I am in the process of prepping the wings and have some questions.  I am doing most of the work with Aeropoxy Lite and the  4” x 30” 3M fairing boards with 80 grit paper.  I should add that I’m not looking for perfection, just straight & smooth to the naked eye, without significant negative aerodynamic consequences.  Having no prior experience, I guess I’m trying to figure out what is “good enough” without going all the way to paint.  I have worked only on the top of the right wing and should mention that I have by this time essentially covered the entire surface with filler and sanded it down, checking with a guide coat (flat white quick-dry spray paint); the guide coat showed sanding marks essentially everywhere.

 

One concern is that top wing skin drops down from ~ 19” out (where the gap is < 0.005”) to the inboard edge about 1/8” (see attached photo.  Seems to me that would require an excessive amount of buildup.  If this is worked as a smooth transition, will it be noticeable?  I assume there would be no significant effect on the flying qualities of the wing.   I have the same situation at the wingtip.  I have 2 – 2x2x65” Al tubes that I can use as longboard sanders and am using one as the straight-edge as shown in the photo (BTW, the backlight in the photo is a 2x4’ fluorescent shop fixture).  I’m sure that gaps of 0.005” or less are acceptable, but at what point does a depression become noticeable (what depth spread over what length, assuming smooth transition over at least a few inches)?  And is a 65” longboard too much?  The factory says they use the 3M boards.

 

Next, I know that the board should be used in an “X” pattern (45 deg to long axis) but should the board be parallel to the long axis of the wing at all times, or should it be parallel to the LE or TE near the LE/TE, transitioning in a fan pattern to parallel to the spar over the spar (see attached graphic)?  Does this make sense to anyone?

 

And what about either covering the entire surface with filler first and then sanding, or trying to find & fill the low spots, then sanding & repeating?

 

Pat Cohenour

IV-P in progress

patricktc@cox.net