structural fatigue and age

[180Marty]

A question for the engineering types. I see a 185 that is 36 yrs. old,NDH, and maintained well for sale. It has 13,000 hrs. Are the rivets and structure any more likely to fail on it vs. my 52 yr old, 3700 hr. 180?
Thanks, Marty

[a64pilot]

If the structure was identical and the use was identical, then yes. Vary anything and it get's fuzzier. The more varience, the fuzzier it gets.

[sharp]

In my materials class (yrs ago), fatigue failures are linked to load cycles and the amount of loads. Fewer cycles at high loads is similar in fatigue to high cycles at lower loads. So it all depends....

Sharp

[bob turner]

Build new ones. Put sticks in. Make flaps go to 50 deg. P-Ponk gear. Simple STOL cuff and fences. My opinion.

[Steve Pierce]

Real world experience, look at the tops of the wings outboard of the lift struts. Probably find cracks or patches. No engineering background just seen it a lot.

[RCharles]

Steve, How much time did these wings have on them as an average , that you have seen. Also , where are the patches and cracks? are they in the spar ? top or bottom ? Does anyone know how many cub wings have actually failed in flight where the cause was not in the strut itself or the attach point ? Thanks...RC

[pzinck]

Have seen lots of high time cessna with triangle patches .They are usually to repair cracks or tighten loose rivets between top of wing skin and ribs.Most of these were on high time float planes.Steve is right,they are usually outboard of wing struts.

[Steve Pierce]

Top wing skin between the rib at the strut attach and the next rib out like Phil said. Most were 10,000 plus that were used for pipe line patrol flying 100 plus hrs. a month at 300 ft. AGL. The only cracked spar I have found on a Cessna was in the rear spar in the fuel tank bay. The leading edge skin at the tip was cherry riveted on so I assume somewhere in it's life it hit something and according to Cessna that is the weak part of the spar. They sell a neat spar splice kit to repair it in that area. The owner finally fessed up to hitting a bunch of cactus and having someone repair it off the record. I was the bad guy for finding it and fixing it. :evil:

[Dave Calkins]

I see the cracks on Cessnas with far less time than that. Usually float/ski-planes.

Lots of other areas where 180/185's break. The nice thing is that an anal mechanic who's been around them alot will know where to look, every time. The stuff aint' rocket science, but you still gotta know where to look and care enough to take the time to look.

I'm with SHARP. I think it's all about the cycles it's been through.

[Grant]

In reference to Mr. Pierce


The owner finally fessed up to hitting a bunch of cactus and having someone repair it off the record. I was the bad guy for finding it and fixing it.

During a prepurchase evaluation I discovered a serious issue with an aircraft's fuselage structure that was undocumented. The aircraft had received minor damage a few months prior and the damage that was recorded was apparently done so that the repairs would not constitute substantial damage in so far as the reporting requirements to the NTSB. What was repaired, but not documented to circumvent the required reporting to the NSTB, was a replacement of a fuselage former. This former was initially overlooked by me until I had photos developed and I had an opportunity to study the photos of the tailcone section. I suspect the reason this repair was left undocumented is because it would have required a filing of an aircraft accident to the NTSB and filing of a major repair to the FAA which in turn would reduce the value of the aircraft. The repair was done correctly and the aircraft would be worth more if the repair had been documented. Partly because I would not advise my client to purchase this aircraft because of this undocumented repair. Remember "Where there’s smoke there’s fire." If the owner was willing to hide this, what else was he willing to compromise. He obviously doesn't want to fly this airplane anymore. Why else would he be selling it? So be careful when preparing to purchase an aircraft and be sure your mechanic who is reviewing the aircraft is very meticulous. This could be the difference in hundreds of thousands of dollars.

http://analyticalaviation.com/Home/images/Former_Image.jpg

#1 Overspray of zinc chromate onto wiring.
#2 Painted Rivets - All the other rivets inside tailcone area are bare.
#3 Former was painted in place with mis-matching zinc chromate meaning it was most likely not repaired or replaced by the manufacturer prior to delivery and more likely part of a larger repair but left undocumented for reasons previously discussed.

Grant Wallace

[Hyrdflyr]

I did a pre-purchase some years ago on a 185 being represented by a well known aircraft broker on Lake hood as "NO damage History". Before I looked at the airplane I started to review the logs in the broker's office. Starting with the airframe log, I just randomly opened a page. The first entry said "replaced left wing".

I took the purchaser outside and asked him if he wanted to spend $75,000 with the broker or look elsewhere. He found one across the lake the next day and it was a good one. Paid cash too.

I expect Alaskan aircraft to generally have had airframe repairs if they've been here some time , and done correctly, I don't usually discount them to prospective purchasers. I know of, and have had a hand, in total rebuilds that resurrected and airframe to much better than factory new standards, but the logs detail all of the work done and the aircraft is represented as "rebuilt" and doesn't suffer from the revelation.

Transparent falsehoods are just the beginning of a bad deal 99 times out of a hundred.

[bob turner]

Yeah - like this is a problem on only a very small percentage of airplanes that have been around for a half-century!

[Grant]

I'm not suggesting that all aircraft, no matter the age, should be considered trash because of an unethical owner at some point. I am suggesting that a person who is representing the buyer, and furthermore representing himself as a professional in this field, to be of a high moral standard. Look, the people, who are in many cases not "Mechanically Inclined" or " Regulatory Scholars", would miss most of what we catch. It is our job as mechanics, technicians, brokers, or other to educate and inform our clients as to the best course of action, to be first and foremost safe, and second to protect their investments.

Step away from your soap box Grant

[behindpropellers]

In reference to Mr. Pierce


The owner finally fessed up to hitting a bunch of cactus and having someone repair it off the record. I was the bad guy for finding it and fixing it.





#1 Overspray of zinc chromate onto wiring.
#2 Painted Rivets - All the other rivets inside tailcone area are bare.
#3 Former was painted in place with mis-matching zinc chromate meaning it was most likely not repaired or replaced by the manufacturer prior to delivery and more likely part of a larger repair but left undocumented for reasons previously discussed.

Grant Wallace

That looks like a tough one. What if the line that goes outside was leaking and some corrsion was fixed on the bulkhead? Scuffing and repainting would constitute for "serious damage"?

[a64pilot]

You pretty much have to assume that the number of conventional gear aircraft that have seen use in the bush and happen to have a little age on them that have no damage is very little if any at all. I pretty much take the opinion that most anything that I can afford will have had damage at one time or the other. I try my best to find it and ensure that it was repaired in an airworthy manner. Damage history dosen't scare me off, I assume the've all been damaged at some time or another and the person that admits it is an honest person.

[Grant]

I did'nt want to go too deep into this but the damage occurred when the step to get on to the wing (Which is connected to this former) contacted the ground during a landing where the right main collapsed at very slow speed. They replaced the step and the skin was not damaged, but to make the repair look as if nothing happened they had to replace the former to make the skin "Pop" back out. Here is the whole story.....

The aircraft is a Seneca V
Seneca Pilot Left seat
Baron Pilot Right Seat


Anyway, on a landing the pilot bounced the airplane and the Baron pilot grabbed what he thought was the flaps and put them up actually grabbing the gear. At the same time the airplane was in "mid bounce" and the WOW circuit was in the flight condition. He realized his mistake and corrected. At the same time the airplane came back down but the right main had enough time to unlock. Now the gear is still down but the right main is unlocked and the right main collapsed during a left hand turn to the taxiway.

Documented Damage:
Right main landing gear door
right wingtip
both props
both engines

Undocumented Damage:
Former that supports the entry step onto the wing


According to the definition of substantial damage in NTSB 830 the documented damage does not require reporting. However, the damage to the former and its subsequent replacement would have required a major repair, in turn a 337, and a damage history.

Now what they were trying to avoid is a damage history and a percieved loss in value. What really happened is that the aircraft is now out there with a good repair but no documentation of that repair. That is a bad thing for the next guy who buys it because as owner operator he has to be able to show that his aircraft is airworthy. With no yellow tag or documentation for the part or the work that was performed it will be a near impossible task to prove airworthiness.

I am sure some of you are saying i am being unrealistic, maybe, but the facts are what they are.

[Grant]

You pretty much have to assume that the number of conventional gear aircraft that have seen use in the bush and happen to have a little age on them that have no damage is very little if any at all. I pretty much take the opinion that most anything that I can afford will have had damage at one time or the other. I try my best to find it and ensure that it was repaired in an airworthy manner. Damage history dosen't scare me off, I assume the've all been damaged at some time or another and the person that admits it is an honest person.

Agreed, The problem I have with these situations is that some people think it is okay to not document damage as long as it is properly repaired to save a filing of a 337. Damage is not a bad thing at all but not providing documentation for the repars is a bad thing.

[Dave Calkins]

I think that prospective purchasers that believe 'no damage history' means 'perfect airplane' are idiots.

also: anyone that believes 'no damage history' is an idiot.

Oh, and get a real pre-purchase inspection. The scope of such an inspection would be the same as an annual inspection. That way you know if the paperwork is good and if the airframe is acceptable. Everything else is just a crapshoot!

Later, DAVE

[fireball111]

My experience in airplanes repairs is very minimal but i agree with Grant after any repairs its not original and should be in the books. A picture is worth
a thousand words and gives buyer something to watch for.

[landesskis]

As the airplanes get older, the inspections need to be more in depth. Unless you know the history of the aircraft and the pilot that flew it, a vigorous inspection needs to be done. At least Aluminum has a memory and you can see what has happened over its life.

Gary

[aktango58]

Early 180/185 wings, 10,000 hours and you should have some of them triangle/trapazoids up top. Yup, strut out. The more turbulance, heavy landings, floats and skis, the more you got them.

If you have original wings and that much time without some patches, take a magnifying glass and look at the rivits on top of the spar, from the strut out. Look especialy by the rib.

Grant: Good eyes!

Marty, Both planes are too old for a concientious pilot like yourself. Best I should come down and take it off your hands. Want an alley cant in trade? :wink:

[aktango58]

That was alley CAT, And some times can. :drinking: :drinking:

Sorry, will learn to spell when I can no longer fly. 8)

[180Marty]

aktango58 wrote


Marty, Both planes are too old for a concientious pilot like yourself. Best I should come down and take it off your hands. Want an alley cant in trade?

Ha!!! Maybe I should, but not quite yet.
Marty

[180Marty]

Thanks for all the input and keep it coming. :D
Marty

[gdafoe]

FWIW . . . . . With advancing age I have sure noticed considerably more structural fatigue. :o