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Yaw Problem

Sully73

Active Member
I have just begun my Phase I flight tests. I noticed my plane yaws to the left. The ball is one diameter outside the right hand center bracket on take off then straightens out a little in flight but still yaws left. To fly straight I must use the ailerons to turn to the right which causes me to fly right wing low. I have done a quick check but so far have not found anything obvious.

Any suggestions?
 
p-factor will send your nose left, especially in high torque/slow speed situations (take off, slow flight). More right foot is expected in these situations. when in cruise, should be more centered. If not, adjust rudder trim.
 
It is also common to install a trim wedge on the rudder to center the ball in cruise.
It's common to use a lot of right rudder on take off/climb out (even after the trim wedge is installed).
 
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I have just begun my Phase I flight tests. I noticed my plane yaws to the left. The ball is one diameter outside the right hand center bracket on take off then straightens out a little in flight but still yaws left. To fly straight I must use the ailerons to turn to the right which causes me to fly right wing low. I have done a quick check but so far have not found anything obvious.

Any suggestions?

Suggestions? I apologize for being so blunt, but maybe rent a 152 and pay a cfi for some refresher training. The proper fix to the ball out of center is to use rudder to correct the yaw, not to bank the airplane and continually fly in a slip.
Now as to the yaw itself: First thing I would check is the alignment of the landing gear legs, wheels, and, if installed, fairings. You need to jack up the plane to properly check this, as the gear legs move down and forward once weight is removed, rotating some, in flight. Or, as others said, give up on a fix (a half ball out is a pretty subtle mis-alignment) and install a trim wedge on the rudder, sized for cruise.
 
To be clear, I understand how to counter yaw using the rudder. Unfortunately this also causes aerodynamic drag. The question is how to fix whatever is causing adverse yaw in flight. I will check the fairings as Mr Blunt suggested but what other possibilities should I re-check? Is something rigged wrong? Should my vertical stab be adjusted off center?
 
To be clear, I understand how to counter yaw using the rudder. Unfortunately this also causes aerodynamic drag. The question is how to fix whatever is causing adverse yaw in flight. I will check the fairings as Mr Blunt suggested but what other possibilities should I re-check? Is something rigged wrong? Should my vertical stab be adjusted off center?

A wedge shaped trim tab on the rudder is the common solution. Anything you do to offset the P-factor is going to add drag whether it is adjusting the vertical stab, a rudder trim tab, etc. Why not do the wedge and be done with it?
 
You have to decouple sideslip and roll since one feeds the other. You will always need right rudder on takeoff so do the test at your cruise speed. Center the ball with rudder only and maintain wings level with lateral stick (make sure fuel us balanced). If you need significant lateral stick it can be the aileron height relative to the rear spar or the aileron trailing edge shape. There are numerous posts on those topics. You need to fix the roll because it will feed in to sideslip. Once you get the roll sorted out and you have wings level with the ball centered then you can put a tab or wedge on the rudder, making sure that the fault doesn’t lie with the gear fairings or wheel pants. The amount of drag you will add with a tab or wedge will be so small you won’t be able to measure it. We aren’t even looking at a kt. Flying with sideslip will add considerable drag.
 
I would suggest that you remove the wheel pants and gear leg fairings. Then fly the plane and if doesn't fly true find the problem. Once corrected reinstall the gear leg fairings and wheel pants. It is much easier to find problems with trim problems with a lot of the variables removed.
 
To be clear, I understand how to counter yaw using the rudder. Unfortunately this also causes aerodynamic drag. The question is how to fix whatever is causing adverse yaw in flight. I will check the fairings as Mr Blunt suggested but what other possibilities should I re-check? Is something rigged wrong? Should my vertical stab be adjusted off center?

The fix is to put a trim tab on the rudder to force it into the position you are putting it in with your feet. There is no escaping the drag penalty, assuming you haven't introduced this yaw yourself with fairings that have not been rigged correctly. Designing an airplane is all about manipulating benefits and penalties of various components, when it comes to drag.
 
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... Is something rigged wrong? Should my vertical stab be adjusted off center?

You could- but would be a HUGE repetitive process to get right. Think of redoing that intersection fairing a few times:eek:, reworking the front spar attach point a few times:eek: (and don't even think of slotting those mounting holes!!!)

Go with a wedge
 
You could- but would be a HUGE repetitive process to get right. Think of redoing that intersection fairing a few times:eek:, reworking the front spar attach point a few times:eek: (and don't even think of slotting those mounting holes!!!)

Go with a wedge

Yeah. Go with a wedge or traditional trim tab. To be honest, those will only help in the given set of conditions to trim it to. For example, if you set the tab for cruise at 170 mph you are going to need to exercise your feet at least a little when you are going 180 or 160 (same if you adjusted the stab so...). It's just physics. I've seen a cool little rudder cable tensioner device to help with that for Vans side-by sides but nothing for the 4. That would be nice, but it's a small price to pay for the grins you get. My tab (not a wedge) is set for 170-175 mph cruise in clean air. That's where I spend most of my time on cross country trips.
 
I would suggest that you remove the wheel pants and gear leg fairings. Then fly the plane and if doesn't fly true find the problem. Once corrected reinstall the gear leg fairings and wheel pants. It is much easier to find problems with trim problems with a lot of the variables removed.

How do you know it is not the wheel pants or gear leg fairings causing your problem?

DO THIS FIRST!

Then, if necessary, add a tab.
 
VS off center

You could- but would be a HUGE repetitive process to get right. Think of redoing that intersection fairing a few times:eek:, reworking the front spar attach point a few times:eek: (and don't even think of slotting those mounting holes!!!)

Go with a wedge

Definately don't change the holes but as a data point, the VS on the 7 is mounted off center. The mounting plate has about 1/4 off center joggle.
 
Vertical offset

Definately don't change the holes but as a data point, the VS on the 7 is mounted off center. The mounting plate has about 1/4 off center joggle.

No: I would not do it after-the-fact. I offset my vertical knowing it needed to be and, while it improved in-flight trim, still had to add a rudder trim tab. Now: feet on the floor at "normal" cruise (152 kts).
 

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Definately don't change the holes but as a data point, the VS on the 7 is mounted off center. The mounting plate has about 1/4 off center joggle.

True, but that offset is no less drag than moving the rudder over via a wedge. Any way you slice it, it will create drag to push the plane back to neutral if it doesn't go there naturally.
 
Offset

True, but that offset is no less drag than moving the rudder over via a wedge. Any way you slice it, it will create drag to push the plane back to neutral if it doesn't go there naturally.

I was only pointing out the 7 VS is offset by design. I suspect it was done for that reason but I'm not an aeronautical engineer.
 
To be clear, I understand how to counter yaw using the rudder. Unfortunately this also causes aerodynamic drag.

I’d wager that the current forward-slipping fuselage and deflected ailerons cause more drag than a slightly deflected rudder.
 
Update:

To be clear, I understand how to counter yaw using the rudder. Unfortunately this also causes aerodynamic drag. The question is how to fix whatever is causing adverse yaw in flight. I will check the fairings as Mr Blunt suggested but what other possibilities should I re-check? Is something rigged wrong? Should my vertical stab be adjusted off center?

I found the LH gear fairing to be 1/4" out of alignment (high). I will fly it and post another update.
 
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