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Likes: Is there a way to tell if a covered -18 rudder assembly is constructed of the original 1025 carbon steel or the newer versions that are constructed of 4130 low-alloy steel? Thanks in advance!
PA-18 Rudder Steel Identification
Is there a way to tell if a covered -18 rudder assembly is constructed of the original 1025 carbon steel or the newer versions that are constructed of 4130 low-alloy steel? Thanks in advance!
Dig through these Dockets (https://www.supercub.org/forum/showt...601#post819601) Somewhere in the test documents it mentions part material by aircraft serial number or year. I don't know how to tell them apart visually. Maybe a pin punch test? Just guessing.
Gary
I have a PA-12 with -18 tail feathers. I'm going to dig through my paperwork some more tonight so hopefully the purchase receipt is in there or it is spelled out in my logbooks somewhere.
"In a Piper engineering change order (ECO) dated June 3, 1974, the specified material for the rudder post was changed to normalized AISI 4130 low-alloy steel with the same dimensions. The material change to 4130N was incorporated into the P/N 40622 engineering drawing at Revision U in June 1974. The P/N 40622 rudder can be installed on PA-12 and PA-18 airplanes and some other single engine Piper airplanes."
"The PA-12 and PA-18 airplanes were designed for static load conditions as dictated by the regulations in place at the time. However, in service, the loading conditions on many parts of the structure, including the rudder, are not static and contain dynamic alternating or repeated (fatigue) loads. It is well documented that fatigue failures in metal occur at stress levels well below the static strength stress levels. Aircraft designed in accordance with modern regulations must account for fatigue loads."
"All 4 failed rudders examined had evidence of corrosion on the exterior surface of the rudder post in the vicinity of the fractures." Prior evidence of surface blasting or scratching was also noted (my words).
Gary
Last edited by BC12D-4-85; 01-28-2022 at 03:29 PM.
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If you read that NTSB report they say the change was made in 1974. I seem to remember a Piper service document that called out a test involving a chemical that could be applied that reacted differently between 4130 and 1025. Pull the steering arm and inspect for internal corrosion. Found some pretty scary ones where rust would keep falling out as long as I tapped it on the ground.
Not an expert in recall but the Dockets linked in #2 didn't stress internal corrosion over external pitting and corrosion. Have a look at their lab analysis pictures and text. It would appear that an internal sleeve could be inserted at the top to reinforce the problem area? Otherwise any AD requiring replacement would devastate the fleet.
Gary
To determine if you have 4130 or 1025 using nitric acid , do a search for AD69-23-03. There is an old post on this site . Turns yellowish orange or brown if 1025 with a drop of concentrated nitric acid on clean tube
Doug
I remember reading that somewhere and couldn't find it today. Thanks for posting this.Originally Posted by brown bear
This is what happens to a mild steel tail post after 70 years
mydoghasa170 thanked for this post
That’s a different problem than what the tentative AD is addressing but a good reminder that there are other areas to keep an eye on in addition to. Good stuff.
This is what happens to a mild steel tail post after 70 years
Thats what I did on my 180 cub during rebuilding.
lt was as a preventative measure responding to the resent failures.
Inserted 4130 tube to about 6 inches below the hinge. Very easy to do.
Ed
http://www.supercubproject.com/drawi...s/A3310113.pdf
Maybe remove rudder and steering horn. Brush out internal corrosion with shotgun brush (10ga?) and solvent (like Hoppes?). Coat internal tube with corrosion proofing. Insert 3/4"chromoly tubing (full or only inside trouble area) and blind rivet through both tubes at top as witness mark. Not an A&P so take this as only a suggestion.
Gary
This is a recommendation by the NTSB to the FAA. The NTSB recommends lots of things. There are tens of thousands of these rudders out there and 6 have failed and majority on floats. Not discounting the need to inspect but I kinda doubt the FAA will pursue an AD at this point.
Here are a couple of methods for determining steel alloys.
The main elemental differences between the 1025 and 4130 is the absence of Chromium (Cr) and Molybdenum (Mo) in the 1025. The Manganese (Mn) percent by weight is about the same for each.
The main alloying elements in weight percent for 4130 are: Cr - 0.8-1.1 and Mo 0.15-0.25.
I think the best test method for determining 1025 from 4130, is an Energy Dispersive X-ray Fluorescence analyzer (ED-XRF). The test is non-destructive and there are portable handheld devices available. If there is a metal scrap yard around, they may have one.
Sorting 4140 from 4150 (verichek.net) This link refers to the difference of the Mn concentration between 4130 and 4150, which are small. My assumption is it would be an easier determination between 1025 and 4130 with the Chromium differences.
The nitric acid test is interesting. If there are any images showing the differences with this method or a direct link about it, please post.
One method which has been around for a long time is the spark test. A trained eye might be able to see a difference between the plain carbon steels and low-alloy steels. I think a Dremel tool would suffice as the spark generator.
The figures below give the spark patterns of different metals and alloys.
Generally you wouldn’t use rivets in steel structures. The common method would be to do rosette welds to hold the sleeve in place.
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Thanks for the welding note above. I hope it gets resolved w/o a widespread AD. The tail beacon's effects would seem to contribute something to the side bending moments over time. I need to reread their analysis of that.
Floats use the rudder lots in flight especially if longitudinal stability is minimal. Then there's the water immersion of the lower tail area climbing on step and settling in after landing.
Gary
I post with trepidation alongside all you brilliant folks - for likely obvious reasons. And I get nervous when I keep thinking something that seems to go against the grain of all you smart folks! So I keep wondering if I am missing something as regards this topic -
This thread, the other one currently running titled "Cub Rudder Failure," and the older Sept. 2020 series on the same topic over in the "Oops, darn it . ." thread are all new info to me and are sufficient to have me headed at the paper work for my late-1940's PA-whatever to see if I can tell if my rudder was ever replaced with one built from 4130 steel. If so, I will smile and go about my business. If not, I will simply beat feet to Airframes Inc - give them the requisite $800 for a new rudder in 4130 steel - recover, paint, and install it - and sleep peacefully. I am not rich, and am in an apparent minority of folks here with a PA-whatever valued in only the mid-5 figures that I have to maintain with significant levels of my own sweat equity - and yet this seems to me to be an easily fixed issue without any worry over decimating the fleet or even my wallet. The threads have done what they ought - alerted me to a potential problem that I want fixed on my birds more than anyone at NTSB or FAA. I am headed at it irrespective of any potential AD. In other words, the info presented here is sufficient for my risk management philosophy to make me assure that I have a 4130 steel rudder.
But some of what's here has me worried that I am not worried enough! Is there an undercurrent of concern with this issue that it could cause the FAA to require complete replacement of all airframe components made of 1025 steel? What all would that be? And such an AD, if realistically approaching, would truly decimate lots of aircraft and wallets? What really at stake? I know some folks can only sing the "Be very very afraid" song where our largely intrusive and unhelpful government is concerned - but would some of you please post your thoughts that explain the worst we might really be facing as their bureaucratic approach to this particular series of structural "failures" marches on. Specifically, will my replacement of my old 1025 steel rudder with the new 4130 steel one be sufficient to preempt further AD demands for this issue.
Thanks, Steve
Steve if I had a Piper rudder I'd go have a conversation with whoever you trust to maintain your plane. Agree on a plan for airworthiness and quit worrying. In this rudder case correlation of the various factors the NTSB notes does not mean causation in my opinion. After all the studies they kicked the can to the FAA.
Gary
The biggest problem with jumping on replacing the rudder (or any other component) with a pending AD is that what you choose today as the replacement may not satisfy the eventual AD requirement. Best solution for now is inspect what you have and decide on a course of action based on that inspection. If you are really worried about it, cut the fabric Bach around the area above the upper hinge and look under magnification. Truth be told, about a 10 lb load pushing on the top of the rudder on both sides will likely show any deficiency.
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There are 20,000 plus airplanes out there effected. I have rebuilt, repaired and maintained a lot of them and am not jumping to conclusions. We have had several Safety Advisories in the last 10 years that did not result in ADs. The last few the FAA Engineers that specialize in these issues with Piper have reached out and asked our advice. That has not happened yet that I am aware of.
I think the real threat to tube and fabric aircraft is the lack of experience at maintenance facilities, coupled with the expense of doing research.
For instance, I am now aware of a maintenance effort that will cost the owner over $3000. Had I known about it three weeks ago, I could have saved them $2600 of that. I did the research right here, and Steve Pierce had the solution for me within hours.
A totally different problem occurred Friday, and almost resulted in a "strike" aircraft. We found a service bulletin that allows continued operation - but finding such things requires owner involvement. Cherokee shops don't really have the background or the time to do the research.
Preflight your aircraft. Every now and then, check those clevis bolts on the rudder horn - they might be a more likely failure point.
Another thought on this at -30F....Cub balanced elevators and rudders are somewhat similar. Both are exposed to prop blast, air loads, and weather. Don't know about how much relative rotation about their axis occurs in flight over time. Rudder hinge tubes originally were 1025 7/8x.035; elevator's 1025 7/8x.049 (http://www.supercubproject.com/drawings/main.aspx). So the elevator tube was thicker and most never had a beacon stuck on their end. Both get gust locks installed.
Gary
Anyone heard specifics outside of what’s discussed in this video from Airframes? https://www.youtube.com/watch?v=TzahaGCwhzw&t=4s
No notice of proposed rulemaking for an AD.
The 2 of those I have heard of cracking both had big beacons on them, serious corrosion, and weren't straight (they looked like they had been straightened at some point). I wouldn't worry all that much, quick inspection, worst case replace or sleeve it.
were the failures exclusive to those who had the anti collision light on top of the rudder?
https://www.faasafety.gov/files/noti...A-18_REV_D.pdf
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