What is the influence of drag on an airliner's block fuel consumption? I am not sure how widely the software is used, but I am using Piano-X to investigate the influence of total aircraft drag on block fuel consumption and noticed something odd. It is my hope that someone familiar with the software can assist me.

If I decrease the total aircraft drag both the block time and fuel consumed increases, which is the opposite of what I would expect. As expected however, the block fuel/min does decrease.

Shown below is the results from the investigation for the drag systematically decreased :


I expect that the block fuel/time would decrease but don't understand how the total time and fuel will increase for decreased drag.

Is there a rational explanation for this?

The software documentation only states the following concerning drag calculation:

"Aerodynamic drag is calculated in detail (as a function of lift coefficient, Mach number, and Reynolds number) and tuned with actual lift/drag data (‘polars’) whenever these are known. You can either factor the drag uniformly using one overall value or you can adjust certain items individually."

My approach was to vary total drag, i.e. induced and parasite drag simultaneously.

I will add that the software calculated total block fuel including estimates for both taxi's and the climb-out etc. Now in taxi drag doesn't have an influence, but I doubt that this will make such a large contribution.
I would suspect that reducing drag in this case would be result of reducing airspeed. If your drag coefficient 1 is for a certain speed, slowing down would cause smaller fuel flow but increase flight time and hence increase total consumption.