Timeline for Is it incorrect to say that "passenger jets like to cruise at higher altitudes because there's less drag"?
Current License: CC BY-SA 4.0
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| Nov 18, 2020 at 23:41 | comment | added | Zeus | @Rory, it depends on what you mean by "optimal cruise Mach". If you are climbing at the best AoA (L/D), you'll be flying faster and faster (in terms of 'normal' airspeed, TAS). Mach may be increasing still faster, because the air gets colder (thus the speed of sound drops). So eventually, as I said, one of two things will happen: you'll hit the Mach limit, or you'll run out of thrust. (You'll be increasing your thrust setting in the process, even though the absolute thrust and fuel consumption (per hour) won't be significantly changing). | |
| Nov 18, 2020 at 23:24 | comment | added | Zeus | @MichaelHall, I'm not sure it would be a clarification, because it requires to introduce the concept of IAS. It doesn't normally appear in aerodynamic formulae: it exists for pilots. | |
| Nov 18, 2020 at 1:38 | comment | added | John K | @RoryMcDonald most airliners already cruise above the troposphere except in the tropical lats where the trop is closer to 40000 ft. At mid latitudes it's in the low-mid 30s, and in the north in the 20s, and as low as the teens in the arctic in winter. | |
| Nov 18, 2020 at 1:33 | comment | added | John K | @MichaelHall don't you mean less drag at the same TAS? The drag at the same indicated a/s should be the same, the dynamic pressure being the same. | |
| Nov 18, 2020 at 1:14 | comment | added | Rory McDonald | Ah yes, this all makes sense. To clarify, will an altitude be reached where the optimal cruise Mach for an aircraft will no longer provide enough lift at maximum L/D? Can this altitude be above the troposphere, and can flight planning put the plane above the troposphere to extend range? Thanks, this question has been on my mind. | |
| Nov 18, 2020 at 1:03 | vote | accept | Rory McDonald | ||
| Nov 17, 2020 at 23:56 | history | answered | Zeus | CC BY-SA 4.0 |