FAA Issues SAIB for MLG Tie Struts

[barnstmr]

Re: FAA Issues SAIB for MLG Tie Struts

Hi Terry,
I think that taken in context its not about this issue of making tubes thicker for repair but rather of making them thinner walled due to the added strength of 4130.
Dave

Dave,
I think it can be argued both ways. But regardless, the point is still that the FAA is going to look for a blessing from an authorized engineer.

[Guest]

Re: FAA Issues SAIB for MLG Tie Struts

I'll explain further. The larger material was welded in almost the full length of the tie strut...there was about 2" of the original material left on each end and it broke at both welds without any other distortion to the strut. It could very well be that the welds were bad...they looked nice, but the metal actual looked brittle of crystalized where it broke. imagine my surprise when I touched down...hit a little hump in the grass strip and down she went skidding to a stop. I do believe Hank is correct in my case..the loads concentrated at those locations and the rest was history.

Any pictures of the joint?

Was the weld joint along a long shallow 30 degree angle to the strut or was in simply at a 90 degree angle to the strut?

Dave

[Guest]

Re: FAA Issues SAIB for MLG Tie Struts

Dave,
I think it can be argued both ways. But regardless, the point is still that the FAA is going to look for a blessing from an authorized engineer.

Hi Terry,

Whether we agree here or not is not as important as good relationships. So I just want to say that while I may vigorously debate something I do not mean to insult/offend/tick-off...

I hope that you have not been distrubed by the debate that is not my wish.

If I did distress you that's my foul and I apologize for that.

Dave

[TMc]

Re: FAA Issues SAIB for MLG Tie Struts

My replacement tubing is the same thickness as original. If you look at fig 4-44 and imagine one of the outside tubes is not there and the insert is the original tube, that's what I did. The table calls out for overall insert lengh of 9", I did 4.5" with the rosette welds (4 instead of 8) in the proper place and of the proper size, all called out for in that figure; as well as the 45 degree angle at the end of the tube.

I determined that the transfer of stresses thru the splice would be the same whether there was a second outer tube or not. If you look at fig 4-44 in halves, you have 4 rosettes and one 45 degree weld transfering the stress to the next tube. I wasn't being lazy, I just thought that since the original size tubing isn't available, and the next obvious replacement tube is slightly larger (I.D. matching the original tube O.D.) it worked in my favour to simplify the splice. That's how I justified my repair. But I may be wrong, that's why there are DERs (and for that matter IAs who catch the brillant ideas of mechanics like me...hehe)

It would not seem impossible to complete the repair exactly how it is in the book, if I decide to go that route. I would have to cut off the original tube up another 4.5", add the 4 rosetts, redo the 45 degree weld...then the tricky part...welding the new outer tube into the cluster at the top (near the bungees).

[Guest]

Re: FAA Issues SAIB for MLG Tie Struts

ahh , 45 degrees,

my bad I had 30 degrees in my head, should have looked at the figure more closely.

thanks!

DDave

[Dano"T"]

Re: FAA Issues SAIB for MLG Tie Struts

When I recover my landing gear, I'm adding the ski brace....that would eliminate any inherent weakness in the gear IMHO. If it's rusty, I'll repair it like TMc did and still add the ski brace. (see other thread called "ski brace")

[PA1195]

Re: FAA Issues SAIB for MLG Tie Struts

A local recently had his right gear diagonal quit holding hands while on skis. Separated mid-span and no brace was previously installed. Gear bent up until the safety cable caught then bent/broke the upper A-frame at the gear legs. Got lucky...it happened at my camp so they had tools and fixits close. I wasn't there. Rumors that both gears were internally corroded and drain holes installed per SB.

"Repair or replace any strut suspected or confirmed to have corrosion. We also recommend you repeat the inspection annually. Failure to detect and replace a corroded MLG tie strut can result in failure of the main landing gear with concurrent damage to the airframe structure." Well yea!

Gary

[PA1195]

Re: FAA Issues SAIB for MLG Tie Struts

I was informed today of two more landing gear failures this winter in Alaska. Can't confirm that or the cause and part location. It came from a current FAA employee so ...I suggest those that care about such failures inspect the gear per the SAIB information above.

Gary

[Mike S]

Re: FAA Issues SAIB for MLG Tie Struts

Thanks for bumping this thread, I checked my tie struts and discovered no holes.

[PA1195]

Re: FAA Issues SAIB for MLG Tie Struts

Lots has been discussed here previously so no need to repeat much. Basically the Taylorcraft and Cub (and probably others) can develop internal corrosion in parts of the landing gear that eventually weakens the assembly. The bulletins discuss the problem and suggest a means of compliance. There may be others.

I feel the challenge is for owners to become active and share the process with maintenance. Maintenance folks should be aware but unless it's a Service Bulletin or AD they may not as most are already overwhelmed with existing airworthiness compliance.

Please note this other airworthiness problem that cost two their lives and lots of later issues. Dave Wiley and the fuselage strut fitting failure while on floats. Despite years of self maintenance it apparently went undetected, or worse yet, possibly ignored. Let's not let that happen again if a self-imposed inspection will help.

Gary

[Nefj40]

Re: FAA Issues SAIB for MLG Tie Struts

Had a rotted one collapse last fall here in Ne. also. Owner was lucky that it happened in a way he didn't get the prop.

[PA1195]

Re: FAA Issues SAIB for MLG Tie Struts

In #37 I noted what likely happened in succession with the local failure. The bungee safety cable probably caught the upper gear arms but it still bent them enough lower the wing. The other two I noted in #38 were 2nd hand reports so don't know the details.

If no holes were previously drilled I'd remove the gear and follow the bulletin's steps to check for corrosion.

How to repair any corroded tubing is beyond my skill set but is suggested earlier in the thread. If in Alaska I'd send them to Atlee Dodge's repair facility and let them handle the problem. Otherwise replacement may be indicated if corrosion (external or internal) is extensive.

If this issue continues there will be repercussions and mandates.

[Mike S]

Would round tubing for the tie strut be a bit stronger than streamlined, or not that much difference? (4130, 1.5" o.d., .049 wall)

[Robert Lees]

No, the original design was just fine. It's the same amount of metal, just streamlined.

Round tube has >4 times the drag (guess why ALL wing struts are streamlined in section <G>

[Hank Jarrett]

We did a wind tunnel check and the drag on the wires supporting the stabs is as high as a rear strut! Round vs streamlined! It makes a BIG difference.