SonexBuilders.net

Just passing this info onto the forum:

I came across a video of a recent near tragic incident relating to rudder failure. It appears this is an anomaly incident that could have been caused by strapping the airplane in-properly during transport??

note: The intro clip is not his plane. Luckily there was no accident.

https://www.youtube.com/watch?v=D_Q8iVHhK_s

Thanks for posting. That’s my video. I would love to hear from anyone who’s seen anything like this before. At the moment I don’t know that it’s ever been trailered but I’ll reach out to the original builder about it. Appreciate everyone’s input on this scary situation. (Onex 090)

Scary!
My guess is that CCP-42 rivets were used instead of 44's

Just conversation. NOT saying you were wrong in ANY way.

1. Good catch.

2. And this is why I pick up the tail of my Sonex during the walk around. It's only about 25lb on the tailwheel - and picking up the tail allows for a thorough inspection of everything back there.

3. This particular rudder failure is somewhat unique to the design which is not common. Not unknown - just not as common as here. More planes have some kind of rudder horns which are easier to push and pull on to inspect.

4. Spin recovery - There is a non-PARE method that MIGHT work where you don't have a rudder. It works on a Cessna 150/2 and 172 that I am aware of as I have practiced it (with the CFI who showed me it). I do NOT advocate it as routine. It needs about 3,000ft of altitude and you have to finesse the end of the recovery to be sure you don't secondary stall or end up spinning the other way.

I haven't actually tried it on my Sonex as even with pro-spin controls and IN the correct CG range - I find it hard enough to spin the plane normally!

5. Good catch.

Wow! I sure am glad that was found before the flight and no accidents resulted.

I haven't seen the assembly of the Onex rudder, but if it's anything like the stub rudder on the Waiex, I'm guessing there are small angles inside of the rudder skin that attach the rudder skin to the thicker drive plate. If that's the case, it would appear that the angle pieces are all broke except maybe part of one. I don't see any tears in the skin itself so it must be the pieces that connect the drive plate to the rudder skin.

I seem to recall there was a fairly recent Service Bulletin for the Waiex that dealt with the rudder hinge and possible tears in the skins. Perhaps these are all related somehow? Something must be putting stress on the bottom of the rudders, causing these failures.

Regardless, this was a good catch! Well done preventing a very serious issue!

Thanks for the video. I keep my tail on a sawhorse due to space constraints (too many catamarans in the hangar). I'll add that to my preflight list.

Good catch ... but I believe this should have been caught much earlier as there was reportedly a pre-purchase inspection and two conditional inspections done. To say that this would not likely be caught on a routine preflight is a little misleading. I like lifting the tail & twisting the rudder during preflight. Not saying I couldn't have missed this but just giving the way I do it.

But the main takeaway for me was seeing the problem while watching the video. Then I went to look at the comments for the video and noted that Sonex Tech also saw it and pointed out what was at least one major contributor to the near failure:

Kerry Fores states:

"The most likely reason for this failure is the NON-STANDARD, NON-SONEX tailwheel pushrod. The top-mounted pushrod on this aircraft was prying the the rudder drive rib down. The kit-provided pushrod and installation has the tailwheel pushrod mounted UNDER the drive horn. This was a builder modification that was not thought out. Many builder modifications and "improvements" lead to unintended consequences. We see it all the time"

Look at the binding of the rod and the slop that is in the rod ends. How does that not get caught during a walkaround inspection? Forgive me if I come across a bit brash but my instructor warned me when he said, "never cheat yourself out of a good preflight."

I'm very thankful you caught this and by the Grace of God you are still here to pass on a warning to us all. Yes I will more thoroughly inspect my plane now that you have pointed this out. Thanks for doing so!

I took a look at mine:


Mine is not stock - I used one of Peter's links. The stock link was giving me fits trying to make it fit. There is a possible evidence of the locknut contacting the horn. I think I'll make the bolts one size longer, and add a couple of washers on both ends.

Also note I used solid rivets to fasten the horn to the bottom of the mini rudder. Also not to plans. It makes me happy though.

Kerry says "The top-mounted pushrod on this aircraft was prying the the rudder drive rib down". It seems like the torque moment is the same from the top to the bottom. The thru bolt should see roughly the same load.

If we think about a landing load, as seen from the left side of the airplane, the bending up of the tail spring will cause a counter-clockwise moment induced at the thru bolt. The moment is similar whether from the top or bottom. In fact, the rod end bearing should reduce the bending moment compared to the fixed pushrod Sonex uses.

The slop in the rod ends is another story. It could be causing some impact momentum on the bolt similar to hammering. I could see lots of taxing working on those rivets. I think the investigation needs to look further at the rivets, holes, previous life, etc.

Kerry has an excellent point about second hand airplanes. You just never know what its been thru. It was mentioned in the video comments about possible trailering. Its VERY destructive on airplanes if not done and monitored properly.

Bryan,
What's that line going right across your control horn???