The Short Wing Piper Club is proposing an alternative method of compliance (AMOC) that would blunt much of the cost and inconvenience posed by a sweeping airworthiness directive set by the FAA last week. The AD, which mandates replacement of the rudders with posts made of , covers almost all 31,000 high wing Pipers produced up until the 1960s but the final number affected will be much lower because of fleet attrition and retrofits already completed. Nevertheless, the final tally will be in the thousands and will cost operators thousands of dollars as written. The club says its AMOC can reduce the cash outlay and potential downtime that would result from a massive backlog of orders for new rudders. What follows is the club's own description of the AMOC.
"removed any weld penetration and corrosion inside the tube. Then we will insert a centerless ground 4130N tube all the way up from the bottom to the top affectively doubling the wall thickness. "
What isn’t clear from the article is how the internal “doubler” is attached to the existing post.
If it’s simply inserted then it only provides protection against bending moments, not torque. So it would prevent the rudder from ultimately folding over as in the picture. But the forces on the rudder post are from torque. When the same crack occurs and the original post fails, now the upper half of the rudder would rotate independently from the lower half.
I’d like to see more details about the AMOC to see if and how this is addressed.
Why not x-ray the rudder steel skeleton first… Then decide… from engineering and the drawings…
‘OK; use-as-is’;
‘temp-repair-and monitor’;
fully repair [if able];
critical to replace [with new/same design];
critical to replace with re-designed [all aluminum, composite, etc];
Replace rudder by local fabrication using owner/volunteer talent?
BTW… the rudder serviceability inspection must include…
Visual [steel skeleton, uncovered] and dimensional [jig fixture alignment and misalignment; and rebalance [along hinge-line].
/NOTE/ It is possible, that some/many rudder-tip fold-overs may have occurred simply because the rudder is bent/twisted, out of rig, or out-of-balance [likewise elevators and ailerons].
Rimming to clean corrosion and weld, then pressed in with anti rust material and rosette welded.
I prefer replacing the entire tubing with 4130 chromoly plus any possible repairs and fabric recovery and balance.
