The original Squirrel instructions had a section on how to make a wing with a thick airfoil. I called it the “Alternate Wing” to emphasis the simpler wing.  The simple wing is just as efficient. The alternate one may be more stable though.

It has another section on how to make an 18″ wingspan version.

The 18″ version calls for the “alternate wing”.

Here’s what it said:

You can upgrade the Wing. Add a 1/16×1/8×12 stick as a “spar”. Glue it 1/3 of the way from the leading edge so that it braces the Winglets. Cover the top.

Or, when building, leave 3″ of extra tissue in front of leading edge and after adding the spar, wrap the tissue over the top and glue it to trailing the edge.

18″ Squirrel

Try an 18″ Squirrel. Use 1/8″ square for wing leading and trailing edge. 4″ chord and winglets, 9″ and 5″ stabilizers and an 18″x3/8×1/8 motor stick. I used the alternate wing (needed two pieces of 3/16 to get the height). I also needed a #16 elastic to attach the wing. At this point you may want to use a music wire motor hangar rather than a toothpick. Or just use a pair of toothpicks for more strength. Works well with wheels.