TAIL KIT ON HOLD?

[taildragger]

Is my tail kit is on hold pending the arrival of the quick build fuselage? Since I do not yet have the rear stabilator forward cap, which has all the pre-drilled pilot holes, (See photo) should I:

- Proceed with skinning, rib and hinge drilling assuming the rear rib pilot holes will line up?
- Halt the project until the quick build arrives so that all ribs, rear spars and and rear caps can be properly jigged and pilot drilled?

All stabilator and ruddervator parts are built and awaiting your replies.

[Bryan Cotton]

That was a long time ago for me but I don't think we had the big Y in place when we built the tails.


This next picture was much later:


Much later again we clecoed the tail on. I am pretty sure we trusted the holes and all was well. You don't rivet up the skins until you are drilled, riveted, and deburred.

The sequence should all be in the plans. Worth a study.

[taildragger]

Thanks for sharing those nostalgic photos. I don't have the plans for the rear spar caps and assume they will come on April 22 with the quick build fuselage.

[racaldwell]

TD,

Yes, you should proceed with drilling, deburring, hinges, etc. As Brian said, part of the skin does not get riveted until the Y is installed which for me was when the tail was mounted to the fuselage. You leave one side of the skin clecoed so you can debur after drilling the Y to it. I used solid rivets so I was able to buck the rivets that hold on the Y since the skin was open on one side.

Rick Caldwell
Xenos 0057 24 hrs engine time, 25 hrs TT

[taildragger]

Just to clarify, does the Y have pre-drilled pilot holes for the quick build kit from the factory?

[Bryan Cotton]

My recollection is both the Y and the aft stabilizer channel have predrilled holes. We cleaned up the holes in the Y on the drill press with a #40 bit, and clecoed the parts together. The adjustment of incidence or whatever is done on the front of the tail.

[taildragger]

The front spar cap did, repeat DID COME WITH PRE-DRILLED PILOT HOLES in the tail kit. The quick build fuselage kit arrives April 22, 2022 so I have 11 weeks to figure it out, or should I call Sonex?

I have learned that Sonex cuts it too close on edge hole location tolerances because:

1) Pilot holes are too close to edge. E.g. Due to the "two radius rule", I had to remake the -11 root rib because it's holes were too close to the edge.
2) Sonex assumes builder understands how to build an airplane without step-by-step instructions.
3) Sonex assumes builder will hold tight tolerances on parts to be mated later without understanding the term "tolerance build-up", or "worst-case" analysis.
4) Use of hand tools while cutting and bending ribs and spars almost guarantees poor tolerance control. I have improved my understanding over time but I hope my parts all fit the "two radius rule".
5) I use a digital caliper accurate to one thousandth, but after cutting and bending a piece, still come out 1/16 off-tolerance due to pen width error and my inability to control bend radius or twist.

Two questions:

1) Can additional rivets be used when building a Sonex? This is an exception case where a rivet is too close to the edge and reinforcement is necessary.

2) Can shims be used to adjust minor and major load-bearing parts? Should they be made of steel or aluminum?

[Bryan Cotton]

I've worked at two airframers and 1/16" for sheetmetal is generally a fine tolerance. Shims are a common practice whether it is built by Bryan or by Sikorsky, Schweizer, Boeing, and so on.

I'm not sure what the 2 radius rule is, but 2D is generally the minimum edge distance and 3D is the minimum rivet pitch. You can add extra rivets if required.

I'd recommend you ask Sonex tech support as well as the peanut gallery here. And, go with what they say!

[mbean]

I found the 2 day Sonex builders workshop invaluable as a new builder.
Topics ranging from Tolerances, design features, techniques and building tips were covered.
Highly recommend to give you “factory” answers and instill confidence early in the project.

Mike Sonex A model #1694

[taildragger]

Thanks for your thorough reply. Here a photo of an unacceptable rivet spacing and a re-made -11 root spar for my Xenos stabilator.
I should attend the Sonex Workshop. Just have to look at when and where.