Writer: Paul Tomblin, Private Pilot, ASEL-IA, High Performance and Complex, currently inactive
Concorde had a maximum cruise altitude of 18,300 meters (60,039 ft) and an average cruise speed of Mach 2.02, about 1155 knots (2140 km/h or 1334 mph), more than twice the speed of conventional aircraft.
The higher you go, the thinner the air. This gives you a bunch of trade-offs to consider when you’re designing an airplane. Going higher means
- Less drag
- less lift
- less air for your engines to use to burn fuel
- more pressure differential on your pressurization systems
- more metal fatigue for each pressurization cycle
- more time to get to cruising altitude
- fewer other aircraft to get vectored around so possibly more direct flight routes
- less noise on the ground
The designers of the Concorde obviously thought the plusses of going high outweighed the minuses. Probably the aerodynamic drag was the biggest plus factor.
One thing that’s interesting about Concorde is that initially they start cruising at a lower altitude, and climb higher as they burn off fuel and get lighter.
I remember once I was at a nearby airport (only 50 miles from home – I was trying to build up cross country hours) and there was a Mooney prepping to return home as well. I noticed he had an oxygen system and asked him what altitude he was going to fly home at, and he replied that he’d filed a flight plan for 12,500 feet. I had flight planned for a flight home at 2,500 feet because we were flying past Letchworth Canyon which is a lovely view. I’m not sure why he was going that high, but for such a short flight I wonder if he wasn’t going to spend a huge percentage of his flight climbing and descending. But the Mooney is a lot faster plane than my Piper Archer, so maybe the climb time wasn’t as big a deal for him.