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Cracked fuselage

mike mcs repair said:
I'm still scratching my head at how/why those tubes broke in that area in front of strut (rear gear fittings) on floats....
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Good morning Mike. Can't answer your question directly, but for what it's worth. I have seen a couple float planes that landed hard on the water and was surprised at the results. I watched one at the Greenville fly-in 20 yrs. ago that stalled and dropped about 10 or 12 feet into smooth water. The lower longeron bowed up something over an inch between the main gear fittings. I don't know if it broke or not but it surprised me at the time that it bent at the location. It was a 180hp A model with no electrics. A great performer. I competed against it several times when Dan Dufault was flying it for the owner. Dan did not bend it, the owner did. Just found it interesting.
 
Everybody has an opinion. Some have experience and some just an opinion based on pocketbook. I have been involved in more fuselage repairs than I can count. I would inspect what you have. Someone could have drilled a hole close to that tube and let water in it. I have repaired plenty of tubes like that on a covered airplane. Look everything over and determine it is not the tip of the ice berg. If you feel there are other issues with the frame I would recommend stripping it down, inspecting and most likely sand blasting prior to making a decision. The other issue is do you have someone that can repair properly. Some do not and it makes their decision to buy new easier.
 
Virtually every tube on that airframe is replaceable. In fact several people on this site have built entire fuselages from a pile of tubes, so at face value it would seem as though there should be no difference in replacing vs. repairing. It also would appear, at face value that only a person who has repaired multiples would have the right answer, but at the end of the day the right answer is yours.

Most repair vs replace choices are easy. One or even a few tubes, are far easier and far cheaper to replace that an entire fuselage. Sometimes it is indeed a money vs time balance. At some point the two meet, and a repair is going to cost you more in both money and time, but again, some people actually enjoy that.

BTW, remember even if you elect to buy new, your old fuse will still have value to a builder somewhere and could possibly help offset a purchase.

FWIW, the fuselage on the wind blown cub I spoke of now belongs to one of the guys that pinned my old cub in the jig. It needed everything from the door posts back reworked, and a new top deck. He enjoys doing that kind of thing, and in my mind will make it fly better than new, and it will likely fly sooner than most could build an entire cub from a pile of new parts. So our answers to the exact same situation were quite different. No right.... no wrong, and all the opinions in the world didn't really matter.

Take care, Rob
 
Having a new fuselage delivered sitting in the crate ready to use is the tip of the iceberg too. Once you go down that rabbit hole you have a lot of work to do. Even if the wings and tail group are in good shape and stored waiting to be mounted switching over all the controls, cables , wiring etc. will take time. Then cover and final finish. Then there will be that other snowball, the "as long as we're this deep into it we might as well do this too". As far as integrity of the original tubing, Piper used a lot of .028 wall in various places on that era fuselage. Having those beefy 5/8 barrel strut forks pulling on potential rust is not comforting. All opinion.
 
Steve Pierce said:
Everybody has an opinion. Some have experience and some just an opinion based on pocketbook.
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and some here are salesman for the new fuselage manufacture....

Like I said, I get paid by the hour, so get paid to REPAIR a fuselage, I make no money if you just buy a new one.....

generally I never spice tubes, I cut them completely out and replace whole tubes to the clusters...

and by the time I put all my mods on, it IS BETTER than the original....
 
I view airplanes as assets. At the end of the rebuild which represents a better investment? There isn't one correct answer. Every owner should consider the question for themselves.
 
As far as how they broke, the geometry indicates that it failed under a longitudinal load. During landing, the CG is continuing forward while you keep the nose up. Combine with a hard landing, the pitch-down bending moment is quite strong. With the weight transferring between wing-borne and float-borne, there is a vertical component acting on the wing strut fitting, too. Most of that should be transferred across to the other strut fitting. I will find out if I have any damage to that tube later this week.

Perhaps, with this cycle repeated over 22 years, with corrosion allowed to start, it was only a matter of time. I am curious about one of the two cracks on the right side. The forward one has been there a while, evident by the amount of corrosion inside. The aft one looks newer.

Does anyone put inspection panels near these fittings to allow for cleaning, greasing or inspection? Seems like it wouldn't hurt.

I got to learn how to do fabric after I pushed the wingtip into the hangar door and refined when we recovered the tail feathers last winter. The fuselage fabric will be easy. Aside from the welding, the rest is just nuts and bolts. And time. Lots of time! But winters here aren't much fun for float flying.
 
An update for everyone: fuselage wasnt just cracked in one spot. We have now had several instances of "this is worse than we thought." First, all lower longerons are bad. Several compression members on the sides are bad. Lots of tubes with paper-thin walls.

Now we are faced with the time-money problem of either repairing or replacing with new. Fun times!
 
A local Taylorcraft had a hard landing - estimate by the welder $3500. A definite "go." Only tubes that were bent were replaced; job did not grow. Bill was $15,000. Owner talked welder down to $10,000.

Wish we had trucked it to Mike or Steve. Makes the new fuselage option really attractive.
 
jadebons said:
An update for everyone: fuselage wasnt just cracked in one spot. We have now had several instances of "this is worse than we thought." First, all lower longerons are bad. Several compression members on the sides are bad. Lots of tubes with paper-thin walls.

Now we are faced with the time-money problem of either repairing or replacing with new. Fun times!
Click to expand...

Seems like a no brainer to me. Go new.

Kurt
 
jadebons said:
An update for everyone: fuselage wasnt just cracked in one spot. We have now had several instances of "this is worse than we thought." First, all lower longerons are bad. Several compression members on the sides are bad. Lots of tubes with paper-thin walls.

Now we are faced with the time-money problem of either repairing or replacing with new. Fun times!
Click to expand...
No surprise at all with a 70 year old steel tube salt water seaplane.
A thought, contact http://bbiaviation.com Ask them about a new -12 fuselage. You can remove the weld on serial number data tag on your old junk and weld it on the new one. The exchange rate is great. Each of your dollars is worth $1.30 in Canada.
I didn't say this :evil:
 
I find it interesting that nobody has mentioned the different metallurgy of the old Piper fuselages vs a new, all 4130 fuselage. That's got to be worth something in my book.

MTV
 
mvivion said:
I find it interesting that nobody has mentioned the different metallurgy of the old Piper fuselages vs a new, all 4130 fuselage. That's got to be worth something in my book.

MTV
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For what the majority of the tubes in a fuselage do, there is no real advantage of 4130 over 1020 or 1025. Most are in compression, and column buckling is more a function of diameter, wall thickness and length than tensile strength. Remember that every tube is sized for a positive margin with 150% safety factor. The only reason to use 4130 in places that weren’t originally 4130 is availability. Most of the tube sizes we use are no longer available in the lower alloys unless you want to buy a mill run.


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4130 does have some pretty marked advantages, namely better strength for equal wall thickness versus mild steel and slightly better corrosion resistance. I don't think simple availability is the reason why every frame maker, aircraft maker, and everyone down the line went to 4130. It's just a better alloy.
 
dgapilot said:
For what the majority of the tubes in a fuselage do, there is no real advantage of 4130 over 1020 or 1025. Most are in compression, and column buckling is more a function of diameter, wall thickness and length than tensile strength. Remember that every tube is sized for a positive margin with 150% safety factor. The only reason to use 4130 in places that weren’t originally 4130 is availability. Most of the tube sizes we use are no longer available in the lower alloys unless you want to buy a mill run.


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Click to expand...

Read the discussions above on this thread and look at the pictures.....there's a heck of a lot more than just compression loads going on in this tubing.

MTV
 
mvivion said:
Read the discussions above on this thread and look at the pictures.....there's a heck of a lot more than just compression loads going on in this tubing.

MTV
Click to expand...

Yeah, Jeromy’s fuselage has some corrosion issues, and likely some low cycle fatigue. That said, 4130 is a harder material. Not sure how it compares to 1020 or 1025 from a fatigue standpoint.


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I'll try to post more pictures later this weekend. It's rough. I put a rubber mallet through one longeron. Others are caving to a wire wheel. It seems that 73 years is a bit too much for this mild steel.
 
Jeromy, are you at Stan and Sandi’s place? I heard someone was there with a Supercruiser doing instruction.


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I work on base, but live in northern MD by Frederick. I’ve only been down there twice since February. I think you showed up once at our QB meeting before all this Covid stuff. Wish I was closer so I could give you a hand getting the Cruiser back in the air. I used to do a lot of seaplane flying when I lived in NY. Did a fair amount of instructing in Lakes, PA-22 on floats, 172 on straight floats, 180, 185, and 206 on amphibious floats as well.


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Low carbon steel (1020 or 1025)is much more malleable. 4130 is harder, can be heat treated, and will work harden when bent or formed. If you don’t take care to cool slowly after welding, you can increase the strength, but at the same time increase the brittleness with 4130. If you use 4130 rod, the weld metal will be very hard and brittle. Always use mild steel rod, with TIG, I use ER70S2 or S6. With gas welding I use RG45 wire. If welding over about .120 (not often with airplanes), it is recommended to pre heat the base metal before welding.

SAE 1020 has about .18 to .23% carbon. 4130 has about .28 to .33% carbon 4130 has about 90k psi tensile in Cond N, but can be heat treated to over 125 k psi(ultimate) 1020/1025 has about 57k psi tensile (ultimate). Both 4130 and 1020/1025 have a modules of elasticity of around 29k psi.


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1025 CD
Yield 54 KSI
Ultimate 64 KSI
Elongation 15%
Brinell hardness 126
http://matweb.com/search/DataSheet.aspx?MatGUID=aa1c987a696e42bd95ddad57e5f3e1c7&ckck=1

4130N
Yield 63 KSI
Ultimate 97 KSI
Elongation 25%
Brinell Hardness 197
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=m4130r

Note the greater elongation of 4130. It will stretch more between yield and failure.

As pointed out above, elastic modulus (stiffness) is the same for both, and that's what matters for slender column buckling.
 
Last edited:
Perhaps I misread it the other day but FAA AC 43.13-1B Table 4-15 selects 4130 filling rod for 4130 metal. This is the only place I‘ve ever seen this and everywhere specifically states to avoid 4130 rod on 4130 metal. If I‘m not misreading this AC it really makes me skeptical of anything the FAA prescribes.
 
Aeronut said:
Perhaps I misread it the other day but FAA AC 43.13-1B Table 4-15 selects 4130 filling rod for 4130 metal. This is the only place I‘ve ever seen this and everywhere specifically states to avoid 4130 rod on 4130 metal. If I‘m not misreading this AC it really makes me skeptical of anything the FAA prescribes.
Click to expand...

Just another WRONG thing in 43.13. Never will be changed.

Look at the bend radius chart twords the bigger end. Someone was whisky-ing and playing with their slide rulers when that table was made....

Don’t believe everything that’s written.. just because it’s written in a book we are supposed to live by....


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Lots of fuselages out there with mild steel not falling apart. I am sorrybut that one was used and abused, probably some not so good repairs.
 
mike mcs repair said:
Just another WRONG thing in 43.13. Never will be changed.

Look at the bend radius chart twords the bigger end. Someone was whisky-ing and playing with their slide rulers when that table was made....

Don’t believe everything that’s written.. just because it’s written in a book we are supposed to live by....
Click to expand...
Not the only factor. A large weld section can create an adjacent stress concentration notch. And an asymmetric weld can be worse yet. Also, the rapid rate of heating / cooling with tig or mig can cause self-quenching. Lots of variables - - - So a yielding weld filler can help compensate.
 
Well first of all this corrosion condition on 73 year old 12 Airframes isn't going away.
Trying to decide weather to dive into a massive welding project or simply buy a new 4130 airframe is not really the point
here. What should be is: the simple fact that from a resale perspective; regardless
of who did the work......... Generally speaking, A Cruiser with a brand new 4130
fuselage, is a different animal altogether than a patched up wanta be, when it comes time to sell it.......
Anyone that thinks 1025 tubing is just as good as 4130; has obviously never whiped a Cub around in the tundra, without the tail boxed in, with a load of moosemeat onboard, only to find the fabric saged and tail twisted. [emoji17]
So if you are a welder yourself and wanta
"Fix er up cheap" get an old fuselage ( or bed frame ) and have at it[emoji2955]. Or if your not
this is a "no brainier" as when you are done
with "patches" say it's worth 60 grand, now
Compare that to same 12 with a brand spanking new 4130 airframe that will easily
fetch $80K. Where is the extra $20k, you had to put up front, right on the back end!!
It isn't really going to cost jack, you saved a year in time (at least) your back in the air,
And the word around is " that thing has a brand new fuselage.[emoji6]
Good Luck
E

Sent from my moto e5 go using SuperCub.Org mobile app
 
Gordon, does a post-heat have as much effect as a pre-heat and then weld?? I’ve had mixed teachings over the years, but mostly with pipe.
 
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