Seventy years ago, a young pilot from West Virginia risked his life to punch through an invisible barrier in the sky.
The flight that made aerospace history wasn't supposed to go quite the way it went. Chuck Yeager's flight plan that day called for him to approach the sound barrier, but not break it -- yet. And the flight plan definitely didn't call for him to be flying with two broken ribs that he'd hidden from his flight surgeon by going to a veterinarian in town. Yeager's ride is one of the greatest stories in aviation history -- and one of the most colorful. One of its often-overlooked lessons, perhaps, is that breakthroughs don't happen when you're ready for them. Sometimes, they happen on a day when you've got a few broken ribs and you just want to get things over with. And sometimes they take you a bit by surprise.
The Wall in the Sky
Sound waves travel through the air just like waves travel through water, but much faster. At sea level, sound travels at about 761 MPH. At 45,000 feet, a bit above the altitudes where most commercial airliners cruise, the air is much thinner, and sound travels at about 660 miles an hour. And once upon a time, everyone thought that was as fast as an aircraft could ever fly -- an unbreakable speed limit imposed and enforced by the harsh laws of physics.
As aircraft approach the speed of sound, shock waves build up on the wings, interfering with the airflow that produces lift and keeps the plan in the air. In the late 1940s, most scientists agreed that by the time an aircraft reached the speed of sound, the shock waves just rip it apart. This was what scientists, engineers, and pilots called the "sound barrier."
Some - like the team of Army Air Corps engineers at Muroc Army Air Base (now Edwards Air Force Base) in California thought it might actually be possible to push past the shock waves approaching Mach 1 and come out the other side -- but the attempt would be a terrible risk. All in all, when Chuck Yeager agreed to pilot the X-1 to the speed of sound, all anyone knew at the time was that there was a good chance he wasn't going to survive the attempt. If he succeeded, it would be, as his commanding officer put it, "this most historic ride since the Wright Brothers." If he failed, he would be dead, and the notion of supersonic airplanes would probably be buried along with him.
The Orange Beast
Although he was aware of the risks, Yeager says he just saw himself as a test pilot doing his job, and his job was to fly the Bell X-1: a 31 foot long, saffron orange rocket plane with 28 feet of thin, straight wings sticking out from its bullet-shaped fuselage. Jet engines at the time couldn't achieve the speeds required, so Bell opted for a Reaction Motors XLR11, fueled with ethyl alcohol and liquid oxygen. Yeager named his plane "Glamorous Glennis," after his wife, just as he had named the P-51 Mustangs he flew during the Second World War.
The Army Air Corp's plan was to make a series of flights, venturing a little closer to the sound barrier each time, and then giving a team of engineers from NACA a chance to to study the data from sensors mounted on the X-1's wings. Above 0.85 Mach, no one was sure what would happen; wind tunnels at the time couldn't produce greater speeds than that, so there was no way to test the aerodynamics. Shock-wave buffetting set in around 0.86 Mach, on powered flight number six. Yeager later compared it to driving on a rough road in a car with bad shock absorbers.
Because the Bell X-1 couldn't take off from a runway like a normal aircraft, it had to be dropped midair from the bomb bay of a B-29 bomber, which meant that 12,000 feet above the California desert, Yeager had to climb down a ladder and drop feet-first into the waiting rocket plane, then wait in the darkness of the bomb bay for the bomber to make its dive and release him.
"The wind blast from the four bomber prop engines was deafening, and the wind-chill was way below zero," he wrote in his autobiography Yeager. "I had to bounce on the ladder to get it going, and be lowered into the slipstream. There was a metal panel to protect against the wind blast, but it was rather primitive, and that bitch of a wind took your breath away and chilled you to the bone."
And on the day he broke the sound barrier, Yeager had to do the whole thing with two broken ribs. Over the weekend, he had taken Glennis out for a nighttime horseback ride in the desert, and after an hour or so, the young couple decided to race back to the barn. As Yeager told the tale later, "Unfortunately there was no moon, otherwise I would have seen that the gate we had gone out of was now closed." He tried to swerve and miss the gate, but instead ended up flying off his horse and cracking two ribs on landing.
Yeager knew that if he went to the flight surgeon, he'd be grounded. Rejecting that option immediately -- and overriding his wife's protests -- he instead went to a local veterinarian to get his ribs taped up. None of the Bell X-1's controls required much reaching, so Yeager reasoned that as long as he could climb into the aircraft and shut the door, he could fly.
The door turned out to be a problem, though. Normally, Yeager had to reach up and pull the door shut once he'd settled into the cockpit of the X-1, but with the broken ribs, he couldn't reach. Project engineer and fellow test pilot Jack Ridley devised a solution in the form of a sawed-off broomstick, which Yeager could use to extend his reach and pull the door shut.
Neither of them realized that broomstick was about to become part of aerospace history.
Surprise Sonic Boom
Yeager was still a few flights away from the scheduled attempt on the sound barrier, and the October 14 flight plan called for just 0.97 Mach. But around .965, the needle on Yeager's Mach gauge went off the scale. The buffetting stopped, leaving the X-1 flying so smoothly that, as Yeager put it in his autobiography, "Grandma could be sitting up there sipping lemonade."
Then NACA observers on the ground radioed in to say that they had heard the rumble of a sonic boom. Yeager had broken the sound barrier, and not only did his aircraft not shatter against an invisible wall of compressed air, it barely gave him any sign at all.
"After all the anticipation to achieve this moment, it really was a let-down," Yeager recalled in his book. "It took a damned instrument meter totell me what I'd done. There should've been a bump on the road, something to let you know you had just punched a nice clean hole through that sonic barrier."
In fact, a few days after his historic flight, Yeager found out that he may actually have broken the sound barrier without even realizing it on [date]. Close to the sound barrier, shockwaves interfered with the airspeed gauges on the X-1's wings. Yeager had planned to reach 0.955 Mach on that flight, but when the engineers finished with the data, they said he had reached at least .988 Mach -- and maybe even gone supersonic. The gauges made it impossible to be sure, and nothing dramatic had happened.
"Later on, I realized that this mission had to end in a let-down, because the real barrier wasn't in the sky, but in our knowledge and experience of supersonic flight," Yeager wrote.
