Peter wrote:
because a best-perf climb is not good for engine management reasons
My climb profile in autorouter is the one I follow. Not book performance. It is up to the user to configure the aircraft profile to reflect their real-life profile.
Hourly fuel burn is the same at FL180 as it is at FL060, but TAS is 16% better, hence the better MPG. On the other hand you do burn fuel to get up to your chosen cruise level. I burn 26 gph during climb vs 16 gph duirng cruise, and I climb at a lower TAS than cruise which contributes towards a higher total MPG. If getting up to the chosen cruise level takes 30 minutes, I will have burned 10 USG more than in cruise, at 120-130 IAS.
Autorouter explicitly says that the “Optimum FL” screen takes the climb performance into account in the computations, but it does not mention the descent, so I assume that it does not account for the reduced fuel burn during descent. The descent from FL250 takes 35 minutes during which I burn 12-14 gph instead of 16 gph, and the TAS is somewhat higher than during cruise.
Here is a better example with same headwind component at several altitudes which does show lower fuel brun at the higher altitudes.
