The stabilator on the RV-12 as built to plans has squared-off tips, giving it, in the opinion of most builders it seems, an unfinished look. I always sort of liked the look, but very much disliked the tooling holes (12 or so can be seen in the pic below) in the end ribs as well as the many holes in the wing tips where the tabs are bent and riveted and other holes in various places on the fuselage. I'm convinced that all these holes were left
there in order to dirty up the aerodynamics to keep the speed below the LSA limit of 120 knots. My plan all along has been to embark on an extensive aerodynamic clean up as soon as the FAA hands me the airworthiness certificate. The stabilator also was limited to exactly an eight foot span to keep it legal for trailering on the highway. Tips put it over the limit.
A couple of after-market companies make and sell rounded tip fairings and I've seen quite a few RV-12s with them installed (legal only after the airworthiness certificate has been awarded), but I couldn't decide if I liked them, other than the fact that they close all the offending holes.
Then, fairly recently, the Mothership got in the game and offered an officially-blessed kit. What actually pushed me over the edge was doing the recent service bulletin 18-02-02 (covered in the previous post). Complying with this SB involved drilling out a lot of rivets (punching their steel mandrils into the interior of the spar box) and drilling a lot of new holes in the spar box. All this
resulted in quite a bit of debris in the spar box where it couldn't be reached. It occurred to me that removing the end ribs as required to install the new tips might allow me to shake out a lot of the debris. It still had to exit the few holes in the sides of the spar box, then make it through the lightening holes in all the ribs. I could hear all the crap rattling around in there and I couldn't stand the thought of flying that way. Tips it would be!
Installation of the tip kit involved drilling out 94 rivets to remove the existing end ribs (remember, I have achieved world-class status as a rivet remover), then replacing the end ribs with new ones reversed so that the flanges are out rather than in. With the end ribs out, the shaking commenced in the driveway outside the shop. I may have resembled a sign-spinner on a street corner in LA. Along with a small amount of metal, I started seeing bits of shredded fabric, and I knew immediately
what that meant: mice had built a nest (shown in the pic above) in the spar box. Visions of metal severely corroded by mouse urine danced through my head. Inspection with a super-bright flashlight showed the nest to be not far from one of the few holes in the spar and I was able to hook most of it with a bent coat hanger and extract it (shown in the picture above). A sudden epiphany lead me to tape a flexible piece of PEX tubing to the Shop Vac hose. With this rig (pic at left) I was able to suck out not only the remaining bits of the mouse nest but all the metal debris which started all this.
At this point I inspected the entire interior of the stabilator with a bore scope to look for mouse urine corrosion. Happily, the only spots I found were on the end ribs which were removed and replaced with the new ones in the kit. A few small corrosion spots were found on the interior skin adjacent to the end ribs. These were sanded and primed.
I keep live-capture traps set all the time in the shop (yeah, I'm that tender hearted), and had trapped and relocated a couple of mice a year or so ago. Nothing since. They had to be the culprits.
The new end ribs have to be straightened by fluting the flanges, just like all the other ribs in the
airplane. The kit instructions say to modify the fiberglass flanges which slide underneath the rib flanges, making appropriate notches to clear parts of the spar, shop heads on rivets, and the humps produced by the fluting. Lots of trial fitting here.
The instructions say to trim the fiberglass flanges to 15/32nd of an inch, which really means something less than 1/2 inch. If this isn't done, the flange won't slide all the way in. I used a Dremel tool with a sanding drum to "scallop" the fiberglass flange to
clear the fluting humps. Files were used to make the rest of the notches. I was not completely pleased with the cosmetics of the finished product, but I keep telling myself that perfection is the enemy of flying your airplane.
