From: David Megginson <[EMAIL PROTECTED]>
> Alex Perry wrote:
> > That's a point. Once the engine stutters/quits due to carb ice,
> > you have to make it take a while for the ice to go away again.
> > ... and it takes quite a while ...
> Once the engine quits, it's too late for carb heat, isn't it?
Not if you're quick ... and lucky. If the engine wasn't originally heavily
leaned, then the reduction in airflow through the venturi will richen the
mixture early enough that the engine quits due to mixture before the opening
is completely blocked by the ice. At that point, applying carb heat means
that the rotating prop is sucking warm air (which helps a bit), using full
throttle minimizes the braking effect of compression and keeps the prop
rotating as much as possible, and leaning the mixture avoids flooding it.
... but this does not reliably work, so you simply move the three
levers to those positions and immediately do the ABC for engine failure.
_Then_ you use the checklist, consider fiddling with the primer etc etc.
Of course, if the air filter ices up, applying carb heat fixes it quick!
If the engine runs rough, the EGT drops rapidly to the CHT ... and of course
when it stops then both quickly decay towards OAT due to the air cooling.
Anybody wanting to simulate should have fun guessing the intake temperature.
> I had my engine run rough once and suspected carb ice, but it smoothed out
> the second I put on carb heat, so it obviously wasn't ice -- I was probably
> just a little too lean.
Sounds likely. It takes a while to burn significant ice deposits off.
A side point is that it is dangerous to fly heavily leaned beyond max RPM
in conditions where there is any chance of carb ice, even on fuel injected
engines. There will be no indication of any icing problem until
the blockage is sufficient to return you past max RPM, to the rich side,
and then reduce the airflow still further. It is then hard to melt off.
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