Pages 18-05 and 18-06: Flaperons

With the main part of both wings closed (hope I didn't leave any tools in there), the flaperons are the only thing left before starting the finishing kit (inventoried!).  The worst thing encountered so far is match drilling pre-punched holes in the aluminum flaperon leading-edge skin into the much harder stainless steel tube which is used as a counter weight for the flaperon.

My experience match drilling anything has not been positive, and this was by far the worst.  The #30 drill tended to "walk" in contact with the stainless, elongating the holes in the aluminum.  After this happened a couple of times I started drilling a #40 pilot hole first, then drilling the #30.  Worked much better.  I've always dreaded having to drill anything into stainless steel.













The next problem involved squeezing solid rivets such that either the manufactured head or the shop head would be seated against a curved surface.  I didn't want to machine a flat surface into the piece

since that obviously would weaken it.  The squeezer dies also wouldn't clear the flange.  The picture shows my options.  It seemed intuitively clear that the manufactured head wouldn't work at all on the curved surface.










I ended up grinding a flat surface on the cylindrical surface of the flat squeezer die (hard to see in the third pic) and putting a radius on the intersection of the two flat surfaces on the die (shown in the pic).  I also spaced the die out from the squeezer jaw with rivets.  Squeezing the shop head onto the

curvature worked fine.  The result is also shown in the third pic.  The shop head easily conformed to the curved surface.







The aft flaperon skins presented a new PITA right off the bat.  There were notes on the skin packaging warning that extreme caution should be exercised when unpacking in order to prevent damage, the reason being that these parts seem to be the most fragile I've encountered so far.  I suppose the flaperons need to be light, and therefore thin, to avoid flutter.  To make matters worse, the protective blue plastic was difficult to remove, especially on the inner surfaces.  And, for the first time in all the plastic removal I've done, a layer of sticky crap adhered to the aluminum when the

plastic was pulled off.  Somewhat belatedly, I discovered that if I apply the pulling force at right angles to the aluminum rather than at something between 135 degrees and 180 degrees as I was doing, the aforementioned sticky crap was not deposited on the aluminum.  Unfortunately, this was impossible on the inner surfaces.  Mineral spirits seem to get the deposit off with considerable effort.  What a waste of time.





Page 18-06 warns the builder to be certain that the tapered aft portion of the skins doesn't bulge out from the flaperon ribs but rather lies in a straight line against the ribs (see pic below).  Considering that this is matched-hole construction and the parts are riveted together, I don't see how the skins have any choice but to lie flat against the ribs.  Maybe I'm missing something here.  A revision in the build manual specifies a Cherry (stronger) rivet for the holes nearest the trailing edge in place of the usual LP4-3 rivets.  I suppose this is to positively

eliminate any bulging.  Unfortunately, I had to order the newly-specified rivets and am dead in the water until they arrive.

After pondering the bulging skin issue a bit more,  I think the manual is referring to the skin between the ribs even though it says "lie flat against the ribs."