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.

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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 :-)

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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