a runway. In preparation for the move, in September 1946 the Langley Lab sent a team of 25 engineers, technicians and administrative personnel to Muroc to provide technical support for the flight testing. This group, headed by aeronautical engineer Walter C. Williams, was designated the Muroc Flight Test Unit, and would form the nucleus of what would eventually become the NACA High Speed Flight Station. [17, pp.161-163]

Before the X-1 project, Walt Williams had been assistant head of the Langley Laboratory Flight Research Division’s stability and control section, and his association with the X-1 project began shortly after its start in 1945. Then he had been assigned to coordinate test requirements among Bell Aircraft, the Air Force and NACA. Then from January to March of 1946, he was assigned as NACA project engineer during preliminary glide flights of the X-1-1 being made at Pinecastle AAF. As a result of these tests it was clear that air launch operations of the X-1s were feasible and the decision was made to move to Muroc. [17, p p.158-159]

The NACA Muroc Flight Test Unit with the X-1-2 and B-29 mother plane behind them. NACA photo

The Muroc Flight Test Unit was made up of 25 NACA employees and two Air Force civilian employees:

  • Engineer De E. Beeler was in charge of the Research Engineering group and was supported by engineers Eugene D. Beckwith, Hubert M. Drake, Harold R. Goodman, Milton D. McLaughlin, and John P. Mayer
  • The Computing Section, who translated raw instrumentation measurements into engineering data, was headed by Roxanah B. Yancey and included Phyllis Rogers Actis and Dorothy Clift Hughes.
  • The Operations staff was headed by Joseph R. Vensel supported by: Howard C. Lilly and Herbert Hoover (pilots), Clyde G. Bailey, Elmer W. Bigg, Donald E. Borchers, John J. Gardner, Charles M. Hamilton, Harold J. Nemeck, Richard E. Payne, and John W. Russell (assigned from the Air Force)
  • Gerald M. Truszynski headed up the Instrumentation Division composed of Frank M. Hughes, George Minalaga, LeRoy Proctor, Jr., Arthur W. Vernon, and William C. Beedle (assigned from the Air Force).
  • Secretarial support for the entire Unit was provided by Naomi C. Wimer.

[42, p.1]

Muroc Army Airfield in 1946. The NACA Muroc Flight Test Unit and the two X-1s were housed in the large hangar furthest from the camera at right center. The runway extending out into the dry lake bed is at the top of the photo. U.S. Army Air Force photo
Roxanah Yancey, head of the Computing Section, in front of the women’s dormitory. NACA photo

Lancaster, California, the nearest town to Muroc having usable civilian housing was about 50 miles distant, so most of the Flight Test Unit staff elected to stay in World War II housing on the Muroc base. Those living singly had access to barracks and dormitory facilities that, even in their prime, were only a small step up from primitive. For example, in the frequent howling windstorms, blowing sand would would filter in around the not very tightly installed doors and windows. Married families could find accommodation in former Air Force family quarters which they soon called “kerosene flats” because of the smell left by their kerosene heaters. In some compensation for the quality of the base quarters, a double dormitory room cost $7.38 a month while a single dorm room went for $12.00. For comparison, a single bedroom apartment in Palmdale or Lancaster, over 50 miles away, cost $75.00 to $100.00 per month. It is not surprising that most stayed on base.[53, p.9, 24]

With the death of Jack Woolams in August 1946 while practicing for the Cleveland National Air Races, Bell test pilot Chalmers Goodlin took over X-1 flight testing. He was to commence testing at Muroc with X-1-2, and on 7 October 1946 X-1-2 was delivered by B-29 express to the Muroc flight test facility, complete with XLR11 rocket engine. In the mean time, X-1-1 was delivered back to the Bell factory to have its engine and a new 8% thickness wing installed. Goodlin made his first glide flight in the X-1-2 at Muroc on 11 October, an then made three more glide drops on 14 and 17 October and 3 December. [17, pp.175-180]

Powered Flight

Bell Aircraft’s test pilot Chalmers Goodlin took the two X-1s up to Mach 0.8, fulfilling Bell’s contractual requirements. NACA photo

Goodlin made the first powered flight of an X-1 on 9 December 1946, achieving Mach 0.75 and 35,000 feet. On 5 April, X-1-1 with engine installed was delivered to Muroc by the B-29, and between the two airplanes, Goodlin and Bell pilot Alvin Johnston (one flight) made 20 powered flights up to Mach 0.8 fulfilling Bell Aircraft’s contractual requirements. The Air Force then asked Bell Aircraft management if the company was willing to accept a contract modification to take the X-1-1 supersonic. Their reasoning was Goodlin was familiar with the plane, and to have an Air Force test pilot take over the project at that time would require a slowdown in the project while the new pilot familiarized himself. General Yeager also conjectures that perhaps senior Air Force officers thought it would be better to have a well paid civilian pilot risk his life than require a relatively low paid air force test pilot take the risk. [38, p.18, 21] [80, p.94]

Bell Aircraft was willing to accept the contract modification, but Goodlin threw in a monkey wrench. He wanted a bonus of $150,000 to take the X-1 supersonic; and it must be remembered that in 1947 that was a lot of money. Not only that, but Goodlin wanted it to be paid in installments over five years. Bell was willing to come up with the $150,000, however company lawyers were hesitant about the legality of spreading it over five years because of tax evasion implications. Negotiations between Bell and Goodlin began to drag on, delaying the project. Frustrated senior Air Force officers decided that to keep the program moving, the service would take over flight testing and directed COL Albert G. Boyd Chief of the Flight Test Division at Wright Patterson AFB, and in charge of a cadre of 125 Air Force test pilots, to select a pilot. Boyd explained the project to his test pilots and asked for volunteers. Then he applied his selection criteria to the volunteer list. Even though one of Boyd’s criteria was an unmarried pilot, Capt Charles E. Yeager, married, kept coming to the top of the list; having qualifications that over rode the “unmarried” requirement. [80, p.96]

Going Supersonic

Capt Charles E. yeager and the Bell X-1-1. NACA Photo

Boyd asked Yeager if he was interested in taking over the project and Yeager responded that he was interested and that if selected he would like to have fellow pilots LT Bob Hoover as backup pilot and CAPT Jack Ridley as flight engineer. Boyd agreed, but told the trio they should first travel to Bell at Buffalo, NY, and get briefed on the X-1, even to the point of firing the rocket engine while the craft was chained to the ground, before they made a commitment. They came back ready to take on the project, and were so assigned even though they were among the most junior test pilots at Wright Patterson, and had been picked (in mid June 1947) over many other more senior and more experienced test pilots. [80, pp.94-98] [19 pp.107-109] [81, p.237]

When the Air Force decided to take over X-1 flight testing, they met with NACA representatives on 30 June and 1 July 1947 to decide how flight testing would be apportioned between the two X-1s. They agreed that the Air Force would use X-1-1 to explore the outside of the flight envelope’s Mach number and altitude boundaries, whereas NACA would undertake a more deliberate and detailed investigation using X-1-2 to explore stability and control in the transonic region. It must be realized that the purpose of the two planes was not to set records, but rather carefully explore transonic and supersonic flight, gather data, and write research reports. NACA technicians then installed different instrumentation packages in each plane to suit its unique research mission. X-1-2 instrumentation would include measurement of: structural loads via strain gages, control wheel and rudder pedal forces, control surface deflections, speed, altitude, 3-axis accelerations, angle of attack and yaw angle, turn, pitch & roll rates. wing pressure distributions at 400 points, and fuel pressure. The X-1-1 did not have as complete or as heavy an instrumentation suite as the X-1-2. Much of this data would also be sent by radio telemetry to the ground during flight. A camera would also record the pilot’ s flight instruments. [42, pp.2-3] [81, p.239]

The X-1-2 shown here was instrumented for stability and control studies and carried about 500 pounds of instrumentation. The X-1-1 being tested by the Army Air Force had a less comprehensive instrumentation suite. NACA drawing
Another view showing the X-1-2 instrumentation package. NACA photo

Walt Williams, head of the NACA Muroc Flight Test Unit, would later write of the time when the Air Force and NACA were getting ready to start their X-1 research flights:

It would be well to point out here that our NACA group, along with the Air Force Flight test group and the manufacturer, was in many ways a very lonely group and was alone in backing. Top management of all concerned gave their wholehearted support to the program; however at the contemporary level and intermediate supervisory level there were many dismal predictions, such as:

  • “The program will fold right after the first powered flight as soon as the airplane blows up.”
  • “The drag is too high, you cant even get the speeds.”
  • “ From what we know, the airplane will come completely apart a little above 0.9 Mach" number.”

These and other similar comments were common. But, it might be said, like the little bumble bee, we went ahead. In addition to these known fears and comments, England, who had been attempting such testing, had lost the DH-108 in transonic flight, killing the pilot. This led the British to adopt a policy of model testing and possibly remote guidance for the airplanes before they would ever attempt manned supersonic flight. This, without question, set their effort back an unmeasured number of years. These things were all hanging heavily over our heads. [42, p.3]

The X-1-1 in powered flight. NACA photo

If the reader watched the movie “The Right Stuff” she might have gotten the impression that Chuck Yeager was selected one day, and the next day he made his sound barrier breaking flight; because activities have to be compressed in time in movies. In actuality he made 12 flights (11 in X-1-1 and one in X-1-2) before his momentous Mach 1.06 flight. His first drop flight on 6 August 1947 was a glide flight as would be the next two. Then on 29 August he made his first powered flight, achieving Mach 0.85. As did the Bell pilots, Yeager thought the X-1 was, “A joy to fly.” By 10 October he had worked up to Mach 0.997. Walt Williams writes of that flight: “It wasn’t felt that it was a clear-cut case of a sonic flight. It was only a matter of repeating the previous flight, but to a slightly higher speed ...” [42, p.3]

The next flight was on 14 October, and Yeager was concealing that he had two broken ribs caused by a fall from a horse at Pancho Barnes’ Happy Bottom Riding Club two days before. At 10:20 that morning the mother plane reached the 20,000-foot launch altitude. Yeager very painfully lowered himself down the ladder to the X-1’s door and squeezed feet first through the small opening. CAPT Ridley had left a sawed off piece of broom handle in the cockpit to allow Yeager to get some leverage in the painful process of moving the door latch lever. After recovering from a near stall caused by the B-29’s too slow launch speed, Yeager fired all four rocket chambers until he achieved 36,000 feet; and then shut down two of the chambers. He leveled off at 42,000 feet and Mach 0.92, and then fired chamber 3. With three chambers firing the X-1-1 accelerated until the Mach meter (which only registered up to Mach 1) jumped off the scale. He knew he was supersonic. Years later, General Yeager would write, “We were flying supersonic! And it was smooth as a baby’s bottom: Grandma could be sitting up there sipping lemonade. I kept the speed off the scale for about twenty seconds, then raised the nose to slow down.” [80 pp.128-130]

Walt Williams would later write, “In this flight, the now typical jump in the airspeed and altitude readings occurred, caused by the bow [shock] wave passing over the static pressure holes. There was then little doubt that highly publicized and feared “sonic barrier” had been breached.” The X-1 project was classified secret and the Air Force put a tight lid on the achievement, however, there was much celebration and not a few parties by people in the know, and word eventually filtered out. On 22 December 1947 the news magazine Aviation Week announced the record breaking flight, and on that same day the Los Angeles Times, in an extra edition, had the banner headline “U.S. MYSTERY PLANE TOPS SPEED OF SOUND.” A threatened Air Force lawsuit against Aviation Week never materialized. [42, p.3] [39, p.19]

Click here to proceed to Chapter 4 of the Experimental Research Airplanes and the Sound Barrier - The D-558-I Skystreak Project .

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