carb heat

I have a 2006 RV6A. The Carb heat is the stock heat that has no effect on the engine. I understand that Vans has a modification that is much more effective. I see some of the heat attachments but am not sure which one is the new modification. could use some help

I installed one of these after having the concerns you are having. Haven't flown yet but hear good things about the setup.
http://www.robbinswings.com/

I installed a Robbins Wings carb heat muff on my -8. It gives a good RPM drop during run-up (~50rpm) and a steadily increasing carb temperature... I haven't waited for the carb temperature to max out but I'm sure it's a lot better than the Van's design... I also blocked the sides of the inlet flange with pieces of aluminum angle so that all the air passes through the heat muff. The 2" scat seems to be sufficient air for my O-375 though I haven't tried it yet in flight.... Another thing to test, only 7 hours so far... I figure I could always use partial carb heat or open the FAB bypass a bit for warmer air if I notice a problem with air volume...

Robbins

I used Robbins and placed the carb heat inlet flush to the plate so no air vent path. I get about 40 rpm drop with carb heat (slick mags) during run up. I picked up some carb ice around Lake Michigan in November. the carb heat cleared it.

Edit: this is one I used, not Robbins. Sorry.
http://aircraftproducts.wicksaircraft.com/item/aircraft-exhaust/ss-heat-muff-single-outlet/ec100-020?

If you have electronic CD spark on one or both sets of plugs, is there less drop in rpm when testing carb heat?

You are correct, the stock "juice can" carb heat muff is a joke.

Here is what I switched to.

I have a carb heat probe on my plane and found out that when I slow down, my carb temp goes up, even without carb heat. Your mileage may vary.

Being the side vents are blocked off where does the hot air go when not using the carb heat?

Bird

bird said:

Being the side vents are blocked off where does the hot air go when not using the carb heat?

Bird

Click to expand...

Good catch. You want those openings to dump the hot air, just like the cabin heat valve dumps the air when closed.

Heat

On the top of the airbox there should be a generous gap between the flange and the airbox to provide an escape route for the hot air. Otherwise you have the potential to burn the exhaust pipe under the heat muffs. Most spam cans dump the hot air out the aft end of the airbox.
You do not need a lot of heat on a Lycoming, especially with a tight cowl. The exception would be known structural icing conditions when you are really just using the "carb heat" for alternate air.

Went to Robins muff, Van's stove pipe has always been a joke.

hot air dump?

I too have upgraded to the Robbin's muff a few years ago, and see a decent 50+ rpm drop now, over the barely perceptible stock tube.

a couple of things to consider ( I am not a thermodynamic engineer).

1. when the carb heat is 'closed', there really is no 'flow' of hot air to worry about....as ma pappy useta say...."if it ain't going out the back end, t'ain't nuthin' entering the top end."

2. the Robbin's design, while superior to the soup can, lets air in the slot, around the pipe, and immediately down the hose to the carb....giving it very little time to get hot. I am sure it would be superior to drill the end plates of the tube, and close the slot, especially in the centre. Lotsa guys have added stainless steel wool, or a coiled spring, to increase the heat transfer.

Ok, so this muff relies on engine vacuum to draft air through the muff. Interesting.

Bird

bird said:

Ok, so this muff relies on engine vacuum to draft air through the muff. Interesting.

Bird

Click to expand...

Not really... Robbins works very well.