Landing gear bolt broke

[Kai]

Joe,
We used ordinary Unbrako class 12.9 capscrews with mm thread. Our selection was based on our reaming out the holes in the engine mount and the gear legs to ø8mm (mind you, not cleared by Sonex tech, but we felt we had to do something). The thread length of the smaller dimension Unbrako´s is 28mm. For a 50mm shank, this would indicate a M8x1.25x80 capscrew bolt. According to the US Unbrako datalog, this carries part# 103070. You will have to check your engine mount for the exact shank length of the bolt.

[DCASonex]

While building, I noticed what i thought was a bit too lose a fit for my bolts and after contacting Sonex, enlarged the holes for a tight fit on 5/16" bolts. No hint of any loosening despite many not very pretty landings. Info from Sonex at the time they changed to plain cad plated bolts, was that they initially followed the advise that Cadmium should not be used with Titanium, but on further investigation, when broken bolts started showing up, was that Cadmium with Titanium is only a problem at elevated temperatures.
David A.

[peter anson]

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

Yes, the various standards say it's a no-no although it's mainly a problem at higher temperatures. I was not happy about using cad plated bolts so used 1/4" 12.9 Unbrakos. Had to use pretty long ones to get enough unthreaded shank. I changed them recently after more than 800 landings. I think it's worth gluing the joints too. On original assembly I used PR1422, a rubbery fuel tank sealant which despite its purpose of only sealing fuel tanks is enormously strong. When I recently reassembled things I used Loctite because that's what I had in the tool kit. Some types of Loctite can fill fairly big gaps.

Peter

[Skippydiesel]

I am not the origional builder and may have my "wires" crossed but think I may have a Grove undercarriage - do these bolt concerns include Grove?

[n502pd]

Joe,
We used ordinary Unbrako class 12.9 capscrews with mm thread. Our selection was based on our reaming out the holes in the engine mount and the gear legs to ø8mm (mind you, not cleared by Sonex tech, but we felt we had to do something). The thread length of the smaller dimension Unbrako´s is 28mm. For a 50mm shank, this would indicate a M8x1.25x80 capscrew bolt. According to the US Unbrako datalog, this carries part# 103070. You will have to check your engine mount for the exact shank length of the bolt.

Thanks much! come condition inspection time I will take a real close look at my original bolts for indications of movement. question, where did you get the reamer?
And another question.. did you also do the axel bolts to 5/16Th too? TKS!

[Skippydiesel]

I am not the origional builder and may have my "wires" crossed but think I may have a Grove undercarriage - do these bolt concerns include Grove?

I did get my wires crossed - my Sonex has Tracy O'Brien legs - however question still valid.

[mike.smith]

Nearly 600 hrs on my airframe. No issues with the gear bolts. Cad plated per Sonex. Cad plated and titanium is a non-issue at the most severe temperatures human being and airplanes are exposed to.

[Bryan Cotton]

I'm curious why some people have issues and some don't. Is it a bolt fit issue? For those with broken bolts, how easy are those bolts to put in? Same question for the guys with higher hours on one set of bolts.

I think I had to tap mine in with the light plastic hammer. Snug fit.

[Kai]

Thanks much! come condition inspection time I will take a real close look at my original bolts for indications of movement. question, where did you get the reamer?
And another question.. did you also do the axel bolts to 5/16Th too? TKS!

Joe,
This is Europe- getting your clammy hands on a ø8mm metric reamer, is not rocket sience. And no, we did not do the axle bolts, although we replaced the original stainless ones with AN4 as suggested by Sonex SB, which were again substituted with 1/4 in Unbrako 12.9.
Kai

[Kai]

I'm curious why some people have issues and some don't. Is it a bolt fit issue? For those with broken bolts, how easy are those bolts to put in? Same question for the guys with higher hours on one set of bolts.

I think I had to tap mine in with the light plastic hammer. Snug fit.

Bryan,
I already aired the same in a previous post. Although I can´t be sure, my gut feeling is that this is not a bolt fit issue. I am looking more towards the way the axles are oriented in the airframe. Pure speculation from my side, but I would expect excessive induced gear leg torque issues if the axles are not aligned exactly according to instructions in the drawing. I don´t know, I am still on the same set of anno 2006 Aerotrainer tires: wear is minimal.

This is in direct contrast to comments from Kerry. When he learned that we were operating on fairly rough grass fields, he maintained that while operation on a flat and even grass surface was certainly within the design capabilities, the plane had never been intended for operation on rough grass surfaces.

Whatever the cause- after we went Unbrako 12.9 the issue went away.
Kai