Learn why Concorde produced a double sonic boom, why it continued throughout supersonic flight and why acceleration happened over the ocean.
In real-world aviation, Concorde created sonic booms because, at supersonic speed, pressure disturbances from its nose, wings and other surfaces could not travel ahead of the aircraft. They merged into shock waves that swept across the ground as abrupt pressure changes, heard as a boom and usually as Concorde’s characteristic double boom.
How Concorde’s shock waves formed
Concorde’s speed caused ordinary pressure disturbances around the airframe to combine into strong shock waves. Below the speed of sound, those disturbances spread ahead of an aircraft; above it, the aircraft overtakes them and they collect along a trailing Mach cone.
In ideal conditions, the cone’s half-angle at Mach 2 is about 30 degrees. When that cone intersects the ground, an observer experiences a sudden pressure change rather than hearing a sound emitted only at the instant Concorde crossed Mach 1.
The engines and reheat increased conventional aircraft noise, but they were not the fundamental cause of the sonic boom. Any sufficiently large aircraft travelling supersonically creates shock waves. Our detailed account of Concorde’s shock cone and operating history covers the wider aerodynamic context.
Why was Concorde’s sonic boom a double boom?
Concorde’s double boom came from two dominant shock fronts that reached a distant observer in quick succession. The first produced a rapid pressure rise; the second marked the rearward change in the pressure signature.
The aircraft actually generated numerous local shocks around its nose, engine intakes, wing and other surfaces. As those shocks travelled away, they tended to merge into a strong forward shock and a rear shock, producing the familiar N-shaped pressure trace measured at ground level.
Describing these as the “nose boom” and “tail boom” is useful shorthand, but it simplifies a more complicated pressure field. Atmospheric conditions and the observer’s position could make the reports sound separate, merged or less distinct.
Did Concorde boom only when it broke the sound barrier?
No. Concorde generated a sonic-boom signature continuously for as long as it remained supersonic and its shock waves reached the surface.
“Breaking the sound barrier” is not a one-off explosion. A person at one fixed location heard a brief boom because Concorde’s moving shock cone passed over that location once. Someone farther along the route heard it later as the boom carpet moved with the aircraft.
Concorde therefore did not create one isolated bang on accelerating through Mach 1. It produced a moving corridor of sonic-boom exposure throughout supersonic flight. Its airports, approaches and departures remained subsonic; the aircraft’s Mach 2 cruise profile and acceleration sequence explain where the supersonic phase fitted into a flight.
Why did Concorde accelerate over the ocean?
Concorde generally accelerated to supersonic speed over the ocean because sonic booms disturbed communities and civil supersonic flight over populated land was heavily restricted. The aircraft still produced booms over water; route planning moved most of the resulting boom carpet away from populated areas.
Operational crews used specified acceleration and deceleration points rather than selecting them casually. The permitted pattern depended on the service, airspace and local restrictions, which is why our summary of Concorde’s routes and operating patterns includes far more oceanic flying than its subsonic contemporaries required.
What changed the sonic boom at ground level?
The boom heard on the ground depended on more than Concorde simply exceeding Mach 1. Its strength and character were affected by several interacting factors:
- Altitude: Greater height allowed the pressure disturbance to spread over a wider area, generally reducing peak overpressure at a particular point.
- Aircraft geometry and lift: Concorde’s slender fuselage, delta wing, weight and lift distribution shaped the pressure signature.
- Flight path: Climbing, accelerating and turning could alter or concentrate shock waves rather than producing the uniform footprint implied by a simple cone diagram.
- Atmospheric conditions: Temperature and wind layers refracted the waves, sometimes weakening them, focusing them or creating secondary booms.
- Observer position: Distance from the ground track, terrain and nearby structures changed how sharply the two reports were perceived.
Concorde’s cruise altitude of roughly 50,000 to 60,000 feet reduced the ground-level effect compared with the same pressure signature generated much lower down, but it did not eliminate it.
Inside Concorde’s cabin
Passengers did not hear the external double boom in the way somebody beneath the flight path did. They travelled with the aircraft producing the shock system, so its cone did not sweep across them as it did a stationary observer.
There was no explosive cabin bang when the Mach indicator crossed 1. Passengers continued to hear the aircraft’s normal cabin, airflow and engine noise while the shock waves propagated outwards and behind Concorde.
How flight simulators represent the boom
A desktop flight simulator cannot create a physical pressure wave, so Concorde add-ons reproduce the effect with programmed sounds or gauges. The FSX and Prepar3D Concorde package with a sonic-boom gauge provides one example.
A common modelling mistake is to play a single bang inside the cockpit at exactly Mach 1. A more realistic simulation treats the boom as an external-observer effect associated with the aircraft’s continuing supersonic flight, although most simulators do not calculate full atmospheric refraction or a geographically accurate boom carpet.