R916 Rudder Trailing Edge gap

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....

rudder trailing edge

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

Rudder trailing edge

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?

Angle?

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 ?

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

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.

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

RV-7 Rudder Trailing Edge

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?

Keep working on it

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.

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

I don't have my drawings handy, but IIRC there is a dimension on the print to position the wedge fore-aft before you drill the assembly. I think the dim was 1/16" stickout past the rudder skins. Looks like your wedge may be too far forward.
Note the elevators have a similar process, but different dimension, than the rudder.

The skin dimples may be touching, I needed to hit mine with a file a little bit.

The countersinks need to be pretty deep but make sure you sneak up on it. I bought a 2nd AX wedge when I went overboard on my first try.

The hole will enlarge on the wedge because it is so thin. Make different templates of dimples for 3/32 and 1/8 rivets. Use the same material thinkness as the area on the project for the template. Dimples are a bit different shape (size) from one thickness to the other so you may make two different thickeness for each rivet size. Use them as a guide to make sure the countersink is deep enough. I liked using scrap J string for one thickness for a guide as it is easy to hold on too.

I am still having trouble with this. I have tried countersinking a bit further but there is still a gap. I also tried sanding the dimple down a bit, with the same result.

I found that moving the rudder skins back and forth the dimple would set in the wedge better, but still not great. I dont want to pro seal and rivet to find the skins not set correctly.

With clecos in the holes, the cleco's only hold down against the thicker part of the wedge, not the thinner trailing edge, which makes this problem more noticeable. Yes I believe drilled them correctly and not just parallel with the skins.

Is this normal? I am still concerned about countersinking to far. I notice the knife edge in the countersink on the trailing edge and dont want to go too much further.

Haydn, I'm about to the same point you were here. How did you solve this problem?

Hi,

I think what I noticed was if the rudder was all cleco'd up and sitting on the bench mine looked like this as well, but if I lay the rudder flat on the bench that gap would close up. Also if you squeeze the trailing edges together the aex wedge would find 'home' and the gap mostly disappeared.

When you inspect the trailing edge with the clecos in the clecos are mostly holding down on the leading edge side of the dimple. Take the clecos out and squeeze together with your fingers. You should notice the skin sits down better

I didn't want to continue countersinking as it was starting to get a knife edge on the thinner side of the wedge. I also filed a tiny amount off the dimples

Also I forgot to edge roll the trailing edge of the skin before I riveted, which would make this look worse.

My rudder ended up reasonably straight, but I do have a few slight buldges between some of the rivets, which make it not look as good as it should be.

Hope this helps

Haydn

Edge Rolling Rudder Skin Trailing Edge

Hmmmmm, they didn't say anything about edge rolling the skin before attaching to the AEX, and I haven't seen that in any other photo's. Looks like that would make it more difficult for the dimples to mesh properly with the countersinks in the AEX.

Anyone else out there do that before gluing their skins to the AEX?

In case anyone is interested, I checked with Van's tech support and they said DO NOT edge roll the trailing edge, just glue it directly to the AEX, otherwise the skins will not sit flat against the AEX.

So, Haydn, you did just fine by "forgetting" to do this.

I used Mr. Kalinsky's method to countersink my wedge. Scroll to the bottom of the page to see the set up he used for a drill press. It's slow, but works very well. You need something to keep it stable because in order to have the skin dimples fit, the holes in the wedge will be enlarged because it is so thin. This method worked for c/s the trim tab spar as well.

http://www.kalinskyconsulting.com/rvproj/rudder.htm

Here's a photo of checking the depth of the counter sink using a 0.016 coupon dimpled for #3 countersunk rivets. At the correct depth, the coupon lays flush with no lateral play. I used the countersink cage directly on the rig in the photo. You WILL knife-edge and enlarge the holes in the wedge - no big deal in this area. I "think" that fact is mentioned in the instructions.



Here's a not-so-good photo of the result (I used VERY thin layers of proseal between the skins and wedge, laid down with an acid brush trimmed to ~1/4"):