R916 Rudder Trailing Edge gap

[flyer76]

Finishing the rudder, a little concerned about the gap between the skins and the R-916 trailing edge. Its a consistent gap - not sure if its due to the stiffeners,countersink on the 916, or just the cleco's....

[NDrv8r]

It looks like the countersinks on the trailing edge may not be deep enough. The skin dimples bottoming out?

[flyer76]

I will check if skins are bottoming out. I used the CS for the rivet call out. Should I adjust the bit to make the CS deeper and wider?

[FlyingArcher]

It might be a problem with how you held your drill perpendicular related to the wedge.
Do your bottom countersinks look circular?
Your upper countersink seem to be OK, because the gap maily appears on the bottom. You really have to keep the coutersink cutter perpendicular to the wedge.
My 0.02 ?

[mototopo]

I can't see it in the pictures, but I would check for stiffeners interference also.. they shall not touch each other.

[Bullseye]

Paul,

I had the same trouble on my practice kit (way to help with real experience, huh?) and found that I had to countersink more than the plans called out to get the dimples to seat properly on the practice kit wedge. It was trial and error, but ended up looking pretty good. I'm gonna get strated on my rudder in a month or so, so feel free to ignore.

Also, I am very proud to see your copy of the FAR/AIM so close to the project. Good man.

[jaybell]

I have a similar gap on my 7A rudder, and can see the skin dimples standing off the wedge with the help of a flashlight. Unfortunately, I did not notice until after riveting. Too bad, since the trailing edge turned out nice and straight, and now I am considering drilling it out. I have some received some advice to "go fly", but I'm not decided yet.

With hindsight, I did not countersink deep enough. I did countersink very accurately by mounting my countersink cage to the drill press and having a helper hold the countersink cage from spinning, then lifting and pressing the wedge into the cage and cutter. I feel this is safe, but I'm not sure I would try it without a helper; it takes three hands to manuver the material and keep the cage from spinning. Don't push directly underneath the spinning bit, push just outside the cage perimeter. Also, remember face protection and to secure loose clothing and hair

Now, before I make more mistakes, I have a question about riveting the skin to the narrow aft section of the top and bottom rudder ribs: How do others do this? I milled down part of bucking bar to 1/4" so it fits, but it works marginally because most of the bar's mass is not in line with the gun, and it is still to big for the furthest aft hole. I plan on using blind flush CS4-4 rivets for this, but the rib is so narrow the left and right side rivets interfere, preventing one of the blind rivets from seating firmly against the skin.

Any suggestions?

Jay Bell
half-way through the tail, quick-build on order

[jayjabour]

I had the same issue, but I noticed a gap before I applied the epoxy. I removed most of the gap by countersinking the wedge holes more deeply. I began to think I was weakening the wedge. I went ahead and applied the expoy, let it set, then rivetted. In the end the edge is straight (measured less than .10" deviation), BUT, there is a significant gap (measured at about 0.080"). I felt I did not get the epoxy layer thin enough before I clecoed the edge. I also think its OK to fly, BUT, (despite my wife's comments about me not leaving well enough alone) I think I will redo the rudder skins. I suspect the comment below about keeping the drill perpendicular to the wedge while drilling is important, and I may not have been very good on that. I was wondering if I could do a better job by NOT using the epoxy, just go ahead and rivet with clecos holding the edge. Any thoughts?

[sf3543]

In my experience, riveting doesn't usually pull things together, if they aren't properly prepared in the first place.
For whatever reason, whether the countersinking isn't deep enough or the stiffeners are holding the skins apart, make sure you fix it before you proceed.
The clecos should hold everything in perfect alignment, in this case.
Once you are satisfied, then epoxy or proseal the pieces together and let it cure while it is clecoed in place.
You can come back and rivet later. This will prevent your riveting from deforming anything.
If there is a little epoxy in the rivet holes, you can easily clean that out with a deburring tool before riveting.

[haydnc]

How far should I countersink. I have done the 2-3 clicks past flush but mine looks like it needs a little more.

On the trailing edge the countersink from each side has met each other in a sharp edge.

If I countersink further the hole will start to be enlarged. Do I keep going to get the dimples fully seated in the wedge or take a middle ground?

Thanks