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Top Cat

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Can anyone provide and brief over view of the RV-12 cabin heat system?

I've searched this site and haven't found anything definitive as to how the RV-12 cabin heat works. The SLSA doesn't come with detailed system descriptions.

I've taped off a portion of the oil cooler and in this colder weather it has nicely reduced the time it takes to reach the required 122F temp. In flight it has kept the oil temps higher.

I've noticed the CHTs are at the low end of the green on the ground. It's enough to make the cabin heat effectively make the cabin warm prior to take-off. At cruise however the CHTs drop into the top of the lower caution range (just below the green band). Cabin heat is thus lower too.

Appreciate any input. Thanks very much!
 
Air enters through the opening in the front of the cowl, and is ducted past the oil cooler along the left side to the coolant radiator. A flap type door controlled by the cabin heat control determines whether the air coming off the back of the radiator is dumped out, or forced through the perforations in the firewall near the pilot's feet.

In cold weather the heat will be insufficient unless the air flow is reduced, thereby raising the temperature of the cylinders and coolant. Some inventive folks have designed cockpit controlled doors to modulate the air flow. Personally I just fabricated an aluminum plate with a flange at the top that can be slipped in front of the top half or so of the radiator to block airflow there. It is secured by a couple of sheet metal screws. It's the same principle as the old winterization covers that are sometimes used on Cessnas and Pipers.

This brings the CHT temps up nicely into the green range, and gives you good cabin heat.
 
I suspect that the cabin heater system in the RV-12 SLSAs is the same as in my RV-12 ELSA. Basically, ambient ram air enters the front of the cowling, flows back through the left-side cowling duct, and through the coolant radiator into the cabin (or out the cowling exit - depending on the position of the HEATER control knob). The amount of heated air entering the cabin is controlled by a large flapper door mounted on the firewall - the door is controlled by the HEATER pull control on the panel. Quite a lot of heated air can pass through the radiator into the cabin when the door is fully open. However, the amount of heat provided is proportional to how hot the radiator is -- on a COLD day, the amount of heat transfered from the radiator to the air may not be sufficient to ensure a toastly cabin.

Reminds me of the "heater" system in the old VW Bugs - you don't get much "heat" until the engine gets really warmed up.
 
Thanks guys!

So I'm right in saying that cabin heat is proportional to the temperature of the coolant?

I can improve oil temps in the winter by partially covering the oil cooler with metal tape, reducing the cooling effect of inlet air.

I can do the same with the coolant radiator although it's a bit more difficult to access? By restricting the cooling/cold airflow to the radiator I can effectively warm the coolant and thereby increase the air temp of the air going towards cabin when the flap/door is opened using the cabin heat control? What's the best way to do this?

I know some of you builders have cleverly designed shutters etc as a permanent control fix and I believe Vans is working on that as an option for the SLSA.

Lastly, the cabin heat system has nothing to do with air from an 'exhaust muffler' and everything to do with the coolant temperature, correct?

Again, thanks for your answers and input!
 
Cabin heat is related to coolant radiator heat. Oil cooler and exhaust system are not a factor in cabin heat.
 
Thanks David!

The oil cooler is easy to duct tape. The coolant radiator seems less accessible. How do you restrict cool airflow in lieu of a fixed shutter?
 
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Do NOT apply tape to the aft side of the water radiator. It can come off, fall onto the exhaust pipe and catch fire. Do not ask how I know! :D
I made an aluminum cover for the exposed-top-aft side of the water radiator. It is fastened using hinge pins similar to the cowling hinge pins. The cover is easily installed or removed without tools and without removing the bottom half of the cowl. My cabin heat actually works now.
 
Takes some work but - -

The weather around here changes almost every day. Having the ability to adjust the temp as needed is great. I can be totally comfortable in any temps. Just keep an eye on it so as to not overheat it. 210 degrees CHT really puts out good heat. The more you slow the air, the longer it takes going thru the rad., and thus warms it even more. This mod makes winter flying great. Being cold just takes away the fun.
 
Joe, good point about tape on the cooler radiator. On reflection I decided to forgo that.
In SC we usually don't have really cold temps like you folks in the Mid-west and Northeast.

I might just add a bit more tape to the oil cooler to bring the temps up a bit more. On the ground warming the engine towards 122F I can get more than enough warm cabin air and the CHTs are at the low end of the normal range.
In the air, throttling back for descent, I do see that the CHTs immediately drop into the upper caution range where the cabin air is cooler. To me this would indicate that the coolant temp reflects the engine/oil temp. As it cools from throttling back so follows the coolant. I say this because usually you'd expect the temps to rise somewhat as the cooling effect of the airflow to the engine compartment is reduced. This is no doubt happening but right now the engine still cools more from lower power.

I'm thinking that if I add a bit more to the metal tape over the oil cooler it might be enough (for me in SC) to raise the oil temps a bit more and in doing so up the coolant temp a bit more to give some improved cabin heat.
I have a 3" wide strip on metal duct tape at the top of the oil cooler intake right now. I'll add another inch below that and see how it does.
If this improves things, and right now its not that bad, I may not need to baffle the coolant radiator.

Thanks again for the help.
 
John,

Lately here in SC with 28F OAT it's hard to get the oil temp above 208F with the tape I have on it now. When its about 45F I can get it up to around 218F.
I'm keeping a good eye on the temps so as to avoid getting too hot.

Right now, with this cold snap I think adding a bit more will help get the oil temp up a bit as well as improve the coolant temp. As temps improve to more 'normal' for SC I'll remove the extra tape.

I think, for me, this may just be the best adjustment, and I'll forgo adding tape to the coolant radiator.

You're right…cold gets old, quickly!

Bill H,

Thanks for those links! Very informative!
 
john just got my -12 and trying to dial in also. flying in north GA. 28 degree oat with one strip of tape on the oil cooler the oil temps stay between 190 and 210, the cabin heat was non existant, landed and fabbed up the 5.5 x 7 aluminum plate slid in between cowl seal and radiator and cabin heat is very good, also cht temps are good.
 
To clarify - -

I have a REIFF engine pre-heat. I also installed an oil thermostat. I also designed what I call a "Heater Damper Door". I leave the 150 watt engine pre-heat on all the time in the winter. I also cover the engine compartment with a packing blanket and clip it together in front. When I get to the airport, my entire engine is over 90 degrees. The oil therm warms the oil to 122 degrees BEFORE I can get to the end of the runway. NO WARMUP TIME LOST. The heater Damper Door keeps it very comfortable in any weather. Takes all these mods and a very good cabin seal system to make this an all year around good plane for cold climates.
 
Went flying today and it was 32F at the airport.

I had installed metal tape 3" wide over top part of oil cooler. I was getting oil temps in the 208-214F range proportional to OAT. CHTs were usually 147-148F at top of lower caution range (below green normal range). Got nice heat on ground but in the air the airflow cooled things down.

Today I added another half width of tape to the oil cooler.
At 5450 rpm got oil temps between 222F and 225F. CHTs were 154F in lower green so heat was fine. At 5350 rpm I got 217F-220F on oil temps and 150-151F on CHTs so still got some heat.

After landing I trimmed the extra tape by ?" as the oil temps were close to the top of the oil temp green and I'll see how that does next flight.

It seems that without a baffle on the coolant radiator and increasing the tape on the oil cooler a bit I can raise the oil temps and raise the CHTs a bit along with that, enough to provide enough heat in the air.

Hopefully that'll be enough for this part of SC this winter!
 
Warming the RV-12 cabin

Definitely have seen the rapid drop in oil and coolant temperatures when throttling back and descending from altitude in winter. Coolant temp drops into the yellow zone and the oil gets close too. You really need to take more time on decent and fly with more power to avoid these temp swings in my experience.

I took John Peck's approach and during my annual I created an aluminum cover for the top half of the coolant radiator. But I decided to use velcro strips on the sides to hold it in place on the lower cowl (thinking that if it was too effective, I could easily reach inside and remove it without removing the lower cowl which is a PITA on a cold hanger floor!)

However, in cold weather like today (low 20s F on the ground...much cooler in flight) it's barely enough. So, I've reached inside the cowl and added some additional aluminum tape on the lower half of the rad, similar to what I use on the oil cooler. Better. Not toasty by any means, but was able to fly for a couple of hours earlier today. Still need to be running at full throttle - much less and the air temp is not comfortable. Based on what I've read from our fellow RV-12 comrades in southern states, I was originally more concerned about cooling the Rotax in summer - had not done the oil cooler mod that many have recommended. Ironically, its actually warming that little engine in winter that has been more of a challenge as engine cooling in my summer flying has not been an issue.
 
I will echo John Bender's comments. Want heat in the RV-12 in the dead of the winter? The "Bender" baffle is the only way to go. A thin plate in front of the water radiator will work but this mod gives one much more control. You can then get the CHT temperatures up to 205 to 210 degF which will give you a good amount of heat. In the winter, I will set the yellow-line on the Dynon CHT temperatures to 210 degF. Not very hard whatsoever to fabricate and install. Here is how I installed the relatively simple modification, with a bit of help from John........

Click on the link for a series of photos on the baffle, oil thermostat and the Reiff preheater installation.

Link to Some Photos

Heater Damper Installation Details

All parts for the heater door are locally available with the exception of the control cable which was purchased from Van's, the RV-12 heat control cable.

The photos are pretty much self explanatory. I used 0.090” aluminum plate for the damper (0.080” would probably be OK), some ¼” aluminum rod and fender washers to act as bearings. The cable is attached to the lever arm using a throttle stop screw (your hardware store that repairs lawn mowers will have a couple of styles). Use some cardboard and carefully cut a template that conforms to the fiberglass duct opening at the damper location. Transfer to the aluminum plate, but, cut it a good 1/8” to 3/16" larger on the two sides. You want no more than about 1/16” clearance between the damper and the fiberglass duct when the damper is fully closed. It then becomes a matter of a lot of trial fitting, trimming a bit, checking the fit and repeating. Once your damper is close, but still oversized a bit, drill the pivot holes, attach the upper and lower rods and trial fit and trim for a good fit. Ideally try to offset the rod attached to the top and bottom of the damper, about an 1/8” from the damper top centerline and the damper bottom centerline so the airflow thru the duct will just tend to push the damper open if the cable should come loose. The rivet holes in the fender washers have to be positioned so they do not interfere with damper movement. I added a couple of stops from some scrap angle.

John can and most likely will add his suggestions!!
 
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This boils down to what degree of control you want to achieve. Simple fixed partial cover of the radiator, or more sophisticated cockpit adjustable variable control? Your choice. That's the beauty of experimental aircraft.

There is an important question I haven't seen addressed here. That is, how much latitude does an SLSA owner have in placing temporary or semi-permanent devices on the airplane? Maybe one of you legal-beagles can address that one.
 
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