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Hot Weather Remove (Temporarily) Cabin Heat & Does Cabin Heat Reduce Engine Cooling?

Do you remove cabin Heat in Summer & Does it Help Engine Cooling -multi selections OK

  • You remove cabin heat during summer

    Votes: 5 11.1%
  • You note improved engine cooling when cabin heat removed

    Votes: 1 2.2%
  • You assume improved engine cooling by not dumping high pressure air in lower cowl?

    Votes: 2 4.4%
  • Does not matter/don't care, leave cabin heat installed year round

    Votes: 37 82.2%

  • Total voters
    45

gmcjetpilot

Well Known Member
Hot Weather Remove (Temporarily) Cabin Heat & Does Cabin Heat Reduce Engine Cooling?

Envision the cabin heat system:
> High Pressure Air is removed from the high pressure side of the engine baffle
> Air routed to a heat muff wrapped around an exhaust pipe by flex hose
> Hot air out of heat muff routed to firewall mounted air-box on firewall by flex hose


When cabin heat in use that hot air goes into cabin. However when not in use that hot air is dumped into the lower cowl area near firewall which may affect cooling. One you are pulling air from the upper engine plenum and you are pressurizing the lower pressure bottom of the cowl.

Q: Do you disable/remove cabin heat in summer time? Yes or No
(block the air from the upper baffling, remove heat muff)

Q: Have you observed better engine cooling by bypassing the cabin heat system in summer? Yes or No
(theory - pumping high pressure air in lower cowl reduces pressure differential across the engine cylinders)

Q: Do you guess dumping cabin heat in lower cowl reduces engine cooling because of less pressure differential reducing air flow across cylinders? Yes or No


NOTE: Common wisdom is if you block/remove cold feed air to the heat muff remove the heat muff, or you could cook your pipe and heat muff.
 
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.02

I am not flying yet but I installed a bypass valve in the SCAT tube prior to the firewall valves. The thinking being to still allow airflow through the heat muff but dump it overboard before the firewall. Whether it works or not remains to be seen but it is easy to remove if not needed or it has undesirable effects...
 
Last summer, I bypassed my heat muff to convert my heat outlet to a fresh air outlet so I had two fresh air outlets. Heaven. I plan to do it again. I had no issues with oil temps, but then again, I never have issues with oil temps.
 
I'm up in Canada. We don't know what warm weather flying is.
Just kidding, we might get one warm day a year... or it seems that way.
 
I usually pull the heat muff and block the inlet for summer. Pretty sure it helps when the OAT's are 90+, which can last for months here in TX.
My CHT's rarely exceed 350 even in the summer.
 
Survey does not accommodate my situation. No vote. I removed forced air cabin heat completely so that I can focus on engine cooling. My cabin heat is an electric vest that I plug into the electrical system. No issues with cooling capacity for the 200HP RV-8 or the Rocket.
 
I removed forced air cabin heat completely so that I can focus on engine cooling. My cabin heat is an electric vest that I plug into the electrical system. No issues with cooling capacity for the 200HP RV-8 or the Rocket.

+1.

Also threw away the vacuum pump, the ADF, my whiz wheel, and my scarf and goggles ;)
 
Survey does not accommodate my situation. No vote. I removed forced air cabin heat completely so that I can focus on engine cooling. My cabin heat is an electric vest that I plug into the electrical system. No issues with cooling capacity for the 200HP RV-8 or the Rocket.
Yep that is what B17 crews did in WWII. They had heated flight suits and boot liners, pluse insulated lined gloves and caps. http://www.303rdbg.com/uniforms-gear3.html

Delivering an RV-4 from Seattle to Upstate NY middle of winter years ago, it had a marginal hot air heater. I had to work at staying warm. I was solo but a back seater would have frozen. Being frozen in your plane is not safe. An electrically heated vest would have been nice. My BMW R1150RT motorcycle has heated grips and outlets for heated suits (never used that). Looking at amazon a nice 12v 90w heated motorcycle jacket, draw is 90/12 ~ 7.5 amps.

Two flights with some piccolo tubes would answer the question.
I am a percussionist and don't play one piccolo much less two. Ha ha. Yep that would tell a story. Doing a thought experiment NOT bypassing high pressure air from plenum and dumping into lower cowl would make some difference. Quantifying "some" is the question. Dan - from your +1 on Toobuilder's comment, I understand you have no heater? If yes, how do you stay warm in winter/altitude, same, heated clothing?

Eliminating hot air off of exhaust pipe HEATER has a safety plus. It reduces chance of CO poisoning, and it lowers weight and cost.
 
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... My BMW R1150RT motorcycle has heated grips and outlets for heated suits (never used that). Looking at amazon a nice 12v 90w heated motorcycle jacket, draw is 90/12 ~ 7.5 amps...

Also based on my motorcycle experience, I've seen that if you can keep your core warm (vest), it makes the rest of the body relatively easy to manage. I also have heated insoles, but have never used them. The firewall throws off just enough heat that I don't need them. My wife sitting in back with her feet against the fuselage skin, DOES use the insoles.

The vests and insoles are lighter than the heat muffs and ducting they replace, and they can be left in the closet until needed.
 
You are supposed to inspect and or remove the heat muff system annually. I remove mine in the late spring, inspect things, and then install it in fall
 
You are supposed to inspect and or remove the heat muff system annually. I remove mine in the late spring, inspect things, and then install it in fall

Just my opinion but I don't think the typical Van's heat shroud (which just covers a piece of pipe) falls into the same inspection category as a typical muffler with a heat shroud like found on most certified aircraft.
 
Hyperbole aside, the cabin heat system most certainly does bleed off cooling capacity. Even when "turned off", the typical heat muff still ports a significant volume of otherwise valuable cooling air overboard with no benefit.

That significant amount of wasted CFM could be used to bring cooling under control OR reduce airframe drag (by reducing airflow through the cowl).
 
Michael is spot on regarding the extra cooling air lost with a heat muff system that is installed but not needed for cabin heat.
Many folks have spent hours and hours of work sealing plenum systems so that no cooling air is lost. Then when your cabin does not need heat you are effectively introducing a 2” hole into your upper plenum.
No problem in the winter, but in the summer it would be nice to have that extra cooling air.
When you close your cabin heat valve, that now heated air, is dumped into firewall area.
 
It is a system, what do you really want?

George, there are a wide range of answers but what is the objective? What is the mission and environment and "customer" requirement??

If the engine cooling system (cowl inlet and exit) is designed for a lot of bypass air then what difference will one source of bypass make? As an experiment one could take off the muff and install a bypass valve. Vary the flow (bypass) and measure airspeed change (if that is what you are after) to quantify the change. But clearly there is more.

There are many conditions and results possible. Without an objective we don't know where we are going, what to quantify, and measure progress.

OK as a thought experiment lets say you want: good cooling under all conditions, but also want highest efficiency from cooling i.e. speed. Cabin heat is not an objective, but occupant comfort is desired.

So that can drive a cascade of design changes, inlet size, variable exit, eliminate all bypass and all heating hardware. Additional alternator amperage overhead. Now you can not have high speed efficiency w/o suffering low speed cooling, so here comes a variable exit, and (oops) we need those inlets larger. All this pressure for the exit will drive improved flow efficiency under the cowl. Balloon the cowl and radiant heat becomes more of a problem. Oops, there goes that oil temperature, larger cooler. See where this goes? You have a DanH (or ToolBuilder) system.

A single parameter improvements, even if they provide good benefit in theory, are frequently lost (or muted) in implementation without a corresponding change in the parallel system improvements that it enables.

Now the rest of the story. - High upper chamber pressure on my 7 drove installation of a bypass orifice to balance (reduce) airflow to the muff. My cabin heating is not adequate for temps below 8F without sunshine. It is due to tip up leakage pulling cold air from the aft fuse up my armpits. Another system issue not related to the question at hand. To help answer your question . . . I have high upper chamber pressure and wanted to know how the oil cooler flow affected CHT. The oil cooler shutter was completely closed and fully opened in cruise. I saw minimal change in CHT and no differential changes between cylinders, and no measurable speed change. The test point time was limited due to rising oil temps but it was long enough to detect the measure changes. Being a system thing, your results would likely vary and in a steep high power climb with marginal air flow across the heads it would definitely be a different story.
 
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YQuantifying "some" is the question.

So hook up a manometer and make two flights. The loss isn't huge, but it's there. Bobby Looper told us an ECI R&D project established a deltaP loss of about 1" H2O for each 1 sq in of leak area. I've not confirmed it myself, as I'm not cutting a 2" hole in a baffle wall for the experiment.

Dan - from your +1 on Toobuilder's comment, I understand you have no heater? If yes, how do you stay warm in winter/altitude, same, heated clothing?

Aircraft was wired for heated clothing, and I put a hot vest on Ms Patti on really cold days. I wear a sweater and an insulated motorcycle riding suit over street clothes, as it's really comfy on a winter ramp. Good to zeroF OAT if the sun is out, maybe 15 OAT when overcast. Admittedly, where I live isn't very cold, 40 to 70 cruise OAT being the usual range, so the suit probably doesn't get used more than 5 flights a year.

I used the same suit to fly a Maxair in the winter, fully exposed to 60-100 mph blast. Electric vest went on at <45F. As Mike said, if your core is warm, hands and feet remain happy.

That significant amount of wasted CFM could be used to bring cooling under control OR reduce airframe drag (by reducing airflow through the cowl).

Yeah, and don't get me started on those silly blast tubes. Again, this is 2020. Let's install accessories with heat ratings at least up to SAE automotive standards.
 
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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?
 
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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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.
 
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!
 
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? :D
 
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. :D

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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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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