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Classic Wings Magazine WWII Naval Aviation Research Pacific Warbird Digest
Final Cut-The Post War B-17 Flying Fortress and Survivors - 5th Edition


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PostPosted: Wed Mar 28, 2012 1:37 pm 
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Posted on the EAA Warbirds of American website. Hope this is an isolated issue that can be resolved and not an overall issue for all the Flugwerk 190's flying today. That would be a bummer for the owners and with the airshow season starting. :(

http://www.warbirds-eaa.org/news/2012%2 ... 0owner.pdf

http://www.warbirds-eaa.org/news/2012%2 ... 20A8_N.pdf

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PostPosted: Wed Mar 28, 2012 2:25 pm 
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Crap! that rivet photo is quite frighting.

Be safe out there folks!

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PostPosted: Wed Mar 28, 2012 2:29 pm 
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The question : the wing are provided assembled in the kit, or in pieces ? I suppose that could made all the difference between one isolate plane problem and the whole fleet of planes...

Just my 0.2 cents

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PostPosted: Wed Mar 28, 2012 2:33 pm 
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Very shoddy workmanship! Glad it was found before anyone was injured!

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PostPosted: Wed Mar 28, 2012 2:52 pm 
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We haven't found any evidence of this problem on the one here-so far I have heard that it is an isolated case on one aircraft...and the warning is a precautionary measure.

Dave

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PostPosted: Wed Mar 28, 2012 2:56 pm 
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Absolutely it is a precautionary measure, and a good one indeed. best it was found and passed on to the other owners of Flugwerk 190's. Good job!

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PostPosted: Wed Mar 28, 2012 7:10 pm 
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I wonder if this might be previous gear collapse or groundloop damage that went undetected?

If there was in fact a gap during manufacturing, the rivets would have swelled into the gap between the layers and wouldn't have been easily removed.


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PostPosted: Wed Mar 28, 2012 7:27 pm 
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bdk wrote:
I wonder if this might be previous gear collapse or groundloop damage that went undetected?

If there was in fact a gap during manufacturing, the rivets would have swelled into the gap between the layers and wouldn't have been easily removed.

Concur, the bucktails seem to be partially extracted from the holes (see the shiny portions of the shanks?) which would indicate they were sheared off in the accident. Incorrectly (or not) deburring would leave gaps as BDK says causing the rivets to swell between the parts always a favorite of structures mechanics causing you to say rude and veiled things about the installers parentage and their mating habits because it is an absolute screaming 'beach' to fix, it also imposes tremendous shear loads on the assembly stackup and weakens it. This looks to be something that either wasn't evident on initial inspection, or wasn't recognised by those inspecting because a gap like that would be a blinking light in a dark basement. But, it's also been proven that experienced inspectors will not see a crack up to 7 inches long in about 20% of cases.
Scary stuff but a great catch!! 8)

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PostPosted: Thu Mar 29, 2012 2:28 am 
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I will admit, there is very little info presented in the PDF file, but I’ll put on my plastic detective badge and take a W.A.G.


In photo 1, I agree. I don’t see any evidence of three-headed rivets, which suggests that gap occurred after the initial riveting. I concur about the significance of that gap.


What I find interesting, is the decision to use rivets in a stack up of aluminum that appears about an inch thick. In my experience, those situations, especially when involving spar caps, use Hi-Shears, Hi-Locks, or similar fasteners, sometimes with an interference fit.


A stack up that thick will absorb most of the hammering impact of a pneumatic rivet gun. It appears this is what happened initially, and the guy riveting, switched to a much harder hitting gun, which created the numerous skin divots visible in the 2nd photo. Those divots are a huge red flag, and after the first 2 were created, the riveter should have been on the phone with the engineer, to devise a better solution. The inspector who OK’d that riveting mess, before paint, should turn in his IA.


I am surprised to see fretting corrosion (smoking rivets) in photo 2. Assuming this is a low time airframe, that suggests an extremely poor fit up of parts and/or sloppy riveting.


In photo 3, the countersunk rivet heads, that are well below the skin surface, suggest incorrect countersinking, either by the factory or the assembly shop. The riveter should have called someone on this after discovering it. Perhaps he did, and had a shop manager tell him to shut up and get the job done. I’ve known shop managers who thought two bricks were sufficient to shoot solid rivets.


In photo 4, the deformed rivet shop heads suggest an untrained individual, which is common in sheet metal repairs, where the dumbest guy is usually chosen for the “dumb” job of holding the bucking bar. I’ve tried convincing shop managers that is not a smart move, but am rarely successful. I often stack up scrap skins in a vise and give the dumb guy some OJT before we tackle the aircraft.


The sheared rivets in photo 4 suggest the aircraft was over stressed in flight or during an accident, or the rivets were an insufficient fastener to handle normal shear forces. I’m gonna go with a W.A.G. of insufficient shear strength.


I’m not surprised at this quality of structural work. Although it is below the level of 95% of the factory workmanship I’ve seen, it is actually above the standard I see in many shop repairs.


I will now put my plastic detective badge back into the cereal box. pop2 pop2 pop2


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PostPosted: Thu Mar 29, 2012 8:22 am 
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Pretty serious and frightening! Just curious wether or not these aircraft have g metres?

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PostPosted: Thu Mar 29, 2012 9:45 am 
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That was a nice, professional analysis tinbender2. It looks like they borrowed a rivet gun from the local shipyard to put that thing together! :shock:

-Pat

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PostPosted: Thu Mar 29, 2012 10:28 am 
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Let's look @ what we have here, we have an abject failure on the part of the installers and whoever did the inspection buyoff on these dangerous fasteners.
In photo #3 every fastener shown is incorrectly driven and are all at least one length too short, prior to shooting, a rivet should protrude from it's hole by at least one diameter, every one of those shown have extremely thin buck tails and every fastener in photo #1 would fail in a pulled zipper manner in pretty short order indicating the fasteners were at least one grip length too short. A properly done rivet buck tail should be one half the shank diameter in height and approximately one and one half the shank diameter and sort of gently rounded on the sides like tiny aluminum biscuits. Most of the rivets shown are 'clenched' or 'horsey hoofed' which shows lack of attention on the part of whoever was bucking as they were tipping the bar which 'pushes' the shop head. Every fastener in photo #1 requires replacing before the aircraft flies again as they are all incorrect and potential failures, that leads to how many other fasteners we cannot see are done incorrectly?
It normally takes about 1.7 to 2 seconds to shoot a rivet, the rivet will tell you how it's doing by listening to it as you hit it, the tone will start out sharp and flatten out as the shank swells to fill the hole and the air is driven from the hole, it sounds weird, but experienced riveters and others can 'background monitor' the sounds of riveting and you'll see them sort of half smile until a bad hit which will cause them to flinch a bit. When struck, the rivet goes 'plastic' and compresses to fill the hole. I'm gonna cuss now by saying two very bad words which may cause experienced shooters to flinch, CRES and MONEL. Both of these fasteners use the bucking process to complete the heat treating of the fasteners, they feel 'greasy' when being shot, are extremely easy to overshoot, and since they get hard when shot, are a very unhappy thing to drill out, same issues when a rivet is shot into gapped parts the shank swells in the open space and locks the rivet in it's hole leading to very bad words being said about whoever shot them, the same process occurs when shooting DD or 'Ice Box rivets'.
In a big stack up, they should have used HILOKS as Tin Bender states because the metal does absorb a lot of the force involved. I too am surprised to see the skins countersunk instead of dimpled, countersinking in thin material causes 'knife edging' which will cause the heads to pull through the sheeting 'popping' them. Accepted practices would have the sheet dimpled and the substructure lightly countersunk to accommodate the dimple.
I hate to say this, but for safety, I would disassemble the entire aircraft and photograph everything I find to be wrong, then have a lawyer contact the German Aviation Authority and see about having the manufacturer cover the costs of correcting the found issues, suspending the certificates of the inspector and perhaps the riveters and having the manufacturer scrutinized much more closely because what I see amounts to blatant negligence on the part of the manufacturer, and this isn't going to be a quick and easily fixed issue and if it was me, I sure as H#ll wouldn't stand still for fixing someone elses problems on my dime.

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Last edited by The Inspector on Thu Mar 29, 2012 11:37 am, edited 1 time in total.

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PostPosted: Thu Mar 29, 2012 10:44 am 
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My question is, does this area look any different from when it was built? Did the bulged skin and depressed rivets just show up, or we're thet built that way?


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PostPosted: Thu Mar 29, 2012 11:35 am 
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The first photo of the wing skin shows a great number of same sized flush die strikes, and why so many away from the driven fasteners?It almost looks like an attempt to recontour the skin to reduce a wave.
Photo 2 shows what appears to be 'suck down' along the fastener line on the spar, perhaps a lack of correct shimming? 'shoot, draw, shoot, draw'

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PostPosted: Thu Mar 29, 2012 2:28 pm 
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Unfortunately there are a lot of unknowns here...

1. Who is responsible for the workmanship?

2. How was the aircraft operated?

3. Is this structure per the original WW2 blueprint or has it been modified (either by Flugwerk or the builder)?

4. Were there any similar problems in service during WW2?

At this point I think we need more facts. Kudos to whoever discovered this issue and brought it to light.

As a general design practice, you never want to have a fastener fail before the structure because then the defect grows and loads up adjacent fasteners with an even higher load. Sometimes the load can redistribute, sometimes it can't and you have a catastrophic failure.

While a Hi-Lok or bolt might have been better, a rivet may have been perfectly acceptable if properly installed in a properly designed joint. A Cessna 150 wouldn't fly very well if every rivet were replaced by a steel bolt, although it would undoubtedly be stronger.


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