The OTHER Knob

August 2021

Another minor reminder, yesterday.

It was hot, around 90 degrees, and the density altitude for my nearly-sea-level airport was 1500 feet. I lined up for takeoff, mindful of the coming performance drop, and shoved the throttle forward.
The drop in performance was more than I expected. I normally see ~2300 RPM about the time the plane breaks ground, but I was 50 feet up with only 2150 or so. Not a problem...yet...but the plane was definitely unhappy.

I dropped my left hand down to the carb heat, and found that it was on. Shoved it in, and the Fly Baby was much happier.

Two comments on this. First, I've been flying this Fly Baby or N500F (which had its carb heat knob in the same position) for about 35 years. I *should* be accustomed to turning the carb heat off simultaneously with going to full throttle. But for some reason, I missed it yesterday.

Second? I've experimented, in the past, with takeoffs with the carb heat on. Didn't experience THAT degree of performance drop. I'm thinking that my previous experiments had been done on cooler days....

In my analysis of Fly Baby accidents, I've seen a couple attributed to failure to turn off the carb heat on takeoff. I appreciate them better, now....

Ron Wanttaja

Return to the Stories Page