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-   -   Cabin ventilation question (https://vansairforce.net/community/showthread.php?t=163292)

amerkarim 08-21-2018 11:16 PM

Thanks Guys

Happy landings :)

Amer

MConner 08-22-2018 07:19 AM

I live in Florida but I think my RV-10 has enough cabin heat to melt the windows. I have flown it several times at 17,500? with OAT in single digits and just a crack of forward heat is more than enough. I have the aft heat scat re-routed to supply carb heat to my 0-540. Just opening the firewall valve on the aft heater and letting in the warm air from the cowling is enough heat in the back for me. I could split the single (forward heat scat in the tunnel) to feed both front and rear vents but don?t feel the need yet. I will not make any permanent changes to the design (removing one heat damper from the firewall) to retain resale value.

Bill Boyd 08-22-2018 07:42 AM

Quote:

Originally Posted by rleffler (Post 1281554)
Possible, but in my opinion not probable.

1. It?s awkward place to reach the front vents. How are you going to control the louvres.

2. You be exposing the tunnel to heat if you block the output ports, whereas the plans doesn?t let heat into the tunnel when closed. This is huge, since that heat is sitting right next to you fuel lines which increase the potential for vapor lock.

I personally think it?s going to be difficult to come up with a solution that beats the plans without a whole lot of engineering and work.

Sincere question, Bob... I don't understand how partially restricting the output vents for the front would expose the tunnel to more heat. Seems like less flow would decrease the heat that could be shed through the walls of the SCAT inside the tunnel. Heated air stagnated inside the tubing could only shed its BTU's once, rather than perpetually if continually replenished by more hot air coming through the tubing.

I agree my plan is not a perfect solution, and I have NO IDEA how well it will work in practice, but I went for it because it offered weight and tunnel heat reduction (one less valve on the FW heating the front of the tunnel). My research in the old "tunnel heat" threads pointed to the heat selector boxes as the likely source of high tunnel temps. I have taken the steps of reducing the heater boxes from two to one, and interposing a layer of Fibrefrax and stainless foil between the selector box and the firewall. If there is too much heat in front or back with this single-control system, I anticipate having PLENTY of cold outside air available to cool off anyone who gets disproportionately hot. May not be perfect, but hopefully workable. I imagine a sliding plate(s) over the front heat vent opening(s), operated by a Bowden cable(s), might be easy to rig up.

I'll be sure to let y'all know in a few years how it's working out.

Carl Froehlich 08-22-2018 09:05 AM

Bill,

Here is a post I did on RV-10 cabin heat. I offer it does what you want, but is much easier and avoids potentially problems.

One other suggestion, replace the 2” SCAT hose in the tunnel with 1.5” hose. Still plenty big enough for rear heat flow but is easier to route in the tunnel. A 2” to 1.5” reducer at both ends makes it work.

Carl

I used some of this between the cabin heat boxes and the firewall, then had it extend over the top of the boxes, then down the front of the boxes: http://www.aircraftspruce.com/catalo...clickkey=31128

The result is the hot cabin heat air, when the heat boxes are shut, bounces off the Koolmat then down toward the cowl exit, not right at the engine mounted fuel pump.

I also put a 3/4” restrictor on the back of the baffle 2” cabin heat SCAT hose flanges (a piece of aluminum with a 3/4” hole with some aluminum tape to hold it on the edge of the flange, the SCAT hose slides over it). This does two things:
- Less air to be heated so less hot air dumped into the bottom of the cowl. The RV-10 heat is way more than I’ll ever need. Even with these restrictors I have just the rear heat on part way on the coldest days.
- Less engine cooling air bypassing the engine, but still enough to keep the SCAT hose from getting too hot.

This setup has worked well - and I recommend it.


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