Service Bulletins 19-08-26 and 16-05-23 Published - Nose gear leg and fork

[Cammie Patch]

We just did this replacement. It's definitely a two person job.
The drill bits work pretty well, but it's not easy for the person in the cockpit to keep the bushings pushed into the hole. Definitely need to drill the holes from the inside, at least until the last bit, to clean it up.
I wrapped the strut fairing with carbon fiber vinyl, and then added a clear layer of protective film on top of that to keep the cowling from scuffing it up when installing or removing.

SBs are mandatory on SLSA aircraft, no matter what they are used for.

[Dvalcik]

Completed my SB today - short 1 min clip



https://youtu.be/3PCZEQr1_xU

[funflying]

Thanks David for the preview. I received my SB gear leg yesterday and will get started tomorrow.

One question, looks like you notched the tunnel flanges? Was this to get a straight shot to drill the gear leg or had this been done in the past?

Thanks, Pat

[Dvalcik]

Straight shot to drill use plenty of boelube. My RV is an EAB, but I don’t remember notching anything.

[joedallas]

A little reverse engineering gives me some questions and conclusions.

How much stiffer is the new front landing gear.

The larger footprint on the firewall.

Higher loads on the firewall, tunnel walls and nose gear.

The point that the inside tube ends.

If it is only welded to the outer tube at one end, is there friction between the tubes at the un-welded end.

Does the point of the stress riser move when the tubes flex at a different rate.

My deliberations

[RFSchaller]

Since Joe opened this door, I?ll add a question: Did the revised FEA predict an interior wall circumferential crack like the one that was found in the failed gear leg without a preexisting flaw? We engineers are curious about everything,🤓

[bobnoffs]

is this last post another way of asking the question in post #35?

[Jeff Vaughan]

I always dread putting the safety wire back on the Gascolator. Such a tight space.
Service the Gascolator during your Condition inspection when you have removed the old gear leg. Easy peasy

[RFSchaller]

Bob,
After your question on my post I went back and reread a lot of the thread to see if I had missed something. What I?m not clear on is did the failed gear leg failure initiate at the predicted point from the FEA? A slightly different location might mean there was some preexisting flaw.

[greghughespdx]

Originally Posted by RFSchaller

Bob,
After your question on my post I went back and reread a lot of the thread to see if I had missed something. What I?m not clear on is did the failed gear leg failure initiate at the predicted point from the FEA? A slightly different location might mean there was some preexisting flaw.

The original leg design has an inherent focused area of high stress concentration, which under significantly high (but possible) loads on the leg can cause the material at the point of focused stress concentration to yield. The result is an affected/yielded area in the tube, from which a progressive fatigue process will start at that same point, once the material has yielded. The progressive fatigue path propagates circumferentially around the tube, starting at the initial tube material yield point and in a non-visible/non-inspectable location (obstructed from view by the metal plate that is welded around the outside of the tube).

Both the FEA and the actual leg failure agree and indicate no other underlying flaw present that creates a risk of initial material yield; there is no other point from which the fatigue crack occurs. The failed gear leg failed exactly how and where the FEA analysis predicted it would after being subjected to the initial event: an operational load sufficient to cause the material to yield, followed by a progressive fatigue crack initiating at that focused yield point.

We fully verified this with our FEA review of the original design. The issue was, of course, verified as no longer present in the FEA of the new leg design. We also validated that no additional or newly-introduced issues were detectable.