IMPORTANT NOTICE: DC-3 fuel flow is currently heavily bugged. Please install the below mod for it to be accurate again. On my test trips, my calculator spits out total fuel usage within 10% of the ingame usage. Depending on flying style its pretty close.
This an excel worksheet I created some time ago for the VSkylabs C-47 in XP11. Data is not yet fully tweaked to the MSFS one but it should do the job.
HOW TO USE:
1. Fill out the green fields.
2. Use the power setting from the "Cruise Power Setting" Box
Have fun an report back with findings. I will tweak this more when I get more data.