Assemble ABS cowls and wheel pants

Model Airplane News, Jun 2002 by Bell, Rick

HOW TO

Basic skills, advanced results

When you buy the latest and greatest kit, chances are pretty good that the included vacuum-formed ABS plastic cowl and wheel pants will need to be assembled. Because of the assembly required, many modelers don't give these ABS plastic parts a second thought; instead, they toss them into the spare-parts box and opt to use aftermarket fiberglass replacements.

The truth is, the ABS parts in kits are usually of good quality and don't require a lot of work to produce strong, durable, lightweight cowls and wheel pants. The techniques and tips presented describe how I assemble ABS parts for a one-piece look.

To produce a good result, you'll need some basic materials such as fiberglass cloth, glue for plastic (or thin CA), putty, styrene plastic and spray contact cement. These are used to assemble and strengthen the parts and improve their looks. For this article, I used a cowl and wheel pant from Midwest's giant-scale CAP 232. Let's take a look.

1 First, trim the parts for proper fit. This step determines how much extra work you'll need to do later. The more thorough you are now, the less filling and sanding you'll need to do later. Be methodical with this step. The cowl and wheel pant parts should fit together easily and not have to be force-fit.

2

When the parts have been trimmed but before you glue them together, scuff the Inside of the cowl and wheel pants

with 60-grit sandpaper. This will give the epoxy (applied later) something to grip.

3 Most cowl and wheel-pant halves have molded-in lips that mate with each other; this provides a gluing surface for the parts. (If

your parts have molded-in lips, skip to step 6.) Some parts, however, are trimmed at the factory and do not have a lip for the mating half. Don't despair; you can easily add a lip using strips of styrene. Many hobby shops have sheets of styrene plastic for scratch builders; I use sheets that are 0.030 thick. This provides plenty of strength yet Is flexible enough to be molded to the shape needed. For cowls, I cut 3/4-inch-wide strips; for wheel pants, I use 1/2-inch-wide strips.

Using small spring clamps, test-fit the plastic strips to the inside of the cowl and note where you'll need to bend the plastic to conform to any curves. Do the same for the wheel pants. Using your fingers, gently bend the plastic to the curve needed; you'll be relieving the tension In the plastic strips when they are glued Into place.

4

Now glue the strips into one of the cowl halves and a wheel pant, and use plenty of spring clamps. For glue, I usually use Oatey Clear PVC Cement (you can also use thin CA); It slightly dissolves the plastic and when the cement dries, the parts will be firmly welded together. Let the cement cure overnight.

5 After the glue has set, remove the clamps and check the lip for any glue residue that needs to be removed, and then test-fit the parts together. Because of the wheel pant's curves, you'll most likely need to trim the lip so the halves can easily fit together. Remember, take your time so you achieve the best possible fit. The cowl should not require much trimming. When you've finished, the parts should again fit together easily.

6

Here's a tip: before you glue the halves together, take a razor blade or a hobby knife with a no. 11 blade and put a slight radius on the inside corner of the mating part. By removing this edge, you allow the parts to fit together more tightly. You'll end up with a more closely fitting seam that requires less filler.

7 Now glue the cowl and wheel-pant halves together. I again use Oatey PVC Cement and plenty of tape, rubber bands, or clamps to hold the parts together. Here are the cowl and wheel pant glued together and ready for reinforcement and seam work.

8

Use 60-grit sandpaper to block-sand and remove any high spots, and then blend the seams together. As you sand, you'll notice some shiny spots; these are low spots that you'll need to fill with putty. Don't worry about any scratches; they'll be filled In with putty and primer later. Now block-sand and further smooth the seams with 150-grit sandpaper to remove most of the scratches. It's a good Idea to wear a mask when you're sanding so you don't Inhale the dust. Now Is a good time to cut out the openings In the cowl and wheel pant (you'll need access to the Inside of the pant for the next step). Use a rotary tool with a cutting bit to rough out the openings, and then use a file or sandpaper to final-shape the openings.

9 Cut some strips of

heavy (4- to 9-ounce) fiberglass cloth about 2 inches wide for the cowl and about 135 inches wide for the wheel pant; you'll use them to reinforce the seams from the Inside. If the plastic Is somewhat thin, you can fiberglass the entire inside instead of just the seam. Also have some smaller pieces of cloth handy for oddly contoured areas and to add reinforcement to mounting holes or other weak areas. Now lay the strips of cloth Into place over the seams. To simplify this job, spray a light coat of contact cement on the cloth; this will help hold it in place when you brush on the epoxy. Mix about 1/2 ounce of slow-curing epoxy in a graduated cup (smaller batches have a longer working time). Thin the epoxy a little by adding some rubbing alcohol to it; a thinner mixture more easily soaks through the cloth and onto the plastic. To apply the epoxy, use disposable acid brushes; they are easily bent to reach into nooks and crannies. Apply enough epoxy to the cloth to thoroughly wet it but not so much that It runs all over the place, and then check for voids; apply more epoxy as necessary. Work small areas at a time, and then move to a different section. Allow the epoxy to cure for several hours.