Foam-Only Biscuits

Test cuts of a nominal 20 mm foam-only biscuit

On Thursday we got the first correctly-sized foam only biscuits cut out of the denser Foamular 250 foam. These are for anti-buckling effect on all our carbon fiber tubes that are less than 35 mm in diameter (in the larger ones we used balsa faced white EPS foam biscuits).  These were cut out of a 4" thick piece of material, and then will be cut with a knife into approximately 1" wide pieces that are slathered with epoxy and plugged inside all the small diameter tubes at regular intervals, to prevent ovalization of the tubes under load that might cause local buckling

Last year we cut some samples out, but found that the wire kerf was making them fit too loosely.  So we bumped up the diameter by about 1.5 mm, and with the kerf, and the slot that allows us to spring it closed a bit, we can squeeze it to a size that fits nice and snug inside the tubes.  (So for instance, the 20 mm biscuit is cut at 21.5, wire kerf brings it back to just over 20, then we squeeze it tighter and insert).

The next step will be to produce more of these and then start biscuiting the smaller diameter tubing, starting with the horizontal and vertical tail spars.

The biscuit inserted into the proper diameter tube (actual biscuits will be cut down to 1" length)

Test cuts of several different sizes

Production cuts of the 20 mm biscuit

Trimming the flashing

Sanding the flashing

Video of cutting a foam-only biscuit

Prepping a foam block to cut smaller blocks for end rib foam core

Gluing guides to the foam

Hot wire cutting a root chord airfoil section

Foam core for a hard end rib of the root chord airfoil ('Rib 0')