New baffles for a Yankee (AA1)
My Yankee is undergoing its annual, so that seemed like a good time for a new set of owner-made baffles for the plane’s Lycoming O-235 engine.
The two side baffles were in absolutely hideous shape. Take a look:
The rubberized seals are in good shape, but the aluminum is in really, really bad shape. take a look at the other side.
Patch after patch can be seen. See that little chunk below the red silicon stuff? That is, essentially, held together just by that bead.
The factory stock baffling is made from 0.032″ 5052-H34 sheet aluminum. This alloy’s biggest advantage seems to be its low cost. A better (and slightly more expensive) grade for engine baffles is 6061-T6. (This is what AA1/5 guru Ken Blackman uses for building new baffles.)
I had enough 0.032″ 2024-T3 in stock, but that grade, while stronger, is more brittle. The 6061-T6 is recommended over 2024-T3 by folks like (the late) Tony Bengalis for building engine baffling. I ordered a sheet from onlinemetals.com, which happens to be about 20 minutes from my place of employment in Seattle. I picked up the order several hours later.
The first thing was to drill out the rivets for the rubberized seal, and then make patterns out of heavy card stock:
Next, I used rubber cement to paste the pattern on the sheet of aluminum, and did all the center-punching for the holes, and drilled the strain relief holes for some of the bends. Being a cheapskate, I optimized the layout to save aluminum and used a jig saw to separate the two sides:
Next, I cut the basic shape on a band saw (and a bit on the jig saw when I ran out of throat on the band saw). After carefully dressing the entire circumference of each part, I drilled and debured the holes.
Each piece had two 90 degree bends with a generous 1/4″ bend radius. I formed a die on a belt sander from 1/4″ bar stock. I have a lousy 48″ sheet metal brake that could have been pressed into service (and I could have used my monster brake), but it was easier to use clamps on the edge of the bench and a block of wood with a mallet.
Here are the final pieces:
The next task is to rivet the rubber seals back onto the baffles. Here they are all Clecoed up and ready for some pop rivets:
Total construction time: About 6 hours, including to time to make the (reusable) patterns. I have another hour to go for the riveting.
I learned this afternoon that one of my cylinders has low compression and needs to be pulled. Since the rear baffle will have to be removed to pull the cylinder, I may just build a new rear baffle. Stay tuned.
Update: For connecting the seal to the baffle, I used Cherry Rivets (MSP-42) with AN-960-6L washers on the rubber and AN-960-6 on the aluminum side. The final products:
