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Rudder trim for taildragger

Arablenz

Active Member
I am 15 hours into flight testing my RV 14 and it has been performing very nicely. As I am new to flying RV aircraft I am looking for some advice.
On climb out with full power I require right rudder but once level and at cruise power, no rudder Input required until above 130 knots .
I then require slight left rudder input .
I think I should install the Aerosport rudder trim system as a wedge on the rudder only helps for the one input , when it would be great to have trim for both climb and cruise.
When doing lateral stability testing it becomes very apparent at the different phases of flight.
Is this a sensible option or are there other thoughts?
 
Some people have installed rudder return springs that were cockpit adjustable for rudder trim. While this works, it'll probably take some experimentation to get right.

This shows part of such an installation on an RV-3. The lower arrow points to the rudder pedal, which is considerably different than yours. The upper arrow points to the pulley which turns the adjustment cable around so it goes back to a spring and the cockpit control.

7vLhCy5.jpg


As you can see, the cable is a very light one. The loads are low.

Dave
 
My RV-14 had the exact same issue. I added the adjustable rudder trim you are thinking about. I found that the springs weren't strong enough. I added a wedge to the rudder and found the combination of the wedge and the rudder trim worked very well.
 
My RV-14 had the exact same issue. I added the adjustable rudder trim you are thinking about. I found that the springs weren't strong enough. I added a wedge to the rudder and found the combination of the wedge and the rudder trim worked very well.
You can double or use stronger spring, especially for the RV14 that has a bigger rudder. But also it would be great if you can verify all your rigging, wheel pants or anything else that is effecting this, and see if there is anything that is causing it.
Mine is a 14A and the only time that I need to hold rudder is on climb, like most planes need it. Other than that, my feet are on the floor.
 
I added a wedge on the right side of the rudder to deal with the cruise trim issue and use my feet for other situations.
 
The RV-14A and RV-14 prototypes have different rudder trim compensation as well (the 14A has a wedge adding a little bit of right rudder trim.... the 14 has a wedge adding a little bit of left rudder trim.

Why the difference? I can't say for sure, but I do know that fixed landing gear has a lot more influence on the aerodynamics of the airframe than a lot of people realize.

Keep in mind that the airflow around the fuselage is in a spiral because of the influence of the propeller rotation. Add to this the influence of gear legs (with wide leg fairings on them) positioned at different points relative to the C.G. (the yaw axis), and it is easy to see why the might be differences between the two airplanes.

As for rudder trim?
Most people add a fixed tab or wedge that trims for the condition that the airplane will spend the most time in (cruise flight). The rudder forces aren't very high and the additional amount of right rudder that would be needed, because of a left rudder tab having been added, is very small.

My suggestion would be to trim using a temporarily installed trim tab, for what ever cruise condition you will likely use the most. Fly for a while, and see how you like it.

A small balsa wood wedge (about 1.5 inches wide X 6 inches long X 1/8" max thickness would be a good starting point), attached with clear plastic packing tape works well (it is what we use for all of our flight testing).
 
Thankyou all for your replies. It is good to know that others have the same need for rudder trim.
I have flown with my leg and pant fairings on and off and have eliminated them as having any effect on yaw.
I will do as Scott suggested and then see if I need the Aerosport trim as well or instead of the wedge.
Great support here.
Regards
Roger
 
Last edited:
Just updating that I did as Scott kindly suggested and plane flies beautifully hands and feet off in cruise now.
How does everyone that needs a trim tab attach theirs permanently to a painted surface?
I am thinking proseal or avery strong automotive double sided tape but wondering if I need to remove the paint for good adhesion.
 
I did see a photo someplace of a trim tab attached through the rear position light/strobe.

It appeared to be a simple and elegant solution.
 
Thanks for your suggestion Carl. Certainly I hadn't seen that idea before but I think I will keep to the wedge as that is what I have made up.
 
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