Warringah Radio Control
Society Incorporated
(Incorporated under the Association Incorporation Act 1984)

 HOW TO MAKE FOAM CORE WINGS
PARTS REQUIRED:
  • Battery charger
  • Templates
  • Battery
  • Foam block (or two)
  • Ruler
  • Veneer or Balsa
  • Cutting bow
  • Glue (latex glue, Scotch 77, spray glue or epoxy glue)


1. MAKING THE TEMPLATES
This is probably the most important part of the entire project. Each project requires 2 templates (one at each end of the foam to guide the cutting bow). Each template is made of 2 parts, one is the Base and the other is the actual Section that is intended to be cut. The Base Template should fit either on the top or the bottom of the Section Template so as to extend past the Section Template both at the front and at the back (leading and trailing edge). The template is made of some substantial wood (can be thin ply or 2mm balsa), do not use cardboard.
 
 
 
 
 
 

2. MARKING THE TEMPLATES

Mark the depth of the leading edge stock and the trailing edge stock that you will be using on each of the Section Templates and then divide the balance of the width of the Section Template into equal protions no more than 1" (2.5cm) wide and number each division from the back to the front, trace the lines onto the Base Template as well.
If the Section Templates are different (eg. if you have a tapered wing) then the smaller Section Template should be divided into the same number of divisions as the bigger Section Template.

3. LEFT AND RIGHT WINGS
Don't forget you will need a left and a right wing panel. Just to remind yourself you should write onto the foam block you have prepared what it is (left/right; top/bottom)

4. FOAM BLOCKS
A separate block is needed for each side of the wing (ie. left and right). Using the Cutting Bow, trim the block square so that it is the correct length from the middle of the wing to the wing-tip and the correct width of the foam required between the leading edge stock and the trailing edge stock. Allowance has to be made for any sweep in the shape of the wing.

5. PINNING THE TEMPLATES TO THE FOAM BLOCK
Make a number of pin-holes in all templates so that it can be pinned to the foam block. Doing each wing in turn, pin the Section Templates and the Base Templates to the two ends of the foam block, careful to have the correct part of the template to hang over the front and the back of the foam to allow for the balsa leading and trailing edge stock.

6. CUTTING
Weigh down the foam block sufficiently that it does not move about while you use the Cutting Bow through the block. It is easiest to use 2 people for the cutting process, one on each end of the Cutting Bow (and each end of the foam block and templates)
With a heated Cutting Bow start the cut, moving from the back to the front and each person making the cut at the same division. This is best done by one person calling out the division number that he has reached and the other keeping up with the person calling.
Do the top cut first by moving the Cutting Bow from the back over the top of the Section Template until it emerges at the front of the template.
Then remove the Section Templates and repeat the operation cutting from the back to the front using the Base Template as the guide... Hey presto - one foam core!
Repeat the procedure for the other wing by using the other side of each template.

7. SHEETING THE CORE
Next you veneer or balsa the wing cores. Using your choice of glues you cover from the trailing edge forward and put it back in the foam block with weight on it while it is drying.

CONSTRUCTING THE CUTTING BOW
PARTS:

  • 1.8m of 4x4cm pine (any other timber is OK)
  • 12 volt battery
  • Battery Charger
  • Nichrome wire (or resistance wire)
  • 30cm door spring
  • Nuts & bolts etc.
See the sketch to get an idea of what to do, the most important part is the application of the correct heat to the foam to cut it.
The heat is dependent on the thickness and type of wire (as well as the amount of electricity you put through) and there is a lot of trial and error in obtaining the correct Bow. Too much heat and you will melt too much foam and end up with a rough surface, too little and you will be ripping at the foam instead of cutting it.

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