Author: Dave Garwood
Edition: Model Aviation - 2010/06
Page Numbers: 112,113,114
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Radio Control Slope Soaring

Dave Garwood [[email protected]]

Recipe for finishing a fiberglass fuselage

I have more for you about a favorite building project: a fiberglass-fuselage and sheeted-foam-wing short kit. Once you’ve learned a few construction tips, tricks, and techniques, you will have a wide variety of sailplanes available and you will fly with the satisfaction of having built them yourself.

The April 2010 Slope Soaring column gave an overview of building the short kit, and this column covers one component of that construction project: preparing a smooth finish on the fuselage and getting it ready to paint. The objective is to prepare the model’s surface to accept spray paint.

Fiberglass takes a painted finish well, and that is one of the main reasons I like molded-fiberglass fuselages. The ability to model beautiful, curved shapes and a high strength-to-weight ratio are the other main reasons.

Most of painting is preparation, and most of the preparation is sanding. Paint will not cover scratches, pinholes, and other imperfections nearly as well as you might hope it will. If you don’t sand down that bump or fill that pinhole, the imperfection will show in the final product.

Remember also that when you’re done, a painted model looks fabulous—better than any iron-on “’cote” finish ever looked to me, whether it’s on a scale or sport sailplane. Prepare for a little pain and strain, but the result will be worth the effort.

Following are the steps to prepare a fiberglass fuselage for a paint finish.

  1. Wash the fuselage.

Wash your fuselage thoroughly with warm water and detergent. Remove all traces of wax or mold-release agent that will interfere with paint adhesion. Lightly sand the surface to break the glaze. Flatten any protruding seam joints with a blade or sandpaper block.

  1. Initial sanding.

As shiny and beautiful as the molded fuselage looks out of the box, you do have to sand it to knock off the glaze before you can paint it. The wet-sanding technique is your friend. The water clears the sandpaper and allows it to cut much longer. I sand in a sink with running water, using both handheld sandpaper and a rubber auto bodywork sanding block. Make your sanding go faster and easier by having plenty of fresh sandpaper on hand, so you can change it as soon as it stops cutting effectively. Start with 100 or 120 grit, and then go to 240 or 320, followed by finer grit according to your personal craftsmanship standards.

  1. Primer paint.

Allow the fuselage to dry thoroughly either outside in sunny or windy weather, or inside overnight. The next day, spray with sandable primer from a rattle can. I’ve used both Krylon and Rust-Oleum brands. Set the fuselage aside to dry and then examine it under strong light. As shiny and perfect as the fuselage looked out of the box, you will not know the surface quality until you examine it after it has been primer-painted.

  1. Fill pinholes.

We have a large number of choices for pinhole filler material. Ask your building buddies, pose a question online, or ask at an auto supply store or automotive paint store. I use Bondo glazing compound, which comes in a tube and is applied with a spreader or even fingertips. Wear disposable gloves for easy cleanup.

(Editor’s note: Glazing putty sticks to primer much better than it does to the epoxy or polyester resin bonding the fiberglass. Dave tells us to prime first for that reason and because the pinholes are easier to see after a prime coat. Thin applications of putty are recommended.)

Apply the pinhole filler and let it dry or cure, depending on the material, and wet-sand the fuselage again. Most of the primer paint and almost all of the pinhole filler will be sanded off. Remaining will be tiny amounts of the filler actually in the pinholes themselves.

Lather, rinse, repeat. You’ll go through several rounds of priming, pinhole filling, sanding, letting it dry, and priming it again.

You can stop when the fuselage is smooth enough according to your standards and level of craftsmanship. Don’t be too hard on yourself. If you can’t see it in the air, it doesn’t matter.

  1. Final primer.

When you’re satisfied with the smoothness of the surface, apply a final light coat of primer and do the last sanding pass with very light pressure. This is where the 400- and 600-grit paper will make a difference.

When it’s dry, spray on a light mist of primer to prepare for your finish color coat. On models that will have a light-colored final coat, I use white sandable primer made by Krylon and Rust-Oleum, which keeps the final weight down by minimizing the amount of color coat that must be applied.

You know you’re a sloper when …

Following are a few humorous insights about our sport/hobby from RCGroups. You know you’re a sloper when …

  • “... you wake up and look outside to see the wind blowing, and say, WOOHOO!!!!” —Xpress
  • “... the only weather that matters is wind speed and direction.” —Macgyver24
  • “... every time you see a movie with some mountainous scene you’re thinking, I’d slope that.” —Alex.Schweig
  • “... you would rather buy a couple more slopers to add to your unbuilt fleet than buy a Hi-Def TV.” —DWA
  • “... all your hats have chin straps.” —M.Carlton
  • “... you think a good landing is one you can find.” —rbrush
  • “... your car has dents in it from landings.” —Xpress
  • “... your car always has a slope plane in it.” —trees
  • “... you consider a pretty good landing to be one that requires less than 15 minutes of repair work.” —Cory
  • “... you start to like the smell of the local landfill.” —Rockitglider
  • “... you know a 24-hour Walgreens that carries Goop or Shoe Goo.” —slopemeno
  • “... you are at the flat field and the only one flying because it’s too windy for others.” —skyzkng
  • “... you spend the day at the beach but your feet never touch sand.” —KurtMc
  • “... your wife tells you to go flying so you can come back with a better attitude.” —flyonline
  • “... you see a bird sloping the side of a building and think I should get an alula so I can fly at lunch.” —IHAVAWDY
  • “... you take your son to college and after moving him into the dorms, test the local slope with the wing and radio you had packed in your trunk.” —chip.greely
  • “... you’re windswept, frozen, soaked, and picking up shattered pieces of carbon and glass, and you think it was a day well spent.” —flyonline
  • “... you have a dozen slopers, even the $1,000 kind, and don’t live within 500 miles of a decent slope site.” —Evan D
  • “... after 37 years of slope-side action you still feel sorry for the millions who just don’t get it or even know about it, but sorta glad they don’t.” —Antonsororer
  • “... you can’t get to your furnace to work on it because it is surrounded by unbuilt slope kits.” —rcairnut
  • “... you arrive at the slope with perfect wind conditions and ask yourself why no one else is flying.” —Hawk I
  • “... you look over planes at the power field and think, That would have been an OK plane if he had at least used a half way decent airfoil.” —theBOZman
  • “... you know that there is a far better use for lead than wheel weights. Who needs a balanced tire anyway?” —1-26 Flyer
  • “... you have actually gone to a tire store and asked if you can have the old weights they pull off.” —1-26 Flyer
  • “... you get genuinely bummed when it's a nice sunny and calm day.” —1-26 Flyer
  • “... you know you are a Hard Core Sloper when scratches on the bottom of a $1,600 plane mean nothing to you.” —BillDelHagen
  • “... you demolish a racer in some rocks, but save the V-tail and ballast tubes simply because they are not broken.” —BillDelHagen
  • “... you reach the understanding that if your plane is climbing, you have too little ballast.” —BillDelHagen
  • “... determining where you might live depends on slope opportunities.” —FSD
  • “... a world-class 3-D heli flight just looks like a five-minute-long radio glitch.” —Norjon
  • “... the sound of a jet turbine is cool, but nothing like the sound of a slope plane shredding the air! Now that really gives you the chills!” —rcairnut
  • “... you spend most of your mind's free time on slope designs or daydreaming how to make that perfect turn on a man-on-man slope race.” —Edwinzea
  • “... you had a dream about sloping.” —Xpres

I also enjoyed the RCGroups thread titled, "You know you're a scratch builder if ..." One was "... you've gone through sooooo many hobby knife blades that you have actually taken to resharpening by hand and now know how to get that perfect cut." —snrek

In my next column I plan to cover painting and panel lines to finish a fiberglass-fuselage model. Then I'd like to explore what is available for ARF, RTF, and possibly even bind-and-fly for Slope Soaring.

Sources

Transcribed from original scans by AI. Minor OCR errors may remain.