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Horizontal stab reinforcement question

tamarack

FRIEND
Fairbanks, AK
Some of the horizontal stabilizer front tubes have a short approx 2" doubler welded on to the outside of the tube where the attachment bolt goes through. And some don't.

Is this a year model modification? All of the new horizontal stabs that I purchase have the doubler. But many stabs that I see are not doubled.

When were the doublers installed? Why?

Thank you,

Vickie
 
Hmm, good question! I am thinking it's only on aftermarket stabilizers. Did pawnee's have that? is it so that an aftermarket stab can be used on both aircraft?

Jason
 
Vickie, why did you ask that?

It is a good question. I guess we're in the right place to have someone answer that! D:)
 
I always thought it was to cover up wallered out, mis-aligned holes for the attach bolt...but you say this is happening on NEW stabs?? :eek: Were these stabs produced on Mondays?

John Scott
 
I always thought it was to cover up wallered out, mis-aligned holes for the attach bolt...but you say this is happening on NEW stabs?? :eek: Were these stabs produced on Mondays? John Scott

This brings up some questions. Other than the egg shaped holes, is there any reason for a doubler? Have there been any cracks or breakage in this area on hard use Cubs? Does the doubler stiffen the leading edge enough to reduce the tail shaking? Any thing else?
 
A lot of stabilizers, with and without the doubler, have wallered out holes. Doesn't seem to make a difference. I have never seen cracks there from normal operations, either. The only thing I have noticed is that some undoubled stabilizers are slightly deformed from overtorquing the attach bolts. The reason for the question came up while working on an undoubled stabilizer -- should I weld on the doubler?

Thanks for the thoughts!

Vickie
 
good question.....

http://www.supercubproject.com/drawings/main.aspx search stabilizer shows no doubler....

I know like others have said atlee and the rest double it.... but can't really think of a need why.... not really strengthening the thing much, and most end about where the inner tube ends so it still weak spot outboard end of it... must just be to keep them from wolllering out....
 
Hi Vickie,

It looks like Piper added the doubler tube to the Stabilizer drawing 9/14/64 Rev G. It doesn't specify why but that's when they added it. I would suspect they wanted to reinforce the .028 wall tube at the attach point.

Jim
 
The tail feathers off my '77 Cub did not have the doublers. I weighed them compared to a new set of Air Frames Inc. tail feathers. The Air Frames were right at 1 lb each heavier..... If you have a good set of stock tail feathers.... keep them!

Crash
 
The 82 Cub I am currently putting together has doublers on the front of the Stab.... What size bolt are you using for the doubled stab..?? The book calls for a AN3-13A but that is a bit short, works if not using any washers.... I am thinking AN3-15A would be better...

Brian.
 
I have a 1971 and a 1981 and they both had never been apart and have the doublers. Nothing in the logs about them being replaced.
 
I'm facing this issue right now building an experimental supercub. My thoughts at this point. Most of your front tubes on stabilizer now are .035 wall thickness and 1 in o.d. the Piper drawings require expansion of the first 2 or 3 inches of the inboard leading edge tube. The expansion is to accommodate the yoke cross link tube.
Piper originally used .028 wall thickness. So hone the ID of the .038 tube to receive the cross link tube and reenforce. These are just my thoughts
 
The front and rear tubes on these later stabilizers are a bit closer together as well. Dakota Cub had to change their jack screw yoke as a result.
 
I'm building mine with the VR3 tubing, things are falling within the original dimensions. All except the swag/expansion on the front and rear tubes. The very root rib of the VR3 tub kit falls a little short between the front and rear tubes. If you put the front and rear tubes to the rib cope things will get out of dimensions. This is due to the fact, front and rear tubes isn't expanded. Once you either expand or add doubler , the rib fits.
 
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