Sonic Speed - Supersonic

Speed of sound – the early days

Arnold Fischer
25.09.2018
4 minutes

Man has been dreaming about supersonic aircraft for fast travel from as early as the 1930s. Right up to the present day. Around 1943, the most advanced aircraft with piston engines reached a speed of up to 850 km/h at an altitude of 6,000 metres, which equates to Mach 0.75.

These speeds could be considerably exceeded in specific flying manoeuvres, for instance when nosediving, allowing the aircraft to edge closer to the speed of sound. However, this led to shaking, blockages, changes to the stability of the aircraft and damage to the propellers. This was all new and initially inexplicable. The aim was to reach Mach 1, essentially 1 times the speed of sound. Attempts to investigate the sensitive zone between Mach 0.8 and 1.2 in a wind tunnel failed. The shock and expansion waves generated broke against the walls and “blocked up” the tunnel.

The speed of sound – a projectile-shaped aircraft

The solutions were as simple as they were compelling: power and form. There was simply no alternative to rocket propulsion without a propeller to achieve the requisite force. The projectile of a widely used 50-calibre BMG (Browning Machine Gun) rifle was replicated to create the most effective aerodynamic shape, which was regarded as being exceptionally stable in ballistic supersonic slight. When the sound barrier was officially reached in 1947 – by the “Glamorous Glennis“ Bell X-1 flown by Chuck Yeager – the “race” towards maximum speed was thrown wide open. The Russian attempts at this time were still restricted to wind tunnels and the USA wanted to win this race at all costs. Ultimately the speed of sound was one of the pioneering visions of the time alongside the emerging plans for space flight. However, there is a massive difference between test pilots and astronauts steering rockets wearing pressurised suits exposed to maximum physical stress and facing the ultimate dangers, and a formally dressed flight captain flying passengers while they are nibbling on canapés and sipping champagne. This period was one of the most legendary eras in aviation (check out this article on Chuck Yeager as well) and the race was not over yet.

Fuel, material and shape. A challenge.

For the first time, it was clear that aircraft could fundamentally break through the sonic barrier, but many questions still had to be answered. Was several times the speed of sound possible? How big could supersonic aircraft be, as after all they had a massive fuel consumption. The X-1 only flew for a few minutes and, with the exception of a single take-off in 1949, never launched itself into the air and instead was “dropped” at a huge altitude from a Boeing B-29 or B-50.

What is more, the fuel was also not exactly what you wanted on board for a safe flight from A to B. The ultra-explosive alcohol-oxygen mixture was carried by high-pressure nitrogen into combustion chambers where it ignited.

The materials were a further concern. Which metal alloys were capable of combining maximum stability with minimum possible weight whilst defying frictional heat above Mach 1?

The challenges were self-evident: engineers would have to design powerful engines that were operated with “normal fuel”, overcome the engineering and material challenges and completely redesign the aerodynamics, as a projectile shape was possibly unsuitable for passenger aircraft.

Mach 2 from 1

However, the vision became more tangible. In 1955, scientists at the English Royal Aircraft Establishment in Farnborough considered supersonic passenger flight as being feasible. Even before one record after the next was set high above the Californian desert (the North American X-15 flew at an unbelievable 7,274 km/h at an altitude of 59,000 metres in 1966), the designers went back to the drawing board determined to make the supersonic vision compatible with passenger flight. Tests were carried out on materials, engines were designed and draft designs developed.

In 1959, the Supersonic Transport Aircraft Committee (STAC), specifically set up for this purpose, selected two possible shapes from over 200 designs, only one of which was suitable for Mach 2. And that was precisely what the designers were aiming for: the pinnacle of technical achievement. Instead of stopping at Mach 1, they wanted to go for Mach 2 – twice the speed of sound. It was every aircraft engineer’s dream. A specification was drawn up in France in 1959. The cornerstones: 60 to 80 passengers, a range of 3,500 kilometres and a speed higher than Mach 1. Cooperation with Great Britain started that very same year. The French President Charles de Gaulle personally insisted on the final “e” in its name: Concorde was born.

Main picture Pixabay © skeeze


by Arnold Fischer

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