Ice

Ok, so I don't have an experimental. I do, however, have a carb
on the Continental E-225 in my Bonanza. Its a Bendix PS5-C.

There is no true carb heat on the early Bonanzas. There maybe
something labeled 'carb heat', but what it really is is
alternate air. It allows air into to the carb from inside the
cowling, bypassing the air filter. The cowling air will be
warmer than ambient, but probably not nearly like it would be
if there was a heater muff like there is on other planes.

I have been told that the PS-5C is immune to carb icing which
is why the Bonanza is set up the way it is. I'm not sure I
can buy. Yes, the PS5-C has no float, but it still has
jets and a butterfly valve.

What I can say is that in 14 years of flying this plane, I've
never experienced carb icing with it. And a a fair amount
of that time was in very wet IFR conditions.

I don't know what to think.
--
Frank Stutzman
Bonanza N494B "Hula Girl"
Hood River, OR (soon to be Boise, ID)

On May 21, 9:46 am, Frank Stutzman wrote:

I have been told that the PS-5C is immune to carb icing which
is why the Bonanza is set up the way it is. I'm not sure I
can buy. Yes, the PS5-C has no float, but it still has
jets and a butterfly valve.

The first fuel-injected Bonanza was the J35; earlier carbureted models
are somewhat susceptible to induction icing. I say 'somewhat' because
the PS-5C is a pressure carburetor which injects the fuel into the
throat rather than letting it be drawn in by vacuum; the carb needs
less of a pressure drop in the venturi and therefore sees less of a
temperature drop than a vacuum carb. This makes it somewhat (that
word again!) resistant to icing.

I believe that those Bonanzas also heat their intake air downstream of
the carburetor (proximity to exhaust pipes, oil sump? -- not sure) and
that further reduces the chance of cooling the mixture to the
dewpoint.

As for those slide-valve carbs, they do have venturis -- you just
can't see them because they're made of air! Downstream of an orifice
a high-speed airstream first contracts and then expands, even if
there's only wide-open space there. This invisible venturi suffers
the usual pressure/temperature drop and of course the evaporation of
the fuel droplets makes things worse. Not only can these carbs ice
up, they're notorious in the motorcycle world for doing so. Early
customer fixes involved stove-boxes rigged around the carbs; modern
slide-valve carb bike engines have these factory-made.