Zahlen, bitte! Mach 1.06 for the first time in a flying X-plane

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NASA and US aircraft manufacturer Lockheed Martin are testing the X-59 aircraft to see how to avoid the loud sonic boom during supersonic flight when breaking the sound barrier. The aircraft represents the tradition of American experimental aircraft that take to the air for basic research.

X-planes are mostly developed for basic research, without a specific requirement for direct commercial or military use on board. The goal is to gain initial experience with new technologies or characteristics, which also makes the flights not without danger: Not all uncertainties can be foreseen.

Zahlen, bitte!

In this section, we present amazing, impressive, informative and funny figures ("Zahlen") from the fields of IT, science, art, business, politics and, of course, mathematics every Tuesday. The wordplay "Zahlen, bitte!" for a section about numbers is based on the ambiguity of the German word "Zahlen." On one hand, "Zahlen" can be understood as a noun in the sense of digits and numerical values, which fits the theme of the section. On the other hand, the phrase "Zahlen, bitte!" is reminiscent of a waiter's request in a restaurant or bar when they are asked to bring the bill. Through this association, the section acquires a playful and slightly humorous undertone that catches the readers' attention and makes them curious about the presented numbers and facts.

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It all started with the Bell X-1, a rocket-powered aircraft, with which test pilot Chuck Yeager became the first human ever to break the sound barrier in October 1947. The path to it was rocky.

Aircraft become increasingly faster during World War II

At the end of World War II, jet aircraft like the Me 262 and rocket-powered aircraft like the Me 163 were first used by the German Luftwaffe. Although the aircraft were not yet capable of exceeding the speed of sound due to their design, they pointed the way to the future: increasingly powerful aircraft required new technical solutions for high-speed flights.

Ezra Kotcher, chief aeronautical engineer and Major in the US Air Force, and John Stack, a researcher at the National Advisory Committee for Aeronautics (NACA) — the predecessor organization of NASA — jointly developed the X-1 program.

The goal was to build a demonstrator aircraft that would break the sound barrier, documented. At the time, it was controversial what would happen when a manned aircraft reached supersonic speed.

Aircraft as cargo of a bomber

Together with US aircraft manufacturer Bell, the Air Force developed the X-1, which was alternatively called XS-1 (eXperimental, Sonic). The plan was for a manned rocket-powered aircraft that could fly at supersonic speeds of 800 miles per hour (approx. 1287 km/h) at an altitude of 35,000 feet (approx. 11 km) for two to five minutes. For this purpose, the X-1 was to be launched as dropped cargo from a B 29 or B 50 bomber.

The design of the X-1 was based on developments of the Miles M.52, a planned British supersonic aircraft that was developed from 1942 to 1945. For cost reasons, the British government scrapped it after the war. The data and documents from the development status of the M.52 were passed on to Bell, but whether they directly influenced the development of the X-1 is debated in the specialist literature.

Not entirely by chance, the X-1 resembled a rifle bullet, as they remained stable in supersonic flight. The rocket-powered aircraft was powered by an XLR-11 engine from Reaction Motors with four combustion chambers, which together could produce a thrust of 26.7 kN.

Initially glide flights for control testing

The first flight of the first generation of the Bell X-1 took place on January 19, 1946. In a total of ten unpowered flights, the aim was initially to test controllability before an engine was installed. After further glide flights, test pilot Chalmers Goodlin completed the first powered flight on December 9, 1946. He reached a speed of Mach 0.79.

After further test flights, manufacturer Bell was able to prove the contractually stipulated airworthiness up to Mach 0.8: Everything beyond that was now at the responsibility of the US Air Force and NACA.

The development was divided: The X-1-1 was equipped with thinner wings to achieve the desired supersonic flight. NACA researched further flights with the X-1-2 and, in comparison, with 2 percent thicker wings, driven by research and not by record-breaking.

Experienced pilot of the record flight

Charles Elwood “Chuck” Yeager was selected as the pilot for the first supersonic flight. He was a World War II veteran with extraordinary flying skills, who, for example, was one of the first pilots to shoot down a German Me 262 with a jet engine.

Yeager named his aircraft “Glamorous Glennis” after his wife. After initial glide flights between August 6 and 8, 1947, to get acquainted with the aircraft, his first powered flight was on August 29, in which he remained below the speed of sound (1236.5 km/h at 20 °C and dry air) at Mach 0.85 (1051.025 km/h).

On October 14, 1947, he broke the sound barrier with his X-1-1 (number 46-062) as the first human. Under the atmospheric conditions, the sound barrier was reached at 1060 km/h: He exceeded it at 1125 km/h and reached Mach 1.06 at an altitude of 13100 meters (about 43,000 feet). The supersonic age had begun.

Publicly announced with a time delay

As the program was strictly secret, the US Air Force only revealed the record flight six months later. The X-1 program later reached over Mach 2, and a Mach 3 flight was planned when structural damage was observed on the test aircraft: the limit had been reached for the aircraft.

The X-1 program was followed by over 50 more X-aircraft to date, with the X-59 currently making headlines because its special shape aims to avoid the loud sonic boom. We can look forward to it.

(mawi)