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At what point during flight would Concorde go supersonic? Would it climb to cruising altitude first? Does altitude affect the transsonic difficulties (buffet, need for extra thrust, etc.)?

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Concorde went supersonic during its climb phase to the cruising altitude.

The altitude at which the Concorde can go supersonic was limited by the regulations. For example, the aircraft was only allowed to go at 400 knots during the climb phase between 6,000 and 32,000 ft; also, the aircraft was allowed to go supersonic only after it has crossed the coastline.

As the air gets thinner during climb, the Mach number increases for same IAS, reaching around 0.93 at 25,000 ft and 0.95 at 28,000 ft. After this, the afterburners are engaged and autopilot is set to the cruising altitude (~ 60,000 ft). During this climb phase to the cruising altitude, the aircraft goes supersonic, settling at around Mach 2 at over 50,000 ft.

The flight envelope limitations of Concorde (at one configuration) is shown in this image:

Concorde limitations

Source: pprune.org

The altitude affected the thrust requirements, as more thrust is required for the same speed at lower altitudes due to density. This is one of the reasons for Concorde flying at altitude far above that of subsonic airliners.

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  • $\begingroup$ If it took off from Paris would it still be climbing at the coastline? Or would it hold at a lower altitude until it got there? $\endgroup$ – TomMcW Oct 11 '15 at 23:57
  • $\begingroup$ @TomMcW: Probably would depend on the precise trajectory it flew out of Paris - the coast is much closer going northwest than going west, and much closer going west than going southwest. $\endgroup$ – Sean May 4 '18 at 21:58
  • $\begingroup$ Also, I find it interesting that the Concorde's stickshaker behaviour is defined for altitudes exceeding 60 kilofeet, despite altitudes that high being well outside the Concorde's flight envelope. $\endgroup$ – Sean Oct 25 '18 at 0:47
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    $\begingroup$ @Sean looks like they went up to 68 during tests. $\endgroup$ – Antzi Dec 10 at 9:18
  • $\begingroup$ On the North American routes the Concorde out of Paris would mostly fly out in north westerly direction from Paris anyways due to being the great circle course. On the South American and Asian routes the Concorde would fly a lot longer over land and not go supersonic here due to regulations. $\endgroup$ – Adwaenyth Dec 10 at 13:04

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