Here's what the corner cowl flanges looked like after being trimmed to shape. (They aren't really that white, it's just the flash)
The top cowl overhangs the bottom cowl by about 3/32" at the forward outboard corners, giving it a sort of "overbite" appearance. To build up the lower cowl, I first put packing tape along the mating edge of the upper cowl, then clecoed the two halves together on the workbench:
Then I mixed up a batch of epoxy and microballoon filler:
Filler is applied with a popsicle stick over a light epoxy wipe, then roughly contoured with a rubber squeegee:
After curing, most of it gets sanded away as the new shape of the cowl is formed:
Then comes another round of filling and sanding, and then another. After three iterations, it's starting to get where I want it:
You can see where I filled in some low spots on the bottom of the left air inlet. I think the vacuum bag got partially wrinkled here when the piece was being molded, but it's all smoothed out now.
The fit is pretty good now – no more overbite. I will wait to do the last bit of sanding until I have the cowl back on the airplane and locked in to its final position.
To sand the filler to shape during the above steps, I used a variety of different tools. Each one has its own strengths and weaknesses, kind of like a team of superheroes. Let's run down the dossiers:
Team Member: Two-Face
Background: Was an ordinary piece of aluminum angle until unfortunate particle accelerator accident. Then had sandpaper glued to it.
Zodiac Sign: Gemini
Strength: Squaring corners
Weaknesses: Bad for large areas, sometimes sands where it shouldn't
Team Member: The Strip
Composition: Stainless steel, adhesive sandpaper
Thickness: 0.020 inches
Strength: Good for sanding gap between cowl halves
Weaknesses: Limited applications, sharp edges
Ouch My Hand: What did I just say
Team Member: The Rod
Origin Story: Wooden rod with sandpaper taped to it. Also, bitten by radioactive spider.
Cover Identity: Nuclear-plant employee
Strengths: Inside corners, curved surfaces
Weakness: Flat areas
Team Member: The Block
Alias: The Preppin' Weapon
What Seriously: Yes, that's the actual product name
Yikes: Tell me about it
Strength: Most ergonomic sanding block ever
Weaknesses: Bad for inside corners, goofy name
Team Member: The Saw
Manufacturer: Xacto
Application: Adjusting kerf between cowl halves
There Is No Such Word: Yes there is. Kerf is a word.
Philosophy: Every problem in life can be solved by cutting
Hobbies: Cutting, slicing, windsurfing
Weakness: Not every problem in life can be solved by cutting
Team Member: The Hand
Technique: Holding a piece of sandpaper with your hand
Main Power Source: Engineer's hand (L or R)
Strengths: Contours to any surface; can also open cat food containers
Weaknesses: Stamina, precision, sports
Sanding team, assemble!
