The Bell X-1 (Bell Model 44) is a rocket engine–powered aircraft, designated originally as the XS-1, and was a joint National Advisory Committee for Aeronautics–U.S. Army Air Forces–U.S. Air Force supersonic research project built by Bell Aircraft. Conceived during 1944 and designed and built in 1945, it achieved a speed of nearly 1,000 miles per hour (1,600 km/h; 870 kn) in 1948. A derivative of this same design, the Bell X-1A, having greater fuel capacity and hence longer rocket burning time, exceeded 1,600 miles per hour (2,600 km/h; 1,400 kn) in 1954. The X-1 aircraft #46-062, nicknamed Glamorous Glennis and flown by Chuck Yeager, was the first piloted airplane to exceed the speed of sound in level flight and was the first of the X-planes, a series of American experimental rocket planes (and non-rocket planes) designed for testing new technologies.
In 1942, the United Kingdom's Ministry of Aviation began a top secret project with Miles Aircraft to develop the world's first aircraft capable of breaking the sound barrier. The project resulted in the design of the turbojet-powered Miles M.52, with a maximum speed of 1,000 miles per hour (870 kn; 1,600 km/h) (almost twice the existing airspeed record) in level flight, and able to climb to an altitude of 36,000 ft (11,000 m) in 1 minute and 30 seconds. The fuselage was shaped like a bullet, it had thin wings and a slab tailplane for controlled flight at the speed of sound and beyond. Miles' chief aerodynamicist, Dennis Bancroft, was interviewed many years later in 1997 on his reason for needing an all-moving tailplane in his 1944 design.
DENNIS BANCROFT: We thought the ordinary controls wouldn't work above the speed of sound. So, we had to make an all-moving tail plane, because an ordinary elevator would literally not function at all. We would go up to the speed of sound, lose all air control, and the aircraft would crash.
In 1944, Miles was told to go ahead with the construction of three prototypes. In February 1946, with a first flight expected in the summer of 1946, the M52 was cancelled. In place of the manned full-scale M.52 it was decided to test 3/10 scale models of the aircraft, rocket propelled, dropped from an aircraft, and controlled by an autopilot. On the 10th of October 1948, a model achieved Mach 1.38 (1,690 km/h; 1,050 mph) in level flight.
STACY KEACH (NARRATOR): One year after the X-1's historic flight, Britain broke the sound barrier with a one-third scale model of the M-52. Although unmanned and radio-controlled, it did finally vindicate the worthiness of its supersonic design.
The Bell XS-1 would have a conventional horizontal tail-plane but with trimming available on the stabilizer. It would be required for pitch control when a shockwave was preventing a deflected elevator from altering the pressure distribution and pitching force on the tailplane.
In September 1946, a [[de Havilland DH 108
|DH 108]] tail-less jet aircraft was practicing for an attempt on the world speed record when it experienced violent pitching oscillations at Mach 0.875 and broke up. The Bell XS-1 would have a conventional horizontal tail which provides pitch damping not present in a tail-less aircraft.
The XS-1 was first discussed in December 1944. Early specifications for the aircraft were for a piloted supersonic vehicle that could fly at 800 miles per hour (1,300 km/h) at 35,000 feet (11,000 m) for two to five minutes. On 16 March 1945, the U.S. Army Air Forces Flight Test Division and the National Advisory Committee for Aeronautics (NACA) contracted with the Bell Aircraft Company to build three XS-1 (for "Experimental, Supersonic", later X-1) aircraft to obtain flight data on conditions in the transonic speed range.
Bell built a rocket plane after considering the turbojet alternative. Turbojets could not achieve the required performance at high altitude. An aircraft with both turbojet and rocket engines would be too large and complex. The X-1 was, in principle, a "bullet with wings", its shape closely resembling a Browning .50-caliber (12.7 mm) machine gun bullet, known to be stable in supersonic flight. The shape was followed to the extent of seating its pilot behind a sloped, framed window inside a confined cockpit in the nose, with no ejection seat.
For the design of the XS-1 the many unknowns relating to transonic and supersonic flight meant seeking every available source of information from governmental agencies, powerplant manufacturers and research institutions. Foreign information became available in early 1946, shortly after the first glide test of the XS-1 in Jan 1946, when the British Ministry of Supply cancelled the Miles M.52 and ordered all research reports and other information be sent to Bell Aircraft.
Bell Aircraft aerodynamicists working with NACA laboratories predicted significant longitudinal trim changes during transonic flight. John Stack and Robert Gilruth at NACA recommended that Bell mount the elevator on an adjustable horizontal stabilizer. Bell incorporated the stabilizer with rapid adjustment in pitch to accommodate large changes of trim. A contractor test flight by Tex Johnston showed an unacceptable lost motion between the pilot's input to the horizontal stabilizer and the stabilizer actuator which was corrected before the XS-1 was handed over for the high speed research program. The whole tailplane could be moved or just the elevator at fixed stabilizer settings. It was placed as high as possible above the wing wake with a thinner section than for the wing to separate the high drag rise from the wing from compressibility effects on the tail. Initially, as increases in speed were made in small steps towards possibly unknown control difficulties the horizontal stabilizer was left at its pre-launch angle set on the ground as there was concern that adjusting it at high speed would cause severe control problems. Nevertheless, in October 1947, when test pilot Yeager ran out of elevator authority (no pitch control) at Mach 0.94 it took the test team by surprise until they realized that extra control was available by moving the horizontal stabilizer. The tailplane trim setting had to be accurately set on the ground to ensure a controlled drop at the beginning of a flight. Scott Crossfield relates an inadvertent one-degree error flipping the X-1 on its back after being dropped from the mother plane. The tailplane configuration was carried over to the X-1A series. All subsequent supersonic aircraft would either have an all-moving tailplane or be "tailless" delta winged types.
Swept wings were not used because too little was known about them. As the design might lead to a fighter, the XS-1 was intended to take off from the ground, but the end of the war made the B-29 Superfortress available to carry it into the air.
The rocket engine was a four-chamber design built by Reaction Motors Inc., one of the first companies to build liquid-propellant rocket engines in the U.S. After considering hydrogen peroxide monopropellant, aniline/nitric acid bipropellant, and nitromethane monopropellant as fuels, the rocket burned ethyl alcohol diluted with water with a liquid oxygen oxidizer. Its four chambers could be individually turned on and off, so thrust could be changed in 1,500 lbf (6,700 N) increments. The fuel and oxygen tanks for the first two X-1 engines were pressurized with nitrogen, reducing flight time by about 1+1⁄2 minutes and increasing landing weight by 2,000 pounds (910 kg), but the rest used gas-driven turbopumps, increasing the chamber pressure and thrust while making the engine lighter.
Bell Aircraft chief test pilot Jack Woolams became the first person to fly the XS-1. He made a glide-flight over Pinecastle Army Airfield, in Florida, on 19 January 1946. Woolams completed nine more glide-flights over Pinecastle, with the B-29 dropping the aircraft at 29,000 feet (8,800 m) and the XS-1 landing 12 minutes later at about 110 miles per hour (180 km/h). In March 1946 the #1 rocket plane was returned to Bell Aircraft in Niagara Falls, New York for modifications to prepare for the powered flight tests. Four more glide tests occurred at Muroc Army Air Field near Palmdale, California, which had been flooded during the Florida tests, before the first powered test on 9 December 1946. Two chambers were ignited, but the aircraft accelerated so quickly that one chamber was turned off until reignition at 35,000 feet (11,000 m), reaching Mach 0.795. After the chambers were turned off the aircraft descended to 15,000 feet (4,600 m), where all four chambers were briefly tested.