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Date:         Tue, 31 Jul 2012 11:14:10 -0400
Reply-To:     Hector Zapata <hlzapata@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Hector Zapata <hlzapata@GMAIL.COM>
Subject:      Re: Carburettor Set Weber 44 IDF VW Wasserboxer 2,1
Comments: To: JRodgers <jrodgers113@gmail.com>
In-Reply-To:  <5017F27F.5030807@gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

Very enlightening, thank you. That might explain the loud noise I heard while flying from PR to Savannah, Ga. in a C-130 (8 hour flight, no movies), de-icing using exhaust heat. That was loud and unexpected.

Hector

On 7/31/12, JRodgers <jrodgers113@gmail.com> wrote: > 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


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