Silly question about drilling flanges

[rvrepairer]

Hi, I am building an RV4 empennage and I have a question to which the answer is probably obvious, but I want to make sure prior to drilling all that expensive aluminium.

In cross section, a flange or stiffener consists of a flat portion, then a radiused portion joining the flat portion to the web. It is my job to choose where to drill holes, both longitudinally along the length of the flange, and laterally in terms of the spacing between the web and the outside edge of the flange.

W
W
W
W
W
.C
...C
......C
...........C
...................C F F F F F F F F

Where W is web; C = curve (radius) and F = flange

The obvious place to drill a hole is half way between the web and the outside edge of the flange:


W
W
W
W
W
.C
...C
......C
...........C
...................C F H F F F F F F

But you could argue that the dimpler will mark the radius because it is too close to it, which will work harden this portion and distort the part.

Perhaps it would make more sense to drill the hole half-way along the flat portion of the flange:

W
W
W
W
W
.C
...C
......C
...........C
...................C F F F F H F F F F

Like so.

Or you could contrive arguments that it would make the most sense to drill the hole as close to the web as possible... Or as close to the edge of the flange as possible whilst respecting edge clearances...

I've looked at lots of pictures but it's not quite clear to me which strategy VANS is using.

Next question - if I have a long flange presumably it makes sense to have the first and last rivets in the flange as close as edge-clearances allow to each end of the flange?

Many thanks for putting my mind at rest as to the correct approaches.

 

[PaulvS]

I'm building an RV-6A following pretty much the same process as for RV-4.
Flanges are typically 5/8" wide and I locate rivets in the centre, i.e. 5/16" from the edge, though 1/4" is also generally OK. If the hole is too close to the web it will be more difficult to dimple and rivet. The female dimple die can be ground flat on one side to provide more clearance from the web and radius.
The end rivets are located for adequate edge distance and also to make the overall spacing work out for the row of rivets..

 

[wirejock]

Holes

I'm building an RV-6A following pretty much the same process as for RV-4.
Flanges are typically 5/8" wide and I locate rivets in the centre, i.e. 5/16" from the edge, though 1/4" is also generally OK. If the hole is too close to the web it will be more difficult to dimple and rivet. The female dimple die can be ground flat on one side to provide more clearance from the web and radius.
The end rivets are located for adequate edge distance and also to make the overall spacing work out for the row of rivets..

What he ^ said.
Typically holes fall 1/2 the inside flange. Usually 5/16"
Not 1/2 the outside which would be 3/8 and too close to the vertex.

 

[rvrepairer]

Thank you both.

 

[penguin]

Any steel tool can be ground to improve clearance, but doesn't always improve things!
If the edge is ground off a dimple tool closer than (about) 1/16" (1.5mm) to the edge of the dimple the shape of the dimple will suffer, more is better.
It is possible to buy reduced diameter dimples - mainly for plate nuts (anchor nuts) but work well elsewhere - see Cleaveland site.
Edge distance is key - but I wouldn't get too close, say 8mm from the end.
For a 5/8 (16mm) flange the centre gives plenty of margin for both a 3/32 and 1/8 rivet.
I know these are imperial aeroplanes but as my eyes keep getting worse I find it is much easier using the mm side of the ruler so the centre is 8mm from the edge!
Not sure there is any one "correct" answer, 3 builders in a room will have 3 similar but slightly different techniques...