Bending Trim Tab Leading Edge... does this look right?

danielhv · #1 07-30-2008, 09:12 PM

Not sure if I'm getting the correct bend here... im putting a 1/4" dowel in there, and using the brake in the plans.... just want to make sure its not supposed to be a tighter curve...

BEFORE:

AFTER:

flion · #2 07-30-2008, 11:10 PM

Well, it's pretty sharp for the leading edge but it makes a nice trailing edge. <grin> Just kidding. The radius looks good. Keep bending until you don't have to pull it down to the E607PP spar. What you really want is to keep the surfaces flat right up to the radius, which it looks like you're doing just fine, but if you don't bend the tab some more then pulling the skin to the spar will cause the surfaces to tend to bow out.

danielhv · #3 07-30-2008, 11:17 PM

Quote:

Originally Posted by flion

Well, it's pretty sharp for the leading edge but it makes a nice trailing edge. <grin> Just kidding. The radius looks good. Keep bending until you don't have to pull it down to the E607PP spar. What you really want is to keep the surfaces flat right up to the radius, which it looks like you're doing just fine, but if you don't bend the tab some more then pulling the skin to the spar will cause the surfaces to tend to bow out.

lol, oops! I meant trailing edge! Well the problem is that I cant bend any further with the 1/4" dowel in there... Not sure if I can remove it and bend some more or if that will crease the trailing edge...

FredMagare · #4 07-31-2008, 06:13 AM

Quote:

Originally Posted by danielhv

lol, oops! I meant trailing edge! Well the problem is that I cant bend any further with the 1/4" dowel in there... Not sure if I can remove it and bend some more or if that will crease the trailing edge...

Well, the dowel is just a little insurance to keep from creasing the skin. I used the dowel and a piece of 2x4 and put pressure directly on the dowel. If I were going to squeeze without the dowel inside, I might set it along the outside of the trailing edge and allow part of my squeezer board to rest on that so I wasn't able to put too much pressure on the trailing edge. I don't necessarily see a problem of just putting pressure on the trailing edge without something in there, you just need to go easy so you don't crack the trailing edge.

Good luck.

Mel · #5 07-31-2008, 06:44 AM

No problem doing the final squeeze without the dowel. Just be careful and squeeze a little at a time. Getting the trailing edge right is pretty critical. If not done correctly on the elevators, you can expect cracks later on. My .016 skins are crack free after over 15 years of flying.

rwshooter · #6 07-31-2008, 07:10 AM

You can back rivet the bottom skin to spar if you wait to make your bend and not have to use blind rivets as called out in the plans. Prep everything, you know the drill, back rivet the bottom skin to spare first, while you can still get in there, then make your bend to meet up to the spare. Looks a whole nicer with out the blind rivets!

Robb

docrick · #7 07-31-2008, 12:02 PM

just a little at a time and had no issues with creasing the skin or too tight a radius.

flion · #8 07-31-2008, 12:46 PM

I don't have the 9A plans but if the 'brake' is still a pair of 2x6 with a hinge, you probably made it too well. You want there to be a gap at the hinge, about the same as the dowel. Otherwise you can never overbend the skin enough to keep it from springing back. You can probably make a little more progress by putting the skin back in the brake but not all the way in; say, 1.5". You'll gain a little more angle that way, maybe enough.

As far as backriveting the tab, I was able to backrivet the inner flange on my 6A tab by just curling up the skin. Start at the narrow end and work toward the other. You won't 'unbend' the skin enough to make a difference if you are gentle. The other flange can simply be squeezed. It's easier to squeeze the hinge and flange with the hinge disassembled but you may find the hinge shifts enough to get suddenly tight. I solved the problem by riveting the hinge to the elevator first, while assembled. Then I disassembled the hinge and assembled the tab side with a spare piece of hinge, which kept the hinge straight while I riveted it to the tab. Another tip: fold the hinge so that it is 90 degrees, not flat, while you rivet it. This keeps the hinge aligned in two axis and prevents you from putting a bow in it. This is also a useful technique while drilling hinge - unless we're talking the cowling, where you want the bow.