It’s an interesting historic parallel. Weather permitting, Austrian daredevil Felix Baumgartner is set to break Joe Kittinger’s high altitude jump record this morning by sky diving from 120,000 feet. On the way down he’s going to break the sound barrier without the benefit of an aerodynamic shell like a fuselage, 65 years to the day that Chuck Yeager broke the sound barrier in the Bell X-1. On October 14, 1947, Yeager ushered in a new era of supersonic aviation where faster planes started reaching the fringes of space.
For decades, the sound barrier had been a problem for pilots and aeronautical engineers. Air builds up in front of and around an aircraft as it approaches the speed of sound; it can’t move out of the way fast enough. The air in front of the aircraft increases drag and reducing lift. At the same time, the air traveling over the top of the wing reaches the speed of sound and forms shockwaves that move back and forth. This disrupts the airflow and causes the aircraft to buffet and shake.
Pilots typically lost control in this transonic region – traveling between Mach 0.8 and Mach 1.2 – and in many cases couldn’t recover the aircraft. In many cases, they approached or broke the speed of sound in a dive, meaning they were in a bad situation already.
The National Advisory Committee for Aeronautics attempted to gather data on the transonic flight problem in wind tunnels but the data was no good. The same shockwaves that buffeted the aircraft in flight bounced around inside the wind tunnel. The only solution was to build a research aircraft and just fly it through Mach 1 in level flight.
The NACA and the U.S. Air Force took up the challenge, awarding the contract for the aircraft’s construction to Bell Aircraft. Bell took its inspiration from a bullet since bullets flew faster than sound leaving the barrel of a gun. The XS-1 (for Experimental, Supersonic) was looked like a swollen torpedo with stubby wings and a long tapering nose painted bright orange so ground observers could track it in the sky. It held 8,000 pounds of fuel, but that still wasn’t enough to reach supersonic speeds after a runway takeoff. The solution was to launch it from a mothership in the air, conserving all its fuel for the short powered flight. It would, by default, make an unpowered landing on the dry lakebed at Muroc Air Field (later renamed Edwards Air Force Base). And Yeager was the man to fly it.
Yeager was like some sort of airplane whisperer. He had no formal education in aeronautical engineering but could feel when something as wrong. When a flight didn’t go well, his instinctual analysis of the problem was often the same conclusion engineers came to after a lengthy assessment. Yeager knew that when he was in an aircraft he was the one in charge, not the machine, and he knew he could control the XS-1.
The morning of October 14, 1947, Yeager was in the cockpit of B-29 with his good firend and longtime sidekick Jack Ridley and Bob Cardenas in the pilot’s seat. Underneath the bomber’s belly visible through its open bomb bay doors was the orange XS-1, its cockpit open waiting for a pilot. The flight plan that day called for Yeager to take the X-1 to Mach 0.97, which he was happy to do; he’d broken two ribs the night before after being thrown from a horse and suspected a gentler flight would be safest. But he was tired of conservative flights, edging close to but never reaching Mach 1. This was his ninth flight in the XS-1. He knew how to fly it. Climbing down the ladder through the B-29’s bomb bay doors into the orange aircraft’s cockpit that morning, he decided that unless some unexpected problem developed on the morning’s flight he’d take the XS-1 to Mach 1 on his next flight. Yeager closed the X-1’s cockpit with a sawed off broom handle Ridley had left on the seat – his broken ribs stood in the way of regular procedure. At 20,000 feet, Cardenas released the XS-1.
But the B-29 was flying a little too slowly, and the instant it was free the XS-1 started to stall. It fell more than 500 feet before Yeager managed to get the nose pitched over, forcing air over the wings for lift and regained control. He lit the four rocket chambers of the XS-1’s XLR-11 engine in rapid sequence and accelerated easily to Mach 0.88. The aircraft started to vibrate; flipping on his stabilizer control system smoothed the flight right out. He shut off two of the rocket chambers but kept accelerating past Mach 0.92 and ascending into thinner atmosphere. When he turned his third rocket chamber back he hit Mach 0.96.
Then he reignited his fourth rocket chamber and the XS-1’s Machmeter failed. The needle fluctuated then tipped right off the scale.
After all the anxiety about a pilot’s ability to control an aircraft breaking the sound barrier, the controversy over whether anything even existed beyond Mach 1, Yeager was there. And hadn’t felt a thing. Observers on the ground got the sonic boom as confirmation of the XS-1 supersonic flight, but for Yeager in the cockpit it was a bit of a let down. He’d expected something, a bump or shake in the flight, to tell him he’d gone supersonic. He felt nothing. It was less like breaking through a wall and more like poking through Jello. He didn’t even know how fast he’d gone. His Machmeter stopped at 1 – it was an interesting measure of how little faith the XS-1’s designers had in its ability to fly supersonic.
Underwhelming though it might have felt, the importance of the flight and its impact on aviation were significant. Yeager, who reached Mach 1.06 at 43,000 feet opened the skies. In the decade that followed, pilots pushed later X-aircraft – modified X-1s and its successor the X-2 – to altitudes of 126,000 feet and speeds a shade over Mach 3. Not until the X-15 were these records broken in the 1960s.
Chuck Yeager and Leo Janis, Yeager. Bantam Books. 1985.