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Dave's RV-7A Builder's Log
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Date: 8-9-2015
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Number of Hours: 4.00
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Manual Reference:
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Brief Description: Cabin heat
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To the hangar today with the hopes of finishing up the scat tube routing for the cabin heat system. I had purchased an Odyssey battery this week, so I took that along to see how it would fit, and if inserting and removing would be difficult with the engine mount. Turns out the battery just slides right in and there is no interference anywhere. Every now and then I get lucky. I also added a boot at the master relay terminal to protect against shorts.
As mentioned previously, the challenge with the cabin heat scat tubes is twofold. First, the tubes must curve out, and then up and around to clear the #3 exhaust pipe, but they can’t go too far outboard or they come in contact with the cowling. The firewall forward kit ships with two stainless steel straps that are designed to support the tubes in a couple of different places, so back to adventures with Adel clamps to get those installed. I ended up deviating from the plans (somewhat significantly it turns out) in order to make the run to and from the heat muff. The pictures show the detail, and it looks like the two tubes are touching but there is no contact anywhere along the run. The minimum distance from the lower tube to the exhaust pipe is about ¾”, so I’ll probably put a heat shield there just to be safe. I will also need to put some RTV on the aft engine mount where the supply tube crosses, as it is just barely touching and eventually vibration will cause wear.
The deviation from the plans comes from the fact that the firewall forward kit ships with a 2” hole in the right aft baffle that is designed to accept a flange that is used (I thought) for the cabin heat. It turns out, in another “but first” moment, that the actual design requires the builder to cut a hole in the forward inlet ramp for this purpose, and then to cover the hole in the baffle. Why? I decided that the critical run for the cabin heat is the same no matter which inlet is used, so I just left it the way I had it when I installed the baffles. We’ll see how it all works out.
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Intake tube
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Finished installation...looks pretty good, hope it heats
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