Though there was much in this project that, in 1944, could still have been classified as science fiction, the concept of transonic—and even supersonic—flight was nothing new.  Even by the 1930s, aeronautical engineers had begun to develop ideas for aircraft that could, theoretically, exceed 500 mph. However, their knowledge of the aerodynamic effects at this lower end of the transonic realm was extremely limited.  Calculations suggested that, as an aircraft’s speed moved closer to the speed of sound (Mach 1), it would encounter an ever-increasing amount of drag—a virtual “wall” of air.  A misquote by the British press provided a catchy, if misleading, name for this.  During a 1935 interview, British aerodynamicist W.F. Hilton, interpreting a plotted depiction of airfoil drag, called attention to the fact that “the resistance of a wing shoots up like a barrier against higher speed as we approach the speed of sound.”  By the next day, the concept of a “sound barrier” was irrevocably etched in the minds of the public.

Keenly interested in transonic aerodynamics, by 1939, Kotcher recommended that a transonic flight research program be created, using manned aircraft to supplement the limited data available from the wind tunnels of that time, which became useless at speeds between Mach numbers 0.8 and 1.2.  Similarly, John Stack and his colleagues at the National Advisory Committee for Aeronautics (NACA) had reached the conclusion that the best way to address the challenges of modern aeronautics was through the use of full-sized, specially designed research aircraft. Though they may have agreed on this general idea, these two men, and their respective institutions, would approach the aerodynamic problems associated with increased speed and altitude from vastly differing perspectives and would press for dramatically different goals.

The onset of the Second World War pushed such theoretical pursuits to the back burner, while simultaneously underscoring their importance as theories met reality, often with tragic results. As modern fighters attained higher and higher speeds, particularly in steep dives, they began to experience a phenomenon known as “compressibility”—disruptive shock waves caused by a mixture of subsonic and supersonic airflow. At best, this could render control surfaces ineffective and, at worst, literally tear an aircraft apart.

Despite the production priorities of a world war, advances in aviation design and propulsion gave a sense of urgency to solving the problems of compressibility, as well as other associated challenges.  As Bell Aircraft’s Robert Wolf warned in December 1943, jet fighters would soon encounter the same compressibility effects in level flight that current fighters were experiencing in power dives.  Similarly, the California Institute of Technology’s Dr. Theodore von Karman warned General of the USAAF “Hap” Arnold in August 1945 that “We cannot hope to secure air superiority in any future conflict without entering the supersonic speed range.” The need to address the realities of flight approaching or exceeding the speed of sound was critical.

Of course, United States was not the only nation interested in these topics.  Germany’s research into jet propulsion and rocket technology was well in advance of the Allies, though the full details of this research were slow to emerge as the war went on.  And in October 1943, the British Miles Aircraft Company had been contracted to construct the M.52, which, it was hoped, would reach a speed of 1,000 mph.  In the fall of 1944, an American delegation, including representatives from Bell, visited the Miles facility and were given access to details of the project, as well as plans for the M.52.  Political and technological events contributed to the cancellation of the Miles project in February 1946, before the M.52 had been completed.  Thus, the initiative passed to the United States, which benefited tremendously from British research efforts.

In the months leading up to the conversation between Kotcher and Woods, persistent lobbying efforts had led to a series of meetings and conferences among members of the USAAF, NACA, the U.S. Navy and others. These produced some consensus but much disagreement, as well as little guidance from above as to which organization, if any, would take overall charge of the American efforts in the transonic and supersonic realms.  The result would be separate initiatives: NACA and the US Navy would adopt a more cautious effort to explore transonic flight conditions, while the USAAF would adopt Kotcher’s more aggressive agenda to break the so-called “sound barrier.” As the heretofore leading authority on aeronautical research in the U.S., however, NACA would still play a significant, though sometimes adversarial role in the latter plan.

Project MX-524 came into being in April 1944 as the USAAF’s proposal for a research aircraft.  The specifications for this aircraft were reasonably straightforward, but achieving them would be no easy task.  First, it would need to be capable of reaching a speed of 800 mph at 35,000 feet, though Bell would only be required to assure its safety and controllability up to Mach 0.8.  Kotcher preferred rocket power over turbojet propulsion, though at this point the contractor was given its choice of power plant.  The aircraft would need to accommodate a wide array of instruments to collect the data for which it was being created.  And given the lack of information regarding the stresses that might be encountered at the contemplated speed, NACA required it to be of extremely strong construction, capable of withstanding loads of up to 18 times the force of gravity (18 g’s). What was more, NACA research suggested that to reach the necessary speed the aircraft would have to have extremely thin wings—a seemingly mutually exclusive proposition.

The evolutionary details of the project, along with its associated inter-agency maneuverings and machinations, makes for fascinating, if complicated, reading, but enumerating more than a few of them would take the current piece beyond the space available—and likely beyond the interest level of the average reader.  With the project specifications in hand, the Bell design team traveled far and wide, but brought back very little in the way of useful information on which to base their efforts.   

Like their British counterparts, they turned to ballistics research in their quest for a fuselage design that would provide the greatest stability at supersonic speeds.  Studies in the 1930s had determined that ogival-shaped objects, such as bullets that were arched with a pointed tip, experienced the least amount of drag.  This fact had been borne out in practice by the German V-2 missiles, which had been rumored to have reached Mach 4.

NACA had dictated there would be two interchangeable sets of very thin wings produced, one with an eight-percent chord ratio and the other with 10-percent. When it came to the tail configuration, several recommendations had been made by NACA’s John Stack and Robert Gilruth.  First, the chord ratio should be lower than that of the wings (six and eight percent, respectively) to experience compressibility effects at a different speed than the wings and thus ensure greater stability.  Similarly, the horizontal tail surfaces would be placed higher on the vertical tail to minimize air disturbance coming off the wings.  The final recommendation would have the most far-reaching impact.  While employing a traditional moveable elevator control surface, the entire stabilizer would also be adjustable, allowing the pilot to maintain control of the aircraft when compressibility would render the elevator ineffective.  The British M.52 design had employed a similar configuration, and this moveable stabilizer (today often called a “stabilator”) would remain top secret for some time.

Though a turbojet propulsion system was initially favored by some Bell engineers, circumstances would dictate that a rocket engine was the only choice to reach the desired speed. The XLR-11, produced by Reaction Motors, used liquid oxygen and water-diluted ethyl alcohol to produce 1,500 pounds of thrust in each of its four independently operable chambers, for a potential total of 6,000 pounds of thrust.  It had no throttle, but the pilot would be able to adjust his speed, 25 percent at a time, based on the number of chambers ignited.  Delays in producing the expected turbine-driven propellant pump forced the switch to a high-pressure nitrogen gas system to drive the fuel components into the chambers. This added significant weight to the aircraft while reducing the space available for fuel, and thus had the unintended effect of solving one of many hotly debated questions: the aircraft would be air-launched from a “mother ship” as opposed to employing a traditional ground takeoff.

Bell and the USAAF had agreed that the initial, unpowered glide tests would be conducted at Pinecastle Army Air Base, near Orlando.  This despite the NACA preference that the tests take place at their facility at Langley (VA).  The XS-1 would be dropped at altitude from a war surplus B-29 Superfortress that had been specially modified to accommodate the little orange aircraft, partially inserted into its bomb bay—with about one foot of ground clearance beneath.

The pilot entered the XS-1 through a complicated—and dangerous—series of maneuvers.  Standing on the narrow catwalk of the B-29’s bomb bay, the pilot would mount a flimsy ladder, bouncing up and down to lower it to a point even with the XS-1 cockpit opening. From there, he twisted himself into the small opening, strapping into the seat, securing oxygen lines and his parachute (though a successful parachute escape was highly unlikely). The crew chief, standing on the same ladder, then lowered the cockpit door on a chain to a point where he could push it into place with his backside, whereupon the pilot would engage the latch, securing it in place. All this at 5,000 feet in the air, facing frigid temperatures and 200 mph winds, with only a thin shield to shelter them.

Following an initial capture flight over Western New York on January 10, 1946, the B-29, with the XS-1 fitted with the thicker set of wings tucked underneath, flew to Pinecastle, where the first glide flight would take place on January 25 with Bell chief test pilot Jack Woolems at the controls. Finding the aircraft “delightful to fly,” Woolems completed 10 glide flights in all, interspersed with delays related to landing gear mishaps and other issues. These flights successfully demonstrated the suitability of the launch process and the overall flight characteristics of the aircraft.

In April 1946, 46-062 returned to Bell’s Wheatfield plant, to be fitted with nitrogen and fuel tanks, along with other modifications and the thinner set of wings, in preparation for its powered flights.  These would take place at Muroc Army Airfield (later Edwards Air Force Base), where weather conditions—along with the presence of the huge Rogers Dry Lake for emergency landings—made it an ideal location for flight testing.  Months passed before the B-29, this time with the second aircraft (46-063) underneath, left Niagara Falls for Muroc on September 26.  In the interim, Jack Woolems was tagically killed that August preparing for an air race, and so a new pilot, Chalmers “Slick” Goodlin, would be the first to fly the XS-1 at Muroc.

A brief series of glide flights between October and December satisfactorily tested the fuel dump procedure, but the aircraft was plagued by brake failures.  Further problems with the nitrogen system, landing gear—and even the weather—delayed the first powered flight, which took place on December 9, with Goodlin reaching a speed of Mach 0.795 with only one engine chamber ignited at any one time.  More powered tests followed, with corresponding delays for recurring problems, through late February 1947.  Aircraft 46-063 was returned to Wheatfield, while 46-062 returned following its modifications.

Meanwhile, significant conflicts had erupted between NACA on one hand, and the USAAF and Bell on the other, over the speed and progress of the program.  In particular, the latter were concerned that other aircraft designs were progressing to the point where they might soon equal the performance of the XS-1.  Thus, in April 1947, the Army’s Air Materiel Command took over the program, to proceed on the quicker pace with minimal interference from NACA.  The latter agency, by way of compensation, would receive the second XS-1 for its own experiments.

“Slick” Goodlin made 10 more flights, now in 46-062, between April 10 and May 21, testing the aircraft in stalls and pull ups while also logging adjustments to the tailplane.  Problems with various pressurization systems continued.  Bell was hoping to wrap up its portion of the program by late May when Col. Albert Boyd of the USAAF Flight Test Division proposed a plan for the company to make up to 30 more fights at a fixed price, using an AAF pilot (that would be cheaper than a civilian contracted by Bell).  Bell turned down the plan and thus the AAF looked to a modified partnership with NACA for the next phase of the program.  Though now relegated to a secondary role, Bell could proudly look back on the 37 flights (23 of them powered), which had demonstrated the aircraft and its systems to be relatively safe and reliable up to speeds of Mach 0.82.

For this next phase, Boyd was eager to have one of his own pilots at the controls.  The U.S. Air Force became an independent service branch in July 1947, making inter-service competition—and the need for recognition—all the keener.  The man he wanted was Captain Charles Yeager.  A veteran World War II fighter pilot, the 24-year-old Yeager had great intuitive skill and a keen understanding of engineering that more than made up for his lack of a college degree.

The USAF officially took control of the program, the name of which had been changed from XS-1 to X-1, on July 10, 1947.  The new team at Muroc included six Air Force personnel, with 15 coming from Bell and 12 from NACA.  Among the Air Force men, Capt. Jack Ridley would act as project manager and engineer-in-charge, with Bob Hoover, another World War II fighter pilot, serving as backup pilot to Yeager.  He would also fly one of the chase planes to observe the X-1 flights.  Jack Russell, the crew chief for the Bell flights, was kept on in that capacity, with another Bell employee, Dick Frost, serving both as project engineer and as another chase pilot.  The B-29 mother ship also received a new pilot: Major Roberto Cardenas.

Yeager made three unpowered flights from August 6-8 prior to his first powered flight on August 29, when he reached a speed of Mach 0.85. He was later chastised for exceeding the maximum target speed of Mach 0.8 and for executing a slow roll that caused his number 3 chamber to shut down.  A second powered flight followed on September 4, during which Yeager reached Mach 0.89 with two engine chambers ignited.  He would make three more flights through September 12, reaching Mach 0.925 before returning to Wright Field to be fitted for a pressure suit prior to making the final runs at 50,000 feet.

Delays postponed further flights until October 3, and aircraft 46-062 also received a new actuating motor for its tailplane, allowing for faster response.  Flights resumed with increases of speed to Mach 0.945 on October 8 and Mach 0.997 on October 10, making it clear that the project milestone was only one flight away.  But a non-flight accident almost led to disaster. On October 12, Yeager was riding back in the dark on horseback from Pancho Barnes’ “Happy Bottom Riding Club” with his wife, when his horse ran into a closed gate, throwing the pilot and breaking two of his ribs.  Bandaged, but in severe pain, Yeager alerted only Capt. Ridley to his condition.  Pain or no pain, it was too late for any delays and so the injured pilot had to proceed with the scheduled flight on October 14.  His injury, however, prevented him from latching the cockpit door with his right hand.  Capt. Ridley came to the rescue by cutting a 10-inch length of broomstick, which allowed Yeager to latch the door using his left hand instead.

At 20,000 feet, Major Cardenas dropped the X-1 from the B-29’s bomb bay, whereupon Yeager lit all four engine chambers in sequence.  Adjusting the tailplane setting, he turned off two of the chambers between 35,000 and 40,000 feet.  By the time he leveled off at 42,000 feet he was traveling at Mach 0.92.  Igniting a third chamber, his acceleration continued and, after some minor buffeting, his elevators became effective again at Mach 0.97.  Reaching Mach 0.98, “the needle of the machmeter fluctuated . . . then passed off the scale.” On the ground, the telltale aerial “boom” heard by observers left no doubt that Chuck Yeager had finally accomplished the program’s mission.  Achieving a speed of Mach 1.06 (700 mph) on this historic flight, Yeager later likened the experience, not to breaking a “barrier,” but rather like “poking through jello.”  Per Col. Boyd’s orders, Yeager received no promotion, but did receive the Distinguished Flying Cross. Boyd also insisted that the accomplishment be kept strictly classified for the moment, though predictably this did not last.

Chuck Yeager would fly the X-1 seven more times, reaching a top speed for the aircraft of Mach 1.45 (957 mph) on March 26, 1948. In total, the two original X-1 aircraft made 158 flights to October 1951, providing critical data for high altitude flight as well as speed. The project ushered in the era of supersonic flight while the X-1’s moveable stabilizer would be employed to great effect on the F-86 Sabre fighter, allowing it to dominate Russian MiGs in the skies over Korea.  It remains a standard feature on supersonic aircraft today.  Meanwhile, the problems of pilot escape from the X-1 led to the development of workable ejection seats for the coming generation of jet aircraft.  And the data collected by NACA throughout the project led to numerous additional improvements to aircraft safety.

Bell’s hope of translating the X-1 project to combat applications never materialized, but their efforts set the precedent for using X-planes to conduct aeronautical research and, in so doing, made yet another enduring Western New York contribution to aviation science and history.