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  #31  
Old 08-03-2020, 08:47 PM
scsmith scsmith is offline
 
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In addition to the points that DanH pointed out, the attachment point of the forward spar of the horizontal tail to the fuselage must have been moved aft, so that the loads are no longer directly positioned above the fuselage bulkhead F-610B. This puts loads into the longerons that should not.

In the process of removing the shims and re-installing the horizontal tail farther forward, hopefully the attachment of the forward spar has been relocated to its proper place. And hopefully done in accordance with the plans. Hopefully the incidence angle of the horizontal tail is correct. So it is possible that the horizontal tail is all correct now. The only damage being the extra holes in the longerons.

** Except for the phillips-head screws holding the tail on. Kind of erodes confidence in the IA/A&P that did that.(unless that was just temporary for alignment and real AN bolts were later installed)**

In that case, the primary problem is the one that DanH pointed out. The fin forward spar must have been modified to interface to the incorrectly located horizontal tail. That modification would possibly have changed the torsional stiffness of the fin, which would reduce the flutter speed.
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Last edited by scsmith : 08-04-2020 at 12:02 PM.
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  #32  
Old 08-03-2020, 10:12 PM
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Flyhud Flyhud is offline
 
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The screws appear to be AN525, they have the same shear and tensile strength as an AN bolt of the same size. They also have similar shank tolerances. I’m not advocating or defending the use of these, I would certainly stick with the hardware specified in the plans. Probably not a concern from a structural standpoint though.
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  #33  
Old 08-03-2020, 11:55 PM
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rv8ch rv8ch is offline
 
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Default Fuselage extended?

Is that 1" at the end of the fuselage normal for an RV-6A?

Based on the limited info, seems like a mistake/error was made somewhere, and then a series of other changes were made to correct it. Finding the original error and then working to fix it might be the best solution.

I agree that getting some experienced RV eyes on this will probably save you a lot of time and money. There are some experienced RV builders very close to you I'm sure.

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  #34  
Old 08-04-2020, 04:46 AM
vic syracuse vic syracuse is online now
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Default Please head the advice

Please, Please, Please, DO NOT fly this airplane until it had been thoroughly inspected by someone who will recognize a mistake or modification. Every inch of this airplane needs to be scrutinized.

Vic
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  #35  
Old 08-04-2020, 08:02 AM
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Quote:
Originally Posted by scsmith View Post
The fin forward spar must have been modified to interface to the incorrectly located horizontal tail. That modification would possibly have changed the torsional stiffness of the fin, which would reduce the flutter speed.
My thought too.

Doc, how about a photo of the new VS front spar attach?
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  #36  
Old 08-04-2020, 08:10 AM
FrenchyRV-6A FrenchyRV-6A is offline
 
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Default Rudder flutter

As I read your comments my takeaway is that there is a structural problem and or an aerodynamic problem. Structurally, the reinstallation of the rudder might be corrected by insuring attach bolts are tight (stiffened). The 6 tail uses 1/16th and isn’t mass balanced, corrections made to the 7. Aerodynamically, there may be some flow separation that has shifted slightly and is now exciting an oscillation in the rudder. Addition of mass on the rudder might change the excitation speed. A vortex generator type addition might change the aerodynamics and could be attached with tape so that it can be moved around.
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  #37  
Old 08-04-2020, 08:43 AM
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Quote:
Originally Posted by FrenchyRV-6A View Post
As I read your comments my takeaway is that there is a structural problem and or an aerodynamic problem. Structurally, the reinstallation of the rudder might be corrected by insuring attach bolts are tight (stiffened). The 6 tail uses 1/16th and isn’t mass balanced, corrections made to the 7. Aerodynamically, there may be some flow separation that has shifted slightly and is now exciting an oscillation in the rudder. Addition of mass on the rudder might change the excitation speed. A vortex generator type addition might change the aerodynamics and could be attached with tape so that it can be moved around.
Jean,
There are differences between the RV-6 and RV-7 but they weren't made to correct a problem. The RV-7 has a much higher Vne than the RV-6. There are 2000+ RV-6's flying with the same rudder you have, without any flutter problems or modifications like VG's or counter balance to make them problem free. Making changes like those to solve your issue would just be masking (perhaps temporarily) a bigger issue.

I am willing to help you work through this issue. I sent you a private message via VAF forums. Please reply to that if you desire any assistance.
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  #38  
Old 08-04-2020, 08:49 AM
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Things that make you go hmmmm....
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  #39  
Old 08-04-2020, 09:46 AM
BillL BillL is offline
 
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Quote:
Originally Posted by scsmith View Post
In addition to the points that DanH pointed out, the attachment point of the forward spar of the horizontal tail to the fuselage must have been moved aft, so that the loads are no longer directly positioned above the fuselage bulkhead F-810B. This puts loads into the longerons that should not.

In the process of removing the shims and re-installing the horizontal tail farther forward, hopefully the attachment of the forward spar has been relocated to its proper place. And hopefully done in accordance with the plans. Hopefully the incidence angle of the horizontal tail is correct. So it is possible that the horizontal tail is all correct now. The only damage being the extra holes in the longerons.

** Except for the phillips-head screws holding the tail on. Kind of erodes confidence in the IA/A&P that did that.(unless that was just temporary for alignment and real AN bolts were later installed)**

In that case, the primary problem is the one that DanH pointed out. The fin forward spar must have been modified to interface to the incorrectly located horizontal tail. That modification would possibly have changed the torsional stiffness of the fin, which would reduce the flutter speed.
***Disregard this comment. I mistakenly thought the spacers were the final condition not "corrected"***
Steve, the 1" off-set for the vertical loads transferred from the HS to the fuse will add a couple to that joint and be twisting the HS spar as part of the loading. That would create some vertical displacement to the joint and to the spar along with a small change in incidence. This would be my concern with the change made. I wonder what Scott is going to recommend - - likely correct the whole geometry for the aft fuse to make sure the loading is like the original design. It seems to me that is necessary.
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Last edited by BillL : 08-04-2020 at 04:18 PM.
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  #40  
Old 08-04-2020, 10:35 AM
FrenchyRV-6A FrenchyRV-6A is offline
 
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