AD81-06-08 attach tab questions

[tamarack]

What is the history of AD81-06-08 referring to installing a bracket at the tail brace wire attachment tabs?

This AD only affects PA-18-150's, should I be installing these brackets on the 150hp PA-18-135's? And why does the AD exclude some earlier s/n?

Was there an accident involving the tabs breaking off? Has anyone seen a cracked tab?

Thanks in advance for your experience!

Vickie

 

[Hyrdflyr]

attach tabs

Vickie,

I think they only pinpointed the models that had documented cracking etc. Rather than expanding it to all the models that potentially would have a problem. A legacy from a less letigious age no doubt.

I've added a backup carry through strap to reinforce the tabs on my EXP 12 w/ 160 hp. I also noticed that the tabs were only welded on one side, leaving the unwelded interface to be hard to seal up and prevent corrosion between the tab and the longerons, so I welded it also.

I also ran 3/8 tube stiffeners from the bottom longerons up underneath the rear horizontal carry through tube bracket to stiffen it up also. I also put tube liners in the top longeron tubes, all in addition to the normal tail beef up.

All told the mods add less than a pound, and will increase my comfort level immeasurably when getting hammered in Windy Pass..... I also doubled my rear spar attach fitting on the bird cage...same reason.

 

[Ruidoso Ron]

At the Seminar in Graham, Clyde Smith said that it was limited to a handful of airplanes when they first built SC's at Vero Beach. I asked if I should be concerned about my L-21 (PA18-135) and he said "no". He did mention that it is probably a good idea to put RTV down in the little "V" formed between the tab and the longeron. This will help prevent the joint from rusting.

 

[Steve Pierce]

They tended to crack when they started welding the fuselages with TIG instead of oxy/acc.

 

[bob turner]

But the real question is the logbook - if you have converted an early Cub to the 150 HP configuration using type certificate data (as opposed to a field approval) then you are probably subject to the 150 model A/Ds. That's just my opinion; there are those who will tell you that you cannot simply convert to 150 without a "field approval".

 

[Sgt. Rock]

When I bought my 18-150 in 1983 it had just been rebuilt. Three hours after I owned it I snapped the lower right brace wire fitting. Had the carry through strap installed and have never had a problem since. Ad or no ad I would put it on, cheap light weight. Easier to have done during annual than to find your tail brace wire hanging down loose after that rough landing on the side of some mountain when you are out chasing sheep.
Rock

 

[SuperCub MD]

The tabs should not be welded across the top to the longerons. This creates a stress point and the tab can fail at the weld. Flood the seam with primer when painting the frame, and seal it when covering.

The strongest set up is to make a one piece tab that goes across both sides. A drawing of the one piece tab is in the Northland drawings. A short piece of square tube between the longerons gives a better weld point than the original small round tube.

There is a drawing of the bolt on support plate in a Piper SB, which is a good thing to have on any Cub with original tabs.