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  #11  
Old 02-06-2014, 04:26 PM
David Paule David Paule is offline
 
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FEA is excellent for identifying area where some result is dependent upon local stiffness, which was described earlier as being an issue here. Classical stress analysis, as was probably used originally, is excellent for determining if the basic strength is adequate. And we can see that both give valid results: the structure has proven its strength, and the change in local stiffness is causing local stress increases which is leading to fatigue damage.

Dave

Last edited by David Paule : 02-07-2014 at 08:11 AM.
  #12  
Old 02-06-2014, 04:26 PM
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LifeofReiley LifeofReiley is offline
 
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Quote:
Originally Posted by David-aviator View Post
Would it be a reasonable conclusion that FEA was not performed when the HS originally designed - or perhaps that FEA was not bullet proof then or now?

I am a sceptic of computer generated solutions to complex problems or a conclusion that the human mind is not caple of solving problems without FEA, whatever it is. Computers are wonderful but they do not have a lick of common sense.
Exactly David... Exactly.
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  #13  
Old 02-06-2014, 04:34 PM
ty1295 ty1295 is offline
 
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FEA is a tool available to an engineer. The fact is it should be 1 of many tools in his toolbox though. 1 of the key tools is experience and common sense.

Some engineers coming out of school believing everything the computer tells them which is very misleading.

I am one of those engineers, and my biggest pet peeves is engineers with no common sense.
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  #14  
Old 02-06-2014, 05:01 PM
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Quote:
Originally Posted by DanBaier View Post
Well, in the certified world, people come up with AMOCs all the time (alternative method of compliance). Maybe he'll have something that Vans will acknowledge as an alternative.

Even if not, I would be very interested in what Allan comes up with - as one without cracks and very much on the fence as to which evil is worse (doing the SB or just building new HS when the revised plans come out) - I'd certainly welcome options. The only downside I can see is that one might conclude that, even with Allan's proposal installed, it would be nevertheless necessary to look at it once a year to make sure there were still no cracks.

Dan
.
.... The parts that we are making, after installation will allow full view of the area that is subject to cracking. This provision makes it possible to inspect these areas when desired to verify no cracks or that they are not propagating. As I said in the first post on this thread, "This may not be right for everybody". Thanks, Allan...
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  #15  
Old 02-06-2014, 06:46 PM
RV Wannabe RV Wannabe is offline
 
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Yes, but even if it is for some, like the others have already said, unless Vans accepts, and adopts it, it is not a "Service bulletin fix".
  #16  
Old 02-06-2014, 09:08 PM
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Quote:
Originally Posted by DanBaier View Post
Well, in the certified world, people come up with AMOCs all the time (alternative method of compliance). Maybe he'll have something that Vans will acknowledge as an alternative.

Even if not, I would be very interested in what Allan comes up with - as one without cracks and very much on the fence as to which evil is worse (doing the SB or just building new HS when the revised plans come out) - I'd certainly welcome options. The only downside I can see is that one might conclude that, even with Allan's proposal installed, it would be nevertheless necessary to look at it once a year to make sure there were still no cracks.

Dan
I agree. (Extra letters)
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  #17  
Old 02-06-2014, 09:13 PM
jongurley jongurley is offline
 
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Quote:
Originally Posted by JonJay View Post
Allan, with all due respect, please consider re-wording the title of your post. There isn't a "service bulleting fix". You either comply with the SB, or you don't.
I am sure there are alternate ways of reinforcing the structure here, but, the SB is what it is....
Some people may be confused by your wording. Not trying to be nit picky, but there is already a lot of confusion about SB's in experimental aircraft.

There is only one way to comply with the SB issued by Van's; do the SB as it is written, that is if you care to comply with it.
My thinking to Jay
  #18  
Old 02-06-2014, 09:59 PM
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I have nowhere near the experience of many of you having only built one plane, an RV12. But I study a lot. One thing is clear is that Vans is a master at engineering a fix involving the lowest possible cost and simplicity of the parts involved. Simplicity is key. These are GOOD things. The labor involved is a consideration, but in my opinion it is way down the list. For some (not all) of us, a different balance would be preferable.

If you look at the recent RV12 fuel tank SBs, its all just little pieces of bent aluminum that takes many hours to messily install. Other methods could have accomplished the same end result, but might have been much more expensive to BUY, but involved far less labor. A bunch of us would be interested in such fixes. This HS SB is, I think, another example of this paradigm.

I, for one, am quite open to other approaches than Vans to fix an identified problem. A solution that is great for "during a build" might be quite suboptimal for post-build.

In comparing an RV to other kitplanes, the engineering quality stands far above! Do NOT get me wrong on this. But they are not the only good engineers.
  #19  
Old 02-06-2014, 10:48 PM
jongurley jongurley is offline
 
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When dealing with problems with a SB for a Horizontal stab/elevator on a plane in which im riding in I will trust the manufacturer. but thats just me.
  #20  
Old 02-06-2014, 11:15 PM
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Arie Arie is offline
 
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You are the manufacturer... I think we should give Allan a chance and see what he comes up with. For me I see the SB as a fix for a spar crack . If someone comes up with a mod to improve the strength of the front spar to prevent a crack from forming in the first place ,I will say fantastic. I know Vans engineers are very good, but out of the thousands of builders out there someone will come up with a stroke of genius. Lets wait and see...

Last edited by Arie : 02-06-2014 at 11:17 PM. Reason: sp
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