F4U Versus F6f Carb Icing

[MIflyer]

Everyone probably is already familiar with the attached observations by Corky Meyer, Grumman WWII test pilot. Also attached is a photo of the right root intake for an F4U, showing how the air has a pretty direct route to the engine intake.

But I wonder about the carb icing problem. I have experienced carb icing only once and it will get you attention. But I wonder how likely you are to have carb icing given that the air is going into a supercharger, which tends to warm things up quite a bit.

 

[Joe Broady]

But I wonder how likely you are to have carb icing given that the air is going into a supercharger, which tends to warm things up quite a bit.

Remember that the carburetor is between the first and second stage blowers. At low altitude the first stage is cut out of the induction system (pilot selects "neutral blower") because the second stage inhaling ambient air through the carburetor can generate all the boost the engine can stand. So the designers have to decide where to get that ambient air. Grumman made the decision to use the hot unrammed air from behind the engine. Compared to rammed cold air there's a performance penalty, but they accepted that in exchange for freedom from icing.

Of course as the plane climbs you eventually have to cut in the first stage blower to maintain manifold pressure. In the case of a Hellcat at climb power that occurs at 7000 feet according to the pilot handbook. But the pilot can still choose hot unrammed air by pulling a T-handle on the instrument panel. It forces the first stage to inhale from behind the engine.

 

[MIflyer]

Yes, that is all true. But the real reason that carb ice is such a problem is that the air is cooled not only by the rush through the carb but also by the heat of vaporization of the fuel. On a regular float type carb the air come past the throttle plate and suck the fuel from the carb into the engine. The problem is that the vaporization of the fuel cools much more more. Ignoring heat of vaporization, carb ice probably would not be a problem except for the really extreme areas of the attached chart.

But with pressure injected carbs and supercharged engines the fuel is injected under pressure into the supercharger. I would not think that with that situation carb ice would be nearly as much of a problem. Obviously it can be to some extent, since Corky was made a believer in carb heat by that Wildcat experience.

 

[Tony Kambic]

Here's an image of the B-26 Marauder carb intake ducting. Note there were two intakes above the engine on each nacelle, and they came together near the rear of the R-2800 and down to the carburetor throat. Just above that throat ( where the hand is cleaning ) is a screened panel with a gate that pilots could open or close as necessary to let in heat from the engine.

 

[jmcalli2]

Everyone probably is already familiar with the attached observations by Corky Meyer, Grumman WWII test pilot. Also attached is a photo of the right root intake for an F4U, showing how the air has a pretty direct route to the engine intake.

But I wonder about the carb icing problem. I have experienced carb icing only once and it will get you attention. But I wonder how likely you are to have carb icing given that the air is going into a supercharger, which tends to warm things up quite a bit.

View attachment 601735View attachment 601736View attachment 601737View attachment 601738

Here is a schematic of the F6F induction system found at http://www.enginehistory.org/Installations/F6F.jpg