The the Glamorous Glennis snugly into the bomb bay of its B-29, then filled its tanks with 1177 liters of supercold liquid oxygen and 1109 liters of diluted ethyl alcohol fuel. At Yeager's suggestion, crew chief Jack Russell rubbed the rocket plane's windshield with Drene shampoo, an old fighter pilot's trick to prevent frost from forming on a canopy at high altitude. Finally, all was ready.
The NACA team was standing by the telemetry gear and twin launch crew and test pilot entered the silver and black B-29, and soon its four engines were clattering noisily. At two minutes past ten o'clock, the Super fortress taxied away from its hardstand, the orange XS-1 clasped tightly underneath, received takeoff clearance, and roared down the runway to the east. At 1500 meters, Yeager squirmed through the tiny entrance hatch of the XS-1, in acute pain from his broken ribs.
As the B-29 continued to climb, "Yeager readied Glamorous Glennis for flight. Two P-80 chase planes accompanied the B-29, one escorting the bomber to observe the launch, and the other about 16 kilometers ahead of the B-29 to join the X S-1 after it completed its rocket-propelled excursion through mach 1.
A minute before launch, Jack Ridley raised Chuck Yeager on the intercom and asked, "You all set?" "Hell, yes, let's get it over with," Yeager replied. At 10:26 am., at a pressure altitude of 6000 meters, Glamorous Glennis was launched into the skies over the Mojave Desert. As the XS-1 dropped earthwards, Yeager briefly checked rocket engine operation by firing the four chambers of the XLR-11 engine, shutting down two and climbing away to altitude on the remaining two, pulling away from one P-80. He fired the other two chambers and under a full 26 800 newtons (6000 pounds) of thrust, accelerated for altitude, the XS-1 streaming a cone of fire with bright yellow shock diamonds outlined in the exhausts from the rocket chambers. Further behind, a broad white contrail formed a long spearpoint with the little research airplane at its apex. Second by second the XS-1 was growing lighter, its engine gulping propellants, and the thrust-to-weight ratio rose higher and higher. The plane passed mach 0.8 and streaked on to mach 0.9.
Above mach 0.93, the adjustable stabilizer provided adequate longitudinal (pitch) control. He shut down two chambers briefly while he assessed his situation. All the signs were good; confident that Glamorous Glennis could safely exceed mach 1, Yeager leveled off and fired one of the two shut-down cylinders. Now very light from the amount of propellants that had already been consumed, the XS-1 shot ahead. At about mach 0.98 indicated, the needle on the machmeter fluctuated, then jumped off the scale, leading Yeager to believe the plane was flying at about mach 1.05. In fact, postflight data analysis indicated the XS-1 had reached mach 1.06 at approximately 13 100 meters, an airspeed of 1125 kilometers per hour. The machmeter jump-a hallmark of supersonic flight since-registered the passage of the bow shockwave across the nose as the plane went supersonic. And on the ground, observers heard the characteristic double crack of a sonic boom.