Edge hole distance woes - revisited

[samiam]

Edge hole distances are conspiring to drive me crazy. After hours of work on the rudder today, and really taking lots of time to make sure everything was placed right, I got the basic structure together. Time for the hinge, which is where I ended up with my edge distance problems on the elevator.

Unfortunately, I measured and there is only 3/8" overlap of the rudder skin. Therefore it will be basically impossible to get 1/4" clearances on both sides (see photo link below). What am I doing wrong here???

https://drive.google.com/file/d/0B0U7g1 ... sp=sharing

[Bryan Cotton]

Mike,
I have always been nuts about edge distances. As a former and future scratch builder it was always 2.5D for me unless I had to settle for 2D. Sonex tends to design to 2D from my observations. That means it is very possible to come up short, and I have in a few instances. I can't remember for sure but I think I saw similar issues on the control surfaces. My take is you will probably have good ED on the short flange and hinge. It will probably be short on the short face of the surface. With the tight spacing of the rivets and plus you are going through 3 pieces where the aerodynamic loads are transferred at the ribs that it is probably fine. I would shoot Kerry at Sonex an email and ask him.

I have redone some parts to satisfy my edge distance obsession - namely the angle that bolts the front of the tail down. Took me 7 tries to get right.

[samiam]

Bryan, I knew you would come through with a helpful reply! I agree, and after working on the RV project last year where it was very rare to see a hole come close to minimum distances, yet it seems like the Sonex is designed around minimal clearances with many of the rivet lines placed 1/4" from the edge. This leaves basically no room for error.

I have an email in to Sonex so we'll see what they say when the holiday break is over. I appreciate your input though as I feel like I must be doing something wrong, but the parts are prebent and formed so I'm not sure how I could have ended up with anything better.

[samiam]

Just a quick followup in case anyone is interested -

I heard back from Sonex, and they said the above edge distance is "fine" and that it is normal for the engineering strength built into the aircraft

For my elevator which had a drifting edge distance, the question is only whether or not it is straight. If the hinge is straight (to avoid a binding elevator control), I just need to put in a few extra rivets in between for added strength in the areas with smaller distances.