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-   -   Elevator Trailing Edge Bend (https://vansairforce.net/community/showthread.php?t=137222)

tsw94r 04-28-2016 05:45 AM

Elevator Trailing Edge Bend
 
Hello All,

I'm ready to make the final bend on the elevators. The instructions tell you to follow the profile on the plans, but I can't find the profile to save my life.

I understand how to make the bend, just not what the trailing edge should look like when I'm done.

Tom

wjb 04-28-2016 07:35 AM

The closest thing I found was Dwg 4 zone G-10, which shows a end view of the elevator.

The skin needs to be bent down so both sides touch the spar. I followed the suggestions in the aileron section to make the surface up to the final bend as flat as I could .. use a straight edge from leading edge to trailing edge and check for a concave or convex profile and adjust to make surfaces a flat as you can.

Also, before bending, double check your stiffeners to be sure they won't interfere with each other or the opposite surface when the skin is in its final shape.

Go slow, too. IIMC, it took quite a few pressings to get it just right. Overall, its not a hard op.

tsw94r 04-28-2016 10:03 AM

Elevator Trailing Edge Bend
 
Thanks Bill,

I appreciate the tips. It sounds like there really isn't a profile to go by at least in the plans.

wirejock 04-28-2016 10:12 AM

Bend
 
Quote:

Originally Posted by tsw94r (Post 1074418)
Thanks Bill,

I appreciate the tips. It sounds like there really isn't a profile to go by at least in the plans.

There's some info in Chapter 5. Vans is pretty specific about getting a straight, flat surface up to the bend. I believe the radius is also called out. I used a dowell inside the bend then fine tuned the final bend without it.

tsw94r 04-28-2016 10:59 AM

Hi Larry,

I have read and reread the manual and plans, but can't find any reference regarding the radius of the bend. Section 5 does a good job of explaining how to make the bend, but the manual refers you to the plans for the bend profile.

I haven't started the bend yet, but I'm surprised that you would have the room for a dowel or did you just use it initially to keep the radius from getting too small?

bret 04-28-2016 01:11 PM

I used an 1/8" welding rod.

bret 04-28-2016 01:12 PM

or was it 1/16" have to go back and look at my log

wirejock 04-28-2016 02:53 PM

Doh!
 
Quote:

Originally Posted by tsw94r (Post 1074451)
Hi Larry,

I have read and reread the manual and plans, but can't find any reference regarding the radius of the bend. Section 5 does a good job of explaining how to make the bend, but the manual refers you to the plans for the bend profile.

I haven't started the bend yet, but I'm surprised that you would have the room for a dowel or did you just use it initially to keep the radius from getting too small?

I knew you would call me out!:eek:
Sorry, I can't find it. Maybe it was a VAF tip, but according to my log, I used a 3/16" dowel.
I used a strip of Gorilla tape to keep it from slipping out. After the initial squeeze, it was removed to allow the skins to bend past the final dimension. They reflex so you actually end up bending slightly more than the final angle. The biggest problem is the reflex on the bending jig. Even 2x6 will bend in the middle. I used at least 5 huge door hinges on mine.

hayabusa 04-28-2016 06:10 PM

Now is good time for some forward thinking. Check this thread and anything else you can find on the subject of elevator misalignment or twist.
http://www.vansairforce.com/communit...ad.php?t=96921
Any amount of twist in the elevators will not necessarily become apparent to you if you simply follow the plans. What you will end up with is the elevators in trail as per the balance horn positions relative to the stab, you`ll drill the steel control horns off to the control rod as per the manual, but the inboard trailing edges of the elevators will be off quite a bit and it won`t even be mentioned in the plans.
You need to devise a jigging method to ensure the left and right elevators are a matched pair.
The twist can start being built in from the bend in the trailing edge if it is slightly off.

wirejock 04-28-2016 06:22 PM

Jig
 
Quote:

Originally Posted by hayabusa (Post 1074573)
Now is good time for some forward thinking. Check this thread and anything else you can find on the subject of elevator misalignment or twist.
http://www.vansairforce.com/communit...ad.php?t=96921
Any amount of twist in the elevators will not necessarily become apparent to you if you simply follow the plans. What you will end up with is the elevators in trail as per the balance horn positions relative to the stab, you`ll drill the steel control horns off to the control rod as per the manual, but the inboard trailing edges of the elevators will be off quite a bit and it won`t even be mentioned in the plans.
You need to devise a jigging method to ensure the left and right elevators are a matched pair.
The twist can start being built in from the bend in the trailing edge if it is slightly off.

Good point. I made a jig.
Hopefully they're straight. Guess I'll find out eventually.
Two pieces of melamine.
2 each 12"x 24"
1 each 6" x 36"
4 each studs 1/2 wood thread, 1/2 sheet metal thread
4 each wing nuts matching the sheet metal thread
Trace the end rib on one end piece aligned with the center line and more than 6" away from one end.
Clamp the two together.
Cut the "V"
Drill two holes evenly spaced along the 6" line.
Disassemble.
Place the three pieces on the bench.
Match drill the 6" brace through the ends.
Screw the four studs in the holes in the 6" brace.
Slide the uprights over the studs and install a wing nut on each.
One jig done.
Assemble the elevator in the jig.
Hang two plumb bobs from each end.
Shim the bottom of the jig till the bobs are perfect and it's square and straight.

longranger 04-28-2016 11:00 PM

Quote:

Originally Posted by wirejock (Post 1074524)
...The biggest problem is the reflex on the bending jig. Even 2x6 will bend in the middle. I used at least 5 huge door hinges on mine.

I borrowed the brake a retired carpenter made to bend his RV-7's control surface trailing edges. It uses 2x4s milled flat on the narrow edge, and hinged so that narrow edge does the bending. It works MUCH better that the 2x6 brake per the manual that I used on my RV-4 empennage.


tsw94r 04-29-2016 10:17 AM

I thought about making my brake in the same way, but I made mine as indicated in the manual. So far, I've bent the right elevator about 20 degrees shy of done; going slowly and trying to for a perfect bend.

Thanks to everybody; I picked up quite a few tips.

tswanson 03-04-2018 06:55 AM

Quote:

Originally Posted by wirejock (Post 1074575)
Good point. I made a jig.
Hopefully they're straight. Guess I'll find out eventually.
Two pieces of melamine.
2 each 12"x 24"
1 each 6" x 36"
4 each studs 1/2 wood thread, 1/2 sheet metal thread
4 each wing nuts matching the sheet metal thread
Trace the end rib on one end piece aligned with the center line and more than 6" away from one end.
Clamp the two together.
Cut the "V"
Drill two holes evenly spaced along the 6" line.
Disassemble.
Place the three pieces on the bench.
Match drill the 6" brace through the ends.
Screw the four studs in the holes in the 6" brace.
Slide the uprights over the studs and install a wing nut on each.
One jig done.
Assemble the elevator in the jig.
Hang two plumb bobs from each end.
Shim the bottom of the jig till the bobs are perfect and it's square and straight.


Larry, do you have any pictures of this setup in use? I'm just getting to the step of bending the trailing edges, and I'm coming to the conclusion this is one of those things that I should do myself a favor and make sure I'm prepared to do it correctly the first time.

Thanks!

wirejock 03-04-2018 08:02 AM

Jig or brake
 
Quote:

Originally Posted by tswanson (Post 1243502)
Larry, do you have any pictures of this setup in use? I'm just getting to the step of bending the trailing edges, and I'm coming to the conclusion this is one of those things that I should do myself a favor and make sure I'm prepared to do it correctly the first time.

Thanks!

The parts in the quote are for a jig to build the elevators and ailerons. There are some photos of the jig in use on the "EMPENNAGE" page of my blog.
You mention bending the trailing edge. That would be a bending brake. There's a photo of that too but if I did it again, I would build it as posted before and use the edges of the boards. Look at Miles post #11.

tswanson 03-04-2018 08:03 PM

Quote:

Originally Posted by wirejock (Post 1243516)
The parts in the quote are for a jig to build the elevators and ailerons. There are some photos of the jig in use on the "EMPENNAGE" page of my blog.
You mention bending the trailing edge. That would be a bending brake. There's a photo of that too but if I did it again, I would build it as posted before and use the edges of the boards. Look at Miles post #11.

Ah ok, for some reason that bottom 2x4 was blending into the background for me when I looked at the picture above, so I wasn't sure what I was looking at. The clamps are just handles. All clear now, that looks pretty simple assuming your lumber is flat, smooth, and straight. Thanks.

N329JR 03-05-2018 08:20 AM

Just a quick tip regarding the bending brake construction. I used a length of heavy piano hinge over the full length of the brake instead of multiple door hinges. This provides a really strong consistent bending platform. And as others have indicated... take your time, perform multiple bend iterations and sneak up on the final bend.

az_gila 03-05-2018 09:05 AM

The more detailed :) -6 plans call for a 3/32 typ. radius for the rudder and elevator trailing edge.

BruceW 03-06-2018 12:43 AM

Ha, this brings back memories.
I still have an elevator skin sitting on a hanger shelf from when I somehow ended up with a long-axis 'bow' in the trailing edge. Did something wrong, not sure what now.

I do recall flipping the skin over and back several times while doing the squeeze. That way, if I was doing something wrong or something was slipping, it would balance out on the other side.

It all turned out fine in the end. Only took one throw away skin. :rolleyes:


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