ES CONTROL-I usually use an engine smaller than recommended so it's not very often I run out of fuel. All but one of my glow planes usually come back with half a tank.
But for my electrics I needed a timer and at the time I didn't have the RDS8000 I do now. So I got a cheap stopwatch at KMART and velcro'd it to the radio. For all my planes I ran them on the ground at full throttle and timed them till they were dead/empty. That gave me the worst case senario. After I fly a couple of times I modify it and see how much fuel/charge I usually have left. Here's some pics of the stopwatch.-BW