Sonex new style Machined 4" and 6" Tailwheel

[lgsievila]

If any of you all have the new style tailwheel I would suggest that you remove the 2 #8 screws that keep the control arm from pivoting and check for any signs of wear. If they won't come out it is my opinion they are ready to shear off. Mine sheared off today on takeoff from an EAA breakfast and I nearly wrecked because I had no directional control. Had the fire and rescue trucks standing by when I landed at my home airport because I wasn't sure what was going to happen when I touched down. I lost directional control on roll out but was slow enough that I didn't ground loop-just ran off the runway into the grass.


Further it is my opinion that those little machine screws are not the proper hardware to use in that application-a threaded fastener should not be used in a shear application. I had 87 hours on that new style tailwheel that I purchased directly from Sonex when it failed

[WesRagle]

Thanks Loren,

Good to know. Glad it ended well.

Wes

[DCASonex]

Another reason for differential brakes. They can provide additional steering control in crosswinds as well.

David A.

[Gordon]

Machined Tail wheel Fork

I read you post with concern Loren. I have this new style tail wheel with the 6" wheel and I have 7 hours on my new Onex.

What is the "fix" for this "design flaw" in your opinion.......and if my screws come out okay what should I replace them with........in other words what did YOU do to resolve this?

Gordon......Onex....Hummel 2400

[lgsievila]

I should have been more clear in my description of the failed hardware. A threaded fastener without an grip length at the shear interface is not acceptable in any circumstance. If there are any structural engineers out there that have a differing thought I would like to hear it. I am now aware of three of these machined tail wheels that were sent out with the wrong screws and I know of one that has the correct AN 525 screws. This is a real safety issue and should be addressed in a service bulletin from Sonex.

[thomas]

Loren,

Thank you for sharing this information. I pulled out one of the screws from my 6" tailwheel that was shipped Oct 2016 and it too has no grip or shoulder.

Paul

[lgsievila]

Hi Paul,
I am glad that you checked. One of my friend has the proper AN525 screws so you are now the 4th one that I know is wrong. As I said before, Sonex should send out an immediate service bulletin. Pictures show part of screw that was still on the arm when I landed, missing screws from arm and damage to fairing where I hit the runway marker light.

[SonexFactoryTech]

Sonex Aircraft has been delivering the tailwheel assemblies with stainless steel screws holding the steering arm to the caster since 2013. The hardware has a good track record to date, however, any failure is worth investigating and learning from.

Photos were posted of a tailwheel caster with AN525 screws installed. That tailwheel caster was not delivered from Sonex Aircraft factory with that hardware installed. The head of the screw is too large and contacts the pivot bolt.

Sonex Aircraft is exploring upgrading the hardware that holds the drive arm the caster to NAS623-2-2 screws and MS21042-08 nuts. We will provide more details after we have fitted a tailwheel with that hardware.

For those immediately concerned about their screws breaking, you can inspect them prior to each flight, you should avoid unnecessary movement of the rudder pedals when the aircraft is not moving (this stresses the screws in question), and you should install a full swivel tailwheel if your aircraft is fitted with differential brakes (or restore the original braking system).

Sonex Aircraft, LLC

[lgsievila]

Kerry,
You could have asked and I would have told you that I DO NOT HAVE differential brakes. Don't send out false information!

[bvolcko38]

To SonexFactoryTech
In my five short hours of flying my Xenos I have experienced the tail wheel sliding sideways on the runway due to weather vaning in a crosswind. This may be due to my low time in a tailwheel aircraft, but it can and does happen.
Respectfully,
BV