Friend needs some advice on yaw, y'all...
Here's a copy/paste from his email:

Anyway I did a lot to my cub..i.e. changed all the tail and rudder bushings, the tube liners in the horizontal stab.
and all new cables and turnbuckles in the wings and put on new stainless flying wires on the tail.

But the problem is it wants to fly with the bubble out to the left and we did not do anything that I know of
that should have changed it that much, everything was put back and squared up with a smart level the way
it was before[ at leased I think it is ]. It takes enough pressure on the left rudder to hold it straight that my
leg gets tired. I am sure it is not in the wings it has no roll tendencies.

To me it seems to be in the vertical fin and rudder but there is no adjustment on that, other than
pulling one way or the other with the flying wire tension.

Adverse yaw is inherent in the physical shape of the airplane, not so much the hardware. It sounds like by resetting cable tensions and redoing bushings and pulleys, he will most likely have removed any cable slack and reduced friction. This should allow a greater aileron throw for less stick movement, and with less control force. So for a given stick force and displacement, he is getting more aileron throw, requiring more rudder input to counter it.

That would be my guess.

I recently flew a new super cub, and was surprised how utilitarian it felt compared to everything else I have flown. We were doing a lot of STOL work, and after a constant hour of that I was quite tired, especially my legs from working the rudders. Much more so than a nicely balanced and easily flown J-3 (which still could be tiring in the beginning).

I think it would be wise to not setup the question as "adverse yaw," which is an aerodynamic effect of differential induced drag from aileron input.

It sounds like a rigging issue, and if all he did was disassemble and reassemble the tail, then it's a rigging/trim issue.

What do they call that when the vertical or horz stabilizers have built-in differential AOI, or are askew somehow to counter slipstream effects?

I missed the part about new flying wires on the tail. In that case, Zane has a good point, he could have switched the angle of incidence on one of the tail surfaces. Although I would expect that to be a constant correction, and not just show up as stronger adverse yaw when he/she works the ailerons.

I'm not sure what they call it when they change the angle of incidence on purpose. I remember seeing some WWII high powered fighters with an offset angled vertical tail to help with the crazy amounts of power they made.

Maybe not the correct fix, but the easiest fix might be a stronger LH rudder return spring.

Tell him to take it to a mechanic that knows how to rig a Cub. You can grab the front and back of the vertical fin and twist it, by hand. If all that stuff and the rudder isn't set up right, it won't fly straight. And if he rebuilt the whole tail assembly, and the yaw characteristics of the plane changed......it might just be that he didn't get SOMETHING straight, or more likely, he didn't get something offset as it should be.

As Zane noted, however, none of this has anything to do with Adverse Yaw.

MTV

Zane wrote:

What do they call that when the vertical or horz stabilizers have built-in differential AOI, or are askew somehow to counter slipstream effects?

Is that decalage for the horizontal?

mtv wrote:Tell him to take it to a mechanic that knows how to rig a Cub. You can grab the front and back of the vertical fin and twist it, by hand. If all that stuff and the rudder isn't set up right, it won't fly straight. And if he rebuilt the whole tail assembly, and the yaw characteristics of the plane changed......it might just be that he didn't get SOMETHING straight, or more likely, he didn't get something offset as it should be.

As Zane noted, however, none of this has anything to do with Adverse Yaw.

MTV

This is my thought too. The Cub vert.stab. has to be offset a few degrees to the left to counteract the right turning characteristic. MY mistrake to call it adverse yaw. I think he has to adjust the tail wire tensions to get that offset back to where it's s'posed to be.

He said there is no roll tendency, so it's not the ailerons, is it??

soggyc wrote:

Zane wrote:

What do they call that when the vertical or horz stabilizers have built-in differential AOI, or are askew somehow to counter slipstream effects?

Is that decalage for the horizontal?

The common term is simply "offset".

Decalage describes an angular difference between two flying surfaces, usually the wing and the horizontal. Since there is only one vertical fin, it cannot be set to a different angle than the other (nonexistent) flying surface, so decalage is not a correct term.

Zane wrote:I think it would be wise to not setup the question as "adverse yaw," which is an aerodynamic effect of differential induced drag from aileron input.

It sounds like a rigging issue, and if all he did was disassemble and reassemble the tail, then it's a rigging/trim issue.

What do they call that when the vertical or horz stabilizers have built-in differential AOI, or are askew somehow to counter slipstream effects?

+1...... Check the rigging...

Doesn't sound that screwed up. I would adjust the flying wires for the vertical fin to center the ball.

Offsetting the vertical fin guarantees that you can only get the airplane to fly straight at one airspeed and power setting. Making the airplane fly straight ahead in the power off condition, then adjusting the thrust line to self-correct power and torque, is the technically correct way to do it. However this takes more time and effort than most of the aircraft manufacturers and mechanics are willing to do... so a lot of them just built the airplane crooked and took the easy way out.

westerncolorado wrote:Doesn't sound that screwed up. I would adjust the flying wires for the vertical fin to center the ball.

I don't think the flying wires will affect the fin offset, just the dihedral of the horizontals & the plumb-ness (is that a word?) of the vertical. Twisting the vertical per MTV's post would be the way to adjust the offset if that's what's off.

On the upper two flying wires if you lengthen the right, shorten the left or lengthen the left and shorten the right it moves the back of the vertical fin left to right and right to left without changing the horizontal stabs (if you adjust them equally). I learned that from an old timer and have done it many times to adjust the yaw on a cub. Works for me every time.

Uhhhh..... so the bottom (base) of the fin is fixed on the fuselage, and by adjusting the flying wires you TWIST the upper half of it a little to trim the airplane out?

This creates two distinct problems to my feeble mind's way of thinking. First you twisted the tail of an airplane, making more drag at all flight conditions. Second you have a straight rudder that is hinged to what was once a straight fin, but which you now have twisted. So the hinge pins and tubes are no longer inline. You have enough leverage to still operate the rudder easily, but applying that leverage will simply wear out the hinge system quickly.

Any of you guys ever heard of a tin snips and sheet metal trim tab?

EZ,

For many years, the simplest means of fixing this kind of thing on the Cub has been to simply twist the top of the vertical stabilizer. That is, move the front to the right or left with regard to the rear. It doesn't take much to tweak this, and it avoids having to use trim tabs. That vertical stab is pretty flexible.

You're right, though...changing the tail brace wires is NOT the way to trim the airplane, and would do nothing to fix the issue he describes.

MTV

mtv wrote:EZ,

For many years, the simplest means of fixing this kind of thing on the Cub has been to simply twist the top of the vertical stabilizer. That is, move the front to the right or left with regard to the rear.

OK, that makes a little more sense... I'll buy the idea of tweaking the front fin tube and not throwing the rudder hinges off kilter. At least that's not causing premature wear on a control system.

Come to think of it, I have a distant memory from A&P school that the Tri-Pacer maintenance manual says to tweak the trailing edge of the rudder with your hands to trim the airplane. Can anyone here verify that I'm remembering that correctly or not? I have little or no hands-on experience with shortwing Pipers.

MTV is right, its been about 15 years since I did the last one. The fin should be offset approx 1.5 inches, (this exact dimension has slipped my memory] imaginary line from rear post of fin to top of skylight.

Monte

It's pretty amazing what proper re-rigging will do. Although always a nice flying airplane as long as I've owned her, my P172D always required a little left rudder to fly ball-centered at cruise, and the yokes were canted slightly to the right although the ailerons were even. So I bit the bullet a couple of annuals ago and had her re-rigged (a rather labor intensive process) and the difference is significant. Cruise speed increased, there's no need to push either pedal excessively, and hands off, there's no roll drift or yaw drift.

Instead of tweaking here and there, if it were my airplane, I'd find an experienced Super Cub mechanic and pay the price of proper re-rigging.

Cary

AMEN!!!!!!

Gump