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Rudder service bulletin 1379 2nd December 2022

BritishCubBloke

SPONSOR
Bellingen, NSW, Australia
What do we think of this? Basically mandates replacement if pre 1974 or otherwise found to be of 1025 steel. Have there been failures to cause this?


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This looks like complete BS. A few PA-12’s with rudder mounted beacons break their rudders and now all fabric Pipers have to replace their rudders. What an overreaction. What do all the experienced folks that have been wrenching on these birds for most of their lives have to say about this? How many cracked rudders are you seeing?
 
I don't see PA-12 listed in the models affected portion of the SB. Maybe because Piper no longer owns the PA-12 type certificate.
 
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The PA-12s had PA-18 rudders, if you have a 60 - 70 year old rudder…you might want to replace it…
 
Piper's just protecting their interests and TCDS via a SB for commercial ops. In the meantime is the FAA in NPRM mode yet? The tech data I read for the examined tubes indicated compromised metal was present, not factory new 1025. If it were mine under Part 91 ops I'd look at the rudder tube area above the upper hinge for reduced thickness and potential loss of strength.

Gary
 
You know this is a BS CYA SB when even the non balanced non electrical equipped J-3 rudder is listed.

is this coming from the PA-12 on floats a couple of years ago with the rudder bent over with the light on top?

Not many J-3’s with a light attached to the top of the post either.
 
A local shop is paying particular attention to that tube and rudder hinge bushings. Side pressure is applied to the rudder top to see if it's weakend. Loose bushings indicating unusual wear are replaced. Not sure of the eventual outcome.

Gary
 
It’s a service bulletin, not an AD. That sounds like lawyers advised Piper to cover themselves given the known failures. These planes have lasted longer than they were designed for. Another point, similar to Cessna’s SID, this bulletin isn’t required for the majority of the affected airplanes. It simply establishes that the manufacturer has acknowledged a problem and recommended a solution.
 
It’s a service bulletin, not an AD. That sounds like lawyers advised Piper to cover themselves given the known failures. These planes have lasted longer than they were designed for. Another point, similar to Cessna’s SID, this bulletin isn’t required for the majority of the affected airplanes. It simply establishes that the manufacturer has acknowledged a problem and recommended a solution.

”these planes have lasted longer than they were designed for “, a simple statement to justify a 4130 powder coated new rudder. Especially if yours is not original and has been changed with a tube to support beacon or whatever light attachment. That’s the common denominator for failures. Cost should not be a factor as well.
IMO,
JK
 
Interesting that I cannot find this service bulletin anywhere but here. Not on Piper's website. Where did you get it?
 
The PA-12s had PA-18 rudders, if you have a 60 - 70 year old rudder…you might want to replace it…
Yes, maybe, subject to IRAN. Mine was carefully inspected a couple years ago. It's never had a beacon on top. I agree with the concern.
 
Those potentially affected by this might want to read the NTSB's Docket regarding the failed PA-12 rudders. Pay particular attention to those developed by the Materials Lab and Structures Group. My take is there's not much strength reserve with 1025 tubing compared to 4130, especially when compromised by surface corrosion or vigorous media blasting.

Gary
 
Received this SB from Piper today via e-mail. I'm not aware of any issues with J-3 and PA-11 rudders and none are mentioned in SAIBs for the type certificate [A-691]. The rudder on my airplane was bead blasted, epoxy primed, and inspected before covering in 2013. I won't be complying with this service bulletin.

I wonder if new rudders for J-3s and PA-11s made by Univair and others use 4130 steel. My guess is that to comply with manufacturer specs for a PMA approved part, they are made from 1025 steel, but I emphasize that is a guess.
 
Here's why the NTSB in their rudder loads study concluded 4130 steel is preferred over 1025 for this application. Ftu mentioned below is the ultimate tensile strength of the material. Estimated propeller effects on rudder post fatigue were minimal and worse at idle. Both steels work...one is more resistant to surface contamination and bending stress:

"9.0 Conclusions
1. The material properties of AISI 1025 and AISI 4130 steel show that AISI 4130 has, in some cases, somewhat better corrosion resistance.
2. The ultimate tensile strength and endurance limit of AISI 4130 steel is 64% higher than AISI 1025 steel.
3. The tensile yield strength of AISI 4130 steel is 94% higher than AISI 1025 steel.
4. The calculated bending stress in the rudder post due to the certification maneuvering loads are 28% of Ftu on average for 1025 steel and 17% of Ftu on average for 4130N steel representing a 50% increase in the margin of safety for 4130N steel with respect to the endurance limit.
5. The calculated bending stress in the rudder post due to the certification gust loads are 33% of Ftu on average for 1025 steel and 20% of Ftu on average for 4130N steel representing a 76% increase in the margin of safety for 4130N steel with respect to the endurance limit.
6. The effect of a stress concentration due to a corrosion pit is more critical for 1025 steel increasing the bending stress in the rudder post above the endurance limit for much smaller pit sizes.
7. The propeller blade pass frequency is significantly higher than the natural frequency of the upper rudder post."

Gary
 
Posted this at the SWP site thought I should share:



I think some interested parties shoos work up an AMOC (alternate means of compliance)


-incorporating a sleeve of 4230 tubing inserted through the top and extending past the upper hinge 8”


-chaise”the rudder post with an aproropret tool to get clean and smooth the inside of the bore so the nesting tube will clear without excesse force.


-fish mouth lower end of doubler tube 3” to remove localized stress concentration.


-swab the interior with epoxy primer


- insert doubler tubing with 2226 structural adhesive or equivalent.


Something like this.


couple of observations both the pa12 and pa14 that failed or what 1948-ish aircraft? What are the odds both have original rudders, I would have to say vary slim but…


Both aircraft were on floats during failure and float ops rattle the **** out of the empanage.




Rocket
 
I’ve never seen an issue with a 65 HP J-3 Cub. If this is the case, then might as well replace the whole airframe, since the sky is falling.
 
Float ops require use of rudder, maybe more than other landing gears? They can be directionally or longitudinally unstable when on them in my experience (they can create adverse yaw from float surface area in front of CG). Often additional fins or fillets are installed to help, as well as wing dihedral or the lack thereof being critical. My PA-12 would go play on its own unless constantly corrected. Other float aircraft felt neutral to positive stability. Perhaps the rudder on some planes or some gears gets more of a workout which eventually fatigues the metal?

Gary
 
No fin until the end of ownership. We discussed this some privately...I had those useless springs on the lift handles cables to the rudder. I did try a borrowed ventral fin and it helped but sold the plane before much more trial. The NTSB seems to be fishing in #22 for an explanation of the rudder failures. Corrosion, surface imperfections, top beacons, 1025 strength margins vs 4130, material fatigue, etc.

I'm not a materials engineer, but as a former owner of several Piper 1025 rudders I'd now ask how about doing (or estimating) some dynamic stress testing to failure for the components (versus only the static loads CAR 3 required). Figure out what loads rudders experience (they hint at that via their rudder area affected and area centroid vs rudder post spacing discussion). Test them to failure using the various metal conditions noted plus additional loads from beacons. There's something to be learned here if someone really gives a ****. It's easier just to SB or AD the problem away.

Gary
 
When the NPRM gets posted, be sure to comment. As with the Champ spar AD, there is a chance that lower horsepower aircraft may be subjected to less rigorous scrutiny.
 
Anyone purchased 70% nitric acid for the Piper Service Bulletin 1025/4130 determination test?
 
Mine is 4130, tested with 70% nitric (which was a hassle to get) today. The drop of nitric is actually on the tube in the pictureIMG_3276.jpgIMG_3276.jpg.
 

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