A known characteristic of VHA’s first UH-1 tail rotor blade, part number 2042200-101, is paint cracking along the edge of the largest doubler ply in the doubler stack on both sides of the blade. This crack appears because the doublers are squared off and because the original paint used is less flexible than the composite material that the blade is made from.
The known paint crack appears along the edge of the outermost doubler plies, approximately 10.25 inches (26 cm) from the root end edge of the blade.
Another known paint crack occurs over the bonding strap (see illustration) installed into the upper surface grip plate for static and lightning protection. The conductive adhesive and filler putty that smooths over the braid for paint purposes may shrink and cause cracking of the paint. The paint crack usually assumes the shape of the machined slot in the upper grip plate.
There is no safety of flight concern when either of the paint cracking conditions exists; the blade is still airworthy. We have inspected a number of blades with these conditions and have never found any debonding of, or defects within, the doubler plies that can be attributed to the crack in the paint layer. No repairs are required.
White single stage polyurethane paint may be applied over the paint crack for appearance and to seal out contaminants. Be sure to scuff sand surrounding paint with 320 grit sandpaper prior to paint application.
Van Horn Aviation has taken the following steps to solve these issues:
- We re-engineered the UH-1 tail rotor blades with rounded doublers rather than the straight lines of the square doublers. We received FAA approval for the major change and began manufacturing the new blades in October 2017 under the part number 2042200-103. The new doubler plies may resolve the issue. Note that although the -101 and -103 blades are exactly the same except for the shape of the doublers, they are not interchangeable. For balance, an installed set of blades must be both -101s or -103s.
- We switched to a new type of nanoparticle paint in 2020 that is more flexible and should prevent paint cracking along ply seams. Operators with -101 blades can opt to repaint their blades with the new nano paint.