Crack in Tailwheel Bracket

[GraemeSmith]

Reported to factory. But thought I would mention it here......

SNX-L03-31 - 6” Tailwheel

Time in Service – 285 hours as originally fitted to Sonex Serial 1153 by original builder.

Original Supply Date – not clear – originally supplied to the builder of the aircraft.

Symptom – slight “wallowing” of bracket to tube about the main vertical bolt.

Assumption – Top Hat bushings worn

Finding 1 – The 4 Top Hat bushings and bolt were in fair shape with no significant play between the bushes and the bolt. However the top hat bushes were actually wallowing in the machined - and worn - aluminum part that bolts to the titanium rod.

Finding 2 – See attached picture. I assumed that the “line” was a crack. Removal of paint showed it was probably a machining mark / limit (factory would know better). However closer inspection of “the line” and subsequent Dye Penetrant testing showed a hairline crack had started to develop and propagate in the vicinity of the machining mark. Also not clear about the orange tone / heat discoloration towards the bolt hole?

Action – replaced with new previously ordered.

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Had the tailwheel been abused? Well sure - it came with some "wallow" already present when I bought the plane. I had ordered a new bracket to firm stuff up asap and when the bracket came in - went to fit it. But it was only when I removed paint from the original bracket that the crack became apparent. Till the paint was off - it looked just like a painted over machining mark.

[Matt541]

Good to know, something I'll add to my inspection while 541 is in the garage.

Thanks Graeme!

[Mikegaydos]

Any word from the mfr?

[GraemeSmith]

Any word from the mfr?

My picture currently at the machine shop for review.

Not had any other reports of this.

[Spark6]

Very interesting. Would be curious to know (and there may not be a way to ascertain), assuming no defect with the part, whether the cracking was as a result of prolonged fatigue, or a single (or few) instance of high load. (I.e., would a pneumatic tailwheel increase shock absorption and possibly prevent such damage?)

[peter anson]

It's fatigue. There appears to be a small step left by the machining operation that has formed a local stress raiser and landing gear parts are already pretty highly stressed. You could significantly improve the fatigue life of the part by polishing out the notch using a small cylindrical sanding drum, although if the new parts come painted it might be difficult to pick that a step is there. If you do all your landings on nice smooth runways it might never be a problem.

Peter