“The Air Force is kinda looking down our throats on this flight, aren’t they?” said Chilton. He also knew that Yeager might bust Mach 1 that morning, and, knowing what Welch was up to, noted that there might be an awkward 15 minutes between Welch’s reported performance of test card maneuvers and his eventual return to base. He suggested that Welch stretch out the test card, letting the narration over the radio trail the actual performance of the maneuvers. That way, when people on the ground heard a boom, they might think it was Yeager.
Welch climbed to the 10,000 feet and ran through the lateral and directional stability checks on the test card, but he reported the results via radio to the North American flight test engineer at Muroc on only half of them. He retracted the landing gear and waited for Chilton to slide underneath to check on his gear doors. Chilton gave him a thumbs-up and Welch advanced the throttle to full military power. During his climb to 37,000 feet, he kept reading out the results of the tests not yet reported. As he reached his altitude goal, 2,000 feet above the starting point for his successful sound barrier penetration of nearly two weeks earlier, he once more rolled into a dive of at least 40 degrees and headed westward with the nose of his Sabre pointing directly at Pancho’s. On the way down, he called out the results of the next to last test point on the card.
Once again he experience some wing roll as his airspeed indicator hung up, then popped through to greater readings. Because he had started at a higher altitude, the Mach-related transients were less pronounced than they had been on the first flight. Instead of a gentle, throttle-back recovery like he’d flown on that first outing, Welch left full power on and performed a four-G pull-up, little realizing that this would greatly increase the impact of the shock wave aimed at Pancho’s place. He carefully throttled back and called off his last point on the test card as though he had just completed it.
Welch had shut down and dismounted and was heading for the locker room to drop his parachute and helmet before debriefing with the flight-test engineers when he heard a distant but distinct ba-boom. His watch read 10:30.
A security clamp was immediately placed on Yeager’s penetration of the sound barrier. Consequently, a celebration at Pancho’s was out of the question. Instead the X-1 team started their whoop-de-do at Yeager’s house, and later, when Yeager ran out of booze, they adjourned to Dick Frost’s. It’s not that Pancho’s closed down for the evening. The North American crew showed up, if only to get a reading from their own highly sensitized boom detectors at Pancho’s. Welch and North American pilot Bud Poage were making careful mental notations while ascribing all credit to Yeager and the X-1. Both Millie Palmer and Mona (soon to be Poage’s bride) were on hand to provide authentication, especially of the first boom, which cracked a couple of windows in two of the rooms facing east. Major General Joe Swing, a Pancho’s regular, found it strange that there were two ba-booms some 20 minutes apart. Didn’t it take at least two days to get the X-1 ready to fly again? With only four minutes of fuel at best, it certainly couldn’t make two ba-booms in such a short interval. Welch shrugged and suggested with a straight face that maybe a V-2 had flown off course out of White Sands.
Welch flew the Sabre the next morning. The following week he made four flights and the subsequent Monday, October 27, he flew four flights in one day. He then surrendered the Sabre to Bob Chilton for a couple of familiarization flights. Chilton was no shrinking violet. It is entirely possibly he laid a boom or two on his own. On November 3, Welch commenced a series of high-Mach dive flights, so labeled in his flight log.
This persistent barrage of ba-booms at the Air Force test base finally precipitated permission to use the high-precision radar theodolite facility that had confirmed Yeager’s climb to immortality. Welch’s dives in the Sabre were measured during two flights on November 13. His first dive was clocked at Mach 1.02, the second at 1.04. The ba-booms were finally officially acknowledged, but only under tight security. The North American flight test reports are asterisked with a notation that data concerning speeds in excess of Mach 0.90 have been detailed in an amplifying document under higher security. This amplifying data could not be found in the North American archives. In Welch’s handwritten flight log, these flights are variously classified as “Hi Mach No. Dive” or simply “Hi Mach.” Between November 3, 1947, and the end of February 1948, Welch flew 23 flights in the XP-86 that are so characterized. Almost certainly each flight included at least one incursion into the realm of the supersonic. More likely two or three were made per flight. By way of comparison, during the same four-month period, the X-1 made seven flights, attaining supersonic speed on three of them, but no more than once per flight.
The Air Force’s Wright Field XP-86 project officer, Major Ken Chilstrom, gave a glowing report on the aircraft while flying it to a maximum altitude of 45,000 feet and a Mach number of 0.90 during Phase II evaluation in early December 1947. Why didn’t Chilstrom push the Sabre through the sound barrier? Probably because he was Colonel Boyd’s chief of fighter test. Al Boyd kept a tight reign on Air Force Flight test operations. He had just carefully nursed Yeager through Mach 1 after 28 flights spread over a year and a half. He no doubt had difficulty even conceiving that a prototype fighter only two months past its first flight could be ready to explore the supersonic realm. He was a great friend of Pancho’s and had no doubt heard the rumors that floated out of her hacienda of Sabre ba-booms. But the fall of 1947 was an era in which the sonic boom phenomenon was not yet broadly understood, even by technically very sophisticated people. Pancho had assembled some very nice young ladies, but none were CalTech graduates. Moreover, such knowledge as might have surfaced as a consequence of Yeager’s flight was still highly classified. Similar restrictions were applied to details of the Sabre dances.
Boyd was keenly aware of his route to stardom. He knew the X-1 program has special protection from high places. Being first to go supersonic was important to the Air Force. For the Bell Aircraft Company, it was absolutely vital. The X-1’s sole purpose was to pave a way through the sound barrier. Millions of taxpayer dollars had been spent to make that happen. Now it had been done. For North American Aviation to come along and say “Hey, what’s the big deal? Our new fighter does it as an incidental piece of cake” certainly wasn’t going to be helpful. Boyd could see that it was in the Air Force’s best interests that the X-1 be clearly first by a considerable margin and that the Sabre rattling be quelled as long as it might take to keep the press away.
The Air Force wanted Yeager to push the mark a little higher. On November 6, Yeager raised the mark to Mach 1.35 at 48,600 feet. When the number two X-1 was ready for NACA, the Langley leadership wanted to make sure one of their pilots—Herb Hoover—became the first civilian to break the sound barrier. On March 10, 1948, Hoover flew the NACA X-1 to Mach 1.065. At that point, North American Aviation and the Air Force deemed it acceptable to announce that the Sabre had indeed gone supersonic as of April 26, a month a half after Hoover managed to struggle through.