Brodhead Pietenpol Association

Original Posted By: "KMHeide, BA, CPO, FAAOP"
Hi Dan,I honestly don't know why or even IF this engine NEEDS more carb heat for some reason than any other engine. I do know that the stock carb is very prone to icing up. Maybe it's the placement of the carb, or venturi design, but it will ice up fairly easily. When I interviewed actual Model A flyers before I decided to go that route, I talked to a fair number who had experienced icing.As to HP loss, I would have to image it would be similar to pulling carb heat on a certified aircraft engine, probably a around 50 rpm drop, and you're right, you don't really have it to spare!The usual carb heat fix on a model A works fine. I've seen guys wrap springs around the front pipe inside the can to slow and heat the air. Stainless scrubbees work well too, just be sure they can't get sucked in.I am using a weber carb on mine, and it'll ice up too. I am using what seems to be a very slick carb heat system I got from culver prop/valley engineering. It sounds odd but it has worked for their engines and is working great on my A which is currently on a test stand. It consists of a small tube running from the base of an exhaust pipe (I chose my leanest cylinder) to a hole tapped in the bottom of the carb. The pipe enters the carb base and is aimed into the primary venturi. The hot gas heats the venturi and plenum, NOT the intake air so ice won't form on the metal plenum or venturi because it is being warmed, but the mixture isn't getting heated air. I was worried about contamination from the exhaust gasses, but was assured it didn't occur, which has proved to be the case with mine. No ice, and no rpm drop and no moving parts. So far, so good.Don't see why it wouldn't work on a stock A carb, though like I said, the usual heat box works fine. It also wouldn't be a big deal to fabricate an on off heat box, though I think you'd find you'd need it on much of the time, and since it warms the air, it'll rob you of some rpm.Douwe________________________________________________________________________________Date: Tue, 6 Mar 2007 18:31:13 -0800 (PST)

Original Posted By: Pietsrneat(at)aol.com
The proof of operation will be in actual flight since when we fly we go through different atmospheres which cause carb icing.Sitting on the ground doesn't offer the same conditions.Let us know how you make out in flight especially on a humid day.Sounds like a great system though.I have always been scared of contamination from the exhaust pipe.One never knows when a small hole may appear in the bugger and cause some greef.I especially don't like this when taking cabin heat off for obvious reasons.>From: "Douwe Blumberg" >Reply-To: pietenpol-list(at)matronics.com>To: "pietenpolgroup" >Subject: Pietenpol-List: model A carb heat>Date: Tue, 6 Mar 2007 21:23:35 -0500>>Hi Dan,>>I honestly don't know why or even IF this engine NEEDS more carb heat for >some reason than any other engine. I do know that the stock carb is very >prone to icing up. Maybe it's the placement of the carb, or venturi >design, but it will ice up fairly easily. When I interviewed actual Model >A flyers before I decided to go that route, I talked to a fair number who >had experienced icing.>>As to HP loss, I would have to image it would be similar to pulling carb >heat on a certified aircraft engine, probably a around 50 rpm drop, and >you're right, you don't really have it to spare!>>The usual carb heat fix on a model A works fine. I've seen guys wrap >springs around the front pipe inside the can to slow and heat the air. >Stainless scrubbees work well too, just be sure they can't get sucked in.>>I am using a weber carb on mine, and it'll ice up too. I am using what >seems to be a very slick carb heat system I got from culver prop/valley >engineering. It sounds odd but it has worked for their engines and is >working great on my A which is currently on a test stand. It consists of a >small tube running from the base of an exhaust pipe (I chose my leanest >cylinder) to a hole tapped in the bottom of the carb. The pipe enters the >carb base and is aimed into the primary venturi. The hot gas heats the >venturi and plenum, NOT the intake air so ice won't form on the metal >plenum or venturi because it is being warmed, but the mixture isn't getting >heated air. I was worried about contamination from the exhaust gasses, but >was assured it didn't occur, which has proved to be the case with mine. No >ice, and no rpm drop and no moving parts. So far, so good.>>Don't see why it wouldn't work on a stock A carb, though like I said, the >usual heat box works fine. It also wouldn't be a big deal to fabricate an >on off heat box, though I think you'd find you'd need it on much of the >time, and since it warms the air, it'll rob you of some rpm.>>Douwe________________________________________________________________________________

Original Posted By: "MICHAEL SILVIUS"
Subject: Re: Pietenpol-List: model A carb heatDouwe,Why did you decide to go with the weber carb? And what model are you using?Dan HelsperPoplar Grove, IL************************************** AOL now offers free email to everyone. Find out more about what's free from AOL at http://www.aol.com.________________________________________________________________________________