Date: Tue, 31 Jul 2012 10:26:11 -0500
Reply-To: Tom Hargrave <thargrav@HIWAAY.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Hargrave <thargrav@HIWAAY.NET>
Subject: Re: Carburettor Set Weber 44 IDF VW Wasserboxer 2,1
In-Reply-To: <5017F27F.5030807@gmail.com>
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And here on the ground, depending on the carb and the relative humidity,
icing can start at 45 degrees F. The symptoms are usually gone by the time
ambient temperature gets down to 34 degrees F.
Thanks, Tom Hargrave
www.stir-plate.com
www.towercooler.com
www.kegkits.com
www.grow-sun.com
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of
JRodgers
Sent: Tuesday, July 31, 2012 9:58 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Carburettor Set Weber 44 IDF VW Wasserboxer 2,1
Airplanes - piston types and jets - have combustion air heaters to pre-heat
the air to remove/prevent ice formation inside the throat of the
carb/turbine. A short story about this kind of ice.
Once in Alaska, while on a trip as co-pilot in a Skyvan, was at 12,000 ft
over the Cook Inlet and coming home to Anchorage. Had been cleared to the
Anchorage VORTAC for a hold outside Anchorage prior to landing and began
decent. We were in the tops of clouds and began picking ice, and it would
get worse as we descended through it to below the freezing level. The
captain reached over and flipped both smile heaters switches to the solenoid
valves that routed heat from the turbine compressor sections into the
stainless plenum around the air intake of the engines. Those plenums were
coated with ice. The instant that ice melted that slug of water went
directly into the engine and snuffed out the flame in both engines. At
12,000 feet both engines had quit. We suddenly became a very heavy glider
with a pee-poor glide ratio. WE were out of
7000 feet and nearing 6000 and descending fast before we managed to get the
engines started again. Scared the bejeebers out of us. Everything was OK
after that, except for the seat of our pants and the cones in the captains
and co-pilots seats. An official change in operating procedures followed,
along with some pilot training - Only one smile heat switch at a time was to
be turned on to eliminate dual engine failure.
Carb ice works the same way. Turn on a carb heater on a piston aircraft
- the engine will run rough until it swallows all that water from the
melting ice. Pilots learn to tickle the carb heat, so the ice goes away
slowly, otherwise the engine may quit.
Same goes on these carbs. But with no Carb air heaters, they can be a major
PITA in wet, cold air. Ice can build in the throat of the carb and simply
choke off the combustion air.
It's all about Bernoulli's Principle. Carb has a venturi, venturi's drop the
pressure, increase the air flow speed and drop the temperature. If weather
is cool and moist, heck -even warm and moist - if the temp in the throat of
the carb goes below freezing, whatever moisture is in the air will begin to
plate out as ice in the carburetor. Thus the need for a carb air heater of
some sort.
John
On 7/31/2012 8:12 AM, Tom Hargrave wrote:
> Frost on the outside = frost & ice on the inside and this causes
> serious issues with carburetor performance.
>
> Thanks, Tom Hargrave
> www.stir-plate.com
> www.towercooler.com
> www.kegkits.com
> www.grow-sun.com
>
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On
> Behalf Of Hector Zapata
> Sent: Tuesday, July 31, 2012 4:26 AM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Carburettor Set Weber 44 IDF VW Wasserboxer 2,1
>
> On 7/30/12, JRodgers <jrodgers113@gmail.com> wrote:
>> These carbs don't have carb air heaters, and are subject to icing
>> when conditions are right. Makes operation in nasty weather that much
>> more miserable.
>>
>> John
>
> I thought that was considered good for the mixture. Thirty-something
> years ago I met a mechanic who was very proud of the way he adjusted
> carburators, they frosted at idle, 80º weather...
>
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