carb ice experience

Cub Driver wrote:

(Must be more to carb heat than that. Bypassing the filter ought to
increase performance in every instance, or at least never decrease it.

Yes.

But pulling carb heat on, in the Cub, does definitely cause a decrease
in power.

The heat normally creates a rich mixture, which causes a decrease in power.

George Patterson
Drink is the curse of the land. It makes you quarrel with your neighbor.
It makes you shoot at your landlord. And it makes you miss him.

In article jy67f.6582$%A1.1101@trndny01,
George Patterson wrote:
But pulling carb heat on, in the Cub, does definitely cause a decrease
in power.

The heat normally creates a rich mixture, which causes a decrease in power.


The reduction in power caused by the application of carb heat is mostly
due to the decrease in air mass flow through the engine, i.e. a
reduction in volumetric efficiency.



JKG

In article jy67f.6582$%A1.1101@trndny01,
George Patterson wrote:

Cub Driver wrote:

(Must be more to carb heat than that. Bypassing the filter ought to
increase performance in every instance, or at least never decrease it.

Yes.

But pulling carb heat on, in the Cub, does definitely cause a decrease
in power.

The heat normally creates a rich mixture, which causes a decrease in power.

George Patterson
Drink is the curse of the land. It makes you quarrel with your neighbor.
It makes you shoot at your landlord. And it makes you miss him.

If the carburetor attach flange nuts are loose, the mixture will be very
lean, due to air leaks around the base. Applying heat will enrich the
mixture, possibly correcting a too-lean condition. I have seen a few
planes with loose carburetor attach nuts.

What typically happens, and often under the exact conditions you
describe cold humid morning with frost on the ground is that as you
taxi out ice builds up in the carb reducing the RPM. You wil
subconsously keep adding power to keep it running like you want/need to
taxi. Then when you add power for the run up you will position the
throttle farther open than normal to get the 1500 RPM that you need
since the carb is partially iced up. When you add the Carb heat it will
typically drop a bit and then back up to a higher RPM. The RPM Surge
you saw was simple the result of having more ice that you are used to

I see this quite often in the Champs I Fly and even Cessna/pipers
occasionally.

Brian
CFIIG/ASEL

No mixture control in the Cub!



There is no ground adjustable idle mixture screw on a Cub? I am not
familiar enough with the model to suggest more, sorry.

There will be an idle mixture screw on the carb. He meant that he
has no mixture control on the panel. Most of those basic airplanes
either had no cruise mixture control on the carb, or it was
safety-wired full rich. I have one of those engines in my Jodel, and I
made the mixture control parts for the carb, but I never use it. It
prefers full rich all the time; leaning it just drives the cylinder
head temps too high.

Dan

I had one experience that suggests carb ice makes the mixture too rich.
It was in a Mooney Ranger, I flying a VOR approach, pulled on the carb
heat knob and the damned thing just kept pulling out of the panel. It
broke! (Yes, I tested carb heat on the run up, it was fine.)

As luck would have it was to an uncontrolled airport in snow. The
second hand on the clock said look out and see the airport. I looked
and couldn't see a damned thing. Pushed the throttle in to fly the
miss, not much happened. I tried everything to get power back. Landing
light didn't help, raising the gear didn't, neither did prayers. The
one thing left to yank on was the mixture. I leaned it and the engine
began developing a little power, enough to limp to a nearby airport
with an ILS and get down. So leaning helped, which made me think the
mixture was too rich with carb ice.

By the way, if ever you want to overcontrol an airplane, fly down the
glide slope knowing you HAVE to get down, there wasn't enough power to
do anything else. I'm writing this story, so obviously I was able to
keep the needles crossed and got down. Those mountains in eastern PA
have been known to eat airplanes.

I remember that clearly even though it was 40 years ago. I wonder why?

"Tony" wrote

I remember that clearly even though it was 40 years ago. I wonder why?

You remember trying to pull the seat cusion out of your butt crack,
afterwards? g
--
Jim in NC