Holes for aileron counterweight tube

[Chewie]

Hey guys, I have a question from the shop. This one is being tricky:
When I try to locate the counterweight hole on the aileron nose ribs as shown below so it's butted right up against the flanges, I find there's just not enough meat up there and the hole punches through the front of the rib. Should I remake the ribs so there's more meat, allow the tube to punch through and debur, or scoot the tube back a little and just pop rivet on the bottom side?


IMG_20150711_164027389.jpg

Mark

[Bradrock]

Somebody mentioned using a step drill for these holes, but I encountered similar issues with the front of the rib and flange clearance.
Using an appropriately sized hole saw did the trick. You can get the hole right up against the flange.

[sjt]

I can not find the reference now. I saw that another builder dealt with the problem by putting a shim between the bent flange and the tube. The shim kept the shape of the nose rib from being distorted by a pulled rivet. The only down side was that the weight was not as forward - for balance - as it might be. The upside is that it solves the problem without having to remake ribs, and it is probably more structurally sound.

[Chewie]

Somebody mentioned using a step drill for these holes, but I encountered similar issues with the front of the rib and flange clearance.
Using an appropriately sized hole saw did the trick. You can get the hole right up against the flange.

For sure! I actually don't see how it's possible with a step drill unless you bend the walls back for clearance. A friend lent me some blair hole cutters. He swears by them for sheet metal and I've had great results.

The clearance issue I'm having isn't between the hole and the flange; a shim won't help. See the pic below... this is what I ended up with when I allowed the hole to be tangent to the two walls. I made the tip of the web concave by accident. Ignore the flanges; I was playing with a notcher on this scrap piece.
Mark

[sjt]

I saw the picture of your rib. I myself moved the hole away from the flange. I might have to copy what another builder did. When the hole is further from the edge, it necessitates a shim to prevent distortion. Even when I used my step drill to make them, I would drill each step and examine the hole. I then took a file and removed the material in the direction I wanted the hole to go. This allowed me to stay away from the edge with the final dimension.

The shim will eventually be between the flange and the tube. If you did not use a shim it would distort the skin when the rivet is pulled.

Apart from the inconvenience of having to make shims, I will have to have my counterweight tube slightly heaver since it is not as far forward.

Bob might tell you to keep what you have. When you rivet the skin to the flange, you will have as much structure as any patch might have provided.


I do not know why your picture did not display in your original post. I hope it will display now.

I also include a picture of my rib. Either way the skin that wraps around the rib is the source of the strength. It certainly is not that little bit to the left of the hole.
Bob shows a pop rivet that goes thru the left most bottom flange.

If you have enough material for that pop rivet, it should still work. I can not make out how much material is in the flange that receives the rivet.

I only have the counterweight hole in the appropriate nose ribs.
stan

[Chewie]

SJT, you were right, Bob told me that little gap won't compromise structure. The hole still has most of its circumference, and as for the flanges a pop rivet might even miss the flanges all together but the skin will be there doing most of the work.
(Incidentally, there's a nice Patrol video on Bob's website, including side-by-side take-off comparisons with another super cub - style plane)
Good point, not all the ribs will need holes.
Thanks!
Mark

[N3UW]

For sure! I actually don't see how it's possible with a step drill unless you bend the walls back for clearance. A friend lent me some blair hole cutters. He swears by them for sheet metal and I've had great results.

The clearance issue I'm having isn't between the hole and the flange; a shim won't help. See the pic below... this is what I ended up with when I allowed the hole to be tangent to the two walls. I made the tip of the web concave by accident. Ignore the flanges; I was playing with a notcher on this scrap piece.
Mark
[ATTACH=CONFIG]temp_1430_1436730846436_759[/ATTACH]

Chewie,
I did it with a step drill. I mounted the step drill in a drillpress and cut a hole into a piece of double 3/4" MDF that was clamped to the table. I then center the hole over the nose rib to get it where I needed it. I then drilled holes into the MDF through the jig pin holes in the rib to lock it into place. I then drilled all the righ ribs and then repeated for the left ribs. They were perfect and all matched. The MDF also keeps the step drill from possibly moving if you have play in your drill press.

[Chewie]

I'm guessing you're jig is flanges down? Mine is flanges up so a step drill would not work. At any rate... I'm passed that step!

[N3UW]

I'm guessing you're jig is flanges down? Mine is flanges up so a step drill would not work. At any rate... I'm passed that step!

I did it flange up. I placed the step drill in the chuck so the chuck would clear the flanges. How did you end up cutting the holes?

[Chewie]

John,
I did mine in a similar fashion:
IMG_20150714_222444694.jpg IMG_20150715_221853721.jpg

I used the same fixture for both left and right; the jig can be flipped over go switch between right and left flanges. A 1/8" pilot locates the blair cutter.
Re: drill, I'm just thinking it's a step drill so the next size up above 3/4" would start striking the verticals since it's tucked so close into that corner.
Mark

[Gavin Chester]

044.JPG Flange Down