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  #1  
Old 03-10-2019, 12:01 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 3,764
Default Clearance - Heat Muff to Cowl

When I follow the 5/8" minimum clearance from the exhaust pipes to the firewall bottom flange, that leaves my heat muffs pretty close to the cowling. I haven't measured it, but it looks like 1/2" or so.

I know there are decent heat shield products available, but 1/2" seems really tight.

Is this typical?
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  #2  
Old 03-10-2019, 12:08 PM
rocketman1988 rocketman1988 is offline
 
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Default Fiberfrax

I am planning on using a layer of fiberfrax on the inside of the cowl in those areas...
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  #3  
Old 03-10-2019, 12:11 PM
Kyle Boatright Kyle Boatright is offline
 
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Quote:
Originally Posted by rocketman1988 View Post
I am planning on using a layer of fiberfrax on the inside of the cowl in those areas...
Same here, but is your clearance that tight?
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  #4  
Old 03-10-2019, 12:22 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Default

I would bet that I am close to 1/2" at the tightest clearance on my 6 though the bulk of the muff has much better clearance. I used a quality reflective product (layer of f/g plus aluminum layer) in all areas near exhuast and have had no issues.

The heat muff is not a real concern area. It is flooded with cool air and I would expect that it's exterior wall is 800*+ less than the exhaust pipe. I believe the big concern for clearance should be the bare exhaust pipes. If you don't mind the clearance at the firewall, you run the risk of mechanical abrasion.

Larry
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Last edited by lr172 : 03-10-2019 at 12:27 PM.
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  #5  
Old 03-10-2019, 12:42 PM
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AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,178
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The heat muff on the left side of my O-360, RV6A, has basically had zero clearance for 1650 hours. No way, no how is that thing not gonna hit if I keep the pipe itself away from the firewall. It's a little chafed where the muff hits the radius of the cowl to scoop junction, but no big deal.
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  #6  
Old 03-11-2019, 07:32 AM
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Bill.Peyton Bill.Peyton is offline
 
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Location: St. Louis, MO
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The clearance from the heat muff to the cowling is tight. 1 to 1/2" is what I ended up with. To prevent the cowling from being exposed to all this heat, you need to use reflective insulation. ACS has the self adhesive stuff in sheets that should be laid out on the lower cowl anywhere the exhaust gets close to the cowling. I believe I ended up using 4 sheets. I also painted the inside of the cowling with the same Jet-Glo paint used to paint the aircraft. Around the edges of the self adhesive sheets I carefully applied a small bead of black high heat RTV to prevent oil from penetrating the adhesive. 900 hours and still looks like new. The light shown is the Aerosport light kit.

[IMG][url=https://flic.kr/p/WeE13y]
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  #7  
Old 03-11-2019, 10:36 AM
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rleffler rleffler is offline
 
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Location: Delaware, OH (KDLZ)
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Quote:
Originally Posted by Bill.Peyton View Post
The clearance from the heat muff to the cowling is tight. 1 to 1/2" is what I ended up with. To prevent the cowling from being exposed to all this heat, you need to use reflective insulation. ACS has the self adhesive stuff in sheets that should be laid out on the lower cowl anywhere the exhaust gets close to the cowling. I believe I ended up using 4 sheets. I also painted the inside of the cowling with the same Jet-Glo paint used to paint the aircraft. Around the edges of the self adhesive sheets I carefully applied a small bead of black high heat RTV to prevent oil from penetrating the adhesive. 900 hours and still looks like new. The light shown is the Aerosport light kit.

[IMG][url=https://flic.kr/p/WeE13y]

I'm the same as Bill. No issues after six years. I epoxied the cowl interior and used the same product as Bill.
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