Bolt tension at airfoil joint and washer pressure
Each airfoil was supported by 4 hexagon bolts with pairs of nuts which
clamp the wood airfoil. The bolts and nuts joints were further tightened
by using spring washers. The plate washers will hopefully distribute the
stresses to a wider area on the wood. The selected size for hexagon bolts,
nuts, plate washers, and spring washers were M3. Calculation on the tension
in the bolts caused mainly by an assumed airfoil imbalance and partly
by centrifugal force showed sufficient strength. The estimated pressure
between the flat washer and the airfoil wood surface (across the grain
direction) was calculated as 300g per 1mm2. The wood will probably be
dented in after some time of fast rotation and repeating assembling disassembling.
Joints on centre of airfoil
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