This process is noteworthy because it will prevent cracking in the forward spar of the horizontal stabilizer, originating at the stress relief notch at the inboard end of the spar flanges. Basically, the modification makes the spar caps softer, by removing portions of the upper and lower caps and installs finger doublers to distribute the load into the upper and lower spar straps. We chose to incorporate the SB instead as preventive maintenance. Installation of the mod kit is challenging as it requires removal and installation of rivets in very confined space between the upper the lower skins. Consistent good rivet removal technique is essential so we did a lot of studying and talked with local airframe shop mechanics on how best to remove rivets: we used a punch to punctuate the dimple at the center of each rivet, used one-size-smaller drill to remove a portion of the center of each rivet, used a soft chisel to remove the factory head and used a punch and a pair of wire cutters to wiggle the rivet shop head out of the hole. We made no changes to the design of the modification , but we made some process improvements:
- we left the flush-heat rivets in the center of the forward spar, i.e. we never completely separated the left half of the stabilizer from the right, which made the stabilizer much easier to handle and maintained alignment of the L/H and R/H halves of the stab
- we using the rivet removal drill guide shown here; not sure why Vans does not mention this, made proper removal of rivets much easier.
Successful removal of the forward rib
and strap attachment rivets:
which will now include the finger doublers and new aft rib angle in the stackup.
Here is what the installed SB looks like on the forward spar face,
and on the aft spar face (R/H side)
and LH side:
and with ribs re-installed, awaiting touch-up prime and paint.
No comments:
Post a Comment