Cowl Cutting & Baffle Tensioners

The Sika has cured on the rear window.  There's a bit of a mess for me to clean up, but for the most part everything lined up pretty well and the window is setting where it needs to. I still need to clean up the rollbar area and put a final bead of Sika on it to make the transition to the rear window look a little nicer.  I'm waiting to do that until I see if I need Sika out for anything else though - easier to do it all at once vs a little here and there.

I'm still chipping away at the lower cowl fit.  What a pain!  The right vertical side is where I needed to extend the edge.  The flox worked really well here, other than being a nightmare to sand.  This picture is before I took it down to the final edge - a lot of work for 1/32-1/16" addition.  It looks nice and consistent now though.

I had originally built up the bottom (inside) of the cowl with flox to try to get it to lay on the fuselage better.  About 5 hours of sanding later, it turns out that didn't work.  Oh well, there's a lesson in everything I guess.  So I pretty much sanded the entire flox addition off the bottom and am now almost back to where it was from the factory.  That factory shape still doesn't work though, so I need another solution.  The only thing I can think of at this point is to cut a relief in each corner to give the bottom the flex it needs to bend up toward the fuselage edge.

The cut lets the bottom snug up against the bottom fuselage flange since it's no longer constrained by the strong cowl corner.  I will push the cowl into position, then fiberglass over the cut to hold the shape. Once it's dry I will pull it back off and put more fiberglass (probably flox again - yippy) on the outside to fill the crack and smooth the outside shape.

The corners and bottom of the cowl need to be pushed in while the epoxy cures.  A few well placed boards did the trick.  I made a small square of fiberglass (3 layers about 2x2) and put it in position on the inside over the crack.  I'll know tomorrow if it was a success or not.

I can't do much additional fitting while the lower cowl dries.  The top cowl gets inlet ramps to help smooth the air out as it enters.  They don't fit very well (shocking, I know).  I put them in position as best as I could guess and drilled some holes to hold them.  They will get epoxied on once the top and bottom cowl are in place and attached to each other.  The instructions warn that epoxying them with the top off will cause fitment problems because they will make the top cowl more rigid.  So everything has to be in position while the epoxy cures.

This is a little out of order, but the other day before the lower cowl went back on I worked on the baffle tensioners.  Each cylinder has a couple of baffle sections that wrap down and around the cylinder fins.  These have to get pulled snug to the cylinders and held there (otherwise the air pressure will just push them away from the cylinder and allow air to leak past without actually cooling the fins).  Each cylinder on a side has a baffle on the outside and inside fins, then they get tied to the matching baffle extension on the other cylinder.  There are a lot of ways to do that, but the most common are with stainless rod that you thread each end of and use nuts on, or safety wire.  Van's supplies stainless rod.  All of the experienced builders say it's a real pain though, and safety wire is the way to go, so that's what I went with.

Each baffle has a flange with a hole in it that the safety wire can go through.  My first approach was to cut a small piece of stainless rod for the wire to wrap around.

I put the L on the rod to insert it into a second hole.  I'm using large safety wire, and it doesn't hold the rod very tight.  By having the second hole in the flange, the rod can't go anywhere.  I slid some old brake line over the safety wire to protect it from rubbing against stuff.

The rods worked fine, but then I saw that an even easier method that most people use is to simply wrap the wire around a washer.  There is very little tension on these baffle pieces, so the wire really just holds them in position vs pulling them much.  The washer is plenty of surface area.  When I pull out the high temp RTV to seal all of the baffle gaps, I'll put a dab on each washer to keep them from vibrating.