I learned about fuel flow from flying a PA28-236 for about 4.7 hours from TABS!!! (and the subsequent misfire on the ILS....) But that was a long time ago and something I NEVER repeated.
Anyway I know that my current plane does 31L per hour average....by experimentation and lots of flights, which matches the book figures. Still because we never really know how much fuel is onboard, other than our calcs (fuel is not visible after an hour per tank, even with over 100L onboard - 170L tanks) I'm going to get me one of these:
