Originally Posted by
Capt Chambo
RENURPP highlights an interesting conundrum, which is, is it better to descend to be able to fly at a reduced IAS>TAS>G/S, but with a higher fuel burn, or should you continue at altitude maybe changing your cost index to zero, and accepting the delay in the holding pattern, but "probably" burning less fuel overall?
Don't confuse endurance with range/efficiency.
If you have to lose time, the best way is go low and slow.
If you stay high and hold, you will burn more fuel than if you go low. Staying high keeps the TAS high and therefore parasite drag high and a high power setting to maintain speed resulting in high fuel flow.
Go low, much lower TAS equals lower drag resulting in a lower thrust setting and fuel flow.
On my type, best endurance is found in the very low 20s ie minimum drag.