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Cabin heat pressure differential

Kaldragon

Member
So after being unhappy with the amount of heat I was getting out of my cabin heater last winter I removed the original air distribution...well, whatever the builder/one of the last owners was trying to so. I strapped a scat tube onto the outlet and routed it straight at my rudder pedals. This helped a LOT, but I noticed something strange...

I get next to no flow at all when the cabin heat is pulled to full, but dramatically more (probably 4x the flow or so) at partial settings, probably maxing out at about half the full heat.

Anyone else have this issue? To me this makes me think that for some reason, even with a dedicated baffling inlet scat tubed to the heat muff that the cooling air below/aft of the baffling is somehow higher pressure than what's on top of the cylinders. I've been delaying simply taking off the scat tube from the heater to the firewall penetration to see if I get better airflow, but now that the aircraft is down for maintenance it has me wondering if I'd get better heat that way...
 
With the lower cowling off, can you look at the cabin heat valve and check what it’s doing? I don’t think the design allows for going over center and closing again, but that’s where I would start.
 
P thread drift,

I have wondered why the heat or fresh air comes into an RV cabin. Sure, there are small leaks at numerous places like flaps, rudder cables and empennage. But can these account for the significant flow from the firewall heater valve or an RV10 side vent ?

Dan H suggested years ago that a good negative pressure outlet would need to be experimentally sourced with a sensor tube and manometer. I assume something like a 2” hole would be required. Does anyone know where to put it ?

Also, would a NACA vent backwards on the fuse bottom or side enhance heat/cool airflow ?
 
Cockpit outlet

I installed a vent on the baggage compartment wall assuming the flow across the empennage was decent and all the holes for control surfaces were already there. Probably means I'll have to vacuum (clean) there sooner or later for the inevitable dust.

Works great for me. I plug it up when I run the AC.
 
Update: I went and removed the SCAT tubing from the muff to the cabin heat box and took it for a flight... didn't put out much heat but there was MUCH more pressure. I think I'll try the opposite the next flight, reinstall the connection from the muff to the cabin, and uninstall the tube from the baffling to the muff plus tape over the hole in the baffling. It seems strange that there's more pressure behind the baffling than forward of it though...
 
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