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Ryan Allen
PostPosted: Sun Sep 25, 2016 6:00 pm 
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My fresh air comes in at the front of the lower cowling, and is routed through my lower cowl area through scat tubing. When I open my fresh air vent on the firewall, the air incoming is hot. I have never bothered to fiddle with it because I have the opening cut in the rear of my canopy. Now I want to fiddle with it. I was thinking I would insulate the scat tubing to try and keep the air from getting hot before it got into the cockpit. Anyone have any ideas about the best way to either 1) insulate the scat tubing or 2) keep the fresh air cool using another method.


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Bill Williams
PostPosted: Sun Sep 25, 2016 6:50 pm 
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On my S18 I have inlets located just inboard of the wing gap with scat hose running from the inlet to a eyeball vent on the dash. There is enough fresh air that you cannot open a chart without it blowing it into the luggage compartment. At altitude we shut them off. I made the inlets from 1" PVC, split a piece of PVC tubing, heated it with a heat gun and let it form over the leading edge, glued the tube to the flange and riveted it to the wing. Placement of the inlet is just below the center of the airfoil to prevent water from filling it up when it rains, flying in rain has never been a problem


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Rich Brazell
PostPosted: Sun Sep 25, 2016 8:33 pm 
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Is your fresh air routed thru a heat/cool air box ? One with a butterfly valve so you can switch the air source from hot to cold or a mix ? ???

RB O0


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Ryan Allen
PostPosted: Sun Sep 25, 2016 9:11 pm 
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Nope, I have my cabin heat and fresh air vents coming through separate holes in the firewall. I am surprised, but the only thing I can figure is the lower cowl area is heating up the air around the scat tube, therefore heating up the air passing through the scat tube, and into the cockpit.

Typing this has given me another idea to try. I think the fresh air is getting slowed down inside the lower cowl, before it gets to the scat tube. I'm going to try and stick some scat into there and see what that does.

I realize my summary above about the path of the fresh air doesn't make sense, but I cant find a way to clearly type it. You can see the fresh air inlet inside my air scoop. It comes out of the air scoop, and up into the inside of the cowl, where it is a run of scat tube to the firewall.


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fytrplt
PostPosted: Sun Sep 25, 2016 9:21 pm 
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I once measured the air temp at the firewall. It was about 155 degrees.

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Rich Brazell
PostPosted: Sun Sep 25, 2016 9:47 pm 
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Still trying to picture this ? Is there an inlet attached to the lower cowl that allows air to enter or is the scat tube just sitting there at the front of the lower cowl trying to catch any "cool" air that happens to pass by ? ??? I have a NACA vent on the lower right rear of by S-18 cowl with scat tubing to the firewall (copied from a very early NL) . The attached pic shows the NAVA vent . :o

RB O0


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jrevens
PostPosted: Mon Sep 26, 2016 3:05 am 
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Ryan,
I wonder if using SCEET duct instead of SCAT might make a difference for you. Since the SCEET is lined, it should have less heat transfer from the warm engine compartment. It might be that the next size smaller duct could make a difference... possibly greater velocity through the duct and less heat transfer to the moving air also.

Rich - you sure do nice work!

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Ryan Allen
PostPosted: Mon Sep 26, 2016 7:26 am 
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Rich, yes, that is how mine is set up. Thank you for the pic. I will try sceet tube John. Good idea about the size too.


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