I have spent a little time experimenting with rudder trim, and I think it would be worthwhile to share my experiences with the group.  I know that most of you are probably saying "Why?" to the concept of rudder trim for our STOL aircraft.  In most cases, it is probably not necessary.  However, I found it useful.  I'll explain.....

The Aerosport IO-375 makes 195 hp, and lots of P-factor.  With that power plant, one can point the nose up and go.  In the 801, I can also haul a lot of weight, and sometimes take a nose-high attitude for quite a while to reach cruising altitude when I fly heavy.  This is especially true when the weather gets hot, as it often does in Tennessee.  All of this takes a lot of right rudder, often for long-ish periods of time.  So I decided to experiment with rudder trim.  I did not see any other posts on it, so thought it was worth sharing. I imagine my experience would apply to all of the 'all flying rudder' varieties.

First I added a flat trim tab to the bottom rear of the rudder, attached by a simple piano hinge, and driven by a Ray Allen servo.  I found this to work very well and to be very effective.  It easily delivered the necessary rudder force to compensate for full power P-factor in a Vx climb (55 mph for me).  Here is a picture of my initial setup:

After this success, I decided to take the next step and integrate the tab into the rudder.  I made a new rear rudder skin and removed a segment that I chose for the trim tab.  I made three ribs for this and added a U channel to the front.  I mounted a piano hinge to that U channel.  I mirrored the U channel in the body of the rudder and riveted it to the skin and adjacent ribs.  The piano hinge attached the two U channels or the right side of the rudder.  Ray Allen servo was mounted on a 10-degree angle toward the left-sided trim tab arm.  Here is the completed update....

So if you ever wonder, does rudder trim work on our 'all flying' rudders, the answer is yes!

Probably not necessary for most, but in my case a useful mod. 

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Comment by Daniel Niendorff on September 26, 2019 at 7:13pm
Thanks David. I have a feeling I will end up looking at that once I get the floats up and going. Please post your results if you beat me to it!

Another note:
It’s worth pointing out (and typing here for future readers who may try this) that I found the first trim tab I made - placed at the base of the rudder - to be more effective in creating yaw. I’m guessing this is because there is nothing in front of the hinge at this point. Both tabs work, but you get more bang for the buck (or for the square inch of trim tab) in the lower position. The upper position seems to require more travel for the same amount of yaw.
Comment by David J. Beaulieu on September 24, 2019 at 7:02am

Nice work and thanks for posting Dan.  Start considering a ventral fin (maybe) once you get flying with floats.  I find there is a bit of 'fishtailing" during cruise with my setup.

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