"Tman" x@x wrote in message
. ..
Flying a lot of 152s and 172s with carb heat lately. When inbound, I've
been taught to pull the carb heat "on" downwind, hey actually use it as a
power control to slow the plane just a bit mid-field, and then more
importantly, just leave the thing on till clear of the runway and cleaning
up. No matter what the temp, humidity. And to have it on at all times
when the RPM is less than the green band. Kind of a preventative.

A few times I have been coming in on short final and needed a burst of
power due to a sudden downdraft, or needed to pour on a little juice cause
my approach was coming up just a bit short. Moving the throttle forward
1/4 to 1/2 inch, i.e. giving it a little juice but certainly not a go
around type of thing, often times I would get a stumble, hicuup, drop in
RPM'S for 2-3 seconds before the horses responded.

Lot of convective turb lately and that power really comes in handy at
times on mid to short final. Kind of a shocker when the engine doesn't
respond quite nicely.

This has happened on a few birds, especially on hot days. I think what's
happening is the engine is just too rich, hey I've got the mixture all the
way in, it's hot (air less dense), and it's (way) hotter with the carb
heat on ( air much less dense), all enriching the mixture, and when I put
on a little power the accelerator pump in the carb over-enriches the
engine for just a little bit; causing the stumble.

Other pilots and the A&P just tell me to pour on the power a little
slower.

I think I'm going to follow a new SOP. Turn the carb heat off on
mid-final. Reasoning: no carb, esp a warm one is going to ice up in 30
seconds, sets me up better for a go-around, and will prevent this stumble
business (I did test it out at altitude, and it prevents or at least
seriously mitigates the stumble).

thoughts?
T

What's going to happen if you actually do have carb ice which hasn't burned
off by the time you turn carb heat off? I'd much rather attempt a go around
with the carb heat initially on than attempt a go around with the lingering
effects of carb ice.

I have no idea what DA you're talking about, but what you're describing is
trying to correct a problem with the mixture by controlling it with the carb
heat. If you're landing at a high DA airport, you shouldn't have the
mixture full rich. Setting the mixture on downwind is the solution to the
problem. On a 152 or 172 you can also have your hand on the throttle with
your thumb on the carb heat. It should be a natural reaction to push both
in together or push the carb heat in first on a go around.