The Race to Break the Sound Barrier

The sound barrier was broken for the first time, in level flight, 71 years ago, but who was the first person to fly faster than the speed of sound?

Text by Divan Muller
Bell X-1 photographs courtesy of the US Air Force

The official answer

Chuck Yeager is arguably one of the most famous pilots of all time. He became a P-51 Mustang ace during World War II by shooting down 17 Axis aircraft – an impressive tally that includes an Me-262 kill. His first five kills were achieved in one mission, making him the first usaaf pilot to become an ace during a single mission. Of course, Chuck Yeager didn’t become famous by shooting down enemy aircraft; his fame came with a much more significant event that only came after the war.

On 14 October 1947, Chuck Yeager broke the sound barrier in level flight in a Bell X-1 called ‘Glamorous Glennis’. The X-1 didn’t have enough endurance to take off under its own power, so instead it was carried under the bomb bay of a B-29 Superfortress. Similar to other X-1 test flights, the B-29 climbed to an altitude of 25 000 ft, before starting a shallow dive. Once 240 mph had been reached, the X-1 was released from the B-29’s underside. Chuck Yeager then ignited the liquid oxygen and alcohol powered rockets and accelerated to a speed that exceeded Mach 1. However, the question remains: was he the first man to fly faster than the speed of sound?

The other side of the story

The following account is mildly controversial and the accuracy of the sequence of events is still debatable. Our story begins with another World War II ace, albeit from a different theatre of the war. George Welch was one of four P-40 pilots who managed to fight against Japanese forces (and claim four kills) on the day that Pearl Harbour was attacked. After a successful wartime fighter pilot career, George Welch became a test pilot with North American Aviation. On 1 October 1947, (two weeks before the Bell X-1’s attempt) Welch conducted high speed dives while test flying the XP-86 – the prototype Sabre. During one of these dives he experienced all the telltale signs that he was passing through the transonic speed range. In fact, he even caused a sonic boom. Welch reportedly repeated the feat seconds before Chuck Yeager’s official attempt. Naturally, this would be quite embarrassing for those who had spent huge amounts of money on an aircraft that was designed solely for the purpose of ‘breaking the sound barrier’. It would therefore make sense to cover up the fact that the same could be accomplished sooner by a conventional, affordable aircraft, which could actually be used in a time of war.

Were there any other candidates?

There have been many tales of World War II fighters breaking the sound barrier, while diving to escape enemy aircraft. One fact that we have to bear in mind is that one could not rely on air speed indicators to be accurate when approaching transonic speeds. For example, P-38 Lightning pilots have claimed on several occasions that they broke the sound barrier while referring to their asi readings as proof, even though Lightnings had very low Mach limits when compared to contemporary fighters. Mustangs and Thunderbolts had better initial dive speeds than Spitfires, but because of their thin wings, Spitfires could reach superior Mach speeds. During flight trials at the Royal Aircraft Establishment, a Spitfire Mk XI reached a speed of Mach 0.92 during a dive from high altitude. Perhaps we shouldn’t ask whether these propeller driven aircraft could dive at supersonic speeds, but rather whether the pilots survived to tell their stories.

The most credible account from the Second World War is the one of Hans Guido Mutke, an Me-262 pilot. In an effort to intercept a Mustang, Mutke initiated a 40 degree full-power dive from an altitude of 36 000 ft. The German pilot experienced a sequence of events very similar to those experienced by Chuck Yeager. Even so, the air speed indicator’s needle stopped at the end of its range and the aircraft obviously didn’t have any testing equipment installed. Therefore we can’t be absolutely sure – let alone prove - that Mutke did fly supersonic. Messerschmitt did conduct high speed dive tests and reached the conclusion that one would lose control over the Me-262 at Mach 0.86. In theory, if one would exceed that Mach number, the aircraft’s nose would pitch down, with the resulting negative G-forces severely compromising the fighter’s structural integrity. Some variants of the Me-262 were estimated to have Mach limits as high as Mach 0.96 at cooler air temperatures, but these were never confirmed by official tests. The bottom line is that it is quite possible that World War II aircraft exceeded Mach 1, while diving toward or away from enemy aircraft – shortly before disintegrating or hitting the ground.

Arguably, the least credible claims of early supersonic aircraft are probably those that involve the German designer, Alexander Martin Lippisch. He was responsible for a number of fascinating aircraft designs and is said to have successfully built supersonic, rocket engined gliders. Some conspiracy theorists claim that he designed fighters resembling ‘flying saucers’ (also known as ‘Foo Fighters’), before retreating to a secret Antarctic base.

What about the Russians?

The Bell X-1’s historic flight took place during the Cold War; therefore news of this accomplishment was kept secret for a while after the actual event. Could the same scenario have taken place on the other side of the Iron Curtain? At the end of the Second World War, an uncompleted German prototype was evaluated by the Soviet Union. This aircraft, a rocket-powered DFS 346, was intended to serve as a supersonic reconnaissance plane. The Soviets, assisted by German engineers, developed further examples of the concept, which were eventually, and ironically, launched from a captured B-29. Interestingly, pilots had to lie on their stomachs while flying a DFS. Although theoretically capable of transonic speeds, it cannot be confirmed that any of these aircraft actually broke the sound barrier. In the end, the first Soviet aircraft to officially fly supersonic was the Lavochkin La-176 – an aircraft similar in appearance to the legendary MiG-15. This was accomplished in 1948, while diving at full power.

What is the final verdict?

The fact that Chuck Yeager flew faster than the speed of sound on 14 October 1947 cannot be disputed. The event was well documented and the flight was monitored by accurate equipment. George Welch’s claims of reaching Mach 1 before Yeager are without substantial proof, however, shortly after Yeager’s flight, it was established that the XP-86 was capable of reaching supersonic speeds during a dive. In fact, the first female pilot to fly supersonic did so while piloting a Sabre. Then there were other fighter pilots, who fought in World War II, who claimed to have broken the sound barrier long before Chuck Yeager and George Welch.

Who was the first person to accomplish this feat? Until sufficient proof has been accumulated to change history as we know it – you’ll have to be the judge.

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