Working with the fiberglass cowl halves just takes time. There have been many cycles of positioning the cowling, marking, removing the cowling, trimming or drilling. Rinse and repeat, as the saying goes. Figuring out how to compensate for a poorly made cabin heat muffler shroud is burning extra hours. Epoxy filler takes a really long time to cure. Who knew?
The basic size and shape of composite cowling, as it came from the factory, has some challenges. I attribute the issues to factory processes. I believe parts were removed from their molds before the epoxy was sufficiently cured. This resulted in some distortion around the edges that became firmly set into the parts. I’m having to work around that, and in some places, I’m actually going to need to correct the shape. More on that next month, I expect.
A significant amount of building up has been necessary. The material I’ve used is Polyfiber SuperFil. SuperFil is epoxy-based, not polyester. I avoid polyester fillers because I’ve observed deterioration over time. Time will tell how well SuperFil holds up. The batch of material I’ve acquired, when mixed, ends up being somewhat pasty and difficult to spread evenly. It takes all of 24 hours to set up, and in cold weather, considerably more time to fully cure. The time adds up. Days and weeks go by with not a great deal to show.
SuperFil is not exactly what I’d call fragile, but it’s not super tough either. It adheres well and sands well. I’ve tried to confine usage to places that don’t need to flex a great deal, as I think it might be somewhat vulnerable to cracking. In the future, I may try epoxy and microballoons. I don’t know if that will be any better, but I know it’s a popular and proven way to go.
As part of my firewall forward (FFW) kit, I received a new-style exhaust system, compared to what I’ve seen supplied for other Sling 2 builds. So far, I think that’s good. As sometimes happens with new parts, early production teething issues can creep in.
The cabin heat muffler shroud doesn’t fit. I noticed this early on and the factory sent me a new part (and part number), but it too doesn’t fit with the muffler. There are also some holes that should match at the overlap seam. They don’t. Obviously no QC standards were applied at all – I’m sorry to say. No excuse. (end rant) I could push for a yet another part from the factory, but don’t want to wear out my welcome any more than I have. At this point, I’m reasonably certain I can adapt one of the parts and build on.
I’ve learned – too late – that my choice of spinner was probably not a very good idea and that it brought me perilously close to a disaster that befell another Sling 2 builder who tried to use this same spinner. He had to buy a new cowl. I think I’m going to squeak by, but just barely. The setback necessary to accommodate the rear facing spinner bulkhead flange, competes with the available circumference at the rear edge of the cowl where it overlaps around the fuselage. Exhaust and engine clearances near the lower front of the cowl are also reduced, the farther back the cowl sits. At some point, luck runs out. I think perhaps the new-style exhaust may have saved me. The other builder had the old style. Nevertheless, I’ve come absolutely to the edge of a self-induced failure that would demand a new cowl. It’s very, very close.
I may still be in trouble with the cowl. The front lips of the upper and lower cowl haves have spacing and alignment issues that I’m working to correct with filler. The plane of the cowl ring formed at the front, nearest the spinner, is not the same as the face of the propeller hub. The engine mount introduces considerable right thrust and the cowling appear to have almost none. This results in an inconsistent gap on the left and right sides, just behind the spinner. When it’s all said and done, there’s going to be very little gap between the spinner and the cowl. I cannot set the cowl back any further. As it happens, I have a friend who designed and built an airplane 35 years ago with a similarly (and intentionally) small spinner to cowl gap and it has been absolutely fine. I think mine will be too. It’s sure going to look nice. Ultimately, time will tell if i get away with it.