May 14, 2018 – I got hold of Van’s instructions for fitting the cowl without the prop in place. The instructions say to cut PVC spacers 2 1/8″ long for a constant-speed prop, then attach the spinner backplate using those spacers.
It turned out that I had jumped the gun modifying my backplate for the prop already, so I had to borrow one.
I ran 2″ tape around the firewall at the edge. This provides a known 2″ distance for cutting the aft edge of the cowl later on.
I placed the top cowl on the engine. I don’t have much extra material at the firewall to play with, but it’ll work out.
I taped some 1/4″ pieces of molding to the front lip of the cowl to act as spacers to give me a uniform distance from the prop backplate. I’ve also padded the top of the engine with a towel and some magazines to give me the correct height.
One nice thing about the airplane being on its gear is that now I can roll it outside on nice days to work on it.
I wanted to see how the lower cowl fits. so I cut out slots to clear the gear legs, then put it up into place.
I tried using a strap to hold it together, but the strap just slid forward because there’s really nothing for it to hold onto. I temp-drilled a couple of holes for some clecos to hold the cowls in place. It has taken a little while just playing with the cowls, and standing back and thinking about what’s going on, but I eventually developed a plan.
The worst fit on the cowl is the nesting area just outside the spinner in the inlets. I have to sand a little bit, then put everything back together. The fit is slowly improving.
I am using the Skybolt fasteners on my cowl instead of the stock hinges. I decided to start working on the flanges that are installed on the firewall before I worry too much about the final cowl fit.
The first step with these flanges is to get an idea of where the fasteners will be that are on the cowl split lines at the firewall, then locate flanges from there. I figured out a tentative cut line for the aft edge of the cowl, and the split line between the cowls, then marked a likely location for the fasteners on the left and right sides. These fasteners will be the intersecting fasteners between the firewall row and the cowl split rows going forward.
I marked where that flange would probably be located, then started placing flanges up around the top of the firewall. The Skybolt instructions suggest 3.5″ spacing between fasteners. I couldn’t get even spacing that way, but 3.25″ worked pretty well. The center flange might require some adjustment, but that measurement worked for me all the way around.
The flanges have joggles and they overlap, so once I finally drilled and clecoed them, I took out each one and trimmed the overlap, based on where a rivet would be located.
Still have a lot of work to do, and things might look a little rough in these pictures, but I feel better about this than when I started.