Aln Jackson wrote
>>I understood that the Europa's leading edge wing profile is more critical
than most. In view of this, it is somewhat surprising to learn that the
foam is being delivered an eigth of an inch wider than the spar...<<
The reason the core is thicker than the spar is to allow for the overlap of the
skin when the trailing edge is glassed.
The leading edge profile is critical. Particularly the nose radius and the first
few inches. The important thing is not ot have any wavyness of the surface. The
test is a 3 thou (inches) feeler guage which should not pass under a steel rule
pressed down with two fingers two inches apart. After filling and profiling of
course. Aft of the main spar is less critical.
A trick some people have used to persuade the LE skin to wrap round behind the
spar is to lightly wedge a PVC 90 deg edging extrusion over the corner. It's
important to avoid bubbles between the skin and the top of the spar. The odd
bubble behind the back of the spar is acceptable. Don't forget when making
repairs to carefully taper the layup back under the repair to achieve a minimum
20 :1 ratio scarf joint.
One thing to watch when the wing or any other flying surface is finished and
stored is proper support. Epoxy does fully cure for weeks unless post cured in
an oven. Trailing edge close outs, e.g. the aileron and flap close oputs are
best held apart with foam blocks cut to shape otherwise slight shrinkage will
occur and the ailerons may well be bigger than the gap they should fit into. The
same is particularly true of the fin trailing edge. Its worth supporting
trailing edges with a long straight edge then warming to prevent waviness
developing.
Finally don't try for knife edge traing edges on flying surfaces. Boundary layer
effects seem to make thick (up to 3/16", even) trailing edges perform better on
control surfaces. In fact a thick TE is needed on the stabilator anti balance
tab to prevent stick free oscilations.
Graham
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