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Does anyone block off the cabin heat inlet during summertime?

S

SwimmingDragonfly96

Well Known Member
Been working on my CHT issues ever since I got my plane, and I can manage okay for now, but I still have to think about them more than I want to, especially in summer.

Everyone makes a strong point about blocking every single potential air leak in the baffling to get the air flowing past the fins, but I don't see many people talk about the giant 2" inlet behind cylinder number three that dumps air directly into the lower cowling when the cabin heat isn't being used.

I was doing my condition inspection with the builder the past couple weeks and brought this up with him and he got super curious if it could help as well. We put some aluminum tape over the inlet behind cylinder 3, but I'm a little hesitant to fly with it. Without flowing air, would my heat muff overheat or something? I have a Robbins setup. Does anyone else have any anecdotal data about their CHTs when they block this off?
 
I can't imagine the heat muffs would melt or anything, but you could easily check by doing a warmup with the cowl off then hit them with a temp gun.

I block off the heat during the summer, but I remove the muffs as well. I was considering running the scat tube direct to the firewall flapper to get more fresh air. Have yet to test it.
 
Mine is taped off from 50% to 90% and has helped the cyl temp drop another 10 to 15 deg.

At alt of 14,000 ft its getting cool enough at minus 3 celsius that I'm starting to need some heat so this has worked out ok for the summer.

Much cooler I will need to open it up again or find another solution.

I agree that not having any air flowing through there that there is a risk of overheating the scat and possibly a fire or some smoke at least. Its only rated for 500 deg F.

Maybe some flexible stainless steel tubing and then put a door in there for a complete by pass to help on the cylinder cooling?

Tim
 
I usually remove my heat muff and block off the 3" baffle air inlet prior to going to KOSH each year. It's about a 30 minute job.
 
I block mine off every summer with foil tape, but I don't remove any of the hardware, never noticed anything wrong the muff or scat tube afterwards. I also don't remember there being a great reduction in CHT's between the 2, but maybe that's because OAT is so high by the time I block it off. My original reasoning had more to do with why dump all that heat right onto the vent/firewall when it's not even needed? CHT's concerns were secondary. When it's 110+ OAT, even "fresh" air coming in the NACA vents is heating you up.
 
I pull off the heater scat every year and block the inlet, reinstall when the weather starts getting cold. I leave the muff on but with both ends open.
 
Walt said:
I pull off the heater scat every year and block the inlet, reinstall when the weather starts getting cold. I leave the muff on but with both ends open.
Click to expand...

I agree with Walt. If you're going to leave the muff on, it should be open.
 
I removed the heat muff and ran SCAT hose from the intake to the cabin heat vent. The air coming into the cockpit is still warmed beyond ambient, though, so I will probably just tape over the inlet. It’s Florida, and I pretty much stay below five grand or so.
 
I guess those that disable their cabin heat in the summer either never fly very high or they only fly on sunny blue sky days.

Midsummer cruising at 12,500 under a high overcast it is more than cold enough that I use cabin heat…
 
rvbuilder2002 said:
I guess those that disable their cabin heat in the summer either never fly very high or they only fly on sunny blue sky days.

Midsummer cruising at 12,500 under a high overcast it is more than cold enough that I use cabin heat…
Click to expand...

.....or you have seat heaters to keep your buns warm:)
 
rvbuilder2002 said:
I guess those that disable their cabin heat in the summer either never fly very high or they only fly on sunny blue sky days.

Midsummer cruising at 12,500 under a high overcast it is more than cold enough that I use cabin heat…
Click to expand...

....or you live in the south!
 
Or you're a polar bear like me who needs freezing air blasting on them at all times! I rarely use the heat during the winter, and only ever for the GIB. I also put in heated seats, which my passengers love but I never use.

Does blocking off the heater inlet really help CHTs? I never noticed.
 
Maybe a good question is, why not just have the valve be open/close to allow maximum cooling on the cylinders when the valve is closed?

After spending hours tweaking our baffles trying to maximise our cyl cooling especially on # 3, it seems like a waste of cooling to be dumping fresh cool air into the bottom cowl and pressurizing it.

Is it due to the risk of over heating the scat tubing and the heater muff? If so, maybe there is a way we can isolate the scat from the heater muff and maybe have a stainless steel heater muff?

Im sure its not that simple otherwise it probably would have been done.

Tim
 
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riobison said:
Maybe a good question is, why not just have the valve be open/close to allow maximum cooling on the cylinders when the valve is closed?

After spending hours tweaking our baffles trying to maximise our cyl cooling especially on # 3, it seems like a waste of cooling to be dumping fresh cool air into the bottom cowl and pressurizing it.

Is it due to the risk of over heating the scat tubing and the heater muff? If so, maybe there is a way we can isolate the scat from the heater muff and maybe have a stainless steel heater muff?

Im sure its not that simple otherwise it probably would have been done.
Click to expand...

It has been done - my RV has been flying since 2012 in Minnesota with just such an arrangement, and there are others that have been doing so longer than mine. Tom Berge was mfg/selling a slide valve for this purpose; I have one with two inlets - one for each heat muff. When it's closed, no air flows through the system, and there has been no issues with the tubing, the muffs, or the exhaust pipes in about 1400 hours of operation.

I'd definitely recommend this approach over the usual flapper arrangement - it's more compact, doesn't need to be blocked off, and doesn't steal cooling air from the upper plenum when not needed. Given the satisfactory service history of the RVs I am aware of that have such a setup, I don't see a downside.
 
ChiefPilot said:
It has been done - my RV has been flying since 2012 in Minnesota with just such an arrangement, and there are others that have been doing so longer than mine. Tom Berge was mfg/selling a slide valve for this purpose; I have one with two inlets - one for each heat muff. When it's closed, no air flows through the system, and there has been no issues with the tubing, the muffs, or the exhaust pipes in about 1400 hours of operation.

I'd definitely recommend this approach over the usual flapper arrangement - it's more compact, doesn't need to be blocked off, and doesn't steal cooling air from the upper plenum when not needed. Given the satisfactory service history of the RVs I am aware of that have such a setup, I don't see a downside.
Click to expand...

I thought my RV 4 had something similar but its been sold and I have no way of checking at the moment. I didn't have the EMS in it so I wasn't chasing the same stuff and never really paid attention to my CHT as what I didn't know was never a big concern. In short managed it like a flight school 172 from the 70's when no one had an EMS at that time in SE AC.

But on my RV9A Im trying to seal it up tight and I'm out of options and the cabin heat dumping to the lower cowl seems to be the last of the low hanging fruit.

Any idea on where I can get a hold of Tom or his valve?

Thanks
Tim
 
I do know for a fact is that my carb heat on the 4 like most of our planes that have it, is either open or closed and it doesn't dump anywhere when not in use. Over heating has never been an issue.

So, any reason why the vast majority of us are doing what we are doing and haven't modified this to benefit our cooling issues?

I just received an email back from Tom and it appears that he doesn't support this product anymore.

Tim
 
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Has anyone actually measured a CHT difference with the cabin heat scat blocked off? Are we "arguing" about the benefits of something anyone has established actually acts as a benefit?

FWIW, I tried removing the scat tubing and blocking off the baffle one summer and didn't really notice much difference in my CHT's, but maybe that's because I had other baffle issues that masked what could have been a benefit.

Just curious.
 
I have.

Going from 50% of the hole taped off to 80% taped off it was 12 to 15 deg drop across the board. Certainly 15 deg on # 3 cyl putting it now in the high 390s.

This was after I piddled around with all the other little leaks under the inter cyl baffles and anywhere else I could see light.

Tim
 
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I live in east Texas. I completely removed the heat right after I bought the plane. Not needed down here :)
 
FlyFastJP said:
I live in east Texas. I completely removed the heat right after I bought the plane. Not needed down here :)
Click to expand...

Lol well today it was -4 Celsius or 25 deg F at 15,000'. Starting to cool off here and starting to need some heat in the cockpit.
 
I just wanted to update this thread.

I taped off half of the cabin air inlet behind cylinder #3 and it dropped my CHTs about 10-15 degrees across the board which is nice. I spoke with Rick Robbins who designed the cabin heat muff on my plane, and he told me that I should actually have BETTER heating cutting down that 2" inlet to 1-1.5", so sounds like a win-win to me. He said the 2" hole is optimal for slow planes, but overkill for our quicker ones.

Thanks everyone for your replies.
 
SwimmingDragonfly96 said:
I just wanted to update this thread.

I taped off half of the cabin air inlet behind cylinder #3 and it dropped my CHTs about 10-15 degrees across the board which is nice. I spoke with Rick Robbins who designed the cabin heat muff on my plane, and he told me that I should actually have BETTER heating cutting down that 2" inlet to 1-1.5", so sounds like a win-win to me. He said the 2" hole is optimal for slow planes, but overkill for our quicker ones.

Thanks everyone for your replies.
Click to expand...

Yes, it does make a difference. Id like to change my cabin heat valve to more of an open/close valve and not a full deflector that dumps it into the lower cowl pressurizing it.

Anyone aware of something that can easily retrofitted? I thought on my RV4 that I sold that it had a slider that was open or closed? Is anyone able to confirm what the 4s have?

Thanks
Tim
 
I recall that Vetterman Exhaust recommended not leaving the heater shrouds on the exhaust pipe without airflow through the shroud as the differential heating would damage the exhaust pipe. Like others have said, I live in southeast Texas and removed my cockpit heat system altogether. We just don't need it here.
 
brad walton said:
I recall that Vetterman Exhaust recommended not leaving the heater shrouds on the exhaust pipe without airflow through the shroud as the differential heating would damage the exhaust pipe.
Click to expand...

I’ve neither seen nor heard this, and the several aircraft that have the shrouds (mufflers might be a different issue) installed without airflow when heat is selected off suggests there is no issue. Can you provide a link or a reference?
 
The carb heat on my 4 didn't have airflow through it and was closed 99.9% of the time. There wasn't a problem in close to 800 hrs.

Im sure depending on the distance from the exhaust port could have a long term impact so distance accordingly and monitor.

Tim
 
ChiefPilot, I did a quick search and did not find the quote from Clint Vetterman I was looking for. But, please note that the firewall mounted heater boxes flow air whether open to the cockpit or not. When closed, the flow simply dumps airflow into lower cowl but continues to flow air through the heat muff/ shroud. Clint Vetterman also cautioned against use of exhaust pipe wrap commonly used in auto racing
 
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SwimmingDragonfly96 said:
I just wanted to update this thread.

I taped off half of the cabin air inlet behind cylinder #3 and it dropped my CHTs about 10-15 degrees across the board which is nice. I spoke with Rick Robbins who designed the cabin heat muff on my plane, and he told me that I should actually have BETTER heating cutting down that 2" inlet to 1-1.5", so sounds like a win-win to me. He said the 2" hole is optimal for slow planes, but overkill for our quicker ones.

Thanks everyone for your replies.
Click to expand...

Imagine the cylinder head cooling loss that passes through your oil cooler that's not needed for take off and the first 5 minutes of climb.
 
brad walton said:
ChiefPilot, I did a quick search and did not find the quote from Clint Vetterman I was looking for. But, please note that the firewall mounted heater boxes flow air whether open to the cockpit or not. When closed, the flow simply dumps airflow into lower cowl but continues to flow air through the heat muff/ shroud. Clint Vetterman also cautioned against use of exhaust pipe wrap commonly used in auto racing
Click to expand...

I don't think wrapping the exhaust is really the same thing, since that is designed to trap heat in and almost always runs the entire length of the pipe.

As I mentioned above, I've got one of Tom Berge's slide valves (as do a number of other folks around the Twin Cities area) which flows no air when cold. It controls two muffs, one muff on each side of my IO-360, and has been working without issue or any obvious damage to the exhaust or muff in about 1400 hours of operation. It just doesn't get that hot that far down the pipe - where there is cooler air flowing over it.

I'd be interested in actual data showing why it's stressful or harmful - empirical evidence seems to suggest otherwise.
 
rvbuilder2002 said:
I guess those that disable their cabin heat in the summer either never fly very high or they only fly on sunny blue sky days.

Midsummer cruising at 12,500 under a high overcast it is more than cold enough that I use cabin heat…
Click to expand...

Or wear a sweatshirt. I live in the south and have only ever used the cabin heat twice in three years. The greenhouse effect (sunlight required) is usually enough to keep the cockpit warm enough when I close down the ventilation nozzles, but I wear a light sweatshirt and sweatpants when I plan to fly high. I did notice that my #6 CHT improved when I blocked off the outlet (Super-8 with an O-540 and the outlet is directly behind the #6 cylinder).
Having it blocked off is not a permanent thing though and I do not advocate permanent removal. I did it because of an exhaust repair that made the muff not fit so I took it off and blocked both the outlet at the plenum and the inlet at the cabin heat valve on the firewall. I plan to reinstall when I replace the entire exhaust system...crossover system to 3-into-1 is happening soon. My biggest worry about deleting the cabin heat is not comfort...it's keeping the windscreen clear on decent from cold to warm, moist air and perhaps even condensation on the electronics. I want to have the option available to heat the cockpit if condensation occurs. But so far no issues.
 
gasman said:
Imagine the cylinder head cooling loss that passes through your oil cooler that's not needed for take off and the first 5 minutes of climb.
Click to expand...

Yup, that's on the agenda. Put this https://antisplataero.com/products/oil-cooler-air-shutter in there and keep it closed until oil is at temp then open up as needed.

I have to agree with ChiefPilot that the Tom Berge's slide valves are probably the answer but unfortunately Tom doesn't produce them any more.

The Carb heat muff on my RV4 was closed or dead ended 99.9% of the time and I never had or seen any problems with it.

Tim
 
SwimmingDragonfly96 said:
I just wanted to update this thread.

I taped off half of the cabin air inlet behind cylinder #3 and it dropped my CHTs about 10-15 degrees across the board which is nice. I spoke with Rick Robbins who designed the cabin heat muff on my plane, and he told me that I should actually have BETTER heating cutting down that 2" inlet to 1-1.5", so sounds like a win-win to me. He said the 2" hole is optimal for slow planes, but overkill for our quicker ones.

Thanks everyone for your replies.
Click to expand...

is there any explanation to that? sounds very cool as I am struggling with unsuficient cabin heat. I like the idea of reducing cht during summer too.
 
Blocking off SCAT tube

I was going to block off or at least partially block off my SCAT tube from the plenum area to the heater block but cam across this statement on Vans’s Aircraft web site.

“Air heated in the heat muff must continually flow to keep from overheating components and destroying items such as the muff or the scat tube.”

I know continually flow is rather open ended but it concerned me enough to not go down this path. I get plenty of heat even in the winter time in Ohio and was not worried about reducing the output. I can barely stand to open the heater box more than 25% before closing it again. My issue is my second battery is located down low next to the pilot heat box (would not recommend a battery installed low on the firewall ) and wanted to keep it as cool as practical. My heat box is plans 14A early kit. (Looks like a triangle and does not have a 2 in outlet on the bottom as some box’s have). I’m going to modify the box to add a 2 in aluminum outlet for a SCAT tube that will run to the cowl tunnel exit.

BTW my other battery (plans 14A location) never exceeds 135 F in its location. (I’ve monitor both batteries with external thermocouples).
 
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I have a 2” SCAT hose going ot the heat muff (two hoses on the RV-10). I installed a piece of aluminum with a 3/4” hole (orifice) on the baffle SCAT hose flange (hose side) with aluminum tape. The SCAT hose goes over this.

This provides continuous air to the heat muff(s), but not nearly as much as before. The volume air coming into the cabin is greatly reduced but I think hotter when the cabin heat flapper valve is fully open.

I find this a good compromise between stealing engine cooling air in the summer and cabin heat in the winter. CHTs are 330* - 360* in cruise in the summer.

You can experiment on the size of the hole in the aluminum orifice to fit your needs.

Side note - I use a 3” (RV-8) or a 4” (RV-10) butterfly valve on the hose going to the firewall mounted oil cooler. I find I need to at least partially close it on summer days once I get to altitude.

Carl
 
I have eliminated the heat muff on 3 RV's. Cabin heat inlet air is drawn through a scat tube positioned to pick up hot air exiting the oil cooler.
I think this was suggested in the RVAtior before the turn of the century.
Simple and light.
The air is plenty warm but I don't live where it is terribly cold.
 
Yes on my first RV I removed it for a long time. saved weight and possible CO poisoning..... How to stay war? 90 on the ground, at 10,000 feet it is 70F..... In winter in mild locations flying low, you can do what motorcyclist do, wear warm clothes and even have electric underwear!!! :eek: No jokes please. Ok joke away but make it good. The B17 crews were in an unpressurized plane flying in the flight levels, with headed suits and O2 Mask.

When I sold my RV-4 awhile back, I was paid to deliver it. I flew from Seattle to upstate New York, middle of winter. A cold front, weather so bad, settled in north central USA, freezing rain, sub zero temps, weather below IFR approach mins, East WA, ID, MT, WY, ND, SD, MN. Not to mention crossing Cascades and Rockies no way. I flew South, to about Tonopah NV (aliens near area 51) spent night. Had a fun 3 day COLD trip across the middle / lower half of USA, Topeka NV, Topeka Kansas, Harrisburg PA, and short flight flight 4th day. Recall spent a night in Tonopah NV, MoAbout Memphis turned back up to the North East.

I HAD ONE HEAT OUTLET under panel. With one register up front I could not stay warm. OAT was way to cold, too much heat loss out of the fuselage (no real insulation) and canopy. The one wimpey heat muff not great. No passenger so that was OK. What I did was take my jacket off and turn it around, threw it over my shoulders, over the control stick, using some clips making a heat tent. It worked well. I had a winter cap on, covering my head and ears. Normally I am not flying 8 hours a day in winter at altitude. However it worked. Not a fan of being cold.
 
SwimmingDragonfly96 said:
Been working on my CHT issues ever since I got my plane, and I can manage okay for now, but I still have to think about them more than I want to, especially in summer.

Everyone makes a strong point about blocking every single potential air leak in the baffling to get the air flowing past the fins, but I don't see many people talk about the giant 2" inlet behind cylinder number three that dumps air directly into the lower cowling when the cabin heat isn't being used.

I was doing my condition inspection with the builder the past couple weeks and brought this up with him and he got super curious if it could help as well. We put some aluminum tape over the inlet behind cylinder 3, but I'm a little hesitant to fly with it. Without flowing air, would my heat muff overheat or something? I have a Robbins setup. Does anyone else have any anecdotal data about their CHTs when they block this off?
Click to expand...

This summer I removed the heat muff and scat tube, along with blocking off the cowl inlet ramp hole to the heat muff, all to reduce lower cowl pressure. Didn't do a before/after measurement, however have 80 hours of after data. I'm very happy with CHTs- takeoff climb angle is 7.5 degree, reduce RPM to 2500 at 500 ft AGL. On a 70 degree OAT day at San Martin E16 airport (281 ft elevation), max CHT is 364 degrees on cylinder #2. On a 100 degree day I see 385 degrees. CHTs increase until altitude begins to rolloff horsepower. The engine is a port, polished, flat tappet Lycon built IO360M1B with a 206 hp dyno measurement. Cowl is a stock Vans, baffles are stock Vans except for silicone baffle material- basically, no heroic measures. Hope this helps! :)
 
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"Tom Berge slide valve"??

Anyone have a photo, or something on this Tom Berge slide valve? A crude sketch, artful description?
 
BillL said:
Anyone have a photo, or something on this Tom Berge slide valve? A crude sketch, artful description?
Click to expand...

Hey Bill,
Since I am a detail person, I used some blue painters tape to cover the inlets I’m winter. It looks super cool! HA!!
 
I’m considering changing my newly minted RV-9A from using scat tube/exhaust based heat to oil cooler scavenge heat. Key reason is two fold…. It’s too dang hot right now with my present setup. If I pull cabin heat knob out 1/4" I almost roast in the cockpit. 2nd reason and possibly better reason…. I have the infamous Lycoming stumble issue at low rpm’s. What I can see is that the dump of super hot air through the firewall heat valve is aimed straight at my mechanical fuel pump and lower cowl.

I think that hot air may need diverted down at a minimum or change the temp source (Lower temp) as a better choice.

Thoughts?
 
BillL said:
Anyone have a photo, or something on this Tom Berge slide valve? A crude sketch, artful description?
Click to expand...

Here's a picture of mine. Note the slide portion with the hole to accept the push/pull control cable (with appropriate fitting). I have two heat muffs, one on each side, and the tubing goes to the appropriate fitting on the slide valve.

53347921099_f3d9f92c54_o.jpg
 
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