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  #1  
Old 10-08-2019, 10:48 AM
Mort04 Mort04 is offline
 
Join Date: Oct 2017
Location: Michigan
Posts: 32
Default Elevator twist question

So, I think I made a mistake that may induce a twist into my right elevator. A year ago I dimpled, clecoed and match drilled the skins to the skeleton on my right elevator without bending the trailing edge. Looking back I am not sure why I thought that was a good idea.

My question is;

Will this induce a twist, and if it does, is it ok to match drill the holes again once everything is straight?

Do I need to buy a new skeleton?
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  #2  
Old 10-08-2019, 12:38 PM
Bavafa Bavafa is offline
 
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Location: Sacramento, CA
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It will help if you include which model RV is this. Having said that, I am not sure why that would induce a twist, if any, it puts unnecessary strain on the skin.
There are relatively easy ways of checking for twist in the control surface after riveting has been completed. A large and flat surface, like a large table saw or granite counter tops are good ways of laying it flat and see if all four corners are touching.
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  #3  
Old 10-08-2019, 01:43 PM
Mort04 Mort04 is offline
 
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Quote:
Originally Posted by Bavafa View Post
It will help if you include which model RV is this..
Thanks for the reply, this is an elevator for an RV-7. I guess I am just paranoid about building a twist into my control surfaces after doing a little research on bending the trailing edge of the elevators.
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  #4  
Old 10-08-2019, 09:21 PM
Scott Hersha Scott Hersha is offline
 
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Not sure if this would induce any twist, but if you are willing to deviate from the plans of an engineered airplane, I think you are in trouble going forward on basic construction of the first kit if this is your first airplane. You are a homebuilder, so go for it if you want, but be willing to live with the circumstances of your new ideas. Maybe it will work out, maybe it won’t. Almost countless plans have worked out in the past - I would say most have followed the designers plans on basic airframe construction. There is definitely room for deviation in the way things are done, but looking in to the why of the deviation might expose a reason. That bent trailing edge might induce a certain amount of stability that prevents a twist or other some misalignment in the rest of the part, I don’t know, but you should have a reason for deviating, and I assume you do. Make some measurements to make sure everything is true, and build on.
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  #5  
Old 10-09-2019, 09:23 AM
Mort04 Mort04 is offline
 
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Quote:
Originally Posted by Scott Hersha View Post
Not sure if this would induce any twist, but if you are willing to deviate from the plans of an engineered airplane, I think you are in trouble going forward on basic construction of the first kit if this is your first airplane. You are a homebuilder, so go for it if you want, but be willing to live with the circumstances of your new ideas. Maybe it will work out, maybe it won’t. Almost countless plans have worked out in the past - I would say most have followed the designers plans on basic airframe construction. There is definitely room for deviation in the way things are done, but looking in to the why of the deviation might expose a reason. That bent trailing edge might induce a certain amount of stability that prevents a twist or other some misalignment in the rest of the part, I don’t know, but you should have a reason for deviating, and I assume you do. Make some measurements to make sure everything is true, and build on.
Scott, I agree 100% that deviation from the plans can cause issues. With that being said I have zero plans of deviating from the plans. The only Thing I did was match drill out of order. Which is why I raised the question on whether or not I needed to buy a new skeleton, start over, etc. The RV-7 plans call for a bent trailing edge on the elevators. With all do respect, where did I deviate from the plans?
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  #6  
Old 10-09-2019, 01:03 PM
Bavafa Bavafa is offline
 
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I don't mean to get in the middle of this, but I hardly consider this as a deviation from the plans. Shortening the elevator, widening it or changing the airfoil would be a deviation.
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  #7  
Old 10-09-2019, 05:01 PM
Ralph Inkster Ralph Inkster is offline
 
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Mort. To determine how much twist you may have introduced into the structure, fabricate 2 brackets that will suspend the hinge pins 3” above your table. Space the inboard trailing edge 3” above the table, than measure the height of the outboard trailing edge. If yours is a prepunched kit, the distortion shouldn’t be that far off.
Another thing you mentioned in your OP, that you dimpled, clecoed, than match drilled. The normal sequence is Cleco together, match drill, than dimple. Makes the assembly geometry closer to true.
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  #8  
Old 10-10-2019, 09:02 AM
Mort04 Mort04 is offline
 
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Quote:
Originally Posted by Ralph Inkster View Post
Mort. To determine how much twist you may have introduced into the structure, fabricate 2 brackets that will suspend the hinge pins 3” above your table. Space the inboard trailing edge 3” above the table, than measure the height of the outboard trailing edge. If yours is a prepunched kit, the distortion shouldn’t be that far off.
Another thing you mentioned in your OP, that you dimpled, clecoed, than match drilled. The normal sequence is Cleco together, match drill, than dimple. Makes the assembly geometry closer to true.


This is a good idea, I think I will use this technique to check for twist. I also have a nice flat granite counter top I was thinking about checking it on as well. I'll build a jig that is square and assemble the elevator in the jig do reduce twist, then I'll rivet, and build on!
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  #9  
Old 10-10-2019, 12:16 PM
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wirejock wirejock is online now
 
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Default Elevator jig

You might consider building a jig. Pretty quick to fabricate from melamine shelving. Built both of mine and the ailerons and flaps in one.
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  #10  
Old 10-10-2019, 12:27 PM
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Mel Mel is offline
 
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Remember that a tapered elevator will not have "flat" upper and lower surfaces.
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