I've a 72" span Dymond Tiger Moth that is coming along nicely, but I’m starting to have second thoughts about the cowling. Specifically, I wonder if there will be enough cooling. I took some photos and would appreciate informed opinions.

The YS91AC mounts inverted on a plywood bearer, and there are ¼” balsa “cheek cowls” that support the ply. So the air flow is pretty much into the left side (1” x 2” cutout), and out around the exhaust pipe. A bit of air can flow out the bottom of the cowl, where the gap is about ½” x 4” wide. The air is flowing around the exhaust side of the engine, but doesn’t look like it will get to the head or intake side.

The directions mention a preference for an identical 1” x 2” cutout on the right side of the cowling. Not scale, but sure beats an overheated engine. I could just try the cowling as-is, and see if there is a problem. But if it obviously needs more airflow, it would be easier to make the cutouts now.

Penny for your thoughts,

You may have enough cooling just like it is. You will probably fly the airplane at partial throttle anyway, so the engine won't be working as hard. Try it before cutting the cowl more.

Good Flying!

Thanks, Dave, I appreciate your consideration!

Dave,

I've had the Tiger Moth up for about ten flights now, and it's a real sweet plane. Last couple of flights I noticed that if I get aggressive and spend most of a 10 minute session at high throttle, the engine "sags" - drops down to idle, and only returns to a higher throttle setting after 5-10 seconds. This happens after about 6-8 minutes of flying. Could this be symptomatic of overheating?

Thanks,

That would be my guess. Why not put another opening on the other side of the cowl to match the one you already have.

By the way, what fuel, prop and plug?

I run Wildcat YS 20/20, an OS F plug and a 16x6 prop - gives ~9,200 rpm at full throttle, static.

I did put an aluminum baffle in the intake, to direct half the airflow to the intake side of the engine. I also think it needs more open area to exhaust air out of the cowl. I'll open up the bottom of the cowl behind the intake side and see if that helps. Would like to keep it somewhat stand-off scale, but if that's not enough cooling, I'll put in the mirror image intake opening.

Thanks for the advice, Dave.

Back off to a 16x4 or 15x6 prop and lighten the load on the engine. Might be enough to keep you from cutting more holes.

Ok!

Let me know.