I was thinking of using the AS5046 airfoil which takes more of the spar caps
than the RAF48 by virtue of the more extreme angles. The original plans only
differ in dimension at the wing tip end, so that when shaved to size the largest
discrepancy is at the outer most end having the least load. My own empirical
analysis based on formulas published by US Department of Agriculture Forestry
Service document at http://www.fpl.fs.fed.us/documents/fplrp/fplrp343.pdf
Shows the KR2 outer main spar is designed more than 5 times stronger than
needed for the distributed compressive load and minimum deflection under load
at 1200 lbs. gross. It looks as though the massive size of the spar caps are
to handle the shear load concentrated on the AN3 fastener holes used for the
wing attach fittings. Loading calculations show that the weakest part of the
spar system are these holes. The spar itself as a box beam could have spar
caps half the designed height and not fail before the AN3 fasteners pull out
of the attachment end. However there are many variables not calculated. The
numbers for minimum material condition and modulus of elasticity for straight
grained Sitka spruce were gathered from various sources which closely agreed
with each other.
