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  #1  
Old 09-06-2018, 07:10 AM
atalla atalla is offline
 
Join Date: Jul 2014
Location: Whistler BC
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Default Elevator trailing edge bending

Hey everyone. I have a video out of me bending my left elevator skin. I would love some advice from all to see if Iím going too far or not. Iím also a little worried that the skin on top of the stiffeners is concave by a mm or so. Could this have happened during back riveting? Should I be worried.

Not meant to be click bait
https://youtu.be/qc2BrjaE4O8

Thanks in advance for your time.
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  #2  
Old 09-06-2018, 08:22 AM
wirejock's Avatar
wirejock wirejock is offline
 
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Default Bend radius

Looks pretty close to me but mine isn't flying yet.
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  #3  
Old 09-06-2018, 10:41 AM
atalla atalla is offline
 
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What flight characteristics would result in a slightly concave elevator? Is longatudical stibility effected?
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  #4  
Old 09-06-2018, 11:06 AM
Bavafa Bavafa is offline
 
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Default

You will probably not notice any difference in flight characteristic with that much concave but if that is a 1/4" dowel, I would certainly go to a thinner dowel 1/8" would be a good size.
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  #5  
Old 09-06-2018, 01:01 PM
atalla atalla is offline
 
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A 1/8 dowle was used but I was thinking of going to 3/32
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  #6  
Old 09-06-2018, 01:33 PM
rv7charlie rv7charlie is offline
 
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Location: Pocahontas MS
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IIRC, fatter, rounder trailing edge gives lighter control feel but less effectiveness; sharper gives slightly heavier feel but more effectiveness.

I'd get uncomfortable going smaller on the dowel than what the plans recommend; otherwise there could be cracks in the future.

Hmmm; Red Seal... My dad used to love the Red Seal engines in his Studebakers.

Charlie
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  #7  
Old 09-06-2018, 01:49 PM
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Bullseye Bullseye is offline
 
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Here's what I wrote back in 2010 when I ran into this same question:

The key for me was to use a dowel (while moving the TE away from the brake after each "squeeze") then, WHILE BEING VERY CAREFUL, proceeding with no dowel.




Quote:
Anyway, after a ton of VAF research, Orndorff video watching, and builder website reading, I settled on the "other" method, which puts the hinges on the long face, and really only bends with the short side of the 2x4 (or 2x8 cut in half). You really only want that much bending the skin anyway, because the bend needs to occur locally at the radius, not away from the trailing edge. If the wood is imparting force in the middle of the skin, you will end up with the dreaded "bulge."
Here's my bending brake being assembled. I had six hinges, so why use them. I grabbed these 2x4, which were nice and straight, and just long enough for the trailing edge. I'll need to replace these for the flaps and ailerons. I read somewhere they need to be more like 5 feet long for those.
Here it is after assembly. On the left, you can see my skin, that needs to be bent. In the middle, the three dowel rods I purchased. While I was standing in the store, 1/8" seemed too small, so I bought a few different sizes at $0.50 each. Of course, everyone was right on, 1/8" is perfect.

Quote:
I'm going to put the trailing edge of the skin in the little opening at the bottom of the brake (as it is oriented in the picture).
First thing, I screwed my bending brake to my 2nd workbench with one of the bending surfaces flush with the bench top.
Then, I put the 1/8" dowel into the trailing edge of the skin and taped it in place. (Not shown in the following picture, because I was recreating the process for the camera. Look 2 pictures down for the dowel rod.) Then, you put the skin in the brake all the way against the hinges, and start bending.
This is not a fast process. It takes a surprising amount of force. I thought it was going to be a one shot deal, but it takes a lot of bending. You start with the skin against the hinges, then bend around the dowel. That took a whole bunch of times (I was stopping a lot to inspect). Then, you move the skin a little away from the hinge, and bend again. This allows you to really form the edge around the dowel.

Quote:
If you pretend there is a dowel rod in there, this would be the first bend.
Here's where I could get to with the dowel rod in place.

Quote:
About halfway there.
Then, you remove the dowel rod and keep going, same deal, but a lot more gently, because I didn't want to squeeze the trailing edge too much (now there is no dowel rod to prevent squash-age.

Quote:
I thought this was good enough, but this is about 3/4 the way there.
Of course, because I thought that was good enough, I clecoed the skeleton into the skin.

Quote:
It's starting to look like something that could be considered an elevator.
But, after grabbing my straightedge, I'm getting some "fall-off" before the radius. This happens because the radius hasn't been formed well, and then you pull the skin down to the skeleton, and it bends close to the trailing edge. It's not terrible, but I know I can do better.
It's not the dreaded bulge, but it is some pretty good "fall-off."

Quote:
Near the inboard edge.
Hmm. I unclecoed, and grabbed this shot. I'm about an inch from where I need to be, and the tension I am putting on the skin to pull it to the skeleton is causing that slight bend near the trailing edge.

Quote:
About an inch.
I put that bad boy back in the brake and kept going. This time, I used two BFPs (the "p" stands for pliers. I'll let you figure out the "b" and "f") on either side of the brake and finished it up nicely.
There we go. I made up that last inch, and now it rests right where the skeleton would go.
Here's an end-on shot.

Quote:
How great is this? A perfect bend.
Let's get out the straightedge.

Quote:
Another place on the elevator.

Quote:
And again, no fall-off. So happy!
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  #8  
Old 09-06-2018, 07:56 PM
atalla atalla is offline
 
Join Date: Jul 2014
Location: Whistler BC
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Wow thanks so much Andrew! Great name btw.
I like your approach. I think Iím also going to remove the dowel and gingerly continue. I was also very surprised as to the force needed to bend the tail surface. I also believe that the skin should not be under any tension and should meet the spar with no stress.


Thanks again
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  #9  
Old 09-06-2018, 07:58 PM
atalla atalla is offline
 
Join Date: Jul 2014
Location: Whistler BC
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Quote:
Originally Posted by rv7charlie View Post
IIRC, fatter, rounder trailing edge gives lighter control feel but less effectiveness; sharper gives slightly heavier feel but more effectiveness.

I'd get uncomfortable going smaller on the dowel than what the plans recommend; otherwise there could be cracks in the future.

Hmmm; Red Seal... My dad used to love the Red Seal engines in his Studebakers.

Charlie
Plans donít call for a dowel. Just experience and advice received on VAF.
Red seal is Canadaís interprovincial standard for tradesman. They must have been good engines!
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RV-7 Left Elevator in progress.
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  #10  
Old 09-07-2018, 04:04 PM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by atalla View Post
Plans donít call for a dowel. Just experience and advice received on VAF.
Nothing in the instruction set for the empennage, either? I swear I read somewhere what the radius should be, but I don't have my construction manual handy here at home.
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