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Possible Rudder Airworthiness Directive

7 failures out of 31,000 rudders. I am not concerned. I know of many far worse issues with our airplanes than these rudder posts

I just read a news story about some sort of proposed automotive recall (airbags maybe?).
They quoted someone as saying something about recalling xxxxx number of cars due to only x numbers of problems being overkill.
It immediately made me think of (proposed) AD's like this one.
 
Well, again I am with Steve. One AMOC has to be to allow a 4130 post welded in to the old rudder. But the better alternate will surely be an insert - a 4130 tub shoved up in there and held with epoxy. I could go for rosettes, but they are overkill.
 
Inspection should include pulling on the top of the rudder with some specified amount of force. Calculated max aerodynamic load times the standard 1.5 safety factor.
 
Inspection should include pulling on the top of the rudder with some specified amount of force. Calculated max aerodynamic load times the standard 1.5 safety factor.

Gordon, in here is a link to the two Docket Numbers the NTSB has developed. They conducted stress analysis and examined some of the affected rudders. I takes more horsepower than I have to transfer their data into the side force loads you suggest. Maybe you could have a read of both via their Docket page and see what you can come up with?

Until then, there's the "Larsen Test". He gives them a good sideways push, and if they survive they're good to go for now.

Gary
 
Not very informative. I just glanced at the proposed AD and did not see any allowance to replace the post on existing rudders - something that could probably be done for $200 each, in moderate quantities.

Of course, 30,992 rudders could be produced inexpensively once the jigs are all set up. Right now, onesies and twosies are $800 each. Not gonna break my bank, although I will need three.
 
Gary, I'm not qualified to evaluate the aero loads on the rudder top, however I do believe that the Larson Test, when integrated with a TLAR evaluation, should be appropriate.
 
How about removing the J-3 cub, Vagabond and ragwing pipers under 135HP all together? I’ve yet to see any official documented and presented rudder failures on those models. IMO This is an absurd and expensive “shotgun” proposal.


Here is the direct link to add your comments to this proposal AD.
https://www.regulations.gov/commenton/FAA-2023-1893-0001

edit to add, General Aviation is going down the tubes, this will hurt a lot of Piper owners who can barely afford it in the first place. What’s going to be the next obscure all inclusive AD?
 
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Thanks Steve Pierce….you could make money replacing tons of rudders, but instead, you understand pilots and their aircraft and try to do the right thing…I’m restoring a J3 for a guy, and he opted to replace his rudder, that’s fine, his choice. I was more concerned about his rudder pedals…the return springs have worn nearly through the tube. IMG_0604.jpg
 

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To reiterate what I think I read in the proposed AD...
150HP+ and a rudder mounted beacon = 2 years to replace rudder
150HP+ or rudder mounted beacon = 3 years
Neither of the above = 5 years
 
To reiterate what I think I read in the proposed AD...
150HP+ and a rudder mounted beacon = 2 years to replace rudder
150HP+ or rudder mounted beacon = 3 years
Neither of the above = 5 years

This does seem extreme when you consider 7 failures out of 39,000 rudders over a period of about 70 years +/-.

I haven't read the reports. How many of the failed rudders had been hand straightened in their past without any log book entries? Don't try to tell me that this hasn't been done.
 
To reiterate what I think I read in the proposed AD...
150HP+ and a rudder mounted beacon = 2 years to replace rudder
150HP+ or rudder mounted beacon = 3 years
Neither of the above = 5 years

kinda screws over the J’series and some PA series over a blanket rule, doesn’t it.
 
Another potential contributing factor, the NTSB's materials analysis notes, is prior surface abrasion and blasting material imbedded in the metal. It takes a read of the two Docket packets linked in Post #34 to see why they arrived at that conclusion. They looked a load factors and the potential location of those air loads. They also considered stress from flexing over time, which was worse at low rpms I recall.

Basically the 1025 barely meets the current design criteria for strength under specified conditions. Fix is to replace or strengthen in the weak location I believe.

Gary
 
Turns out that a 3/4” OD 4130 tube slips right in to my spare J3 rudder. It will take about 45” of tube to go well beyond the stressed area, and sit right on top of the steering arm casting. spruce has .035 and .049. The .035 adds about a pound; the .049 closer to two.

The fit is tight enough for no rattling around, but not so tight that it has to be driven in. A little epoxy cement would make it slide in easier.

Our J4 has three hinges on the rudder. I wonder if some of them have stainless rudders - ours has stainless elevators.

i haven’t typed up my comment yet - maybe I can find some data on relative bend resistance between 3/4 and 7/8 tube first.
 
Why 45”? Why not go a few inches above and below the point of failure? A 6” sleeve would do everything a 45” piece would.

15 years ago I bought into the idea to toss mild steel and replace with 4130. Nothing lasts forever. Extending the life of 70 year old airplane parts is a questionable investment.
 
Here is what I think I will send - I am still looking at it:

I am preparing my submission. The folks at the Federal Register say they do not really like repeat comments, such as one might send to a Congressperson. I am sure multiple comments will make a difference, especially those kinds of comments that say "since there have been no failures in J3/J4 aircraft, I submit that they should be omitted from the AD.


Anyway, here is what I think I will submit:


Re: Docket 20213-1893, proposed AD 2023-00389-A


I submit that:

Since there have been no reported failures in J3/J4/J5 aircraft, that these aircraft should be dropped from the proposed AD.

The AD does not allow for the simple replacement of the main tube in the rudder with a 4130 tube. This is something that is easily done in the field. Similar airframe repairs have been done for almost a century on damaged tube structures, and are allowed by AC 43.13.

The FAA should consider an inner tube as a fix for the problem. A 3/4" OD 4130 tube can easily be inserted from the bottom ( I have tried it) and the fit is snug, but not force-fit. A 45" length will cost under $30 (not including shipping) and can be inserted from the bottom to rest on the tailwheel steering arm casting. It cannot escape.


The existing 7/8 OD tube can easily be cleaned out using a shotgun barrel cleaning kit. Once any contaminants are removed, a good quality epoxy cement can be used to anchor the inner tube in place and add to strength. It will also serve as a corrosion inhibitor. (Note that this is not a good idea for an otherwise unairworthy rudder - if cracks or corrosion exist, the rudder should be replaced/repaired whether or not there is an airworthiness directive.)


The 4130 inner tube is available in various thicknesses. I suggest that .035 wall is adequate - a quick computation indicates that a 24" length of such tube can easily support a 200 lb load in the center, with a safety factor of 1.235. (On-line calculator roguefab.com) By contrast, the 7/8 tube on the new rudders will have a safety factor of 1.716, assuming .035 wall and the same load.


If one needed to approach that safety factor, an inner tube of .049 is available. It would yield a safety factor of 1.634. That, with whatever strength is left in the original 1025 tube combined with the bonding strength, would yield a rudder almost totally compliant, at the cost of only approximately two lbs. If the .035 wall is sufficient for category III airplanes, it would add less than a pound. Neither of these weights are significant for a J3 or J4 application. The .049 wall tube is actually cheaper by almost half.


There are all kinds of advantages to including an inner sleeve approach - cost is just one. Simplicity is another (I note that some category III aircraft have triple hinge rudders, and those may not be available at all). The big deal is those aircraft with expensive paint schemes. Matching a complex scheme with paint that costs several hundred dollars for each color and requires special equipment to apply could easily add $2000 to a new rudder project.


Please consider expanding the options if you determine that this AD is required for all 1025 steel rudders.
 
Bob Turner; with all due respect....I love what you are doing and wholeheartedly agree with proposing an alternate solution. But to really attempt to swing the meter a bit...my opinion would be that to include a brief test and results...would be significantly more favorable than what is currently offered.

Most folks don't realize that the FAA doesn't have many subject matter experts left, those positions filled these days, with "compliance" folks, rather than actual engineering....you know...the kind with MATH involved...You will note that ALL of their findings are observations or anecdotal. No stress Calcs of any kind were performed. (or at least not included in the report).

It would not be difficult to build a simple test fixture, simulate the mounting points of the rudder on the aircraft, cycle test to failure a few test specimens. The results and accompanying engineering report would be valuable as gold...and increase the likelihood of a favorable AMOC decision many fold.

Test labs, are plentiful in the aerospace business, my experience is that testing like this, would probably be under $8k and a fixture could be built for under $1k.

Specimens for failure proving and specimens for AMOC acceptance would be required.

simulating the loads would not be overly difficult (from what I have seen) which is to state that the failures all have commonality...heavy on the end, some level of excitation during flight and linear, sideways-downstream yielding.

What I believe the FAA is concluding for themselves is that the 1025 substrate is suffering from probable work hardening, most likely from a combination of heat affected zone from welding, combined with the much more significant live loads imposed by the increased mass of the beacon. They are guessing, as Gordon eludes to..that the original design, is inside the failure modes safety factor. ( they are probably correct too ).


4130 is a much better material choice and particularly if post-weld stress relief was included in the fab process...I guarantee no-one stress relieved the 1025...Given that most, if not all of the 1025 rudders were gas welded...the variables keep adding up...but heat affected zone in the proximity near to the weld, is likely, as is work hardening over the life-cycle of the beam.

This would be a great time, to raise a little funding, build a fixture, test to failure coupons and demonstrate passing coupons to higher than required safety factor and offer a well planned AMOC to the community, via the FAA. Not only would this strengthen the community, but...could improve the FAA stance, if we demonstrated our willingness to be a part of the solution, along with the knowledge and acumen to resolve our aging needs.

Again...please don't take my two cents, as criticism...it is definitely not intended as such. I think your solution makes an absolute ton of sense and I think the FAA's proposed AD is over- reach.

They do, however have an obligation to address the issue, once it has been brought to light.

With much respect,


Steve.
( I am feeling lucky to have bought my oversized PA-14 Rudder out of 4130 last year for the Fat Beast).
 
FatCub300,

Respectively, please read the NTSB's analyses I linked in Post #34 for the two Dockets. Two extensive lab and mechanical reports. If that's not sufficient, then what else is required? Not saying there's more, just asking. The FAA is the parrot in a cage here, in my opinion, just repeating what the NTSB has provided them.

Gary
 
Gary, the link on post #34 takes me to a link that says that link is currently not working.

I'd like to read the NTSB report, but thus far haven't gotten me grubby mitts on it...My point was simply that we would need to provide an engineering report, showing that testing was performed in a controlled and certified test lab and that the proposed AMOC meets or exceeds the certified requirements. Again...I'm experimental already...and my Rudder is 4130 and has no upper beacon...I'm happy to help though!!

Steve
 
HI Bob, that’s a good write up, but I feel we are trying to move the goal post for the J series etc, giving them ammo.

We Give these government people an inch they’ll take a mile plus extra. I sent my comment with a hard “doesn’t apply” and show us “documentation” for the lower HP non-installed Rudder monstrosity beacon housing. Don’t give them ammo, stand up hard line.

The AMOC is a good fix IMO for the other category Aircraft, but shouldn’t be necessary to our aircraft class IIi
This IMO is a completely separate issue to the Big brethren Supercubs, Super Cruisers, etc.
 
Gary, the link on post #34 takes me to a link that says that link is currently not working.

I'd like to read the NTSB report, but thus far haven't gotten me grubby mitts on it...Steve

Hi Steve and others, click on these links then select the various NTSB rudder studies and loads. It may not be 100% of what's needed to develop an AMOC, but it's supporting data for those that are interested in what's been done so far.

ANC20LA059: https://data.ntsb.gov/Docket?ProjectID=101415
ANC21LA064: https://data.ntsb.gov/Docket?ProjectID=103552

Gary
 
I'm not an engineer, but after rereading the links in #54, I suggest this process as an AMOC. Either assume the existing rudder is pre-June 3, 1974 material (AISI 1025; 7/8" OD; 0.035" thickness), or test as suggested with acid to confirm or deny if desired. Also assume the rudder may be partially compromised from any manner of surface imperfections or prior fatigue loads.

Find someone with the engineering expertise to determine and substantiate if a tubing insert alone (AISI 4130 normalized; 3/4" OD; 0.035", OR better yet AISI 4130 0.049") will equal or exceed the material strength and endurance limits of the post ECO dated June 3, 1974, or current manufacture. If an insert can provide that assurance, I'd ask the FAA to consider that via a professionally substantiated proposal. They are likely to say that without knowing the current condition of the rudder, the insert may have to carry the majority of the stress and subsequent loads.

To finish, here's the NTSB Structures Group's conclusions:

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
 
Gary,
Thank You for the links. GREAT reading. I am shocked they did this much analysis. It definitely lays the ground work, pretty exactly as you have outlined. I also agree on going to .049 wall 4130. The question I have is whether they will consider a sweeping AMOC, without a DER Report?

Steve
 
Steve, ACO approved DER's may be limited in their Structural authority to one situation AMOC's for AD's, as I've read (or understand). That's not to say they can't offer substantiating data for other projects or AMOCs, however.

What's that mean? What I'm suggesting is to include structures engineering data in support of any specific AMOC comments. I've found it's often beneficial to "butter their toast" with substantiating paperwork when working with the FAA, but that's only as an owner. The whys and hows are best left to experienced A&P's and engineers.

Gary
 
Gary,
IF there is anywhere on earth that this might work, it's your back yard...The Northwest Mountain Region eats, lives and breathes Boeing and they are all up to the hiney on 777X re-cert, your advantage is distinct. I'm going to read this all again and really digest, but it is interesting (to me at least) that they went to the trouble they did, sectioning and with SEM and didn't point out much in terms of propagation issues...it all seems to center for them on metallurgy, which is good...their focus is simply on differential strength as equated to ultimate failure and towards the safety margin of the much more modern and favorable 4130. It makes the argument pretty easy to encapsulate....We agree...4130 GOOD...the methodology is a bit immaterial, IF the insert can demonstrate the ability to bear ALL of the load. The only drawback I contemplate, is verifying a significant percentage of surface contact, if a bonded insert is the method.

In the Boeing world, we would probably have to provide X-rayed samples...maybe here demonstrated physicals would suffice. The bonded sub-assembly should be stiffer, stronger and significantly less prone to surface corrosion, particularly if ID is corrosion proofed in an acceptable fashion...( pour, swirl, empty, repeat).

I think everything you've proposed makes sense here. IF...they don't like the safety factor of simple normalized 4130, it wouldn't be hard to evaluate heat treating the tube...125-145ksi is very typical and it will easily go to the 180-200ksi range, if needed...(which I don't think will be necessary )

my gut says the .049 wall in the normalized condition will be a solid improvement.


Steve
 
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