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Bent Rudder

Aeronut

Registered User
Kittery, ME
I got most of the welding done on my new rudder today and in spite of meticulous layout my rudder came out slightly bent. As in when it's on one side the clearance along the tailing edge is not equal to the clearance when flipped. I haven't measured it precisely but get the impression I have a gap of about 0.15" on one side and 0.35" on the other. The gap should be 0.25" on both sides according to my calculations. If you look at the rudder from the top or bottom you cannot see this differential and it looks good. I assume this problem arose because my clamping wasn't adequate during welding.

My question:

Although I'd prefer a perfect rudder, will this amount out of tolerance result in trim issues during flight? Are there ways to straighten this out?

Worst case scenario I'll rebuild it.

Aeronut
 
So it is straight from the top. It doesn't sound very far off.

I don't really follow about what you mean as clearance. The rudder ribs are tapered but flat. If they lay flat against a table, there isn't any clearance I'm aware of.

When I built mine my only real concern was to make sure the balancing portion on the top (forward of the hinges) was lined up through the hinge's leading edge and then the trailing edge.
 
RV, the post is 7/8" thick whereas the trailing edge tube is 3/8" thick which is a difference of 1/2". I expect to measure 1/4" on either side of the trailing edge relative the thickness of the post. When I checked it on its side can tell it's a bit off of that 1/4" mark.

I'll take note of your balancing portion piece you mentioned.

I should grab some pictures and post them.
 
I'm no expert, but I've heard that the proper method for adjusting rudder trim is to twist the top by hand--so you probably are in the ball park anyway.
 
Excellent!

Here are some pictures. IMG_1606.JPGIMG_1607.JPGIMG_1608.JPG
 

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and you will bend the fin ever so slightly to make it fly with the ball in the center and your feet flat on the floor.
 
Steve, so I actually physically manipulate the fin during the flight testing phase after the fabric has been applied? What tools/techniques are used to make this minor correction?
 
It's a highly scientific method by which you hold the lower end of the rudder between your knees and twist the top half one way or another to trim for yaw.
 
It's a highly scientific method by which you hold the lower end of the rudder between your knees and twist the top half one way or another to trim for yaw.

We don't bend the rudder, just the top of the vertical fin

Glenn
 
Steve, so I actually physically manipulate the fin during the flight testing phase after the fabric has been applied? What tools/techniques are used to make this minor correction?

Look at the PA18 rigging instructions. Bend the leading edge vertical fin in the direction the counterbalance goes when you hold the needed rudder to keep the ball centered.
 
Good info. I had read the rigging as bending the upper portion of the rudder itself. Learn something new every day.
 
I guess it was just listening to old mechanics about trimming the rudder. My understanding was you twist the upper portion with the balance tab in the correct direction. I must have misunderstood that it's the vertical fin, not the rudder.
 
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