Jack Erbes is one of the modern day geniuses of foamy construction. Here's his RCG build log of a KFM3 wing for the Blu Baby. My BB32 wings broke in half, so I'm especially interested in this. I'll lightly edit, but the first person voice is Jack's. I'll try this later and do my own writeup if I think it might be useful. Jack writes:
I recently made a KFm2 wing with polyhedral tips for use on my KFoenix Stick and flew it in RET configuration (Rubber, Elevator, & Throttle, no ailerons) and was really impressed with it. It had excellent tracking and control and good rudder authority, which had been a problem with the stock Slow Stick wings. The wing seem to "lean into" the turns nicely as speed increased and as turns were made more aggressively. It was almost as if I were flying a wing with ailerons.
Jack's Instructions are as follows:
The flat center section/polyhedral tip wings are a quick and easy build and have better inherent strength than the two panel wings with dihedral that have a center joint. And I've also found that the flat wings like this have much less need for a spar because the multiple and full width gluing lines create a monocoque structure with very good strength. As an example, the 48" span 11-1/2" chord wing I made for the KFoenix Sticks has two 1/4" dowels (36 grams for the two dowels, and only about $1.50 in cost) and probably has more inherent strength than it will ever need.
So I wanted to get a BB 33 back into a better advanced trainer and sports flyer configuration and decided to make a 33" KFm3 wing with polyhedral tips for it.
1 24" x 48" sheet of FFF (Dow Protection Board III insulation, from Lowes or Home Depot)
1 3/16" x 36" wooden dowel (any wood will work)
Gorilla White Quick glue (any PU glue will work)
Clear package sealing tape (Duck brand "Standard" weight is good)
Colored package sealing tape for final covering/decoration/improved visibility in flight (final covering and colored tape is optional, but it contributes to strength and is very eye pleasing).
Clear Duck tape (fabric reinforced tape, any color would work but I would not be caught dead with a RC plane with the standard gray or silver tape on it)
Bamboo skewers for trailing edge reinforcement at wing center
1/8" wood dowel or 2mm fibreglas rod for leading edge reinforcement
All of the wing parts are seen in this photo, from the top down they are:
- KFm3 50% strip
- Filler strip
- 3/16" x 36" wooden dowel (Crafts section at Wal-Mart)
- KFm3 75% strip (also supports the 50% step)
- Wing panel for KFm3 Sport wing
The wing panel can be made without the templates from piece of foam that is 33" wide and 8" high. Simply mark two points 15-1/2" in from each end (that leaves a the 2" section in the wing center that is over the fuselage), then mark two points 7-1/2" back from the leading edge on the wing tips. Cut a straight lines from the marks on the wing tips to the marks near the wing center and that is the one piece wing panel.