carb ice experience

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

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

If I rememberf correctly (I fly injected engines now) when you pull the
carb heat on you are adding warm air to the air intake, the engine rpms
drop because its less efficient. The drop in RPM does not mean you have
carb ice, it means the carb heat is working.

If the RPMs went up right away you probably melted away exisitng carb
ice.

On 23 Oct 2005 04:23:46 -0700, "Tony" wrote:

The drop in RPM does not mean you have
carb ice, it means the carb heat is working.

If the RPMs went up right away you probably melted away exisitng carb
ice.

Yes, that's indeed how I understood it to happen, as I had seen it
happen on many occasions. But what happened when the rpms surged?


-- 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 23 Oct 2005 04:23:46 -0700, "Tony" wrote:

The drop in RPM does not mean you have
carb ice, it means the carb heat is working.

If the RPMs went up right away you probably melted away exisitng carb
ice.

Yes, that's indeed how I understood it to happen, as I had seen it
happen on many occasions. But what happened when the rpms surged?

What happened when you turned the carb heat off?

moo

On Sun, 23 Oct 2005 06:39:40 -0400, Cub Driver usenet AT danford DOT
net wrote in ::

Did the mag check.
Pulled carb heat on. Whoom! Rpms went up to 1700.

What was the temperature/dew point spread at the time? Was the air
mass wet?

On Sun, 23 Oct 2005 11:59:37 GMT, Larry Dighera
wrote:

Did the mag check.
Pulled carb heat on. Whoom! Rpms went up to 1700.

What was the temperature/dew point spread at the time? Was the air
mass wet?

Hm. There was heavy frost on the grass and frost on the wings and tail
feathers, condensation inside the plexiglass windscreen. I'm sure it
was above freezing by that time, 8:15am. I melted the frost off by
turning the planes into the sun while I did the preflight check.



-- 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
...

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