+xRight now, we take the amount of fuel planned and subtract the taxi/takeoff fuel and landing fuel specified for the aircraft, giving us the fuel available for the enroute part of the flight. That figure is divided by the fuel burn of the chosen power setting at the chosen overall level for the flight, giving the endurance figure.
If there's a better way to arrive at the figure, we are certainly open to it.
I see. A problem with that is that the holding fuel (and the future Final Reserve Fuel) is determined with a (probably) lower fuel flow. Also, the trip fuel includes the climb which is at a higher power setting than cruise. When reading the fuel plan, I would expect that each item contributes to the endurance with its given time.
My suggestion is to compute the endurance as the sum of:
1) The trip time computed by SkyDemon
2) The holding time (and future time for FRF)
3) Time for the contingency fuel – this could be computed either using the cruise fuel flow or as a percentage of the trip time, although using the cruise fuel flow may make more sense. The difference would in any case be small.
4) Time for additional fuel above the minimum, using the cruise fuel flow.
In my example above, this would give an endurance of 3h8m.
Properly, a time should be included for the landing fuel as well, but the fuel flow is not known and the contribution would in any case be small