During a climb, gravity pulls the fuel to the rear of the tank and away from the fuel outlet. Baffles inside of the fuel tank slow down the flow of fuel to the rear of the tank. But if the fuel level is low and the RV-12 is in a prolonged climb, then the outlet port could be uncovered. That is the reason for no takeoff with less than 4 gallons of fuel. If slipping the plane with very low fuel, step on the right rudder to make the fuel move to the left, over the outlet.Is that fuel available in a climb or descent? Or a slip?
Just to get an idea, I took off with 5 gal left: it quickly gets pretty scary! As soon as you lift the nose the fuel level goes into the red. It gets back in the yellow when you level. If you happen to go around with this little fuel, it's good to know that you will still be able to fly the pattern despite the ominous warning. I did not try at 4 gal...
Just making an observation here. Your comment about "slightly irrational fear" caught my attention. I am glad you came to grips with your own thoughts to make that statement about your thought processes. The relatively low probability of having some undetermined amount of lead be so destructive to an engine that it would cause irreparable harm to your engine possibly could be a problem but really is not very probable. Even if it were to become a problem, to worry more about that expense/inconvenience of repairing such damage than you would over the higher chance of fuel starvation causing serious or fatal bodily injury is indeed a bit "irrational".Fair points. It was the one and only time I took off with the small amount of fuel and it was driven by a slightly irrational fear of leaded fuel last year while getting use to the Rotax world. I've since become more comfortable to top up with 100LL rather than take any possible risk of fuel starvation. I change my oil more frequently than even Rotax suggests for my low amount of leaded fuel use so I'm probably just fine. Rarely fly with less than full tank now even for short trips.
If you were trying to land with only 4 or 5 gallons at a fairly short strip with tall trees on either end, would it not be quite foolish to try to land since you would be in the trees if you had to go around?
The RV-12 is approve red for take-off as long as there is 4 or more gallons in the tank, so I see no reason to assume the airplane would be in the trees.
The difference in fuel burn versus speed between 5100 RPM AND 5500 RPM hardly makes the extra 400 RPM worthwhile.