Sonex new style Machined 4" and 6" Tailwheel
Posted: Sat Sep 01, 2018 11:06 pm
by 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
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Sun Sep 02, 2018 10:24 am
by WesRagle
Thanks Loren,
Good to know. Glad it ended well.
Wes
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Mon Sep 03, 2018 8:21 am
by DCASonex
Another reason for differential brakes. They can provide additional steering control in crosswinds as well.
David A.
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Mon Sep 03, 2018 9:23 am
by 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
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Mon Sep 03, 2018 11:26 pm
by 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.
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Tue Sep 04, 2018 11:08 am
by 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
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Tue Sep 04, 2018 12:06 pm
by 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.
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Fri Sep 07, 2018 10:53 am
by 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
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Fri Sep 07, 2018 11:20 am
by 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!
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Sat Sep 08, 2018 8:20 am
by 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
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Sun Sep 09, 2018 7:28 pm
by lutorm
We’re about to replace our old tailwheel with one of these. I’ll check the screws but the heads at least look like the ones pictured here.
One question though: The tailwheel has no hole for bolting to the spring rod. Does anyone have a good procedure for locating the hole so it matches the hole in the rod?
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Sun Sep 09, 2018 11:05 pm
by peter anson
Don’t know if I should buy into this but as well as differential brakes and non-castering tail wheel, I have a pneumatic tire which grips much better than the solid wheels. I regularly use the brakes to tighten up turns on loose surfaces and have even done it on sealed surfaces, although I try to avoid that because I think it is a bit hard on the tire. It helps to have a 3300 to drag it around. Can’t say I have ever worried about breaking anything back there.
Peter
Sonex 894
Nearly 400 landings on the 6" pneumatic tail wheel
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Mon Sep 10, 2018 4:03 pm
by SonexFactoryTech
We erroneously stated Mr. Sievila’s aircraft, which experienced this failure, was fitted with differential brakes. It was not. The differential brakes were removed when the updated tailwheel was installed. We have amended our original post to exclude that statement about the subject aircraft.
We do maintain that differential brakes are not compatible with our tailwheel.
Sonex Aircraft, LLC.
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Thu Sep 13, 2018 6:04 pm
by markschaible
Sonex Service Bulletin SNX-SB-008 has been issued today to address this issue: https://www.sonexaircraft.com/service-bulletins/
If you are not already a subscriber to the Tech Updates Mailing List, it is highly encouraged. You can sign-up via the form at the top of the Service Bulletins web page.
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Mon Sep 24, 2018 2:14 am
by lutorm
Answering my own question from before in case someone else has the same problem:
lutorm wrote:The tailwheel has no hole for bolting to the spring rod. Does anyone have a good procedure for locating the hole so it matches the hole in the rod?
I ended up taking the rod off of the airplane, and mounted it with some V-blocks in the mill vise. After adjusting it so a 1/4" drill went through the hole in the rod, I pushed the tailwheel assembly on, and leveled it to be horizontal. Then I drilled the hole, the drill going through the existing hole in the rod. Worked perfectly (although taking the rod off the plane required balancing the tail on a jackstand while the work was done, which was a bit iffy…)
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Tue Oct 09, 2018 3:06 am
by lutorm
markschaible wrote:Sonex Service Bulletin SNX-SB-008 has been issued today to address this issue: https://www.sonexaircraft.com/service-bulletins/
If you are not already a subscriber to the Tech Updates Mailing List, it is highly encouraged. You can sign-up via the form at the top of the Service Bulletins web page.
I got the hardware suggested in the Sonex SB and wanted to give a heads up: I found that the shanks on the screws were long enough that, without a washer (which is not included in the hardware kit from Sonex), it looked like the nut would bottom out on the threads.
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Sun Mar 15, 2020 3:46 pm
by pfhoeycfi
markschaible wrote:Sonex Service Bulletin SNX-SB-008 has been issued today to address this issue: https://www.sonexaircraft.com/service-bulletins/
If you are not already a subscriber to the Tech Updates Mailing List, it is highly encouraged. You can sign-up via the form at the top of the Service Bulletins web page.
Getting ready to install my tailwheel and spring. The heads on the screws to be replaced per the SB snapped off quite easily when I attempted to remove them. The threadlocker that was used works pretty good. I have no idea how I’m going to get the remaining part of the screws out without butchering the part. My guess is I’ll be buying more stuff.
Re: Sonex new style Machined 4" and 6" Tailwheel
Posted: Tue Mar 17, 2020 12:45 pm
by lakespookie
The SB says to drill out the threads so I would not worry to much about the existing screws I know that heat is pretty good at breaking thread lockers but can change the properties of the metal. Since you have to drill through the part anyways per the SB I would center punch the screw and attempt to use a smaller bit to drill the core of the screw and step up drill bit sized from there once you get closer to the 19 called out in the sb the remaining parts of the screw should just fall apart anyways and if not just continue stepping up to the recommended size 19 drill bit at that point there will be no thread or pieces of the screw left. if you are really concerned drill up until one size smaller than the 19 and ream it the rest of the way there to make sure its square but I don’t think you need to go to that extreme.