Tail post channel cracked due to floor skins not installed?

[Murray Parr]

My yet to be flown Waiex has 2 significant cracks in the tail post channel. I was lucky to find it because it realy isn't obvious and I had done a lot of work around that area without noticing it. It isn't in the same area that is mentioned in the service bulletin for this part and lets face it, this plane is yet to fly. I am not sure what could have caused this but I am a bit suspiscious of the amount of times I have got in and out of the cockpit with the lower floor skin off (it is much easier to be upside down under the panel if your legs can protrude through the lower floor). My thinking here is there is a lot of flex at the tail spring assembly and without the lower bracket clecoed on it is allowed to flex more that intended. I'll try post some pictures and you'll see that the crack is well on its way to extending all the way down either side along the edge of the Y post which would have left the rudder swinging in the breeze if I didn't catch this. Has anybody else encountered this? any other thoughts on how this could happen? I am posting this so others can have a close look and see if they have the same problem either in a flying or not yet flying aircraft.

[sonex892.]

Hi Murray.
Something is not right there. It looks like the damage was done from the clamping pressure when tightened.
Is it possible the temporary 3/16" spacer wasn't used during assembly? If missed it would place the entire tailwheel bracket forward 3/16" from where it should be. That would probably stress things as shown in the attachment photo when the tail fin spar is later clamped down with the bolts.
Steve

[Rynoth]

I think your suspicion is probably correct that repeatedly sitting in the plane without the tailwheel assembly at least clecoed in place could cause this to happen. I'm looking at old photos of my build, and it would appear that if the tailwheel mount brackets (both the fore and aft bracket) are not clecoed or otherwise fastened to the lower longerons, that the entire force of the tailwheel would be cranking on that tailpost channel, with its rivets on the side skins being all that was supporting it.

I left my floor off but I did cleco everything around the tailwheel assembly in place to help support the weight, any reason you can't do this?

[Murray Parr]

Hi Murray.
Something is not right there. It looks like the damage was done from the clamping pressure when tightened.
Is it possible the temporary 3/16" spacer wasn't used during assembly? If missed it would place the entire tailwheel bracket forward 3/16" from where it should be. That would probably stress things as shown in the attachment photo when the tail fin spar is later clamped down with the bolts.
Steve

Hi Steve,
It's been a few years since I put this part together and I don't remember any spacer, could you let me know what spacer you are talking about? Maybe a B model Waiex is different? I can't imagine I would have done anything up to a point where it starts cracking things. I just finished replacing this and it went together as per plans (it did take 3 days though).

[Murray Parr]

I think your suspicion is probably correct that repeatedly sitting in the plane without the tailwheel assembly at least clecoed in place could cause this to happen. I'm looking at old photos of my build, and it would appear that if the tailwheel mount brackets (both the fore and aft bracket) are not clecoed or otherwise fastened to the lower longerons, that the entire force of the tailwheel would be cranking on that tailpost channel, with its rivets on the side skins being all that was supporting it.

I left my floor off but I did cleco everything around the tailwheel assembly in place to help support the weight, any reason you can't do this?

No reason I couldn't have done this, I just didn't give it enough thought. I had seen advice that states not to install the floor skin until the last thing on the project and never thought this through which would have required the brackets to be at least cleco'd in. I cleco'd the floor skin on during a 5 hour trailered move a few years ago but I am not even sure if I put cleco's in the bracket that attaches to the longerons.

[Bryan Cotton]

I had my brackets bolted in before it went on the gear. It seemed easier that way - the airplane was upside down on sawhorses.

[sonex892.]

Hi Murray.
Something is not right there. It looks like the damage was done from the clamping pressure when tightened.
Is it possible the temporary 3/16" spacer wasn't used during assembly? If missed it would place the entire tailwheel bracket forward 3/16" from where it should be. That would probably stress things as shown in the attachment photo when the tail fin spar is later clamped down with the bolts.
Steve

Hi Steve,
It's been a few years since I put this part together and I don't remember any spacer, could you let me know what spacer you are talking about? Maybe a B model Waiex is different? I can't imagine I would have done anything up to a point where it starts cracking things. I just finished replacing this and it went together as per plans (it did take 3 days though).

Hi Murray
Hopefully its all good and sorted now then. Its been a lot more years since I built mine so I just had a look over the plans for my A model. I'm pretty sure these parts are common to both A and B, Sonex and Waiex. The part numbers would no doubt be different.

For the Sonex in this area there are 2 temporary spacers used for assembly one on the lower tail post. A 1/8" spacer at the top which takes the place of the forward spar strap for assembly and a 3/16" spacer taking the place of the rear spar strap in the lower section. The lower spacer is only to space the tail wheel bracket for the correct position before the fin is installed. In relation to your damaged tail post in the photo the top spacer is placed forward and lower is placed to the rear.
Steve