Cabin Heat Plumbing help needed

[Utah-Jay]

I am in the process of designing my cabin heat air flow and need some ideas. My current plan is to have a single flange in the nose bowl to collect air and then a “Y” connector to divert to the two separate exhaust muffler heat sources. For the record I have two of the flanges as I had planned to have one for each side, and this is still doable if it uncomplicated the process

Flange

https://www.aircraftspruce.com/catalog/appages/aeroncaflange.php?clickkey=13173

Y-Connector

https://www.aircraftspruce.com/catalog/pnpages/08-04130.php

My problem is once all is attached from the nose bowl to the two respective exhaust/muffler locations how do I detach things to remove my lower cowl for oil changes and engine inspections? I am sure you guys have solved this problem previously, but I can’t conjure up a good plan so far.

I am visual, so photos help

[Nev]

I ran a scat tube from the rear baffle to provide cooling air to my cabin heater. It does rob pressure from the upper high pressure area above the cylinders, but also allows the cowling to be removed easily.

[Bcone1381]

I have 2018 photos from Bob's Patrol. He ran a separate intake to each exhaust heat shroud. No "Y" was used. The intakes were at the front of the nose bowl cooling air intake ahead of the #1 cylinder. Let me know if you want photos.

[gregc]

Just an idea but I was watching the latest DarkAero video and they are getting cabin heat by diverting air from the oil cooler. Less weight and makes use of a system that we need anyway.

[Archer39J]

Been a bit since I've thought about it, but I'm going to try to take my cabin air from the front baffles. As a precaution I don't want air that's run over the engine as my source for cabin heat if I can avoid it.

[Utah-Jay]

Been a bit since I've thought about it, but I'm going to try to take my cabin air from the front baffles. As a precaution I don't want air that's run over the engine as my source for cabin heat if I can avoid it.

OK, that makes me consider running scat from under the front baffle to the cabin heat muff, which would preclude needing to remove during cowl removal. But I hate robbing my cooling airflow, anyone have an opinion on this?

I have 2018 photos from Bob's Patrol. He ran a separate intake to each exhaust heat shroud. No "Y" was used. The intakes were at the front of the nose bowl cooling air intake ahead of the #1 cylinder. Let me know if you want photos.

I would like photos, so yes please, Thanks

[TimTall]

I didn't have room to run a scat tube from my baffles. I'm running a continental so the air intake is at the rear of the left baffle and the starter is behind the right rear baffle. Besides the space consideration, my air intake is already pulling a ton of cooling air into the engine from the high pressure side of the baffles so i didn't want steal any more for a heater I'm only going to use in the winter.

I put a small naca duct, from Van's (actually a fibreglass copy because they were on backorder) on the bottom of the cowl about 12" aft of the nose bowl/cowl skin line. About 6" off the center line to the right side. I'm sure it would work just as well if it was further off center to accommodate a typical lycoming air intake. I then ran the scat tube back to the exhaust shroud. It's easy enough to reach in through the cowl door to undo the clamp holding the tube to the shroud to remove the lower cowl.

I get loads of air flow through my heater. Way more than i've felt in any other typical heat muff style heater.

[Battson]

OK, here's some general musings which may or may not help

SCAT tubes are easily removed from flanges etc. provided you can get two hands on them. It's possible with just one hand, but it can be painful. So that's one consideration, access.

You want decent air pressure in the system, as there's a lot of tubing involved, and on cold mornings you want the cabin to get some heat while ground running. Mine takes air off the baffle, and the hot air flow is terrible unless the aircraft is actually flying. More intakes will mean more flow rate (this also means more drag). There's another consideration, air flow.

A competing requirement is hot air temperature. If you run one intake onto two heat exchangers in series, you get a lot hotter air - but only a limited flow of air. If you go for two heat exchangers in parallel, then you get a higher flow but the air isn't as hot... My personal choice was using just one heat exchanger, which is the lighter solution, but the cabin isn't exactly a hotbox on those coldest days. Of course the lightest of all is forgetting about the whole system. So there's another choice to make.

The oil cooler idea mentioned above is interesting! You want to be sure the oil cooler works effectively, that's more important than cabin heat.
Thinking about the back-pressure requirement above, for good air flow, the wonder how compatible the two requirements are.... Probably a fun thing to experiment with, provided you have lots of time to spare once the plane is actually running.

The main risk from cabin heat is the exhaust heat exchanger(s), worth bearing in mind that failed cabin heat systems have caused numerous fatalities. I don't see much risk with pre-heating the air using the engine or oil cooler, provided you can meet the above flow considerations - but I can't think of an easy way to do that.... Importantly, the system should be easy to inspect and have a reliably way of shutting it off (stopping it from entering the cabin).Yet another choice for you.

Perhaps a final consideration is engine cooling. I have seen a few installations where there's so much SCAT duct zig-zagging around the tunnel outlet, it's a wonder the engine keeps cool at all. I am talking about all kinds of aircraft now. In some cases, those aircraft did experience occasional overheating issues. Shorter runs of SCAT duct mean less drag and less heat loss, not to mention keeping the cowling inner-space clear for engine cooling airflow.

[Bcone1381]

Here are some photos of Bob's installation that I offered to share with you. I took these because it looks like a simple and resilient setup, possibly an industry best practice for an exhaust-type cabin heat system. I think the photos validate, give example, and confirm a lot of what Battson says in the last paragraph of the previous post. Now, I should mention that I don't have personal experience with this system.

I also have some knowledge of an oil Cooler Cabin Heat system I know of. I'll discuss that later in this post.

Lets look at Bob's setup first. Bob heated air intake is tapped in to the baffling in front of Cylinder #1 of his O-360.
Screen Shot 2023-07-05 at 9.48.48 AM.pngScreen Shot 2023-07-05 at 9.58.01 AM.png
He routed air from the intake using Scat Tube to the L and the R heat shroud. The exhaust system in 2018 was four straight pipes with no exhaust. Each shroud encases two pipes.
Screen Shot 2023-07-05 at 9.49.05 AM.pngScreen Shot 2023-07-05 at 9.49.56 AM.png
Heated air exits the pipes and travels to the heat distribution box. From the box the heat can go only two places....the cabin or the carb heat box.
Screen Shot 2023-07-05 at 9.47.30 AM.png
As I recall my conversation with Bob, I remember that he did not build an exit out of the distribution box. Many will judge that design harshly. I do not. I trust Bob did the design and testing and knows temperature capabilities of the box, firewall, and what is safe and understands requirements of an air exit to keep the system from overheating and causing risk, or damage. This is the first time I was exposed to a box design like this. All other designs I am familiar with let air flow exit out of the box to keep system temperatures down. Bob saw this design feature as an un-necessary drag penalty.

Oil Cooler Heat Source. A friend of mine has been flying a F1 Rocket in Michigan for about 15 years. (Michigan is a state on the northern boarder of the USA. We like to ice fish and ski in the winter.) The F1 Rocket is similar to an RV4 and has a powerful 260 HP IO-540 engine. What's interesting is that he uses the oil cooler to heat his cabin entirely. The oil cooler is mounted to the firewall, and there's a valve that allows the heated air from the cooler to enter the cabin when heat is needed.

I find this system quite intriguing, but I won't be using it on my Patrol aircraft. The reason is that I have a smaller oil cooler and a smaller engine, which affects the amount of heat output available for my cabin. Maybe that will be a future experiment.

[Utah-Jay]

Thanks Brooks

You have given me plenty to consider