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Need Elevator Trailing Edge Advice

S

Stalldog

Well Known Member
I've bent and bent and can't get a good straight flat alignment on the trailing edge. I've bent without a dowel, and the radius looks good to me, but can't quite get things flat enough. One is fairly straight, but the other surfaces are still slightly bent. What say you wise builders?

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Hmmmmm, may have answered my own question. I just checked the flatness over the rest of the elevator, i.e. not at the end ribs, and the skin seems to be pretty flat right up to the radius. Maybe I just need to squeeze the rib flanges a little tighter. I had opened them up some to dimple, so maybe they just aren't quite bent back enough and are affecting the bends at the ends. I'll try tomorrow.
 
One builder I know who I consider a wise builder cut the elevator and assembled it like the edge of the rudder. He needed a wedge piece and said it worked out great. With a bend like is on the elevator, you can't get exact straightness. You can get close, and yours look pretty close. If there is a little flare, squeezing the rib flange in a bit would help out.
 
Rockwood, I'll check the flare on the ribs this evening. Hopefully that's all that's holding out the skin on the edges. Don't think I want to go to the trouble of riveting edges like on the rudder! Now I just hope I can proseal the ends of the stiffeners properly so that I don't get cracks in the edge.
 
The three of us seem to be about the same place in our builds. I just finished my left elevator after struggling with the trim tab some. Made two!

Anyway, yes, I had the same issue with the end ribs. Gently bent them in some and the problem was fixed! Hung them yesterday, and everything seems pretty straight and lines up perfectly, I'm stoked!
 
Damon, since I'll be starting the left elevator soon, what problem did you have with the trim tab that caused you to build two? I've heard there can be issues with it, but not sure what those are.
 
Well, I didn't like the look of the bent down tabs. So I cut them off and made riblets, I did the same for the bends on the elevator as well.

The problem came - when I cut the tabs off, I cut too much - you have to leave well past the relief notches in order for the inboard edge of the trim tab to line up with the inboard edge of the elevator, and the the attach point for the trim motor to line up with the notch in the elevator, and lastly so that there is not a huge gap between the outboard edge of the tab and the elevator. Hope you see what I am talking about, I don't have pictures of my mistakes. The first tab violated all three, it wasn't a deal killer structurally, but it just didn't look good enough for my taste, so I built another. It took a few tries to get the riblets right, and I even made a new spar when I over countersunk the first. I have a 4' bending brake, so it's not difficult to re-fabricate my screw ups, fortunately.

Even after doing all that, after riveting the tab together - except for the leading edge with the hinge - I could see the tab was twisted by sighting down the trailing edge of the tab while holding it in place to the elevator. So check for that before you rivet the hinge to the leading edge of the tab. Actually, check for it before you rivet the tab together!

I untwisted and re-clamped the leading edge and hinge, and riveted it, starting at one end and moving one rivet at a time to the next, checking after each rivet to make sure the twist was still gone. Because of the way the spar and the skin and the riblets fit together, in order to get rid of the twist I ended up with the hinge having a very slight bend in it, but not enough to bind in the small amount of travel the trim motor gives it. If you can build the tab without a twist, you will be ahead of me.

All my trailing edges ended up really straight with both elevator counterweights even with the HS, so no twist there, thank goodness. However, my rod end bearings are one half turn past the maximum 7/8" for the right elevator to not rub on the HS rear spar, and even there the inboard part of the HS skin is rubbing on the elevator at 28 degrees up, so I have some issues there still. Calling Van's today.
 
Wow, the trim tab sounds like a challenge for sure. Oh well, one thing at a time. I may be contacting you when I get into it.
 
Only had a few minutes last night to work on the elevator, but was able to bend the flanges on both ribs slightly, and that took care of the problem. One I still need to bend a little more, but all is good and skins are flat to the bend. Lesson learned! ;)
 
The trim tab was a PITA because it's so small and getting radiuses right etc., was a pain in the neck. I rebuilt mine twice, then just cut the lame "folded over ribs" out.

As for the trailing edge, get it as good as you can, you might just squeeze the radius just a bit, but not too much. When you do flight testing, and if one wing is heavy, you can lightly squeeze a trailing edge on the light wing. You can't do that if you construct a wedge version of the aileron.

You'll be fine.
 
Hey Jim,

Just looking at your 4th picture.....did you proseal (RTV, etc) the ends of your stiffeners?

Yeah, definitely squeeze the trailine edge portion of that end rib a bit.

Cheers,

Brad
 
Need to call you Eagle Eye, Brad. Haven't yet, but I just got back from the Tractor Supply store with the syringes to make the job easier. I was hesitant to add the Proseal until sure about the bending. I wish I had thought to do more prep on the stiffeners BEFORE bending them, but it is what it is. I've been doing so much running around the past two days, and it's so darn hot in the garage, that I probably won't get to the Proseal until Thursday or Friday now.
 
Oh man, you're psychic.....doing the exact same deal here. Got some 50 CC syringes on eBay, but still looking for a long needle. Did Tractor Supply carry those as well?

Thanks Jim,

Brad
 
Brad_in_Indy said:
Oh man, you're psychic.....doing the exact same deal here. Got some 50 CC syringes on eBay, but still looking for a long needle. Did Tractor Supply carry those as well?
Brad
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Brad, Tractor Supply had the syringes, although mine are 35 cc and 20 cc. I've dry run pushing them into the folded elevator and it's a tight fit, but I can get them into the space. You won't need any needles. In fact, the Proseal is so viscous you'll have to cut off the tip on the end of the syringe, or at least drill it out. From what I read it needs to be about a 3/16" opening. You might do a search elsewhere on the subject, but that's what I've read, and it makes sense. Besides, we're squirting a "glob" of Proseal onto the stiffeners, so a 3/16" opening makes sense to me.
 
Brad_in_Indy said:
Thanks Jim! Let us know how you do.

Take care,
Brad
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Well, actually turned out better than I expected. Mixed the Proseal gookempucky into a nice darkish gray using 2 oz of white and .2 oz black, and that turned out to be plenty to apply a nice gum wad size gob on each stiffener. Rather than try and ladel the "stuff" into the syringe, I drilled out the end of the 25 ml syringe with a 1/4" bit, piled up the Proseal into a nice size glob on my mixing tile, and sucked it up into the syringe. Had to stop now and then and burp out the air, but it really worked well. Then I was able to fit the syringe down into the elevator close to the end of the stringers, and pushed the glob out of the syringe. It really worked well. Had to stop and reload one time, but again the original batch was all I had to mix up, and I had a small amount left over, so I made a sample out of that and dated it. I'm told the Proseal will peel out of the syringe once it cures, and that I can scrape it off the ceramic tile with a razor blade, so as far as I can tell, all is good. I cleco'd the skeleton to the skin and will let it set for a day or two, then finish riveting it up. I can't say that I'm looking forward to doing this on a much larger scale with the tanks, but we'll manage one way or the other. ;) Oh yeah, sorry I didn't take pictures, but at least I don't have a Proseal coated camera!

PS: My scale was my weak spot. I need to get one that measues in grams to be more accurate. I was using a digital postage scale, and it worked okay, but I'd rather go with grams than pounds/ounces.
 
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