carb ice experience

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
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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 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.

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 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.