Tail Wheel Trouble

[planeolbob]

Hi Everyone,
Tonight I was checking myself out for night landings now that I have my "Basic Med" completed. It was a cool calm night and I was slowly doing a series of landings at OJC, my home field. I had done 3 landings to a full stop at twilight and one in full darkness. As I was turning onto Gulf taxiway my rod end bearing at the aft end of my pushrod failed. My aircraft did a quick 90 degree turn and my application of my (standard) brakes brought me to a stop. I was off the runway so I called the tower, informed them of my condition and pushed my aircraft back to the hangar. Lucky for me it was down hill to say nothing of where the failure happened.

Here is a photo:

https://www.flickr.com/photos/53052604@ ... 4239615855

I will look into all this in the morning and will let everyone know what I find. I also will take more photos.

I may not make it to the Midwest Sonex Fly In on Saturday (by aircraft). More on that later.

Bob (More luck than skill) Mika

PS: My last landing in full darkness was a greaser. (it was dark and no one could see, so I am sticking to that story)

[mike.smith]

If the bolt snapped, then yes, I've had that happen. Fortunately not during a flight. I had made a new tailwheel assembly very similar to yours. The bolt snapped while I was INSTALLING it, so I made a new assembly. I could only guess that perhaps it was a result of overheating the bolt during welding? Other guesses would be welcome. The re-made assembly has been going strong for a year now.

[peter anson]

Hi Bob, the type of rod end bearing you are using is ideal, it has a large arc of movement, but you are only using half of the arc. If you try dropping the tail from about a foot you will be amazed at how far that tail spring deflects. What's probably happening is that the bearing is reaching the limit of its travel and then the bolt gets loaded in bending. If you look at the broken end of the bolt you will likely be able to see that a crack has grown from the top until there is not enough metal left to carry the load and it breaks.
I'd suggest that you make your steering strut with smaller bends so that the bearings start out deflected one way. Then when the tail hits the ground and the spring bends up, the whole arc of bearing travel is available. In case that doesn't make much sense, here's a pic.

Peter

[planeolbob]

Yeah, that sounds like a plan. I will take a look in the daylight and share.
Bob

[DCASonex]

Bob, Thanks for posting that. Have similar design on mine and just doing annual so will take an extra good look at it.
If you end up making a new link as peter suggests, consider placing the lower bearing on the underside of the tail wheel's attach arm. Flexing of the spring then induces slightly less unintentional steering of the wheel.

David A. Sonex TD

[planeolbob]

Hi Everyone,

https://www.flickr.com/photos/53052604@ ... 4239615855

Here is the new push rod installed. Note I have changed the type of rod end and have a jamb nut up against the push rod. My old system failed at 335 landing. I will replace this unit at 250 landings and carry a spare pushrod assembly in the aircraft. We will see how this works. Note that I have changed the shape of the pushrod a little. Maybe this will help. I used JB Weld inside the rod to lock in the rod end and it is still in the cure cycle.

Bob (driving to the MWSFI) Mika

[N111YX]

Bob, was that an AN quality part that failed?

I hate to see fatigue like that. Budd Davison had an AN turnbuckle in his Pitts S-2 rudder cable loop that failed while taxiing for takeoff. Turnbuckles are commonly used in other control functions but when stressed on every landing, there is more chance for failure. That may be lesson for all of us when selecting hardware for this application. There appears to be a lot of stress channeled through this area and probably magnified by not utilizing springs.

Thanks for sharing.

[WaiexN143NM]

Hi all,
Yes good to have pushrod with ball ends to pivot, because as the tailwheel rod spring flexes the angle changes. The factory supplied pushrod is a fixed rod, so no allowance for flex. Good to keep a good eye on all components of the tail wheel assembly. Remember the late great ken brock, who when landing his thorp T-18 at paso robles ca. Had the whole tail wheel bracket come off, lost directional control, went off runway , filpped over and broke his neck. The main pivot bolt had been ground down from repeated landings and flex, and finally failed.
My waiex is down in tucson, can a few of you take some measurements for neutral length between the pivot holes? Will pass on to blake at flyboyaccessories . They have a neat spring loaded pushrod for the rv vans aircraft, but that is a little long for us. I talked to him last year osh16 about this, told him id get back to him with a length , so he can have their vendor make some up for us sonex drivers. I think with ball ends and a spring loaded pushrod would be ideal.
Please post the length here and i'll pass on to blake.

WaiexN143NM
Michael

[msedwards]

Hi all,
Yes good to have pushrod with ball ends to pivot, because as the tailwheel rod spring flexes the angle changes. The factory supplied pushrod is a fixed rod, so no allowance for flex. Good to keep a good eye on all components of the tail wheel assembly. Remember the late great ken brock, who when landing his thorp T-18 at paso robles ca. Had the whole tail wheel bracket come off, lost directional control, went off runway , filpped over and broke his neck. The main pivot bolt had been ground down from repeated landings and flex, and finally failed.
My waiex is down in tucson, can a few of you take some measurements for neutral length between the pivot holes? Will pass on to blake at flyboyaccessories . They have a neat spring loaded pushrod for the rv vans aircraft, but that is a little long for us. I talked to him last year osh16 about this, told him id get back to him with a length , so he can have their vendor make some up for us sonex drivers. I think with ball ends and a spring loaded pushrod would be ideal.
Please post the length here and i'll pass on to blake.

WaiexN143NM
Michael

Correction, Ken Brock's accident happened at his airstrip on El Mirage dry lake that he used to give instruction on Gyro-copters,other than that your right, tail wheel assembly
failed lost control on roll-out veered of the runway hit a post cartwheeled ended upside down.His wife Marie was with him, survived with only minor injuries, a sad end for a
great aviator and friend of my Dad's. I soloed Ken's Gyro that now resides in the EAA museum, and worked for Ken back in the 1976.

[WaiexN143NM]

Hi msedwards,
Thanks for the correction. Yes El Mirage. Paso Robles, stuck in my mind , with ken, correct me if im wrong again, he was in a gyro accident years ago . Landed, stopped to help another incident , and the free wheeling rotor struck him in the head. Good you knew this great aviator.
You must have worked for him mid 70's in the begining of the rutan era, when ken was producing parts for the varieze.
Hope all had a safe fun memorial holiday weekend. 2017.

WaiexN143NM
Michael