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Looking for expert input on cowl pressures

L

lr172

Well Known Member
The 10 has two heat muffs and the plans call for taking the input air from the baffle ramp at the cowl inlet. I assumed it didn't matter and took the inputs off the rear baffle wall behind #5 cyl as there was a lot more room to work with and seemed to work fine on the 6. I have noticed that I have decent amount of heat. However, most 10 owners say they have WAY more heat than they could ever use and that doesn't seem to be the case for me, as the diverters are open close to 3/4 or more on cold days. I am now wondering if the velocity or volume of air flowing through my system is less than what others are getting due to the input air source location.

I will also say that I took extensive measures to seal up the cabin and have no noticeable leakage anywhere. I suppose this tight cabin could also be a factor in the reduced heat flow.

Looking for some input from the guys that have done a lot of pressure testing inside the cowl area.

Thanks in advance.

Larry
 
My Comanche has an exit air vent on the belly facing aft just below the right rear pax seat. From the reverse scoop there is an aluminum duct that transitions to a scat duct on the aft bulkhead, where the interior outflow vent is. There is no provision for throttling the duct. The Comanche has one heat muff for cabin heat and almost equal to the RV-10 in size, fed to the cabin via 2" scat. The heat is excellent, even at idle.

The Beech Musketeer I routinely fly has a simple outflow vent on the top of the rear cabin that is controllable. It also has very good heat.
 
I built an RV10 with a Showplanes cowl, induction system and Vetterman exhaust system. As a result I took air off the aft baffle for both heaters because the induction system is directly under the cooling air intakes. I get lots of HEAT. I used the aftermarket stainless heater valves. I have a very tight cabin also, with no detectable leaks in the doors. I can't imagine why you would be getting insufficient heat.
 
As Dan H and Rocket Bob are hinting at, you do have to provide someplace for the air to get out. Not much will come in if the air that is already in can't get out.
 
lr172 said:
I will also say that I took extensive measures to seal up the cabin and have no noticeable leakage anywhere. I suppose this tight cabin could also be a factor in the reduced heat flow.


Thanks in advance.

Larry
Click to expand...

Depending on what areas you sealed, that is a very good possibility.

Did you seal the corrugations in the baggage bulkhead?
They are a very effective outflow path.
 
Also

When discussing the heat topic, the exhaust manufacturer needs to be referenced. I think you will find that those with the Vetterman exhaust tend to have the excess heat issue far more than those with the Custom Aircraft exhaust. It is important to know for accurate comparison.
 
rvbuilder2002 said:
Depending on what areas you sealed, that is a very good possibility.

Did you seal the corrugations in the baggage bulkhead?
They are a very effective outflow path.
Click to expand...

No. Just sealed the firewall very well and sealed up all of the openings in the area where the spars enter the fuse and even the holes in the skin by the gear mounts. Door seals have NO leakage and hinge area is fully sealed. I must be getting pretty decent flow out the back, as the fresh air vents are pretty effective and blow a pretty good stream of air, though not quite as strong as what I experience on the 6. I suspect it is not as effective as the exit fairings that Bob mentions.
 
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rocketman1988 said:
When discussing the heat topic, the exhaust manufacturer needs to be referenced. I think you will find that those with the Vetterman exhaust tend to have the excess heat issue far more than those with the Custom Aircraft exhaust. It is important to know for accurate comparison.
Click to expand...

These are vetterman, though clint told me they changed the design several years ago as many 10 owners complained about too much heat from the original design. I believe the original design had mini walls to make chambers, like a muffler. Mine is the newer open style.

Larry
 
DanH said:
Why not simply measure pressures and temperatures?
Click to expand...

Good idea, but the only manometer that I have is a water tube attached to a 1x4. I have been reading the doc you posted. Great info, but will take a while to get through it.
 
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