Building, testing and operating an experimental aircraft

Wheel Pants and Fairings

26 Jul 2014

Before Oshkosh this year, Dad and I had several small but nagging projects that we wanted to get done, the first of which was the wheel pants and gear leg intersection fairings. What follows is a brief synopsis of what ended up being several days worth of work.

The "Sam James" Clay Method The “Sam James” Clay Method

Dad had fit and drilled the wheel pants several months before, so we jumped right in to the “Sam James Method” of intersection fairing fabrication. By the way, they tell me you can just buy these things off the shelf nowadays so you don’t have do build your own from scratch. Do it. Unless, like us, you’re a glutton for punishment, and/or you really want to get messy and learn a lot about what not to do with fiberglass.

Highly Aerodynamic Highly Aerodynamic

We began by laying up some modeling clay around the intersection of the wheel pant and the gear leg fairing, then scuplted the best “pressure recovery” aero shapes we could, using two highly-calibrated metal soup can lids as shapers.

Shaping the Clay Shaping the Clay

We tried our best to keep both clay forms roughly identical in shape, so that one wheel pant didn’t end up being 2-3 knots faster than the other wheel pant. (Don’t all aero mods claim a 2-3 knot speed increase? IDK.) This required a lot of soup-can-lid finesse, lots of water, and some keen eye-balling.

Right Side (Identical to Left Side... I Promise) Right Side (Identical to Left Side… I Promise)

We applied the T-LAR Method (“That Looks About Right”) to verify that we had both molds identical.

High-End Mold-Release Tape from Harbor Freight Aerospace High-End Mold-Release Tape from Harbor Freight Aerospace

When the clay molds were dry, we applied black electrical tape and sandwich wrap around the forms to act as mold release. (I can HEAR you snickering. Zip it.)

Sandwich Wrap Mold-Release Sandwich Wrap Mold-Release

At long last we were ready to do the fiberglass layups. There are no photos of the resin-infusing process, since I was designated as cameraman, fiberglass wetter-outer, and layer-upper for this little project. I am JUST one man!

A Thing of Beauty and Perfection A Thing of Beauty and Perfection

And while we did use an EAA-approved technique for pre-pregging the glass, as you can see we used some very messy and heavy “Knitted E-Glass Fabric” from Aircraft Spruce because Dad had inadvertently ordered a batch and we had it lying around.

Knitted E-Glass Layup Knitted E-Glass Layup

Please, dear readers, do not use Knitted E-Glass. If you're looking at the photos, I don't think I'll have to convice you. Instead try the #7781 Fiberglass Cloth from Spruce (or something similar), which we thankfully began using later on.

Aerodynamic Side View Aerodynamic Side View

As you can see, the layup was nearly a complete disaster (take note of the paperclips holding the trailing edge together), but we managed to salvage things with many hours of trimming and finishing.

Epoxy Micro Mixture Epoxy Micro Mixture

We decided to do an integral fairing/wheelpant setup, so that removing the wheel pants removes the fairings as well. Of course this necessitates cutting a little split down the middle of the fairing layup, and then finishing the trailing edge (such as it was) into a sleek pointy shape.

Dad Gooping Expertly Dad Gooping Expertly

After several iterations of fitting, gooping, sanding and re-fitting, Dad was able to get a reasonably pleasant shape.

Looks Messy, But We're Getting There Looks Messy, But We’re Getting There

Verifying the Joint Spacing Verifying the Joint Spacing

As you can see from the above photo, we had to curve the joint line aft at the top of the fairing, since continuing the line straight up would have chopped off the leading edge a bit. (By the way, our leading edge is about 1/8” thick and totally bulletproof – thanks, Knitted E-Glass!)

High-Build Primer High-Build Primer

After what seemed many days of sanding and filling, we sprayed the new assemblies down with Rustoleum High-Build Primer/Surfacer to fill the pin holes and imperfections. We haven’t had much luck with Rustoleum products in the past, and we have NO idea how this stuff will hold up underneath our final paint job, so we’re wary. But probably not wary enough to go buy a $200 gallon of PPG K36.

Finished Product, For Now Finished Product, For Now

Lastly, here’s a shot of the finished product in the evil harsh light of day. Probably won’t win any awards, but it kinda looks like something that fell off an F-18 somewhere, so, I’m cool with it.

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