Oil cooler for heating air

I have been reading through the archives and like the idea of using the oil cooler for a wintertime cabin heater (or at least for heating the air coming into the cabin). I noticed that a few people apparently have done this, but I have not seen any photos or detailed discussion in my wanderings through the archives thus far. I would appreciate any comments on how well it has worked, if you have installed such a system, and any links, photos, etc. that would help me to get a handle on what it would take to do such an install.

thanks,
greg

Greg, I plan to do exactly that on the -4 I am building, but I have not quite got there yet.

Quite a lot of people are a bit gloomy about the idea, but it is not a big deal because it would not be much work to retrofit a heat muff on the exhaust if it turns out to be useless. Just remember when you make the air gate in the firewall, the air source may change if you decide hot air from the cooler is not a success, and think about that with respect to the routing.

I am in the UK so we dont have Minesotata type cold, but I do plan to put heater elements in the seats also. This is necessary in a -4 anyway, because it is hard to get the heat all the way back there to the wife. Got to keep her warm!

The one slightly complicated bit of the process I see, is to make up a f'glass air collector on the outlet side of the oil cooler. This is more a problem of space in the -4 than anything else though.

All I have to show so far is this, http://gikonfwf.blogspot.com/2008/01/oil-cooler-location.html#links which is nothing really.

There is a bit in the RVator from some years back that is quite positive about this idea.

I hope you get some replies with a bit more to offer than I.

Keep in touch.

PS Some will be concerned about the loss of cooling effect of the oil cooler. -4s tend to run cool I understand, and the -9a I built also ran cool, as does my Supercub. In fact I have never had oil temp problems. I might leave the duct from the oil cooler off for the first few flights, in case I have oil temp problems breaking a new engine in.

oil cooler heater

Steve Sampson said:

Greg, I plan to do exactly that on the -4 I am building, but I have not quite got there yet.

Quite a lot of people are a bit gloomy about the idea, but it is not a big deal because it would not be much work to retrofit a heat muff on the exhaust if it turns out to be useless. Just remember when you make the air gate in the firewall, the air source may change if you decide hot air from the cooler is not a success, and think about that with respect to the routing.

I am in the UK so we dont have Minesotata type cold, but I do plan to put heater elements in the seats also. This is necessary in a -4 anyway, because it is hard to get the heat all the way back there to the wife. Got to keep her warm!

The one slightly complicated bit of the process I see, is to make up a f'glass air collector on the outlet side of the oil cooler. This is more a problem of space in the -4 than anything else though.

All I have to show so far is this, http://gikonfwf.blogspot.com/2008/01/oil-cooler-location.html#links which is nothing really.

There is a bit in the RVator from some years back that is quite positive about this idea.

I hope you get some replies with a bit more to offer than I.

Keep in touch.

PS Some will be concerned about the loss of cooling effect of the oil cooler. -4s tend to run cool I understand, and the -9a I built also ran cool, as does my Supercub. In fact I have never had oil temp problems. I might leave the duct from the oil cooler off for the first few flights, in case I have oil temp problems breaking a new engine in.

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There is an article from one of the racing pilots a month or so ago about doing exactly this, pictures and all. I also saw this and thought of using it in the reverse to duct heat off the oil cooler into the cabin heat. http://www.aircraftspruce.com/catalog/eppages/airduct.php
all that would me needed would be a side duct to dump hot air when not needed.
Mike H 9A/8A

mike109g6 said:

There is an article from one of the racing pilots a month or so ago ..........................
Mike H 9A/8A

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So where is the article Mike? I would be very interested. Can you scan it in possibly? Thanks

oil cooler

Steve Sampson said:

So where is the article Mike? I would be very interested. Can you scan it in possibly? Thanks[/QUOTE
http://lazy8.net/oil cooler exit.jpg
I think that it was Nuisance or AJ or one of there buddies. I'm going to PM AJ.
Mike H

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When the oil is cool, it doens't flow through the cooler

The varatherm (sp?) controls the flow of oil and only opens up when the engine needs the additional cooling. When it is cold outside, you may get no heat.

Do a search, this has come up before.

Oil cooler cabin heat source

One of my hangermates has been flying with this in his RV-8 for a number of years. He later added heated seats because his rear pax were cold. Then he did a super-seal job on his canopy to eliminate air leaks.

My impression is it does not provide as much heat as the normal muffs.

My opinion: stick as closely to Van's design as possible to eliminate wasted time and money unless you enjoy tinkering more than flying.

I considered an interestering variation to this approach (which someone on the forum mentioned) in which the oil cooler dump air is used to feed the heat muff with the muff output then being used as normal.

The gain in this approach is that you get a free (no further plenum outlets needed) source of "warm" air to drive the heater system. The claim was that the warm source air added to the heat output.

I don't think I will be able to use the system as the routing of the feed scat tubing is difficult in my installation (IO-390/Vertterman exhaust) as the only one good place for the muff is at the front of the engine.

Vern said:

One of my hangermates has been flying with this in his RV-8 for a number of years. He later added heated seats because his rear pax were cold. Then he did a super-seal job on his canopy to eliminate air leaks.

My impression is it does not provide as much heat as the normal muffs.

My opinion: stick as closely to Van's design as possible to eliminate wasted time and money unless you enjoy tinkering more than flying.

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From my Lycoming days in a previous life, I have to agree with Vern. In really cold climes, the oil cooler must be blocked off to get oil temp up 190 or so and there will be no air flow through it at all.

The only time this concept makes any sense is flying high during the summer and you want some cabin heat, but even then it won't be as much as you can steal from an exhaust heat exchanger.

My impression is it does not provide as much heat as the normal muffs.

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A friend at my airport modified his 6A to use the oil cooler air as the source for cabin heat. It has worked great for him. A mutal friend who has been in both of our planes on winter night flights says his oil cooler heating system blows mine away (I have Vans anemic heat muff).

It is true that when the vernatherm closes, you are not getting much heat. It is also true that in a decent or using low power settings with a traditional heat muff, you are not getting much heat either.

There are some down sides. It is more heavy and more complated. If you have a cool running engine, it may take some tinkering to get it to work. Good luck.

McFly said:

A friend at my airport modified his 6A to use the oil cooler air as the source for cabin heat. It has worked great for him. A mutal friend who has been in both of our planes on winter night flights says his oil cooler heating system blows mine away (I have Vans anemic heat muff).

It is true that when the vernatherm closes, you are not getting much heat. It is also true that in a decent or using low power settings with a traditional heat muff, you are not getting much heat either.

There are some down sides. It is more heavy and more complated. If you have a cool running engine, it may take some tinkering to get it to work. Good luck.

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With all due respect to Californians, for what sort of OAT's does this claim hold? I completely close off the supply of air to my oil cooler when OAT's are below around 30F, and even then the oil temp only reaches around 180 to 190 F.

Oil cooler/cabin heat

This is more common (and apparently successful) in the canard community. They have difficulty getting warm air from the rear engine forward.

Their common approach seem to be to mount an accessory oil cooler in the cabin, analogous to a heater core in a water-cooled car. An automotive blower fan or marine bilge blower is used to circulate cabin air through the cooler. A firewall mounted valve (like the heater valve in many cars) can control flow of hot oil through the cooler.

The huge advantage to this setup is using warmer cabin air through the heater rather than outside air.

The oil temp in my plane runs about 170 degrees in cruise with OAT in the 20s. That's only a little less than the coolant temps in my car at the same OAT. The specific heat of oil is significantly higher than water, so it should work OK in theory.

An example can be found here.

With all due respect to Californians

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From my friends description (this is the mutual friend) it was high 30?s in California?s central valley. They were going to Reno so they had to fly above 10?000 to cross the Sierras. This was at night so they were probably higher than that. I don?t know what the OAT was at altitude but it was must have been respectable cold even by MN standards

I do know that in my plane, I would have to REALLY bundle up in those condidtions

Greg Arehart said:

I have been reading through the archives and like the idea of using the oil cooler for a wintertime cabin heater (or at least for heating the air coming into the cabin). I noticed that a few people apparently have done this, but I have not seen any photos or detailed discussion in my wanderings through the archives thus far. I would appreciate any comments on how well it has worked, if you have installed such a system, and any links, photos, etc. that would help me to get a handle on what it would take to do such an install.

thanks,
greg

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I use the oil cooler to heat my cabin. The oil cooler is mounted on the firewall, with its own diverging inlet duct from the outside free-stream, and a converging outlet duct that turns to the rear and expels into the free-stream below the plane. I have a 2" aluminum tube that goes from the outlet duct right below the cooler that goes through the firewall, then divides into two ducts that empty out into the cabin just ahead of and between the occupant's feet. The control valve is hinged just below the tube, and when in the off position, is up and closes off the tube. When in the totally open position, it goes forward and down to completely close off the outlet duct, so that all of the heated air has to pass through it. I have only had to use it 2 or 3 times when flying at 11,500' or 12,500' in California spring or fall with a high overcast, minimal solar heating, and OAT of 4C. In those instances, there was way too much heat available, so I had to close the valve to just a small diversion. How this would work in the cold climes I can't say. You don't have much heat on the ground until you do a run-up and get the oil temperature up, so here the exhaust muff could be better. As was mentioned, if you have to close off the oil cooler inlet to get the oil temps up in the winter, that will cut down on the flow, but then you would be diverting all of the outlet flow into the cabin, so that might not be a problem. If you can't get the oil temperature up in the winter, you should also close down on your engine cooling inlets since that is where the oil gets its heat. The vernatherm will always open for some flow if the engine is heating the oil. If you are not getting the oil temp up enough to get oil flow, your engine is too cold, and the oil is not boiling off the water! Keep your engine's CHTs to at least 350F! Low CHTs are just as bad as high. Remember, your engine is rated at no more than 450F in cruise. I like 375F to 395F better. It's sure nice to know that you don't have a CO problem as you could with a leaky heat muff!

One thing is heating, another thing is de-fogging/de-icing of the canopy. To do that, fresh warmed air is needed, recirculation of the air will not work because the humidity will increase. I guess this doesn't matter at 12000 feets when it is cold and dry, but at 0-10 deg C and rain, this can be a real problem, particularly if your clothes are damp from the rain.

I flew a CH-601 once that had a very simple heating system. It was just a hole in the firewall to let in the warmed air in the cowling, adjustable with a sliding plate covering the hole. It worked excellent, but I wondered a bit about some what-if's in case of a engine fire.

flyeyes said:

snip

The oil temp in my plane runs about 170 degrees in cruise with OAT in the 20s. That's only a little less than the coolant temps in my car at the same OAT. The specific heat of oil is significantly higher than water, so it should work OK in theory.
snip

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Well, maybe. Except that when you are flying with an OAT in the 20's, there is little oil flowing through the cooler, since the vernatherm has shut most of it down. The volumetric flow through a car's heater core must be many, many times that of an oil cooler restricted by the vernatherm.

Where did you find that oil's specific heat is greater than water? I believe oil's specific heat is about half that of water, and about the same as ethylene glycol. A mixture of water/ethlylene glycol would be about .75, with oil around .5. These are per unit weight, so volumetrically the difference would be even greater.

AlexPeterson said:

Well, maybe. Except that when you are flying with an OAT in the 20's, there is little oil flowing through the cooler, since the vernatherm has shut most of it down. The volumetric flow through a car's heater core must be many, many times that of an oil cooler restricted by the vernatherm.

Where did you find that oil's specific heat is greater than water? I believe oil's specific heat is about half that of water, and about the same as ethylene glycol. A mixture of water/ethlylene glycol would be about .75, with oil around .5. These are per unit weight, so volumetrically the difference would be even greater.

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I realized I didn't know off the top of my head, so I looked it up here on the fly. D'Oh! I was looking at the english instead of Metric units. You are right.

I still think it may work though--several of the canard types have reported good success.

I realize that it's probably easier to heat what is basically a styrofoam cooler, but I'm already ahead with a bigger motor than most EZs and oil splash on the pistons ;-)

Of course, if Al Gore is right, it'll be a moot point pretty soon anyway....

Guys....listen to the cold weather fliers - they know of what they speak! It's not anectodal, it's from real world experience in RV's that regularly fly in really cold weather. Bill, David and Alex are 100% spot on. In really cold weather you cooler will/should be blocked off entirely, as will some of the inlet air. Every winter I use the famous Stein Duck tape trick on the air inlets, tape off my oil cooler with Aluminum tape, block the back with a plate and still have to work to keep the temp up. If you're talking "chilly" weather this may be fine, but really cold weather in an RV means a 100% blocked off oil cooler - even with a vernatherm. If you feed cold air over it (and it's not getting oil to begin with), the whole exercise is a waste - IMO based on real world cold weather flyin for almost 10 years in my RV (Same as Alex has for yearly repeats of real world experience).

Sure, some may have read or heard that it works in some planes somewhere at some temperature, but in a well cowled RV in a really cold environment I can't see any possible benefit to all the extra work/weight you'll add putting cold air over an oil cooler that doesn't have very warm if any oil going through when it's already a contest to keep the oil warm to begin with.

I won't ramble on, because if you choose not to listen to the guys from MN who know cold weather flyin then I'm not going to change your mind anyway. With all due respect, 4oC ain't cold! I know it gets colder in other places so MN isn't the worst, but it is a hotbed of RV experience from guys (other than me) who have been flying/experimenting for years with trying to find ways to keep warm in below zero (F) weather.

Just my overtly opinionated 2 cents as usual! The advice is worth exactly what you paid for it!

Cheers,
Stein

SteinAir said:

It's not anectodal, it's from real world experience in RV's that regularly fly in really cold weather. Bill, David and Alex are 100% spot on. In really cold weather you cooler will/should be blocked off entirely, as will some of the inlet air.

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This is also true at least as far south as southern Wisconsin. There's world of difference between 35? and 10? F (or colder). I have to block off my oil cooler in the winter to get into desired oil temp. range, and this is standard practice for both RV's and some factory planes.

I have two exhaust heat muffs ducted in series, with studs welded on one pipe to increase surface area. This, combined with long johns, makes flying comfortable down to near 0?F.

As a Californian I don?t stand much of a chance winning an argument about heaters with folks from Minnesota and Wisconsin

I will say that flying in even moderately cold temps, your Vans FWF heater installed per plans will not do much.

Done lurking -

A few questions on my part -

Where does the air that blows through the cooler come from that you are sending to the cabin? Can't flames come from the same place? Or, are you using a separate intake that will collect rain?

If it was such a great idea, why haven't the OEM's done it before? I don't think we've had a hundred years of dummies designing airplanes. It's not like other types of heaters haven't been done before. Some of the first large transport aircraft made steam off the exhaust. Worked fine until the throttle was moved. Most all were converted to gas heaters.

I think my choice for serious heat would be a couple of mufflers with shrouds. The factory planes I fly occasionally can produce too much heat for four seats on a cold day. The only hazard being the possibility of carbon monoxide with a cracked muffler.

Back to lurking.

McFly said:

As a Californian I don?t stand much of a chance winning an argument about heaters with folks from Minnesota and Wisconsin

I will say that flying in even moderately cold temps, your Vans FWF heater installed per plans will not do much.

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Something must be wrong with my little O-290 as we have flown it with 20 degree OAT's and the cabin heat, installed per plans, just about cooks us out.

N941WR said:

Something must be wrong with my little O-290 as we have flown it with 20 degree OAT's and the cabin heat, installed per plans, just about cooks us out.

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Much of it has to do with how well the cabin is sealed. I have liquid heat as per an auto and at 14F my legs are warm but above the belt line, it is cold. There's a blast of cold air from the aileron holes coming up the stick that is down right uncomfortable even though the stick is sealed with the seat cushion.

There's a lot one can do to make this a better environment but flying on such days generally is no fun so I don't do it much nor will I spend much time sealing the cabin. I figure with climate change is in full swing, a leaky cabin is a plus most of the year.

Thanks for the discussion and input. Sounds like the best plan (for me at least) will be to stick with the standard oil cooler installation but install two exhaust muffs, one for each side. Reno is colder than CA, but certainly not MN. I might eventually try something with the oil cooler, but would rather get flying first!

cheers,
greg

Mine works great!

I'm the friend McFly was taking about. I'm generally a lurker but I thought I might be able to add some input as I am currently using my oil cooler to heat my cabin with great results. The original Vans exhaust muff is sitting in the hanger producing about as much heat there as it did on the plane. The oil cooler heater works so well that on moderate days it is difficult to keep it comfortable (not too hot). I ended up changing to a throttle cable so I could get finer adjustments. If you open it up completely even on cold days it produces a blast that one can only stand for 5 seconds. My friend calls it the heater from ****. Then we flew into Reno the OAT was close to 0 degrees F at altitude. Worked great until decent. You could definitely tell when the vernatherm (sp?) opened and closed. It got colder, but never uncomfortably so. I imagine if I was coming down from 35,000 feet it might get bad, but I think I might have other worries- like how I got attached to 737 that drug me up there! I'm installing seat heaters for descents on cold days, but more because I'm redoing the seats and can, than because they are really necessary. I was concerned about fire so the flapper is constructed of stainless. If there is a fire (or oil cooler leak) the flapper will be closed as it normally would with any heater. Added bonus, I don't need to worry about co2, which in my opinion is far more likely than a fire or oil cooler leak.
My reasons for always lurking is I have noticed sometimes some people can be hard on each other on this site. With that in mind, I'm not interested in defending my install...just offering up my own personal experience with the performance of mine. Hope this helps.

Gem930

Welcome to VAF

Great write up, don't be a lurker, be a contibutor.

The cabin is usually at less than static pressure. That hole in the back of the fuselage where the elevator spar passes through is in a region of higher pressure, close to static pressure. The result? Air enters the back of the fuselage and comes forward into the cabin. The leaks on the canopy around the joins is usually of the low pressure variety, lowering the cabin pressure. Make sure your cabin is sealed at the bulkhead behind the baggage area to keep out that cold air.

I'd be most interrested in a second oil cooler in the cabin as discussed with the EZ's, what did they do to control oil flow for changing seasons and weather?? A valve under the cowl to devert oil from the FWF cooler to the cabin cooler sounds good but doesn't allow for control from the cabin?

I'm not real interrested in the muff due to CO poisoning and anemic output and the shrouded air from the FWF cooler has the same issue as well as creating a much larger firewall hole which defeats the point of a firewall!

GEM930 said:

I'm installing seat heaters for descents on cold days, but more because I'm redoing the seats and can, than because they are really necessary. I was concerned about fire so...

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GEM930, welcome to the forum. That is some good info for those who wish to go that route.

One thing to be careful about with the electric seat heaters. Some time back when I was thinking about them, someone posted on here about a car fire he was involved in where the seat heaters caught the seat on fire. Not something I wanted to test at altitude, thus I skipped the install. That said, a number of people have installed them with good success.

Others, one thing to improve the efficiency of your exhaust heater muff...
Get some two inch exhaust wrap from a speed shop and wrap just your heater muff. This simple change will cook you out of the cabin.

GEM930 - thanks for the input.

GEM930, thanks for your input. It is realy encouraging to hear that not only VANS/the RVator think this is a good alternative, but to hear of your good experience.

As you say, keeping clear of the CO2 is a big plus, as is the fact that the system should weigh less.

How much heat can you get?

Oil Cooler v Heat Muff heater

Oil Cooler Cabin heater - There are not many or any factory planes using oil coolers for heat. Why? I don't think it's because they did not think of it in the last 70 years. It might be a clue about design choices, trade-offs and return for effort. As far as LongEz's their cabin is much smaller in volume and much better insulated than a RV. Still I don't think oil-cooler cabin heat is common in LongEz's (could be wrong).

How hot can you get the air for the oil-cooler? It depends on oil temp/flow into the cooler. It also depends on air temp/pressure/density across the oil-cooler. Doug does not want "rocket scientist" heat transfer equations on the forums, but lets say on a 90F day, your oil-cooler raised air temp going through it 80-90F. However on a freezing day that total temp rise goes down, let's say in half (or more). The air of course is colder and more dense to start with. The engine is also running cooler so oil temp is less. The oil cooler might only raise air temp 40F on a 10F day. You will be cold. Besides temp, there air flow (pressure/volume). Oil coolers have little fins & tubes for air to pass through, significantly dropping air pressure (more than a heat muff). The air pressure coming out of the cooler may be pretty weak. If the cabin is air tight, your hot air can't get in. A good cabin air exit vent improves air flow. If cabin air pressure is higher due to leaks, than the oil cooler's low pressure flow will be nill; you're going to be cold.

HEAT MUFFS, suffers as well when the engine is running cooler due to low outside air temp or lower power settings, just as the cooler does. Hot exhaust air starts out at say 1,800F (3,000F-4,000F in the combustion chamber). You can do to get more heat out of heat muffs. Heat studs (welded on), making your pipe look like a porcupine, adds more surface area. The heat muff goes over the studs. Check with, either AWI or AEI for the stud welding service. (Pic) Also keep the SCAT short; Route the air into the heat muff downstream (@cool end). The exit air from the muff to the cabin is at the higher temp end. How about DUAL heat muffs? Larger, longer heat muffs? Increase SCAT from 2" to 2.5" to reduce pressure drop? (There are no off the shelf 2.5" parts, so that's a negative, requiring custom parts and FW air valve.) Heat muffs get a bad name because the ones Van's sells are too small for cold climates. Coastal Oregon is wet not that cold. I think 50% of the problem is leaky cabins and 50% undersized heat muffs. I know how tight it is under the cowl, so fitting bigger any thing is a challenge.

Is the oil-cooler cabin heat worth all the effort? Good luck if you try it and let us know how it works. There is always just dressing warm (I'm not kidding). Not having little cold drafts squirting cold air on you neck is a plus. You have to think of the RV as a motorcycle, are real fast one with a really good fairing. Regardless of what you do, most RV's are uninsulated, will always leak and do not have a good exit air vent.

Wild Idea? (heated clothing & liners for snowmobiles & motorcycles) Link, Link, Link The amps are kind of scary in the 3 to 7 amp range for each item. Don't laugh but another trick is a blanket. If you can get some of your hot air vent air under the blanket, its very comfy. Just attached it under the panel and over the stick and chest. Kept, legs, hands and chest warm. It saved my life on a winter coast-to-coast flight.

Sounds like the biggest challenge to using an oil cooler is weight and complexity.

The Vernitherm issue can be bypassed with ingenuity, I am certain. Doesn't the oil always circulate through the oil filter even if it bypasses the oil cooler? If that is true then using one of those remote oil filter mount kits would provide an opportunity to splice in a variable bypass valve (controlling that some/none/all of the oil passing through the filter first diverts to the cabin heater coil). With that you can ensure a controllable rate of fresh hot oil into the heat exchanger.

Sealing the cabin is also great, but requires some thought as previously mentioned to provide a "controllable leak" at a strategic location to ensure a measured supply of fresh air into the cabin. No taking a nap while flying, please!

Thanks to everyone for the ideas. I may supplement my muff with an oil heat exchanger in the future, 'cause sometimes it gets down to 5 degrees F. when I want to go visit mom in the winter. That is -25F at 10k', or "danged chilly" in almost anyones' vocabulary. Even with sealing, I don't think the muff will cut it under those circumstances...

Those Rutan Builders are Clever

Here is great write up (very detailed):

http://www.iflyez.com/oil_heat.shtml

Main features are recirculation system with blower and overboard dump valve. Say the +40F temp gain through oil cooler can work, if you keep recycling the air. If you just pump cold air through it, it will not heat the cabin as well.

The second feature is an overboard dump valve (manual). If the engine gets too hot you have to open the overboard dump to get cold air through the cooler.

From his write up there was a trade-off in effort and weight as you would expect. He is satisfied but not a slam dunk. With a tractor engine is should be easier to make work. The KEY to me is a closed loop with a BLOWER.

By using heat muffs on the exhaust, you are using heat that are othervise just lost - allways regardless of outside temperature, with no adverse effect on the engine. The oil circulation system in the Lycoming on the other hand, is not meant to be tapped for heat. The oil flowing through the cooler is controlled to keep the engine oil within set limits in both upper and lower bonds. Certainly bypassing that controller will have adverse effects on the engine, and using only heat from the cooler itself will give you no heat when it is cold.

Old VW's had heat muffs on the exhaust, but when it got real cold this was not enough. The solution was to use a fuel burner. Anyway, the main problem is not the temperature as such, this can be fixed with clothing and insulation of the cocpit and a tiny heat source (in fact with proper insulation of the cocpit, the heat from your body, approx 600W will be more than enough). The main problem is to defrost the canopy so you can see. This requires a steady stream of fresh warmed air into the cockpit and equally a steady stream of humid air out of the cockpit. Recirculation of the air is definitely something you do not want to do, because the humidity from your body (through your breath) will accumulate.

I have finally completed my oil cooler driven cabin heat system. Well in this picture the hose that connects the two together is missing, and I have yet to install the cable to control the flapper valve, but the main work is done. You can see it here.

I will let you know how it works out in a while, though it wont be connected during break in.

I tried it.

Being located in northern Illinois where it gets pretty cold from November through March, I decided to try the oil cooler route. Previously I had one heat muff on the exhaust fed by SCAT from a one inch hole (as recommended by Robbins) in the plenum and it was very marginal. The system I tried this winter was an aluminum plenum on the outlet of the oil cooler with 1" SCAT into the heat muff. I also closed off half of the air inlet openings on each side of the cowling. Due to poof runway conditions (grass runway with record snowfalls this year) I only got to fly one cold day. Before the changes on a mid to upper 30 degree day I had CHT's around 250 and oil temp only 155. After the changes, CHT's 330 to 350 and oil temp 210. Air coming in was warm, but not much volume. Perhaps changing to 2" coming off the oil cooler plenum would help. Opening up the inlets a bit would help flow, but cylinders were barely getting warm enough now. Today I finally got up again and since it was 60 degrees outside, I opened up the air inlets. Oil cooler still routed to muff and oil temps still 210 (normally run 190 when warmer). Time to pup off the oil cooler plenum and hook up heat muff back to original location. Sure am glad it is finally warming up.
Ron Voss
N642R RV-6
angle valve O-320 Catto 3 blade

I'm just thinking out loud here, but has anyone ever experimanted with small 12v electric heaters. They are popular for cars and marine applications and come in a range of sizes. I've seen 12v units powerful enough to heat up a 10x10 room with ease down to very small >1lb 200 Watt ceramic models that seem to perform suprisingly well. Assuming a fairly airtight cabin and perhaps southern climate heating needs, would an electric heater be feasible. It would certainly be drastically easier to install(about 10 minutes) be self contained, and require no large holes through the firewall. The possibility of sucking on exhaust fumes certainly would go down

I suppose that it is a current draw issue. I can only assume that there is a very good reason that RVs don't use electric heat or it probably would have been mentioned earlier.

George

GSchuld said:

I'm just thinking out loud here, but has anyone ever experimanted with small 12v electric heaters.

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I have seen RVs with these heaters, with mixed - mostly poor results. They just don't produce enough heat to overcome air leaks / flow.

kind of what I figured was the biggest concern. A cockpit of an RV-7 would be somewhere in the neighborhood of 50sqft total volume, a third the space of the average 4-door car. It takes suprisingly little heat from a small 12v ceramic heater to heat up the fairly airtight but otherwise pretty thermally inefficient space of a car. It's interesting that the same heater could have such a difficult time keeping up with 1/3 the space in a plane with the same outside temp. I guess that says a lot about the effects of all the minor airleaks possible in a plane. Obviously the heat output required for flying in SoCal would be very different for the Wisconsin flyers, but I guess the thermal efficiency of a bare aluminum skinned airframe with a hard to seal opening canopy is not the greatest. I was thinking that a modest electric fan/ceramic heater might do if the plane was fairly well insulated/airtight and complimented with a pair of heated seat inserts (for the co-pilot's comfort). Another potential benefit of electric heat is the ability to have a digital automatic temperature control thermostat, set it on 72 and forget about it. She would love that. Shut the plane down, the heat shuts down automatically. Read: the wifes likes the idea of a modern, cozy climate controled enviornment and I am persuing my options in whatever strange direction that takes me. I want her to take lots of trips with me, and keeping her as comfortable as possible will be very helpful in that quest.

The 12v heaters are certainly made in models large and powerful enough to flame broil a person right out of an RV cockpit in an Alaskan winter, but as the power output goes up, so does the weight and more importantly current draw. Obviously it would take more and more alternator output to produce the amp requirements for a less modest 12v heater. I wonder if anyone who has done a significant soundproofing job including an solid effort to make the cockpit more airtight has tested to see if the improved thermal insulation/heat retention properties would allow sufficient function of a basic ceramic heater? Anyone? It certainly would have some up sides if it were possible/feasible. Forgive me, I tend to think outside the box (read: functionally wasting much of my own time and occasionally the time of others) My bad

George

I vote for heated clothes

Heated vests work great. I can stay fairly warm on a motorcycle in 30 degree weather at 70 MPH. Should work well inside of the airplane with some heat going.

Heat off the oil cooler.

George, coincidentally I had a chance to test out my oil cooler driven heating. Its not really cold here yet but it is getting cooler.

Despite the oil running cool, around 170F, I am getting a huge volume of pleasantly warm air off the oil cooler. That is successfully providing basic warming and demisting. (I will reduce the volume of air to the cooler to increase the tmp.)

Additionally, I have a heating pad in the backrest of my seat. It draws a bit over 2 amps. At first when you turn it on you notice nothing, but 10 minutes later your back is starting to cook. In a colder climate I might run to a second one under my backside. (The element is made by a company called Greiner for Mercedes B., and weighs next to nothing.)

I am 100% satisfied with this solution for a temperate climate and would not consider a ceramic heater. Might not work in Alaska!

I made a flapper control box mounted under the firewall mounted cooler... It works pretty good.. providing warm air for my wife's feet... (She is in control of the push/pull)... It also has the drawbacks mentioned here earlier (long decents..not much heat, etc.)... however, it does work.. I also have a flapper valve at the air input to the oil cooler for cold winter flying here in Az..... And when closed, the air flow is cut off and not much heat then.... But I can balance the two controls... Also, this setup for me, has worked very well as to oil cooling.. Never have seen over 220 deg... mostly 170-180....Sheldon

Been there, done that.

Works great right up until it gets cold enough you really need it.

It would work fine if you had a good set of cowl flaps to insure the engine (and oil) did not get cooled. But, those would add weight and complexity.

Heat muff on the exhaust works fine provided you insure a) the source of air to the muff is at higher pressure than your cabin and b) you seal the cabin well, leaving only a little leakage for positive ventilation. Sealing also has the advantage of preventing those irritating little "cold spots."