Baffling for Bede BD-4C with Lycoming IO-360

I have spent all of my time in September working on the baffling for the air cooled Lycoming IO-360 engine in my Bede BD-4C airplane. Well, to be more precise, I spent most of September’s evenings and Sunday’s on the baffling. I do have a job and a wife, both of which require significantly larger time investments than my airplane. 🙂

Most airplane engines are air cooled, including the Lycoming engine that I am using. Air enters through holes in the front of the cowling. Bafflling forces the air to follow a single path to the top of the engine and then downward past the cooling fins on the cylinders. The hot air exits through openings at the bottom of the cowling.

For context, here is a photo of the cowling on my Bede BD-4C airplane. Cooling air enters the large hole next to the propeller and another similar hole on the other side. The small hole under the propeller is for air going into the engine for combustion.

I bought my engine used and it came with some of the baffling already fabricated and bolted to the engine. For better or worse, I decided to keep these parts and add onto them. The problem was that the parts had some large gaps in the back corners and did not come together neatly in the front. Let me walk you through this with photos.

This is what I started with at the right, front corner of the engine. You can see that the opening in the baffling is a large rectangle and that the bottom corners are missing. Clearly mating this to the round hole in the cowling was going to be a big job. The other side was better; at least the bottom corners were not missing.

The back corners has problems, too.

I started at the back of the engine. These gaps were easy to fill because the shapes that I needed to create were simple flat pieces with single bends. This is what I ended up with.

I attacked the right, front corner next. It was going to be the hardest and I wanted to get it out of the way. I started by making an adapter from the large rectangular opening that I had to the circular opening in the cowling.

Here is a photo from the back. If you look down into the bottom, you can see that there are still large gaps that need to be filled and that none of the shapes needed are simple, flat pieces of metal with a single bend.

I got busy and made lots of clever parts and ended up with this.

In that last photo, you can see that I have almost all of the gaps filled in… just one more piece to make. Boy oh boy was I proud of myself… until I put the cowling onto the airplane and discovered that the lower right corner of my clever work hit the cowling! I had to cut away some of the metal but at least the hole is a lot smaller now. I will cover this with flexible, silicone baffling material instead of aluminum. My thanks to Candy for figuring out the shape needed and cutting it out.

Here is a photo looking straight down. There are nine pieces of metal in this thing, way more than I think there should be but I am going to let it be for now. One of these days, I will pull the propeller off the front of the plane (to make access easier) and replace all of the baffling with a simpler plenum system.

With the bottom of the cowling installed on the plane, you can see how all of this works together. The gap between the aluminum baffling and the carbon fiber cowling will get covered with more of the flexible silicone material.

Now I am starting on the left front corner, which will be much less work. The cylinders on the engine are staggered and the ones on the left side are farther back, giving me more room to work with.

Once this corner is done, I will make a top, creating a large plenum. The top needs only a single gentle bend in the middle and flanges on both sides so it will be pretty easy to make.