MAINTENANCE ITEM #29 - NEWSLETTER #56
Varga getting old? Got wrinkles in its skin? TRY THIS!
A Varga subjected to hard landings will often have wrinkled stub wing skins around the main landing gear where the upper main landing gear enters the wing. Damage from hard landings may also include a bent outboard stub wing rib, which is only visible by removing the wing joint fairing strips between the inboard and outboard wings. The rib damage usually appears as a diagonal crease in the stub wing outboard rib from an upper corner of the rib at one spar to a lower corner of the rib at the other spar.
This can be repaired by either (1) replacing the rib if you can find or make one, or (2) straightening the rib as much as possible and adding a doubler or doublers to the creased areas of the rib. I like using a doubler because it’s easier, cheaper and, if done well, adds some stiffness to the rib to help preclude a recurrence.
The lower skin can be fixed by patching it with a doubler, removing and replacing the entire skin from forward spar to trailing edge, or replacing just the skin between the fore and aft spars. I like replacing just the skin between the two spars, which I will explain in a minute.
The reason why it is fairly easy to overstress the lower skin in a hard landing is because when the stub wing is manufactured, a split is made in the lower skin so that the skin can be installed around the landing gear. This split in the skin is span-wise from the hole to the outboard edge of the skin and weakens the attachment of the outboard rib to the aft spar.
Replacing the skin just between the two spars allows you to make the split chord-wise from the hole to the aft edge of the skin instead of to the side and leaves a small strip of skin to span between the aft lower rib flange and
the aft spar. It isn’t much but it helps. I also like to increase the thickness of the spliced-in replacement skin to .040 (original is .032), which helps a little as well.
Whether the skin on your plane is unwrinkled (lucky you) or has been repaired, the best thing that you can do to preclude a problem is to add a small .080 thick clip between the lower outboard wing rib flange and the aft spar. The clip should be .080 by 5/8” to 3/4” wide and just long enough to pick up three existing rivets in the rib flange and install two rivets in the spar flange (2024-T3 Aluminum).
It may not seem like much, but this clip spans the gap between the rib and the aft spar and adds considerably to the stiffness of that area around the landing gear. Most likely, this simple fix will prevent any further skin or rib wrinkle problems short of an unintended off airport excursion.
KACHINA DOLL REPRODUCTION DECALS
4 3/4” x 9 3/4” • Printed with 6 colors on premium white vinyl for a 5-year outdoor life.
$40 ÷ $5 postage for a pair (2) of decals
Visit www.VinylGraphicsByGreg.com and click on Kachina Decal for examples and on-line ordering. Installation instructions are shown on-line. I am working on a Shinn logo reproduction and have VG-21 Decals available.