Know How
&
Construction Ideas


 


1.0 Contents


1.1 Overview

1.2 Recommended glues for foam
1.3 Making holes in foam

1.4 Making slots and channels in foam

1.5 Sanding foam

1.6 Cutting foam

1.7 Making cutouts in foam for servo boxes and undercarriage mounts
1.8 Fixing dings in foam

1.9 Balsa sheeting foam
1.10 Final Finishing foam


1.1 Overview

Wowplane models use foam as a primary medium, and balsa/plywood as secondary medium only where necessary. Foam construction is easy, less time and labor consuming and yields an end product with exceptionally clean lines, allowing complex curves for a scale look. It is light, strong, durable and easy to repair. Please read the simple tips below to help master the technique and we are confident that you will be more than happy with the end result.


1.2 Recommended glues for foam

  • 6 minute epoxy for most joints, available from your local hobby shop.

  • 30 minute epoxy for parts that require alignment or squaring, available from your local hobby shop.

  • Gorilla glue where you want the glue to expand and fill voids, available from your local hardware store. Ideal for repairs.

  • 3M M77 spray adhesive for sheeting, available from your local hardware store.

  • Low Temp Hot Glue for internal areas.


1.3 Making holes in foam
 

      Click picture to enlarge
 

  • Obtain brass tubes of 1/8, and inch diameters from your local hardware store.

  • Use an Exacto knife to scrape away the inner edge of the tube, until you have a round sharp edge.

  • Place the sharpened end of the tube against the foam and rotate while applying light pressure.

  • Aim the tube in the direction you want to bore the hole.

  • For deeper holes, bore out a few inches at a time, withdraw the tube and clear any foam buildup inside the tube with a stick.

  • To make a hole perpendicular to the face of the foam, use a wooden block with a hole drilled 1/64 inch larger than the tube's outside diameter. Place the flat face of the block against the flat face of the foam and use the wooden block as a guide, holding the wooden block and foam stable.  


 1.4 Making slots and channels in foam


 
Click picture to enlarge

  • Use a Dremel tool, fitted with a router bit, and a straight edge to guide the router. 

  • Channels are primarily used for routing servos leads, antennas, etc.

  • Alternatively, score two parallel lines with an Exacto knife and scrape out the foam between the lines.


1.5 Sanding foam


 Click picture to enlarge

 

  • Although Wowplane models come with most sub-assemblies already shaped, a few areas do need sanding.

  • Sanding foam uses a slightly different technique than most other materials. 

  • Use 100 grit for rough sanding, 220 grit for smoothing, and 320 grit for finishing, mounted on sanding blocks with rounded edges. Sharp edges will tend to gouge the foam.

  • For the final finish, use a bathroom sponge in place of the wooden sanding block.

  • Sand only in one direction, preferably away from yourself. Use a dust mask or do it outdoors.

  • Periodically, clean the sandpaper face with a wire brush to remove any molten foam build up. 


1.6 Cutting foam


Click picture to enlarge

  • Scroll saw, band saw, utility knife, fine tooth modeling saw, or hot wire or knife, all work well. 

  • Do not try to cut the foam in one move when using a utility knife or modeling saw. Cut 1/4" depth at a time.


1.7 Making cutouts in foam for servo boxes and undercarriage mounts

  Click picture to enlarge

  • Make a tool as shown in the picture. Cut a piece of aluminum 1x1 in square. Drill a hole in the center for a screw and attach it to the hot end of your soldering iron.

  • Use this as a hot stamp to melt cutouts in the foam for servo boxes and u/c plywood mounts.

  • Line the servo box with 1/16 balsa.

  • Alternatively, you can use a Dremel router bit and template to make the cutout.


1.8 Fixing dings in foam

  • Use lightweight drywall spackle, available from your local hardware shop, and sand flush when dry with 320 grit paper.


1.9 Balsa sheeting foam
 

         
Click picture to enlarge

  • Sheeting foam with 1/32 in balsa provides exceptional strength, durability and a great looking finish.

  • Use Monsanto M77 spray adhesive, available from your local hardware store.

  • Read the manufacturer's directions on the spray can.

  • Spray a layer of M77 on the foam and one side of the balsa sheet. DO NOT hold the spray can less than 12" from the foam surface and keep it moving. If the propellant gets on the foam, it will dissolve it. Do not allow the glue or water to puddle.

  • Wait 60 seconds to allow the glue to get aggressively sticky. Do this in a well ventilated area, and use a plastic drop cloth to protect the work surface.

  • Carefully align the balsa sheet along one long edge with the foam piece being sheeted, and smooth it down with the palm of your hand. Do not apply excessive pressure as this can bend and warp the foam piece. 

  • M77 is a contact adhesive and sets immediately on contact. You have only one try to get it right. Practice with scrap foam and balsa first to get the hang of it. It stays tacky for hours, so no need to rush.

  • Continue with additional balsa sheets until the foam surface being sheeted is completely covered.  

  • To sheet round shapes, such as fuselages, leading edges of wings, tail, etc, wet the non-glue side of the balsa sheet with a tissue dipped in water or a water spray bottle, until the balsa starts to curl and becomes soft. This will prevent the balsa from ripping when bent. Seal all seams with a bead of epoxy.


1.11 Final Finishing foam
There are several ways to finish foam. You can use one of the options listed below to achieve a finish that is as superior as any other.

  1. Use Wowplane Liquid Sheeting and just paint over it. This is the least time and effort consuming option and yields a very nice finish.

  2. Balsa sheet the foam and cover with low temp heat shrink covering

  3. Balsa sheet the foam and fiber glass with 0.75 oz cloth and then paint.

  4. Smooth finish foam and fiber glass it with 0.75 oz cloth and then paint.

Shown below are examples of models finished with each one of these options.

 

A10 Warthog
1/32" Balsa sheet covered foam with heat shrink covering


1/32" Balsa sheet  covered foam with heat shrink covering

 B25 Mitchell

Fiber glass over bare foam & Rustoleum Metallic Silver paint. Wowplane Liquid Sheet over foam & Krylon Metallic Silver paint