I have an Edition 1 with Edition 2 upgrades STOL 750.  In my part of the country (East Tennessee), we are plagued with "dirt daubers"/mud wasps when the weather turns warm.  The wasps are very benign as far as not aggressively stinging, but they love to build mud nests in nooks and crannies and an airplane certainly has  those!  Invariably at annual I find at least one mud nest somewhere in the plane - fortunately, they seem to avoid the cowl/engine area, but commonly I've found one in the wing root area or inside the area contained by the flaperon push rod cover.  Obviously they enter the flaperon push rod area via the "banana slot" and I've taken to covering the slot when the plane is in the hangar with a piece of sponge rubber or a shop towel to keep them out.  I have always wanted to make covers for the  access holes below the spar-attaching bolts at the wing root to keep the little buggers out of that area.

I templated the holes and made covers of 0.025.  Basically they have either tabs and/or joggles that allow them to slide into the rear of the holes and then use a single 8/32 button head hex screw to secure them.  Here's the leading edge hole cover:

Click Bond nutplates made it very easy to install nutplates in these confined areas.  They are pricey but for small jobs they make it so easy to install as they use an adhesive and not rivets, so only one hole for the machine screw is required.  The rubber fixture ensures they are perfectly aligned with the hole and keeps adhesive out of the threads:

One tip - it was very difficult to thread the rubber fixture through the hole, so I used a hemostat to get it started through the hole, masked the area off, and then applied the adhesive to the nut plate and pulled it into position - prevents getting adhesive all over everything trying to get the tip of that fixture started through the hole!

I was pleased with the end result:

Due to curvature of the wing root leading edge, there was a slight gap between the cover and the underside of the wing which I sealed-off with a foam rubber seal.  I suspect someone with panel-beating experience could anneal the aluminum and form it to fit without the seal, but that's beyond my pay grade!

Otherwise, I did a lot of filing and fitting to ensure there would be no gaps that the wasps could pass through.  In retrospect, there was likely no need to ensure such a tight fit on the inboard edges of the cover plates - in fact, they could be cut back a few mm and a rubber seal glued-on to match the present wing root seals (I plan to do this in the future).  It also critical that the leading edge cover plate's edge not impinge on the windshield - this could cause a pressure point and lead to cracking the acrylic.

As an alternative, I've seen a fiberglass cuff formed to cover the leading edge hole.  However, my mod is a retrofit mod on a completed plane and I didn't want to risk laying-up fiberglass over my paint job, even with careful masking!  There are more compromises to the fit with aluminum vs 'glass, but it is certainly at least more aerodynamic than it was and it definitely should keep the wasps out!

I posted this here in the Open Forum in case it would be applicable to other Zenith models (does the Cruzer have similar access holes?)

John

N750A