carb ice experience

"Cub Driver" usenet AT danford DOT net wrote in message
...

I've probably fired up the Cub 500 times, and every time until the
most recent one went much the same way, just as my instructor taught
me: when you do the mag check (1500 rpm in the Cub) your last check is
pull carb heat on, and watch the rpms drop a bit. Then, if they climb
back to 1500, you know you had a bit of carb ice and that it has
melted, and you will be especially cautious thereafter to avoid icing.

But the other day, first cold day, I had quite a different experience.
The engine may have been running rough when I taxied--hard to know
with earphones, but I had a feel it was rough. Did the mag check.
Pulled carb heat on. Whoom! Rpms went up to 1700.

Now what was the difference between that experience and the ordinary
one where the rpms drop, then rise back to 1500?

Thanks!


-- all the best, Dan Ford

Check the idle mixture. When you pull carb heat on you are putting hot,
less dense, air through the carbuerator. If you were initially running lean
applying carb heat will improve the fuel/air mixture. Cold day, dense air,
more fuel required.

Allen

On Sun, 23 Oct 2005 12:24:23 GMT, "A. Smith"
wrote:

Check the idle mixture. When you pull carb heat on you are putting hot,
less dense, air through the carbuerator. If you were initially running lean
applying carb heat will improve the fuel/air mixture. Cold day, dense air,
more fuel required.

No mixture control in the Cub!

Could ice in the carb cause the fuel mix to be lean?


-- all the best, Dan Ford

email: usenet AT danford DOT net

Warbird's Forum: www.warbirdforum.com
Piper Cub Forum: www.pipercubforum.com
the blog: www.danford.net
In Search of Lost Time: www.readingproust.com

"Cub Driver" usenet AT danford DOT net wrote in message
...
On Sun, 23 Oct 2005 12:24:23 GMT, "A. Smith"
wrote:

Check the idle mixture. When you pull carb heat on you are putting hot,
less dense, air through the carbuerator. If you were initially running
lean
applying carb heat will improve the fuel/air mixture. Cold day, dense
air,
more fuel required.

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.

Allen


Could ice in the carb cause the fuel mix to be lean?


-- all the best, Dan Ford

email: usenet AT danford DOT net

Warbird's Forum: www.warbirdforum.com
Piper Cub Forum: www.pipercubforum.com
the blog: www.danford.net
In Search of Lost Time: www.readingproust.com

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