Following the first-ever powered flight by the Wright brothers’ Wright Flyer in 1903, it was just a few decades before aviation scientists tackled the challenge of supersonic flight. America, England, and Germany all attempted jet fighter design during World War II. Germany was the first to deploy a jet combat aircraft, the Messerschmidt Me-262. These early jets didn’t go supersonic but revealed the steep spike in the aircraft’s aerodynamic drag close to the sound barrier.
For some time, the public thought the sound barrier couldn’t be passed. In 1946, German-American science writer Willy Ley said most people thought of Mach 1, the speed of sound, as a “brick wall in the sky.” However, as he pointed out, artillery shells, rockets, and bullets regularly passed the “barrier” without being destroyed. Engineers of the first supersonic plane ever built, the Bell X-1, would, in fact, base their design on a bullet.
What was the Bell X-1?
Pioneering the frontiers of aviation science, the X-1 was a research aircraft built by Bell Aircraft Company. The rocket-propelled aircraft wasn’t meant to have either commercial or military applications. Instead, it was a test bed and exploratory vehicle designed solely to successfully pass the speed of sound. While most supersonic aircraft since then have been military – with a few notable exceptions – the X-1 wasn’t initially a fighter design. In this respect, it also broke new ground.
Virtually every aircraft made before then had some purpose other than research in mind, whether commerce or combat. The National Advisory Committee for Aeronautics, or NACA, and the US Army Air Forces Flight Test Division commissioned the aircraft. Bell Aircraft Company ultimately built just seven X-1s. Since the X-1 was meant for research purposes, the seven aircraft included five different variants, labeled the X-1A through X-1E.
Bell X-1: Breaking the “Brickwall in the Sky”
From the start, the Bell X-1 wasn’t meant for long-powered flights. The aircraft’s purpose was to break the sound barrier and fly for a few minutes at or above Mach 1. Scientists and engineers wanted data on airflow and how various aircraft features functioned as it went transonic.
This invaluable data on both transonic and supersonic flight would then serve as a springboard for further supersonic aircraft design. The X-1 was originally called the XS-1 for “Experimental Sonic,” but soon became simply the X-1.
Rocket Engines
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Despite misgivings, the engineers decided early on to use rocket engines rather than turbojet propulsion. The aircraft’s builders directly borrowed its shape from the .50 caliber Browning machine gun bullet. Otherwise known as .50 BMG, 50 Browning, or 12.7x99mm NATO, this large bullet has a ballistic coefficient making it extremely stable at transonic speeds and capable of long-range accuracy.
The X-1 was basically designed as a gigantic .50 BMG bullet with wings. The aircraft was made with straight wings rather than the swept-wing designs revealed by captured German documents at the end of World War II. The swept-wing supersonic aircraft would emerge as a better supersonic solution. However, the X-1’s extremely thin wings, with their precise cross-section, served the purposes of the initial designs.
Limited Lifespan
The aircraft, painted a bright “international orange” to mark it as a test vehicle, originally featured a greenhouse canopy. This was a canopy set into the curve of the fuselage rather than projecting from it in order to reduce aerodynamic drag. The design may have helped early tests succeed but also made ejection seat installation impossible.
Later variants would feature an improved canopy and, eventually, an ejection seat. Bell built the X-1 with a high-strength aluminum fuselage and steel fuel tanks. Nevertheless, rapid material fatigue limited the lifespan of each individual aircraft.
Glide Testing and Subsonic Flights
With the Bell X-1 built, NACA and the USAAF Flight Test Division moved forward with glide testing. The tests started in January 1946 with the X-1 released from the bomb bay of a Boeing B-29 Superfortress bomber. Florida’s Pinecastle Field hosted the first glide tests, with Bell’s chief company test pilot Jack Woolams at the controls. Woolams had already set several records, including taking a YP-59A Airacomet prototype jet fighter to 47,600 feet in December 1943.
Woolams carried out 10 glide tests over the following months, with the X-1 landing successfully after each at 110 mph. Tragically, Woolams died on August 31st, 1946, when his personally owned bright red P-39 Airacobra crashed into Lake Ontario. Woolams had modified the aircraft, supercharging its engine, and was prepping it for a race. The Hoosier State Chronicles said witnesses saw the Airacobra’s tail fall off as it flew out over Lake Ontario. A fiery explosion followed and the plane nosed down into the lake.
Modifications
Woolams’ death potentially delayed the first supersonic flight, which Bell previously said would happen in September 1946. Testing resumed with another private sector test pilot, Chalmers “Slick” Goodlin. Goodlin piloted the X-1 on 26 more test flights. Four were glide flights while the rest were powered but subsonic, edging up to Mach 0.8. Bell continued modifying the aircraft in response to data collected during Goodlin’s flights.
“Slick” lost his opportunity to take the X-1 supersonic when the USAAF took over the testing from Bell. Chuck Yeager’s autobiography says “Slick” Goodlin demanded $150,000 plus extra pay to break the sound barrier. Goodlin himself claimed “the Air Force wanted a man in uniform to break the sound barrier – better PR” and the $150,000 bonus wasn’t the real cause. Regardless, then 1st Lieutenant Chuck Yeager took over the testing.
Supersonic Flight
West Virginian fighter ace Yeager began glide flights in early August 1947 and powered flights by the end of the month. Unlike Bell, which increased its speeds only gradually, the USAAF and Yeager moved swiftly closer to Mach 1. Yeager took the X-1 to nearly transonic speeds on October 10th, accelerating to Mach 0.997.
Yeager fell from the saddle during a horseback ride on the weekend before the scheduled Mach 1 flight. He broke two ribs but hid the painful injury so the USAAF wouldn’t replace him as the first supersonic pilot. The flight began at a dry lake bed in California’s Mojave desert. The B-29 carried the X-1 to 20,000 feet, at which point it slid out of the bomb bay doors into the clear desert sunlight. Launching from the B-29 gave Yeager’s X-1 an initial 250 mph boost.
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The “Glamorous Glennis,” as Yeager called the X-1 after his wife, came to life under the ace pilot’s control. Yeager climbed to 43,000 feet, where colder air put the sound barrier at less than 700 mph rather than the 761 mph at roughly 59° Fahrenheit. Engineers had feared the aircraft would become unstable and start bucketing around at transonic speed, possibly causing Yeager to lose control.
However, as Yeager passed the sound barrier and accelerated to Mach 1.06, the X-1 continued flying straight and true. The only effects were a bow shock ahead of the aircraft and a sonic boom rolling over the Mojave.
The X-1’s design had proven successful, and Yeager became the first man in history to fly at supersonic speed. The flight lasted only a few minutes but gave a wealth of information about the physics of supersonic flying. Many more would follow.
Later Developments
Chuck Yeager, who was promoted to Captain and eventually Brigadier General, continued X-1 flights for several years. He and other test pilots would take various X-1s transonic 78 more times. Yeager piloted an X-1 to 71,900 feet on March 26th, 1948, and flew it at 957 mph, or Mach 1.45, at that altitude. On December 12th, 1953, Yeager achieved a speed of 1,650 mph, or Mach 2.435, at 80,000 feet while piloting the upgraded X-1A.
Yeager finally took the X-1 beyond its design limits, completely losing control of the aircraft and smashing its canopy with his helmeted head. The aircraft plunged at a rate of 1,000 feet per second for 51 seconds. Yeager finally regained control at 25,000 feet and managed to land the X-1A on a dry lake bed.
X-1B, X-1C, and X-1D variants followed. The X-1C was never fully built because it included weapon mounts, but by the time the engineers built it, actual purpose-made supersonic fighters were under construction. The program was almost derailed when X-1A and X-1D exploded on separate occasions. The explosions killed two men and badly injured test pilot Joe Cannon. The problem was traced to an unexpected reaction between liquid oxygen and gaskets made from a material called “Ulmer leather.” Using a different gasket material solved the explosion problem.
The X-1E and the Program’s End
The final, improved model, the Bell X-1E, was the first X-1 to feature a knife-edge windscreen instead of a greenhouse canopy. The engineers were thus able to add an ejection seat. Sockets built into its wings housed 343 strain gauges and 200 pressure openings. This array enabled gathering data about airflow, aerodynamic heating, pressure changes across the wing surface, and structural load.
The X-1E, piloted by test pilot Joe Walker, was supposed to fly at speeds up to Mach 3. However, after reaching Mach 2.24 on October 8th, 1957, maintenance x-rays revealed cracks in the fuel tank wall. The X-1 had provided nearly all the data it could, anyway. NACA retired the aircraft and ended the program, almost 10 years to the day since Yeager’s first supersonic flight. The X-1E became a museum piece and the development of military and commercial supersonic aircraft went ahead.
Bell X-1: How It Worked
The Bell X-1’s ballistic shape was only half the battle for transonic speed. The rest came from its massive XLR-11 rocket engine. Given the small size of the X-1, the cockpit, fuel tanks, and engine filled the whole fuselage interior.
Reaction Motors Inc. built the XLR-11 engine along with later designs. The XLR-11 used a mix of liquid oxygen and ethyl alcohol as fuel. The design didn’t offer variable thrust from each individual rocket chamber – the rocket had only two states, off or on. However, the XLR-11 engine included four chambers.
The X-1’s pilot controlled how many chambers were active at one time. Since each chamber developed 1,500 pounds of force, the pilot could choose between 1,500, 3,000, 4,500, or 6,000 pounds of thrust while flying. The rocket engine developed several nicknames, including “Black Betsy” and “the Belching Black Bastard” because of its black heat-resistant paint job.
The fuel was originally driven into the rocket chambers by high-pressure nitrogen. This changed to a safer turbopump system with the Bell X-1E variant. This final version of the X-1 also used a new fuel, U-deta. This replaced liquid oxygen and ethyl alcohol with diethylene triamine and unsymmetrical dimthydrazine in order to develop more thrust.
Aeronautics engineers hoped the new mix would propel the X-1E past Mach 3, but the fuel tank failure resulted in the X-1’s permanent retirement. Like all liquid fuel rocket engines, the XLR-11 worked by burning the ethyl alcohol fuel and liquid oxygen oxidizer in a combustion chamber. This produced a powerful jet of exhaust gas blasting out a rearward nozzle, creating forward propulsion.
Bell X-1: 5 Must-Know Facts
- The Bell X-1 was the first successful supersonic aircraft, made just 44 years after the first powered flight at Kittyhawk.
- During its first supersonic flight, the X-1 was piloted by World War II fighter ace Army Air Force 1st Lieutenant Charles “Chuck” Yeager.
- The Bell X-1 used a four-chambered rocket with each chamber developing 1,500 pounds of thrust, so the pilot could choose 1,500 to 6,000 lbs of thrust.
- Three of the experimental aircraft exploded, causing two deaths.
- The X-1 went out of service almost exactly 10 years after its first supersonic flight. Its first flight was on October 14th, 1947, and its last was on October 8th, 1957.
Bell X-1: Historical Significance
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The Bell X-1 aircraft’s maiden supersonic flight proved the aerodynamic concepts behind its faster-than-sound design. It showed that stable supersonic flight was possible and that the sound barrier wasn’t a true barrier for properly a designed aircraft. Subsequent flights with fine-tuned X-1 designs provided huge amounts of invaluable supersonic flight data. In fact, the information gained enabled engineers to successfully design scores of supersonic aircraft in the decades that followed.
Most of those aircraft were military jets, but the famous commercial Concorde supersonic jetliner also emerged from the research. So did the Tupolev Tu-144, a copy of the Concorde, possibly constructed based on stolen documents. The small, bright orange Bell X-1 couldn’t carry passengers or weapons, but it broke the ground leading to hundreds of subsequent designs. As the first supersonic plane ever built, it was the progenitor of every other transonic design created from that point onward.