Scale BUSA Super Cub

Nice work getting that figured out. I just went through the thread and couldn't find a pic with the cowl installed over the engine or the intake ducts to the cylinders. I get that the cowl is pressurized, but I'm having a hard time visualizing the air movement inside the cowl from the intake to the cylinders without a tunnel leading up to the front of the cylinders or a plenum sealing the cowl off to force the air mostly through the baffles. Simply pressurizing the cowl won't help a baffled engine. Isn't there holes in the firewall for the intake pipes/carb/exhaust? I couldn't remember how that all ended up. Once again, I'm just speculating because I don't really know the setup that well. Just some night shift brain waves here lol

The firewall is tightly fit to inside of the cowl for the most part, it acts as the barrier between the high and low pressure zones. The air enters the high pressure side cowl through the openings, around the air cleaner opening and the oil cooler opening (I need to make an air cleaner dome yet. The back side of the cowl or low pressure is exposed to a scale opening on the bottom of the cowl with a small scale lip and to the sides of the where the cowl sticks out possibly 3/4" on each side. When the the original two stroke twin was installed you could seethe spark plugs from behind the cowl. Below are a few photos of the two stroke install. I would guess ate area of each side is equal to one of the air inlet openings.


The engine is tightly baffled to the firewall with opening behind each cylinder. In the photo below air enters the cylinders on the exhaust side of the engine and flows through the engine cooling fins exiting into low pressure side though s hole the approximate size of the baffles. The carburetor is located in the low pressure zone and exposed to the warm cooling air, the engines make more than enough power for this scale application.

Tony, I have always read that the exit area should be 3-4X the inlet area to allow for the expanded/heated air to exit.

Just finished reviewing the telemetry logs from yesterday and it appears the right cylinder is waking up. The temperature difference was up to 100 on the early flights and was below 70 on the final flight. The right side is getting hotter and the it seems the left cooled slightly. The right side is also responding to changes in power level. See the attached pdf of flights 1 and 5. The auto scaling has both scaled different but you can see the the right side temps are increasing.

frydaddy08 said:

Tony, I have always read that the exit area should be 3-4X the inlet area to allow for the expanded/heated air to exit.

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Yes I read that as well. That was the rule for ever before we learned how to baffle, my Champ has more intake area than exhaust area but it works fine. It's more about making the cool air flow over the cylinders than around them. Could you image the hole required for 3 times the entrance area on the Champ cowl?

TonyHallo said:

Great day here in Indiana PA. Nobody is here, five flights so far. Left cylinder 280, right cylinder 220, still got some work to do. During landing the left side drops 245f

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Flying by yourself?

TonyHallo said:

Yes I read that as well. That was the rule for ever before we learned how to baffle, my Champ has more intake area than exhaust area but it works fine. It's more about making the cool air flow over the cylinders than around them. Could you image the hole required for 3 times the entrance area on the Champ cowl?

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I think the outboard side of the intakes needs a duct/baffle headed to the cylinder itself personally. A little inverted craft foam scoop if I may

dhal22 said:

Flying by yourself?

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Yes for most of the day, others began to arrive around 1600 because we had our monthly meeting at 1800. I flew four flights alone.