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Cabin Heat Air Supply

majuro15

Well Known Member
Due to my air conditioning, I cannot have the stock cabin heat air supply on the left inlet area. I currently have the supply on the right side rear baffle split to the front and rear heat ducts, but it is not enough airflow to adequately heat the cabin.

I'm considering adding a NACA duct on the cowl and splitting the air to each heat muff then the heat ducts.

My concern is when not using the heat, the air coming in on the low pressure side of the baffles will have to exit the cowl just as the engine cooling airflow. Will this influx of air decrease the effectiveness of engine cooling air? Essentially, will it pressurize the low side of the cowl (enough) to cause issues?

I'd like a few opinions before I cut a big hole in my cowling. Thoughts?

Thanks!
 
Can you run a 3" then split it into the 2 diverters? I would try something like that or find another location to pull from before I cut a NACA into the cowl with possible negative affects on something else.
 
Digital Manometer

Hi Tim,

The only way you will know for sure is with a dual digital manometer to measure the pressure differential between the top and bottom of the cowl .
(lots of cheap sensors that plug into a standard multi-meter are available on-line)

RV-10's have excessive cooling in standard configuration with lots of opportunity to reduce cooling drag left on the table I can only imagine that where you live you would not need the cooling reserve like we do in Australia.
(The coldest I have flown in is -10 Celsius ) so your Naca duct would have an effect, but maybe only minimal.

The only way you will know is with data.
 
Just a thought but do you have enough room on the air outlet of your oil cooler to install a duct to pull air from? No new holes in the baffle required for this scenario and since its air already in the lower cowl you don't change the cooling dynamics.
 
Tim,
I have A/C from Bill Genevero @ Flightline and didn't have to modify the heat air supply, I just wrapped the supply hose in ceramic blanket and SS foil to keep heat off of it as it runs close to the exhaust. I have 1,200 hrs and still the original hose and my AC still works great btw. Not sure which AC vendor you are using but just sharing my experience.
 
I just don’t have any room between the compressor and the first cylinder for the scat flange.

I’m considering adding a second flange near the other one above #6. Another builder has and likes the results. Avoids putting a naca duct in.
 
I put both inlet flanges next to one another on the rear baffling behind #5. Scat run was about the same as for the plans location. Works fine. I definately wouldn't put a naca duct in. If that spot is good for one heat muff, why not the other?

Larry
 
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Copy, I think I'll do that. Les did that too and seems to be better than a naca duct.

Thanks!
 
Question for fluid flow experts

Due to my air conditioning, I cannot have the stock cabin heat air supply on the left inlet area. I currently have the supply on the right side rear baffle split to the front and rear heat ducts, but it is not enough airflow to adequately heat the cabin.

I'm considering adding a NACA duct on the cowl and splitting the air to each heat muff then the heat ducts.

My concern is when not using the heat, the air coming in on the low pressure side of the baffles will have to exit the cowl just as the engine cooling airflow. Will this influx of air decrease the effectiveness of engine cooling air? Essentially, will it pressurize the low side of the cowl (enough) to cause issues?

I'd like a few opinions before I cut a big hole in my cowling. Thoughts?

Thanks!

I have a similar situation. Showplanes cowl, Airflow Systems A/C, higher horsepower IO-540 with oil squirters and 5" RV-14 duct to oversize oil cooler. NACA ducts in each side of the cowl feeding their respective heat muff would be a cleaner installation for me, as well as reduce the cooling air drawn from the normal location either at the cowl inlet ramp or the rear of the right side baffle.

Seems to me that if the heat is not being used, the airflow through the NACA ducts would be choked off and simply flow past the duct. If this is true, the NACA ducts would have minimal to no effect on the lower cowl pressures. Too many years have passed since I took those aero courses...

Bueller? Steve Smith? Anyone?
 
If built per plans, the stock RV-10 heat system produces far more heat than needed.

On my first RV-10 I put a 3/4” restrictor on each 2” baffle SCAT hose flange. Even that was more heat than I needed - I typically ended up with the rear heat cracked open and the front heat off.

My point - if you can get one 2” SCAT flange on the baffle someplace that will be more than enough air to feed both heat muffs (assuming you are using the stock exhaust that has two heat muffs). If that is still too hard, can you get a single 2” flange on the engine intake ramp?

The last option is to find a place to put two 1” flanges that feed each heat muff via a reducer on the heat box 2” flange?

You are right to be concerned about anything that can add pressure, no matter how minor, to the engine exit air area.

I suggest you exhaust these options before putting a NACA vent on the side of the cowl…

Side note - when mounting the cabin heat boxes I recommend putting some insulation between the boxes and the firewall, and having something drape over the front of the boxes (from the top) to direct the hot, dumped hot air away from blasting into the back of the engine (e.g the mechanical fuel pump). This is of special interest on hot days where you are dumping all the heated air. I used this stuff (in addition to the Fiberfrax and SS firewall clad):
https://www.aircraftspruce.com/catalog/appages/koolmat.php?clickkey=7985

Carl
 
Seems to me that if the heat is not being used, the airflow through the NACA ducts would be choked off and simply flow past the duct. If this is true, the NACA ducts would have minimal to no effect on the lower cowl pressures. Too many years have passed since I took those aero courses...
When the heat is not being used, the hot air from the heat flapper on the FWF dumps into the low pressure side of the engine area between the FWF and the engine. So you will always have flow through the NACA ducts you propose. In addition, the heat muff on the exhaust system requires some airflow all the time otherwise its lifespan will be shortened.
 
Thanks for the comments.

Completely ignored the requirement for airflow over the heat muff and the leakage that occurs at the firewall flapper valve when closed.

Given the restrictions I have for available space for an inlet flanged duct on the left inlet ramp, coupled with the more than adequate available heat - a single 2" SCAT hose from the right rear baffle feeding both firewall heater valves through a "Y" is probably a reasonable compromise. I believe others have done this or something similar.

I'll simply remove the muff on the left side exhaust - there are no mufflers on the Custom Aircraft exhaust.
 
I'll simply remove the muff on the left side exhaust - there are no mufflers on the Custom Aircraft exhaust.
When I spoke with Vetterman about removing a muff on the exhaust, they had no problem with it; however, they cautioned that the exhaust would now be exposed to the cowl. They recommended installing a heat shield. Something like the heat shield from Anti Splat https://antisplataero.com/products/heat-shield-system or a roll your own shield. I never did remove the muff so I do not know if it is necessary.
 
Could you Y off of the right side to feed both sides. I don’t think we have ever pulled the heat knob out more than 1/4 of the way. I also ran a 1 inch hose the the rear vents (vs the 2 inch). We have plenty of heat in the cabin.
 
Could you Y off of the right side to feed both sides. I don’t think we have ever pulled the heat knob out more than 1/4 of the way. I also ran a 1 inch hose the the rear vents (vs the 2 inch). We have plenty of heat in the cabin.

That’s what I am considering. Relatively easy to install the flanged duct on the aft right side baffle and Y near the firewall heater valves. We have seat heaters as well.
 
Adequate heat?

As a follow up to previous posts, I’m now not sure that a single heat muff will be adequate given my exhaust system.

I was looking at two of the RV-10’s under construction at Synergy Air South today and noticed that the stock exhaust has heat muffs aft of the collector - so each heat muff is being heated by all three cylinders on each side. Now I understand why many 10 owners talk about the excess amount of heat available.

My Custom Aircraft exhaust (selected for suitability with the Showplanes cowl, Barrett sump and Airflow Systems A/C) uses a single exhaust riser on each bank for the heat muff.

Some of the previous posts indicating more than adequate heat with a single heat muff now have me rethinking doing the same - since it’s likely these folks have the stock exhaust. I was going to Y off the right side heat muff only as the left side installation is considerably more complicated (due to the a/c compressor).

So is there anyone out there with a Custom Aircraft exhaust or similar (heat muff on a single riser) that can give me a pirep on the amount of heat available from this type of system? Thanks in advance.
 
I have the custom aircraft exhaust and after flying in the high altitudes and the north east in the early spring and late fall, determined that one heat muff is definitely not enough. I would highly recommend using both heat muffs.
 
I have the custom aircraft exhaust and after flying in the high altitudes and the north east in the early spring and late fall, determined that one heat muff is definitely not enough. I would highly recommend using both heat muffs.

Much appreciated Tim! We will hook up both sides.
 
Yeah thanks for the info as well.. I face the same situation.
Was pondering somehow coming off of the aft part of the left induction tube, but not sure it'll really get much air in that spot to be worthwhile attempting.. not to mention, I probably don't really have room to do that anyways.

So perhaps another 2" duct in the aft baffling on #5.
 
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