Ola Fremming's homepage


Weight saving holes in foam core wings.

It's quite common to reduce weight of foam-core wings by removal of foam.  Some people make holes in the foam from top to bottom, and even cutting out the cores in a honeycomb shape structure.  These methods do save weight, but in my opinion they have too many drawbacks.  First of all the wing becomes very fragile in the areas with balsa sheeting and no foam underneath, grab a good hold of the wing and your fingers will penetrate the sheeting.  For me the other major drawback is the fact that my usual vacuum-bag method of applying the sheeting does not work, the foam structure is weakened so much that it will be crushed by the force of the bag. My method involve cutting holes in the foam from root to tip of the wing, to maintain the strength of the cores during sheeting the holes are cut after sheeting the cores with balsa.  To enable this the wire to use for hot-wire cutting needs to be embedded into the foam before the sheeting is applied.  The pictures below should explain the process steps:

Use a straight edge and sharp knife to cut a slit for the wire-

 

Push the wire into the slit

 

The wire is in place

 

This picture shows the wing with root-rib in place ready for sheeting.  The rib to be used at tip is shown also.

The sheeting is on and the first hole is cut with the previously embedded wire

 

The holes are cut

 

The total weight saving for the set of wings used in this example (Integral) is 42g.  That may net be significant, but to get a light model weight must be saved everywhere.