Tips for rolling leading edge skins.

[Amit]

Folks,

For the RV-7/9 rudder, the leading edge is formed by rolling the side skins until they meet, and then blind riveting them together.

In order to get the rivet holes to align without any load on the skins, the roll must be done so that the part closest to the spar of the rudder has a smaller radius than the edge closer to the blind rivet line.

I am sure by now there is a best known method to achieve a roll so that there is no load on the skins. What do they teach in the builder help centers? what have the repeat builders found to be a good way to go about this?

I am looking for tips and tricks.

[lorne green]

For rolling the leading edge, this is the way I did it.
One 3/4" steel or copper pipe of suitable length. Two vise grips with curved claws (to grab the curve of the pipe) Duct tape. But not your run of the mill duct tape.
Pick up Super strength duct tape. I used "Gorilla Glue Brand" Tape. Really strong, really thick, Really sticky, Really expensive. Lay down a strip of tape along the entire edge of the skin.
Lay the pipe across the taped egde of the leading edge skin then fold the tape over the pipe. Fasten the vise grips to the pipe ends and roll (with all your stength)
Get someone to hold down the part while rolling. enjoy

[mcencula]

I found that using the pipe and vise grip method only resulted in the start of the bend. The portion near the spar had little to no bend and had to be done by hand.

What I did is lay the rudder flat on the workbench with the trailing edge facing my chest. Then I used my hands to apply some force to curl the leading edge downward, but I also pulled back with a lot of force. A towel on the trailing edge is recommended to avoid a bruise across the bottom of the rib cage.

By changing the contour of my hands, and using a lot of back pressure, you can get the majority of the curvature right up near the spar without actually kinking the skin at the spar.

My friend, Dan Hempy was having problems doing this bend on his elevators. I showed him the technique I used and snapped a shot of the work in progress:



Finished result:



One other note...You'll end up flipping the skins over the top of each other several times. Do the flip all at once with a piece of aluminum or some other sheet. I tried using a popsicle stick to get the skin flip started at one end and then ran it down the length of the overlap. This resulted in one of the skins having a wavy edge.

Good luck,

[DanH]

Make two J-bolts like this to fit your pipe:



Round up a sheet of plywood, some sheet plastic, and the good duct tape. Drill holes to fit the j-bolts near the edge of the plywood, spaced to match your hinge cutouts.

Cover the plywood with the plastic; it is there so the aluminum can slide without scratching. Tape the pipe to the leading edge, loosely bolt the pipe to the table with the J-bolts, and twist as you please. The control surface will slide toward you as the roll is formed. It can't lift and bend a crease along the spar edge, the problem with hand bending.

[Amit]

Thanks to all for the replies.

in Dan's last picture I see the rivet holes do not line up, they are very close at the rudder top, but gradually become further apart towards the bottom.

I am looking for ways or any trick to get them to align better, so that there is virtually no shear load on the blind rivets?

[yakdriver]

I like Dan's set up but as Lorne said get the gorrila brand duct tape and you can roll it up as tight as you want. I tried regular duct tape and struggled with the first elevator. I used the Gorilla tape on the other elevator and rudder and got them to align almost perfect. Took about 10 minutes apiece to do the job. Struggled for over an hour on the first elevator and almost ruined it. Don

[Danny7]

Originally Posted by Amit

Thanks to all for the replies.

in Dan's last picture I see the rivet holes do not line up, they are very close at the rudder top, but gradually become further apart towards the bottom.

I am looking for ways or any trick to get them to align better, so that there is virtually no shear load on the blind rivets?

tape the pipe only to the upper section and roll it some more. You can work the different sections with different methods or amounts of pressure.

[roee]

Originally Posted by Amit

Thanks to all for the replies.

in Dan's last picture I see the rivet holes do not line up, they are very close at the rudder top, but gradually become further apart towards the bottom.

I am looking for ways or any trick to get them to align better, so that there is virtually no shear load on the blind rivets?

Amit,

Ideally, you could achieve the perfect curvature with zero load by rolling the skins using the pipe method, but with an appropriately conically-shaped pipe instead of a normal straight (i.e. cylindrical) pipe. That would be ideal, but not practical unless you have a lathe and lots of time on your hands. Fortunately, it's also unnecessary.

Rolling with a normal pipe can get you close enough (and DanH's refinement on the technique should make it even easier and more foolproof). Optionally, you could then hand-adjust smaller sections of the skin even further, as some people do. But I think that would tend to introduce waviness or other non-uniformity, which ultimately will be detrimental to skin clearance between the control surface and fixed stabilizer (limited by high spots in the uneven curvature), strength (due to unevenly distributed stresses), and aesthetics (smooth curves are pretty, waviness is ugly). I would stick with just pipe rolling.

Finally, a little bit of load in the skin and rivets when it's all buttoned up should not be a problem so long as the load is not excessive. Hard to quantify "excessive" in practical terms, but if you can bring the skins together with only "light-to-moderate" hand pressure to line up the rivet holes, I think you would be well in the clear.

Good luck!
-Roee