jasc15
Pre-takeoff checklist
I was looking up the meaning of the steps in the green arc on some tach gages. In an article I found, I read what is quoted below, which sounds pretty tenuous to me.
Makes me suspicious of the rest of the info i read, but the explanation of the green arc steps being 75% power settings at different altitudes does sound reasonable, since some of them actually show numbers at each step.
Lead also plays the part of coolant in the exhaust stroke of the piston aircraft engine. Since metal is a more efficient conductor of heat that the exhaust gasses, it conducts more specific heat out the exhaust and away from the combustion chamber and, more specifically, the area of the exhaust valve and valve seat.
When lead is precipitated in solid form during the combustion process, a certain amount of it is deposited on the exhaust valve seat. When the exhaust valve closes, this lead film acts as a cushion in the seat, lessening the impact of the steel-on-steel contact and reducing wear.
Finally, the film of lead deposited on the exhaust valve and seat acts as a sealant in that area, becoming a self-replacing gasket that allows greater pressure to be maintained during the next compression stroke.
Makes me suspicious of the rest of the info i read, but the explanation of the green arc steps being 75% power settings at different altitudes does sound reasonable, since some of them actually show numbers at each step.