cubdrvr
SPONSOR
YKN(mother city of the dakotas)
Yes
Piper Rudder Airworthiness Directive Issued
- Thread starter Steve Pierce
- Start date
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skywagon8a
MEMBER
SE Mass MA6
Try this:
acrobat.adobe.com
Adobe Acrobat
sj
Staff member
Northwest Arkansas
Yes, no problem.
bob turner
Registered User
Drift on over to the J3 Cub forum. They posted a pdf for me, which I stored and printed.
skysigns
FRIEND
Yelm WA 98597
is there a pdf on supercub.org
bob turner
Registered User
skysigns
FRIEND
Yelm WA 98597
Thank you
Steve Pierce
BENEFACTOR
Graham, TX
So I removed a rudder on a 1976 Piper Super Cub today. Removed the steering arm, cleaned inside the bottom rudder post to bare steel, cleaned with isopropyl alcohol and tested with 70% v/v nitic acid. Acid stayed clear verifying this rudder post is 4130N steel.
Steve Pierce
BENEFACTOR
Graham, TX
I took an old section of an early J3 that I new was 1025 steel and tested it as well. The acid turned yellow immediately.
btracy
MEMBER
Ohio
Did you ever get anyone to verify what the reference number is?
The reference number is the number FAA assigned to the AMOC and is just below the address on the letter from the FAA that approved the AMOC. They also stamped my request letter with an FAA approved stamp. I think that also has the reference number written in with a signature from the FAA engineer that approved it.
cubdrvr
SPONSOR
YKN(mother city of the dakotas)
Yes, also in the stamp block on the original application letter.
jrussl
BENEFACTOR
Madison, WI
Mikey
FRIEND
Everett, WA
I have a lifetime supply that I got from Walmart online. Anyone in Seattle area that needs some is welcome to it. Just PM me. I’m at PAE. And I’m on the SC map.
Also, I submitted my notice of intent to use the AMOC 772-25-00191 and received a prompt favorable reply from SEA FSDO. I plan on using the bolt option.
Chris
“Mikey”
Also, I submitted my notice of intent to use the AMOC 772-25-00191 and received a prompt favorable reply from SEA FSDO. I plan on using the bolt option.
Chris
“Mikey”
Steve Pierce
BENEFACTOR
Graham, TX
My source is linked on the second page of this thread.
cubpilot2
SPONSOR
Anchorage Alaska
In 2021 I did a full restoration of my 180 hp cub. A friend of mine was one of the first to have a rudder failure while on floats and his account of what it was like to control the airplane and to land safely was frightening to say the least. It was something that I never want to experience.
At that time there was no FAA guidance as to how to correct the problem. It was obvious that a reinforcement was needed now.
Since the rudder was stripped down for fabric and after cleaning and inspecting for corrosion I reinforced the upper post area. This was done by inserting / driving a lubricated 26 inch piece of 3/4 x .035, 4130 in from the top of the rudder post. This required separating from the 3/8 tube and heating the post to reshape to accept the insert. The tube was rosetted into place and then shaped at the upper end to the original spec and incorporated it into the weld. (no upper post on this rudder). Documented the reinforcement on a 337.
My view was that the combination of the two tubes with a combined .060 wall thickness was at least equal to or greater in bending resistance (in the critical area) than a single 7/8 x .035, 4130 tube used in a new replacement rudder.
I submitted all of this history / drawings etc. to the FAA through the AMOC process and I have received AMOC approval allowing the rudder to remain in service as is.
Happy Days
At that time there was no FAA guidance as to how to correct the problem. It was obvious that a reinforcement was needed now.
Since the rudder was stripped down for fabric and after cleaning and inspecting for corrosion I reinforced the upper post area. This was done by inserting / driving a lubricated 26 inch piece of 3/4 x .035, 4130 in from the top of the rudder post. This required separating from the 3/8 tube and heating the post to reshape to accept the insert. The tube was rosetted into place and then shaped at the upper end to the original spec and incorporated it into the weld. (no upper post on this rudder). Documented the reinforcement on a 337.
My view was that the combination of the two tubes with a combined .060 wall thickness was at least equal to or greater in bending resistance (in the critical area) than a single 7/8 x .035, 4130 tube used in a new replacement rudder.
I submitted all of this history / drawings etc. to the FAA through the AMOC process and I have received AMOC approval allowing the rudder to remain in service as is.
Happy Days
BC12D-4-85
SPONSOR
Fairbanks, AK.
^^^^Did they ask for the boiled linseed oil elixir process?
Gary
Gary
cubpilot2
SPONSOR
Anchorage Alaska
Nope.
They accepted it “as is”.
Steve Pierce
BENEFACTOR
Graham, TX
Not sure why they required others to use .049” especially when looking at the specs between 3/4”x .035” and 1025 7/8” x .035.
cubpilot2
SPONSOR
Anchorage Alaska
Not sure either.
Perhaps the status of being welded into position along with the estimate that the .060 combined welded structure should be equal or greater than a single piece of 7/8 x .035 4130 in bend resistance. Equality is all that should be required.
The approval received is restricted to this aircraft only and can not be applied elsewhere.
I am very thankful for their reasonable decision!
Personally .049 seems to be a bit overkill.
But for a multiple use design the Engineering philosophy of “when in doubt build it stout” may have been applied.
This could be to compensate for unknown internal conditions (Corrosion). It sort of treats it as if the strength of the existing 7/8 1025 didn’t exist.
My rudder was in good condition.
bob turner
Registered User
Maybe it's because the applicant asked for .049. It is half the cost of .035, and less than a pound heavier. And yes - a double .035 tube of 1025 steel is way stronger than a single 7/8" .035 4130 steel.
