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Tail gear fitting
http://t18.net/thorpforum/viewtopic.php?f=7&t=8084		 Page 1 of 1
Author:  chuck [ Sun May 07, 2017 4:56 pm ]
Post subject:  Tail gear fitting
Hello gents,

I thought I'd share my discovery today, so that others that didn't build their birds can inspect this tail gear attach point.

I noticed an ever so slight curve on the lower skin where the forward bolt of my tail wheel rod attaches. I removed the inspection plates at the base of the verticle stab to get a better inside view of the attach point, only to find the tail gear fitting had cracked at some point in the past, pulled away and completely separated (see pics). I'll save you all the details, but essentially I drilled out the rivets and removed the fitting. Unfortunately, the story doesn't stop there. Upon inspection of this "aluminum" tail gear fitting I could see the failure occurred at the 90' bend. The real surprise came when I pulled drawing A-591, tail gear fitting, STA 191.75 and found this piece was to be made of .094" 4130 steel! I can now tell someone has been in this section before, it just took 8 years of me owning it before this situation reared it's head. This area is inspected at condition, I can only assume it was an undectable crack then. You will also see in the pics that the stringer has pulled away from the bulkhead and the drilled hole pattern doesn't appear to be correct.

Looks like I've got some work to do!!

Perform a thorough preflight!
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Author:  TonyNZ [ Sun May 07, 2017 6:24 pm ]
Post subject:  Re: Tail gear fitting
I,m just doing 100/annual now so will have an extra hard look at the area. However I do know my fitting is 4130 as I made it myself.
Cheers
Tony
ZK-VMS
Author:  rhartmaier [ Sun May 07, 2017 6:49 pm ]
Post subject:  Re: Tail gear fitting
Chuck,

Both of the tail spring fittings were found to be weak and were beefed up. My father built my plane in the 60's according to the original plans. I don't really remember why anymore, but I can see from the new rivets that I had to remove the aft bulkhead that the rear fitting is attached to in order to make the modification. I believe the forward fitting was easier to replace. Check it out in the newsletters for more info.

Count yourself lucky the tail spring did not fail during a landing in a strong crosswind!

Bob H.
Author:  Ryan Allen [ Mon May 08, 2017 6:54 am ]
Post subject:  Re: Tail gear fitting
How did you get in there to remove that stuff?? That seems like a big chore!
Author:  Fraser MacPhee [ Mon May 08, 2017 1:44 pm ]
Post subject:  Re: Tail gear fitting
Here is the link to the 2011 post about tailwheel attachment repair. Chuck, you are even in this thread......Lang may yer lum reek!!

viewtopic.php?f=7&t=6524
Author:  chuck [ Mon May 08, 2017 4:40 pm ]
Post subject:  Re: Tail gear fitting
Aside from my reeking lum....

Per Fraser's comment, I looked up the 2011 post and discovered the picture I had placed on his thread, shows the very piece that failed. In the picture it's the forward tail rod connecting point, looks black in color. I've got Cubes hooking me up with a new and per plans part.

I was able to access this area and drill out via an access plate that had been previously installed.

Mae bum's oot the windae!

Attachments:
IMG_3409.JPG
IMG_3409.JPG [ 15.84 KiB | Viewed 18086 times ]
Author:  Brent Schultz [ Sat May 20, 2017 4:21 pm ]
Post subject:  Re: Tail gear fitting
We had the same thing happen on our 1978 bird after about 1200 hours of flying time. Had to unrivet the bottom skins, pull out the steel support brackets, made new beefed up ones and then rivet everything back in. Took some doing, but all working well after 200 hours of flying time with new tail rod attach brackets and steel nut plates.
Author:  Brent Schultz [ Sat May 20, 2017 4:21 pm ]
Post subject:  Re: Tail gear fitting
We had the same thing happen on our 1978 bird after about 1200 hours of flying time. Had to unrivet the bottom skins, pull out the steel support brackets, made new beefed up ones and then rivet everything back in. Took some doing, but all working well after 200 hours of flying time with new tail rod attach brackets and steel nut plates.
Author:  t18joe [ Tue Oct 31, 2017 2:11 pm ]
Post subject:  Re: Tail gear fitting
Had the same issue. I had noticed a creeking sound in the tail wheel area when I would move the tail for parking area for sometime. I removed the tailwheel did see anything unusual. I then inspected and aft bulkhead and saw cracks emanating from the two outboard tailwheel attaching bolts. Replaced the steel bracket with a thicker material.
Author:  rhartmaier [ Tue Oct 31, 2017 8:33 pm ]
Post subject:  Re: Tail gear fitting
I believe if you go back and check the old newsletters you will find that it is recommended that both of the tail wheel spring fittings be beefed up. Or perhaps it was to change out the original aluminum rear one for steel, and beef up the front one to thicker material. It has been so long ago I really don't remember exactly, but I do remember that I had to change both of the ones that my father had originally installed. I know it is a lot of trouble, but having the tail wheel fail during a landing with a strong crosswind could be a lot more trouble. It is highly recommended that anyone who did not build their ship should check out all of the service dictated mods that have arisen over the years. Another critical area is in the trim system geometry. Bill Warwick died because this was not done correctly on a plane that he was test flying. One of the old newsletters has a very detailed description on proper rigging of the trim system. That would have been sometime in 1994, the year Bill died.
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