carb ice experience

[Cub Driver]

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

[Tony]

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.

[Larry Dighera]

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?

[A. Smith]

"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

[[email protected]]

Dan
Application of carb heat causes a change in rpm's because it changes
the fuel/air ratio.....NOT because there is carb ice. If carb ice is
present, the heated air will hopefully melt the ice and it will then
cause the engine top stutter a little as it goes thru the combustion
process.
If you have carb ice conditions, you can run with full heat on to avoid
the ice formation. However, on the ground, this will by-pass any
filters and you can suck dust into your carb with the dirty air and a
potential for serious engine problems.
In severe low temps, sometimes it requires full carb heat just to get a
close to useable air density for decent fuel/air ratios.
Another trick to stick in your pilots bag of magic is to use the primer
knob if your engine gets starved for carb ice and stops. The primer
system on most carbureted engines bypasses the carb and goes directly
to the intake manifold. Your fuel schematic should show you that. I've
used it a couple of times to keep the engine runing in severe
conditions around the country. The engine will run for a few seconds
then die again so you keep stroking the primer knob to keep it running
until hopefully the heat will come up enough to become effective again.
The addition of a carb heat gauge is worthwhile for most aircraft
(normal aspirated). A periodic carb heat check in the air doesn't hurt
either.
Discuss the situation with your local mechanic and he can explain it
better. If he can't, find a more experienced mechanic!
Cheers and safe flying

[George Patterson]

Cub Driver wrote:

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

Sounds like you had a lean mixture for some reason. When you hit the heat, the
mix got richer.

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.

[George Patterson]

wrote:

> Another trick to stick in your pilots bag of magic is to use the primer
> knob if your engine gets starved for carb ice and stops. The primer
> system on most carbureted engines bypasses the carb and goes directly
> to the intake manifold. Your fuel schematic should show you that.

The problem with this is that carb ice blocks the flow of air into the engine.

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.

[George Patterson]

Cub Driver wrote:

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

The Selway Kid just mentioned that carb heat application also bypasses the air
filter in most aircraft. IMO, the most likely problem here is a clogged filter.

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.

[[email protected]]

On cold mornings, using summer mogas (which will have a lower vapor
pressure), the fuel doesn't vaporize as easily in the manifold.
Applying carb heat can sometimes improve this and the RPM will rise a
bit. I use the heat on my A-65 on such mornings.


Dan

[Capt. Geoffry Thorpe]

"George Patterson" > wrote in message
news:7lO6f.4165$tl5.718@trnddc02...
> wrote:
>
>> Another trick to stick in your pilots bag of magic is to use the primer
>> knob if your engine gets starved for carb ice and stops. The primer
>> system on most carbureted engines bypasses the carb and goes directly
>> to the intake manifold. Your fuel schematic should show you that.
>
> The problem with this is that carb ice blocks the flow of air into the
> engine.
>
> 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.

It can. But depnding on the design of the carburetor, it can sometimes block
the fuel first. I've seen ice block a booster venturi which shut down the
fuel, but left plenty of room for air to flow...

--
Geoff
the sea hawk at wow way d0t com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

[Robert M. Gary]

I got carb ice almost every time I flew the cub. On cold 6am flights,
the Cub just loved to suck up the ice. I learned to leave the carb heat
in during touch-n-go operations until climbing out because I lost the
engine once after shutting off the carb ice as I was moving the
throttle forward. The engine ran far enough to get me 300 feet up then
started to die. Luckily, turning around at 300 feet is very easy in a
Cub, not so easy in a Mooney. :) I kept a timer for cruise and ran 15
minutes heat off then 15 minutes heat on. I would also often get ice in
the time it takes to taxi to runup. I learned to clear out with heat
first. For some reason, the cub got ice much more than the Aeronca with
the same engine, I think it has something to do with how heat moves
around in the cowl.

-Robert

[Cub Driver]

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]

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]

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]

On 23 Oct 2005 08:27:50 -0700, wrote:

>Another trick to stick in your pilots bag of magic is to use the primer
>knob if your engine gets starved for carb ice and stops.

Ah, but that's on the instrument panel, and I fly from the back seat!

(A time or two, I've not noticed until I'm in the air that the field
altitude wasn't set, and I've had to add/subtract a hundred feet to
TPA etc. One time I was heading off on a crosscountry, and I landed in
a private field so I could set it correctly, which entails getting out
of the harness so as to reach forward across the front seat.)



-- 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

[cjcampbell]

Cub Driver wrote:
>
> 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.
>

The reason it zooms back to 1700 is that the ice melted and you were
giving it enough gas for 1700. The engine running rough on taxi is a
good indication of that, too. The rpms may have dropped momentarily,
but the ice release was apparently very sudden and it appeared to have
just gone up. Did the rpms increase again when you turned carb heat
off? They should have.

[Cub Driver]

On Sun, 23 Oct 2005 15:54:42 GMT, George Patterson
> wrote:

>> Now what was the difference between that experience and the ordinary
>> one where the rpms drop, then rise back to 1500?
>
>The Selway Kid just mentioned that carb heat application also bypasses the air
>filter in most aircraft. IMO, the most likely problem here is a clogged filter.

Yes, it bypasses the filter on the Cub.

Now you scare me. Clogged filter? Got unclogged?

(Must be more to carb heat than that. Bypassing the filter ought to
increase performance in every instance, or at least never decrease it.
But pulling carb heat on, in the Cub, does definitely cause a decrease
in power. In a go-around, the climb picks up as soon as I kick the
carb heat in.)



-- 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]

On 23 Oct 2005 10:51:39 -0700, wrote:

> On cold mornings, using summer mogas (which will have a lower vapor
>pressure), the fuel doesn't vaporize as easily in the manifold.
>Applying carb heat can sometimes improve this and the RPM will rise a
>bit. I use the heat on my A-65 on such mornings.

It was 100LL. There is mogas at the airport, but the sample smelled
sweet and clean, and the mogas is foul smelling. Indeed, that's a
major reason we switched back to 100LL -- the instructors didn't like
to smell the mogas in the front seat.


-- 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

[Happy Dog]

"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

[Allen]

"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

[George Patterson]

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.

[Jonathan Goodish]

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

[Orval Fairbairn]

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.

[Brian]

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

[[email protected]]

>> 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

[Tony]

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?

[Morgans]

"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