Originally Posted by
GordonR_Cape
Dumb question (not a pilot): What was the approximate indicated airspeed (IAS) on these flights? Was the ground speed (sum of true airspeed plus wind vector) more than twice the IAS? If so, is that interesting in any way, or just a numerical coincidence?
The cruise speed controlling parameter is Mach number. (In fact the later part of the climb too but lets not complicate things) The TAS equivalent of that is dependant on the temperature outside at that location and flight level. TAS is IAS corrected for non ISA sea level air density which is a factor of the flight level & the temperature at that level. Yes I know clear as mud, but like many things once it "clicks" and see it all in action it's obvious. But to give you a "ballpark" set of numbers ; FL360 Temp ISA (-56) M 0.80 TAS 460 IAS 265 The groundspeed is the TAS plus or minus tailwind/headwind component.