The 10th anniversary of Concorde's last flight passed recently, and while many long, flowing euologies were written about British Airway's most famous plane, everyone seems to have forgotten that Concorde, whilst impressive, was just one in a long line of supersonic planes. Heck, it wasn't even the first commercial supersonic plane to fly.
To understand the significance of the first supersonic flight, it's important to understand the difficulties of flying faster than the speed of sound. 'Breaking the sound barrier' doesn't mean breaking a metaphorical barrier, like driving a car faster than 200mph; rather, the sound barrier marks an abrupt change in aerodynamics, which, whilst not an actual barrier, presented a number of challenges to scientists of the time.
One of the unique features of supersonic flight is the shockwaves. When aerodynamic flow moves from supersonic (faster than the speed of sound) to subsonic (slower), a shockwave is formed. The shockwave itself is an incredibly thin region, across which there are multiple and violent changes of pressure and temperature -- not exactly a good thing to have sitting right on the fragile wing of an aircraft.
Image credit: NASA
What makes things even harder is that the shockwaves change with the speed of the aircraft. As you may know, air flows faster over the top of a wing than over the bottom. That means that when an aircraft is travelling just a little slower than the speed of sound, air may well be travelling over the wing faster than the speed of sound. That causes a shockwave, of course, and one that sits right on the wing itself, rather than being a bow shockwave, which is the norm for an aircraft travelling supersonic.
Additionally, there's the slight problem that as an aircraft approaches supersonic speed, the drag encountered goes up exponentially, and the lift generated by the wings drops off -- neither of those are exactly good news, and in several cases prior to WWII, fatal accidents occurred when prototype high-speed fighters, both US and German, 'locked up' in high-speed dives, as the wings lost lift.
Collectively, all the problems associated with supersonic flight were known as 'compressibility'. The aerodynamic properties of flight were well documented at speeds lower than about Mach 0.9, and over Mach 1.2, but in between existed the so-called 'transonic gap', an unknown region that sparked the development of the very first supersonic aircraft, the Bell X-1.
Scientists at the time faced a bit of a pickle: they needed some means of studying the effects of supersonic and transonic flight in order to be able to build fast aircraft, but without a test plane flying at those sorts of speeds, there was no way to get the relevant data. As such, experimental aircraft were mooted that could theoretically break the sound barrier.
Image credit: NASA
The most famous of them all, the Bell X-1, went on to be actually built, and piloted by Chuck Yeager. Powered by four rockets, the X-1 was the first manned aircraft to officially break the sound barrier during level flight. However, it quite possibly wasn't the first manned aircraft to do so -- two weeks before Yeager's record-breaking run, on October 1st 1947, a pilot flying for rival company North American aviation claimed to have broken the record in the F-86 Sabre, a prototype aircraft on order for the US Air Force, and one of the first aircraft to make use of Nazi swept-wing innovations made during WWII.
Breaking the 'sound barrier' didn't signal the end of problems associated with supersonic flight, though. Problems with 'pitch-up' (an aerodynamic effect of swept wings that could cause fatal stalls at low speeds) and inertial coupling, a phenomenon that could see a rolling aircraft suddenly roll, pitch and yaw all at once, dogged early prototype aircraft. Not to mention limited the early supersonic fighters like the F-86 and MiG-15, even killing George Welch, the North American test pilot who claimed to have broken the sound barrier before Chuck Yeager.
The supersonic F-104 Starfighter. Image credit: USAF
Even so, by the late 1950s, supersonic flight was commonplace among military aircraft. Developments in aerodynamics like the 'moving T' tailplane, and the area rule for fuselage design, combined with innovations in engine technology like variable-compressor jets and afterburners, saw interceptors routinely exceeding Mach 2, with no shockwave bumps or stalls along the way.
There really remained only one logical step to be made by this point: supersonic passenger flight. By the late 1950s, it was widely believed that the future of passenger flight rested somewhere around Mach 2, and that big brutes like the 747 were just a passing fad.
As such, in the late '50s the British government formed the Supersonic Transport Aircraft Committee; the Soviets began work on the Tupolev Tu-144, and the Frenchies worked on a small supersonic passenger plane named the Super-Caravelle. (Of course, the British and French efforts merged shortly thereafter, to form work on the legendary Concorde.)
However, the first commercial plane to break the sound barrier wasn't any of these supersonic transports (SSTs); rather, the Douglas DC-8, a conventional jet airliner intended as a rival for the Boeing 707 was taken supersonic, largely as a publicity stunt -- it only managed to achieve Mach 1.01, for 16 seconds, whilst in a steep high-altitude dive. However, happening as it did in 1961, the DC-8 held onto its crown as the fastest commercial transport for a good eight years.
Tupolev Tu-144. Image credit: NASA
All proceeded swimmingly throughout the 1960s. The USSR unveiled the Tu-144, their Concorde-answer which, while looking shockingly similar to Concorde, had a different wing design, and used turbofan engines rather than the turbojets that were more desirable for supersonic flight. Notably, though, the first prototype flew on New Year's Eve of 1968 outside Moscow, two months before Concorde got off the ground.
However, while it beat Concorde into the skies, the Tu-144 was plagued by problems for the entirety of its short life. It was notoriously unreliable, suffering 226 failures in just 180 hours of flight. More tragically, the very first production model crashed at the 1973 Paris Air Show, killing all six crew members and a further eight people on the ground.
Those problems didn't get fixed, either -- in a 1978 flight for a number of foreign dignitaries and journalists, systems for the landing gear appeared to fail for almost the entire flight, and an ear-splitting crash siren went off just after takeoff, staying on for the entire flight (or, at least, until one of the cabin crew stuffed a pillow into the siren). Cabin noise was also an immense problem, with it being apparently impossible to have a conversation with the person two seats over.
Concorde, in the meantime, proceeded a little better. The first flight was in 1969, around two months after the Tu-144 first got off the ground, but Concorde, unlike the Tu-144, was a little better in the skies. Although orders weren't quite as hot as the cash-strapped British government had probably been praying for, Concorde was still an incredible technical innovation -- designed in the early '60s, and able to fly London-New York in just over three hours.
Sadly, all good things come to an end, and Concorde appeared to be no exception. A combination of a fatal crash of an Air France Concorde (caused by debris on the runway) and the poor economics of operating Concorde led to both BA and Air France discontinuing Concorde flights in 2003. It's highly unlikely that the Concorde fleet will ever fly commercially ever again, although a group of volunteers are looking at restoring a single Concorde to be able to get it to fly for the occasional demonstration.
Header Image credit: British Airways