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View Poll Results: Do you remove cabin Heat in Summer & Does it Help Engine Cooling -multi selections OK
You remove cabin heat during summer 5 11.36%
You note improved engine cooling when cabin heat removed 1 2.27%
You assume improved engine cooling by not dumping high pressure air in lower cowl? 1 2.27%
Does not matter/don't care, leave cabin heat installed year round 37 84.09%
Voters: 44. You may not vote on this poll

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  #21  
Old 05-24-2020, 07:30 AM
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OZCleco OZCleco is offline
 
Join Date: Dec 2018
Location: Maylands, Western Australia
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We've just completed a myriad of alterations to get our #3 CHT under control, including temporarily blocking the cabin air baffle inlet. Yet to test fly this week but ground run results seem promising.

We also had the cabin heat ducting route forward past the carby to the FAB. Didn't make sense having the scat tubing run laps around the engine bay so we manufactured a new heat box above the FAB connected by 5 or 6 inches of scat tubing.

Even if it turns out there's no appreciable gain in carby heat temps at the very least the installation simply looks cleaner.
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Last edited by OZCleco : 05-24-2020 at 07:34 AM.
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  #22  
Old 05-24-2020, 08:06 AM
jwilbur jwilbur is offline
 
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Location: Culpeper, VA
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Is it a bad idea to leave the heat muffs in place and simply block the fresh air inlets to them? As an experiment I taped over the fresh air inlet on one side and saw improvement to #2 CHT in particular. Now I want to know if this is going to cause unintended consequence if I make this summer-time permanent.
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  #23  
Old 05-25-2020, 07:46 AM
Sam I Am Sam I Am is offline
 
Join Date: Jun 2018
Location: Amarillo, TX
Posts: 24
Talking Gave it a try

After reading this thread, I removed the heat muff and associated tubing Saturday and taped over the hole in the baffle with 3M aviation tape. Waited until Sunday when the temps on the ground were 91 F to make a test run. In those temps historically, my CHT #3 would easily climb to 420 - 430 F climbing out. Yesterday, it reached 399 F on climb out. On returning from the run, I did a go around as this would always stimulate some high temps...not yesterday...385.

Thanks Mr. George for your timely survey!
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  #24  
Old 05-25-2020, 09:26 AM
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scrollF4 scrollF4 is offline
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Quote:
Originally Posted by DanH View Post
+1.

Also threw away the vacuum pump, the ADF, my whiz wheel, and my scarf and goggles
NOT THE WHIZ WHEEL!!
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  #25  
Old 05-25-2020, 09:48 AM
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gmcjetpilot gmcjetpilot is offline
 
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Quote:
Originally Posted by Sam I Am View Post
After reading this thread, I removed the heat muff and associated tubing Saturday and taped over the hole in the baffle with 3M aviation tape. Waited until Sunday when the temps on the ground were 91 F to make a test run. In those temps historically, my CHT #3 would easily climb to 420 - 430 F climbing out. Yesterday, it reached 399 F on climb out. On returning from the run, I did a go around as this would always stimulate some high temps...not yesterday...385.

Thanks Mr. George for your timely survey!
Thank you Sir for the fast flight test and report. Wow that is dramatic and more than I'd guess. How are the other jugs? Did they see an improvement?
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  #26  
Old 05-25-2020, 09:57 AM
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gmcjetpilot gmcjetpilot is offline
 
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Quote:
Originally Posted by jwilbur View Post
Is it a bad idea to leave the heat muffs in place and simply block the fresh air inlets to them? As an experiment I taped over the fresh air inlet on one side and saw improvement to #2 CHT in particular. Now I want to know if this is going to cause unintended consequence if I make this summer-time permanent.
Yes it is thought it best to remove the heat muff if you take off the feed air. Is a bad to leave it on? Let's think about it.

So normally that part of the pipe where the heat muff is cooler relative to adjacent sections of pipe. You are blowing cooler air over it compared to the other near adjacent lengths of pipe. Does this standard heat muff with forced cooling air cause a problem, due to thermal stress of hot to cooler to hot sections of pipe? I don't know of reports of wide spread cracks of exhaust pipes at/near heat muff. Does it happen? Yep, but with regular maintenance it is not an issue. Age of pipes is also a factor. See warning below.

Let's say we keep the heat muff on but take the feed air and to cabin hot air tubes off, inlet and outlet open. Cooling has two modes of heat transfer:
  1. Convective (airflow) - With the muff on and no feed air pipe, there is still some "convection cooling" air flow just not forced, much less. So the pipe will be hotter but how much more than adjacent sections?
  2. Radiant (Infrared heat transfer of thermal energy by electromagnetic waves, which heat muff will absorb) - With the heat muff on the IR heat transfer will be to the heat muff and then from heat muff to the surrounding objects. We can assume the bare pipe with heat muff removed will cool better.

So the sections of exhaust pipe adjacent to heat muff will be hotter with no air fed to heat muff. How much? Is the difference in Temp that much different than with cold air blowing through heat muff. Will the HEAT MUFF get cooked and fail?

Most aircraft exhaust pipes and heat muffs should be Stainless Steel. However some early heat muffs still in RV use are aluminum. I doubt they will love being hotter. My early RV-4 heat muff just wore out where it clamped to the exhaust people. Keep in mind the pipes could be 1500F near the exhaust port so can be abused. My new custom 4-into-1 pipe has heat barbs and a stainless steel muff. It is fairly easy to remove.

Does it make a difference to leave heat muff on without air going in and out? For short term experiment, I think you are OK leaving heat muff on. However remove it for long term. It will also save weight. Also you should remove heat muff every year to look at the pipes for cracks every condition inspection. So take it off.

The only way to settle this is EXPERIMENT. Thermal couples on the outside of pipe (before/after and in heat muff) with air and without.

Pipe crank and CO feed into the cabin can be deadly as you know. Exhaust leak into cockpit (Carbon monoxide) can make you go to sleep (permanently). Get a CO detector, cheap insurance. If you remove tubes but leave heat muff on you reduce risk of CO in cabin. However I recommend if you disable the feed air, remove heat muff for long term use.
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Last edited by gmcjetpilot : 05-25-2020 at 10:48 AM.
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  #27  
Old 05-25-2020, 04:58 PM
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N941WR N941WR is online now
 
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Quote:
Originally Posted by Jvon811 View Post
My heat muff on my -4 also provides warm air for the carb heat.

I know, I know... Lycoming induction through the oil sump on carbed engines, etc... etc...

Those of you with carb's, removing the cabin heat, do you have two heat muff's? Are you going without Carb Heat at all?
Scroll down through these pictures , you will find a picture of my carb heater muff.
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