carb ice experience

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

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" 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.

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

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