Landing gear bolt broke

[Kai]

We have had some experience with broken upper gear leg bolts up here as well. When this happened the first times, we stuck to the SB and replaced the stainless bolts with AN types. In addition, we safetied the bolts in such a way that the lower part of a broken bolt could not fall out (for some reason the bolts always seem to break in the middle). This would bar the titanium leg from rotating and cause a calamity.

However, the problem persisted as discovered during periodic maintenance. It appeared that the suggested 1/4 inch bolts just could not handle the torque loads imposed on the gear legs by the wheel geometry. What we then did was to ream out the upper holes in gear leg and engine mount to 5/16 inch (8mm), and replace the AN4 with Unbrako 12.9 class bolts and long nuts. The whole assembly was torqued up to a considerable pre load on the bolts (12.9 class bolts are extrmely strong!)

After this, the issue went away, and we have been flying happily the last years. Remains the question why the original bolts would break in the first place. We can only speculate that for some reason we could not get the wheel geometry aligned exactly to plans, and that his imposed excessive loads on the bolts.

[Bryan Cotton]

Just landed at home airport, as I turned off runway bolt broke and gear spins in mount. Easy fix with only wheel pant damage but going to change all gear bolts at each condition inspection.

Hi Bryan - please elaborate what/which bolt (s) is this? Photo/sketch might help.

That was Billy's post. I assume it is the bolt that goes through the top of the gear leg in the motor mount. Others have busted this bolt before. Sometimes just one side and they find it during maintenance.

[GraemeSmith]

At my Condition Inspection this year I replaced a bottom axle bolt due to some slop developing and replaced the other axle bolt because I was changing an axle (the little tang to hold the brake shoe mount had cracked). With both bottom ones done - I replaced the tops leg retaining bolts while I was at it. Both showed very slight wearing off of the CAD plating on the AN bolts (builder skipped stainless and went straight to AN).

620 landings by me
??? landings by builder in first 185 hours.
564 hours TTAF

[Skippydiesel]

Just landed at home airport, as I turned off runway bolt broke and gear spins in mount. Easy fix with only wheel pant damage but going to change all gear bolts at each condition inspection.

Hi Bryan - please elaborate what/which bolt (s) is this? Photo/sketch might help.

That was Billy's post. I assume it is the bolt that goes through the top of the gear leg in the motor mount. Others have busted this bolt before. Sometimes just one side and they find it during maintenance.

My apologies Billy/Bryan - would still like an image or two to clarify where the problem(s) occurred.

[GraemeSmith]

My apologies Billy/Bryan - would still like an image or two to clarify where the problem(s) occurred.

If you see this post in the Sonex Forum on FB You can see Day 5 of my just finished Condition Inspection where I cover replacement of those top bolts (with pictures). Pretty sure those are the ones they are talking about.

https://www.facebook.com/photo/?fbid=10 ... 3445473443

[Rofomoto]

The top bolt sheared both ends off of the AN4 bolt. When I removed the titanium rod, the center of the bolt slid out.
The plans call for tightening bolt and then backing off a little with a castellated nut and Cotter pin. I looked at B model plans and the call for elastic nut.

[mccool]

It was my understanding that Cad plated bolts should not be used in the Titanium gear legs

[tps8903]

It was my understanding that Cad plated bolts should not be used in the Titanium gear legs

I use exclusively grass fields. I think I've been convince to ream to 5/16" during my Condition inspection and use the stronger NAS6605 series Bolts. I might even do it sooner time permitting. I just changed the Stainless ones out last month before my first flight. So hopefully they will be good for a few hours. Think I'm just going to drill through the firewall, use 3 washers on the backside for the tight space then seal it with RTV before tightening.

[Skippydiesel]

My apologies Billy/Bryan - would still like an image or two to clarify where the problem(s) occurred.

If you see this post in the Sonex Forum on FB You can see Day 5 of my just finished Condition Inspection where I cover replacement of those top bolts (with pictures). Pretty sure those are the ones they are talking about.

https://www.facebook.com/photo/?fbid=10 ... 3445473443

Thanks for the try Graeme - not on "FB" Trying hard to stay not connected. Being addicted to this Forum is more than enough:)

[n502pd]

We have had some experience with broken upper gear leg bolts up here as well. When this happened the first times, we stuck to the SB and replaced the stainless bolts with AN types. In addition, we safetied the bolts in such a way that the lower part of a broken bolt could not fall out (for some reason the bolts always seem to break in the middle). This would bar the titanium leg from rotating and cause a calamity.

However, the problem persisted as discovered during periodic maintenance. It appeared that the suggested 1/4 inch bolts just could not handle the torque loads imposed on the gear legs by the wheel geometry. What we then did was to ream out the upper holes in gear leg and engine mount to 5/16 inch (8mm), and replace the AN4 with Unbrako 12.9 class bolts and long nuts. The whole assembly was torqued up to a considerable pre load on the bolts (12.9 class bolts are extrmely strong!)

After this, the issue went away, and we have been flying happily the last years. Remains the question why the original bolts would break in the first place. We can only speculate that for some reason we could not get the wheel geometry aligned exactly to plans, and that his imposed excessive loads on the bolts.

Do you have the part numbers for the 12.9 spec hardware you used? I have looked at the Unbrako catalogue, and there are quite a few different ones. I have complied with the SB from sonex before first flight, but the rough grass strip has me worried now!! this inspection I will investigate bolt integrity, and if I can get the stronger bolts, I shall get them in place. Otherwise, I have had zero problems in this area, and am now at a 9000ft hard surfaced ex USAF base! Kind of neat just because of that. Any help with the bolts would be appreciated! Thanks much!