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Jacquescj6
Joined: 20 Dec 2011
Posts: 23
Location: Swakopmund , Namibia
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 Posted: Tue Jan 24, 2012 11:40 am Post subject: Tailplane front spar crack |
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Hi Guys
First thanks for all the help so far.
I have detect a crack in the front spar of my cj6 tailplane any body know how to fix this or should I get a new tail plane?
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cpayne(at)joimail.com
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| Posted: Tue Jan 24, 2012 4:31 pm Post subject: Tailplane front spar crack |
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This condition was detected and addressed back in 1995, possibly before. My CJ as well as three in the same shipment, owned by Alan Beaver and Bill Thornberry, all had similar cracks. A California DER engineered a fix which was accepted by the FAA. It consisted of a doubler made from 4130, bent to fit the inside of the spar and affixed with bolts through the spar. I went a step further and added 2024 ribs on each side to help spread the load so stress was not merely shifted to the spar just outside the doubler.
Many other CJ's were repaired in this manner. Eleven hundred hours later and no additional cracking. Old news, I'm surprised someone found an airframe without the repair. *Every* CJ mechanic should be aware, it was documented numerous times.
Craig Payne
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dougsappllc(at)gmail.com
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| Posted: Tue Jan 24, 2012 6:09 pm Post subject: Tailplane front spar crack |
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Craig,I think we may have had this discussion before, I can't recall for sure, but you are correct in that an fix was engineered, but rather it was actually "accepted by the FAA" is up for debate and really does not matter. It is in my opinion a very poor fix indeed, it simply makes the center of the spar so stiff that it cannot flex, the result is that it effectively shifts the stress the the edges of the doubler as you have correctly stated. If in fact a DER actually engineered this fix he needs to get back to his most basic directives and re read 41-13-5. It would NEVER suggest using an spar doubler of that strength on a alu structure, in that position, let alone something made of 4130 chromemoly sheet. I will admit the solutions are very limited and the basic idea of a U shaped reinforcement with a doubler plate on the back side is most likely the best way to effect the repair but IMHO the reinforcement and the doubler should be no heaver than .040 2024-T3 aluminum, NOT 4130 steel, no not even stainless steel. The structure is made to flex, it cannot flex if you use steel. Yes we have had no failures using the "engineered" fix, but that does not mean the fix was done correctly, it simply means we have not had any failures yet. I have done several with the alu and they have not failed either..................
gotta ask:
Was this newly discovered crack there last year at conditional?
Was that area previously checked?
Is checking for horiz spar cracks on the RPA's conditional inspection check list?
When I was in China many years ago I inquired about this cracking problem and was told that it was caused by the cadets snap rolling the aircraft. I also questioned them about inflight spar failures and was told that there never had been one.
All good food for thought
Best to all from snowy Omak.
Doug
On Tue, Jan 24, 2012 at 4:26 PM, Cpayne <cpayne(at)joimail.com (cpayne(at)joimail.com)> wrote:
[quote]--> Yak-List message posted by: Cpayne <cpayne(at)joimail.com (cpayne(at)joimail.com)>
This condition was detected and addressed back in 1995, possibly before. My CJ as well as three in the same shipment, owned by Alan Beaver and Bill Thornberry, all had similar cracks. A California DER engineered a fix which was accepted by the FAA. It consisted of a doubler made from 4130, bent to fit the inside of the spar and affixed with bolts through the spar. I went a step further and added 2024 ribs on each side to help spread the load so stress was not merely shifted to the spar just outside the doubler.
Many other CJ's were repaired in this manner. Eleven hundred hours later and no additional cracking. Old news, I'm surprised someone found an airframe without the repair. *Every* CJ mechanic should be aware, it was documented numerous times.
Craig Payne
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mark.bitterlich(at)navy.m
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| Posted: Wed Jan 25, 2012 10:35 am Post subject: Tailplane front spar crack |
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Based on Dougs less than positive support for this fix, it would seem that a wise thing to do would be to see the actual recommendations made by the FAA Designated Engineering Representative (DER) regarding the repair of this specific crack.
If the DER did indeed do his job and forward his repair recommendations to the FAA then there should be something on record from the FAA regarding their decision on the matter.
This is exactly the kind of thing that the FAA is there to accomplish. This is clearly a "Safety of Flight" issue and is thus is highly important.
IMHO, the first thing to do is to get a copy of the DER's report. The second thing to do is to find out if it was submitted to the FAA, followed by finding out if it was approved or not.
If someone believes that an existing fix being used on other aircraft is unsafe, and is basically just an accicent looking for a place to happen, then they should probably get with people who have had this "unsafe" fix done and work with them to achieve a safe resolution, that falls within the scope and definition of proper maint. practices perscribed by the FAA. This would probably mean starting a chain of discussion with a new DER, and without question the EAA would be a great help in an effort like this (based on my personal experiences).
Bringing a issue like this to the attention of every CJ owner and adding it to their Conditional Inspection checklist is a very smart thing to do. If you REALLY want to go by the book, there is also a form that the FAA makes available to report conditions like this for make and model aircraft. The problem with this of course is that the FAA always errs on the side of safety and that could easily result in the grounding of this make and model. The T-34 model aircraft comes to mind.
Mark Bitterlich
________________________________
From: owner-yak-list-server(at)matronics.com on behalf of doug sapp
Sent: Tue 1/24/2012 9:06 PM
To: yak-list(at)matronics.com
Subject: Re: Re:Tailplane front spar crack
Craig,
I think we may have had this discussion before, I can't recall for sure, but you are correct in that an fix was engineered, but rather it was actually "accepted by the FAA" is up for debate and really does not matter. It is in my opinion a very poor fix indeed, it simply makes the center of the spar so stiff that it cannot flex, the result is that it effectively shifts the stress the the edges of the doubler as you have correctly stated. If in fact a DER actually engineered this fix he needs to get back to his most basic directives and re read 41-13-5. It would NEVER suggest using an spar doubler of that strength on a alu structure, in that position, let alone something made of 4130 chromemoly sheet. I will admit the solutions are very limited and the basic idea of a U shaped reinforcement with a doubler plate on the back side is most likely the best way to effect the repair but IMHO the reinforcement and the doubler should be no heaver than .040 2024-T3 aluminum, NOT 4130 steel, no not even stainless steel. The structure is made to flex, it cannot flex if you use steel. Yes we have had no failures using the "engineered" fix, but that does not mean the fix was done correctly, it simply means we have not had any failures yet. I have done several with the alu and they have not failed either..................
gotta ask:
Was this newly discovered crack there last year at conditional?
Was that area previously checked?
Is checking for horiz spar cracks on the RPA's conditional inspection check list?
When I was in China many years ago I inquired about this cracking problem and was told that it was caused by the cadets snap rolling the aircraft. I also questioned them about inflight spar failures and was told that there never had been one.
All good food for thought
Best to all from snowy Omak.
Doug
On Tue, Jan 24, 2012 at 4:26 PM, Cpayne <cpayne(at)joimail.com> wrote:
This condition was detected and addressed back in 1995, possibly before. My CJ as well as three in the same shipment, owned by Alan Beaver and Bill Thornberry, all had similar cracks. A California DER engineered a fix which was accepted by the FAA. It consisted of a doubler made from 4130, bent to fit the inside of the spar and affixed with bolts through the spar. I went a step further and added 2024 ribs on each side to help spread the load so stress was not merely shifted to the spar just outside the doubler.
Many other CJ's were repaired in this manner. Eleven hundred hours later and no additional cracking. Old news, I'm surprised someone found an airframe without the repair. *Every* CJ mechanic should be aware, it was documented numerous times.
Craig Payne
===========
rget="_blank">http://www.matronics.com/Navigator?Yak-List
===========
http://forums.matronics.com
===========
le, List Admin.
="_blank">http://www.matronics.com/contribution
===========
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Etienne Verhellen
Joined: 13 Apr 2007
Posts: 141
Location: Belgium
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brian(at)lloyd.com
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| Posted: Thu Jan 26, 2012 10:34 am Post subject: Tailplane front spar crack |
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On Tue, Jan 24, 2012 at 8:06 PM, doug sapp <dougsappllc(at)gmail.com> wrote:
| Quote: | Craig,
I think we may have had this discussion before, I can't recall for sure, but
you are correct in that an fix was engineered, but rather it was actually
"accepted by the FAA" is up for debate and really does not matter. It is in
my opinion a very poor fix indeed, it simply makes the center of the spar so
stiff that it cannot flex, the result is that it effectively shifts the
stress the the edges of the doubler as you have correctly stated.
|
Yes, you are right Doug. We had this discussion on here when the list
was first started. I remember suggesting that the doubler transfers
the stresses to the spar at the end of doubler, just moving the
problem rather than solving it. I suggested a tapered or laminated
doubler so that the stresses are transferred gradually from the
doubler to the spar along the length of the doubler.
OTOH, since no one seems to be seeing new cracking at what appears to
be the new stress point at the end of the doubler, we have solid
empirical evidence that there isn't a problem with the current doubler
design. So even if it appears to be a poor design, the evidence
suggests that it is working OK.
At this point I think I am going to come down on the side of, "if it
ain't broke, don't fix it."
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian(at)lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
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brian(at)lloyd.com
Guest
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| Posted: Thu Jan 26, 2012 10:38 am Post subject: Tailplane front spar crack |
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On Wed, Jan 25, 2012 at 12:32 PM, Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E <mark.bitterlich(at)navy.mil (mark.bitterlich(at)navy.mil)> wrote:
| Quote: | --> Yak-List message posted by: "Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E" <mark.bitterlich(at)navy.mil (mark.bitterlich(at)navy.mil)>
>
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| Quote: | Based on Dougs less than positive support for this fix, it would seem that a wise thing to do would be to see the actual recommendations made by the FAA Designated Engineering Representative (DER) regarding the repair of this specific crack.
|
Well, as I suggested in my last email, we don't seem to be seeing any cracking of the spars that have this mod, even if it appears that the mod may not be the best design possible. The doubler appears to be working just fine. I would counsel that people just keep monitoring those aircraft that have the mod to see if it ever becomes a problem. I would not counsel inventing problems and raising red flags with the FAA if there is no immediate evidence of a problem, and there appears to be no evidence at this point in time.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian(at)lloyd.com (brian(at)lloyd.com)
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
[quote][b]
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samira.h(at)shaw.ca
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| Posted: Thu Jan 26, 2012 10:56 am Post subject: Tailplane front spar crack |
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Please see attached picture.
cheers
Elmar
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mark.bitterlich(at)navy.m
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| Posted: Thu Jan 26, 2012 5:30 pm Post subject: Tailplane front spar crack |
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I don't own a CJ-6, so I really have no dog in this fight. Whatever you all think is best is just peaches with me.
Mark
________________________________
From: owner-yak-list-server(at)matronics.com on behalf of Brian Lloyd
Sent: Thu 1/26/2012 1:35 PM
To: yak-list(at)matronics.com
Subject: Re: Re:Tailplane front spar crack
On Wed, Jan 25, 2012 at 12:32 PM, Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E <mark.bitterlich(at)navy.mil> wrote:
| Quote: |
Based on Dougs less than positive support for this fix, it would seem that a wise thing to do would be to see the actual recommendations made by the FAA Designated Engineering Representative (DER) regarding the repair of this specific crack.
|
Well, as I suggested in my last email, we don't seem to be seeing any cracking of the spars that have this mod, even if it appears that the mod may not be the best design possible. The doubler appears to be working just fine. I would counsel that people just keep monitoring those aircraft that have the mod to see if it ever becomes a problem. I would not counsel inventing problems and raising red flags with the FAA if there is no immediate evidence of a problem, and there appears to be no evidence at this point in time.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian(at)lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
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