Ice

VW-powered plane goes down in the Frozen North, which to me is
anywhere other than Southern California. Pilot walks away from it,
having just bought one airplane's-worth of education. Now he wants to
know why he lost power.

I don't know & tell him so. (Kinda hard to do an accident
investigation via email). But he keeps pinging on me as the Guru of
Last Resort, so powerful my name has been slipped to him under the
table after swearing not to reveal his Source. (Eh? Are these people
serious?)

So I ask him a few questions and based on his answers tell him:
'Sounds like carb ice.'

But that's the one thing he's sure it's NOT. No way. Can't be.
EVERYONE says so. In fact, his particular engine is (or was) totally
ice-proof; didn't even need a carb heat system. Has one of them slide-
valve carbs -- no venturi therefore no possibility of icing. And
besides, he always uses a 'dryer' in his gas, just like he does in all
of his vehicles and he has NEVER had any problems with ice, yada-yada-
yada...

By now it's obvious I'm dealing with an idiot. I offer the fellow a
whiff of reality, pointing out that the 'dryer' was probably a
contributing factor since it not only diluted the energy content of
his fuel, it contained methanol (ie, wood alcohol) which happens to
have an endotherm of about 300 degrees -- twice that of ethyl ethanol
(ie, regular alcohol). The probability that ice was a contributing
factor to his 'unexplained' loss of power is now about 99% and rising.

His response? "That can't be right." And the world's largest kill-file
gains another entry.

--------------------------------------------------------

Carb and manifold icing is simple physics, clearly spelled out in all
the manuals. Even so, you can find messages to this Group from guys
BRAGGING about their ice-proof engines, as if the laws of physics
don't apply to them. (Which is really kinda scary when you think about
it. I mean, these people are allowed to breed and vote and share air-
space with normal people... )

Your life is worth something. (Yes, even to me :-) Don't allow
yourself to be murdered by all those goods friends with their swell
advice. Think for YOURSELF.

Reality may be a bitch but so is ignorance. And denial.

-R.S.Hoover

PS - Gasoline is 'endothermic.' That means it absorbs heat from its
surroundings when it changes its state from a liquid to a gas.
Straight-run gasoline (ie, without additives) has an endotherm of
about 40F, meaning your carb can produce ice cubes on a balmy 72F day.
Or even warmer, if the gasoline contains certain additives. Cooler
day? Guaranteed ice-generator.

Ethanol, that lovely stuff the politicians are pushing, thanks to
ADM's lobbyests, has an endotherm of 150F. Mix that with your gas and
you have to start thinking ice even here in the desert southwest.

But of course, that can't be right :-)

- - - - - - - - - - - - - - - - - - - - - - - -

I posted the above to Yahoo's AirVW Group about six months and
continue to get mail from idiots insisting slide-valve carbs can't ice-
up since they don't have a butterfly valve. I've reposted it here in
the interest of safety. If you know of someone running a slide-valve
carb without any provision for carb heat please give them a nudge
toward reality. -RSH

On 20 May 2007 21:10:52 -0700, " wrote:

Carb and manifold icing is simple physics, clearly spelled out in all
the manuals. Even so, you can find messages to this Group from guys
BRAGGING about their ice-proof engines, as if the laws of physics
don't apply to them. (Which is really kinda scary when you think about
it. I mean, these people are allowed to breed and vote and share air-
space with normal people... )

There's a particular type of homebuilt out there that does not have a standard
carb heat setup...it apparently just uses the ambient air in the engine
compartment. It has an accident rate due to carb ice that's over twice that of
the overall homebuilt fleet.

Ron Wanttaja

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.

Good post, and good reminder. One comment. As I understand it, carb ice
is most common on warm (70 degree or so), humid, days. As the
temperature drops, so does the moisture in the air.


wrote:
VW-powered plane goes down in the Frozen North, which to me is
anywhere other than Southern California. Pilot walks away from it,
having just bought one airplane's-worth of education. Now he wants to
know why he lost power.

I don't know & tell him so. (Kinda hard to do an accident
investigation via email). But he keeps pinging on me as the Guru of
Last Resort, so powerful my name has been slipped to him under the
table after swearing not to reveal his Source. (Eh? Are these people
serious?)

So I ask him a few questions and based on his answers tell him:
'Sounds like carb ice.'

But that's the one thing he's sure it's NOT. No way. Can't be.
EVERYONE says so. In fact, his particular engine is (or was) totally
ice-proof; didn't even need a carb heat system. Has one of them slide-
valve carbs -- no venturi therefore no possibility of icing. And
besides, he always uses a 'dryer' in his gas, just like he does in all
of his vehicles and he has NEVER had any problems with ice, yada-yada-
yada...

By now it's obvious I'm dealing with an idiot. I offer the fellow a
whiff of reality, pointing out that the 'dryer' was probably a
contributing factor since it not only diluted the energy content of
his fuel, it contained methanol (ie, wood alcohol) which happens to
have an endotherm of about 300 degrees -- twice that of ethyl ethanol
(ie, regular alcohol). The probability that ice was a contributing
factor to his 'unexplained' loss of power is now about 99% and rising.

His response? "That can't be right." And the world's largest kill-file
gains another entry.

--------------------------------------------------------

Carb and manifold icing is simple physics, clearly spelled out in all
the manuals. Even so, you can find messages to this Group from guys
BRAGGING about their ice-proof engines, as if the laws of physics
don't apply to them. (Which is really kinda scary when you think about
it. I mean, these people are allowed to breed and vote and share air-
space with normal people... )

Your life is worth something. (Yes, even to me :-) Don't allow
yourself to be murdered by all those goods friends with their swell
advice. Think for YOURSELF.

Reality may be a bitch but so is ignorance. And denial.

-R.S.Hoover

PS - Gasoline is 'endothermic.' That means it absorbs heat from its
surroundings when it changes its state from a liquid to a gas.
Straight-run gasoline (ie, without additives) has an endotherm of
about 40F, meaning your carb can produce ice cubes on a balmy 72F day.
Or even warmer, if the gasoline contains certain additives. Cooler
day? Guaranteed ice-generator.

Ethanol, that lovely stuff the politicians are pushing, thanks to
ADM's lobbyests, has an endotherm of 150F. Mix that with your gas and
you have to start thinking ice even here in the desert southwest.

But of course, that can't be right :-)

- - - - - - - - - - - - - - - - - - - - - - - -

I posted the above to Yahoo's AirVW Group about six months and
continue to get mail from idiots insisting slide-valve carbs can't ice-
up since they don't have a butterfly valve. I've reposted it here in
the interest of safety. If you know of someone running a slide-valve
carb without any provision for carb heat please give them a nudge
toward reality. -RSH

In article ,
N114RW wrote:

Good post, and good reminder. One comment. As I understand it, carb ice
is most common on warm (70 degree or so), humid, days. As the
temperature drops, so does the moisture in the air.


The most ice-susceptible air, I have found, is that between 20F and 55F,
with very high humidity -- not to say that a higher or lower range would
not cause ice.

It is good practice to install carb heat and USE it -- especially in
high humidity conditions.