Thomas Borchert wrote:

1. We're talking density altitude here. So you might well be leaned during the
roll down the runway at 100 ft MSL elevation, if the temperature is high
enough. Not rare at all.

Density altitude cuts the other way as well. If you're flying in cold
weather on a clear day, 3,000 feet indicated altitude might not be that
far above sea level density altitude.

Some day, I'd like to get more information about how density altitude
and my engine interact. By the time the air hits my carb, it's likely
already been warmed up a fair bit, so air density at the carb is not
likely the same as the air density outside the plane.

2. It might make sense to lean even earlier when you want to maintain max
power. One advice given is: Keep the EGT where it was when it stabilized after
took off at full power. If you don't lean, EGT will decrease slowly with
altitude.

That's John Deakin's advice as well, and it seems to work. The only
extra consideration is that you want to keep EGT where it would be at a
sea level (DA) takeoff, not necessarily where it was at *this* takeoff.
It might be worth finding a low airport on a day with close-to-ISA
conditions, and actually marking the glass with a blue marker to show
where the needle ends up, though I haven't gone that far yet.

Again, the winter can be a problem, since a sea-level takeoff on a cold
day can put you far below sea level density altitude, and your starting
EGT may be on the high side.


All the best,


David