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RV8 Manual Rudder Trim

P

Pman

Active Member
Hi All,

For those who have installed an adjustable "manual rudder trim" feature on their flying RV8, can you please share how you did it? Also, it would be helpful to know where you purchased the needed hardware and part numbers?

I'm familiar with how to make and install the many different options of a fixed rudder trim tab, however, I'm interested in a rudder trim system that will provide me control of multiple speed/power ranges.

Thank you!

Mike Perillo
 
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Cable and spring

A friend’s 8 had a knurled knob on the right side that turned a threaded Rod attached to a cable to a pulley on the back of the lower firewall that then attached to the back of the right rudder pedal. He said it didn’t do much but it looked functional to me. Might could put a stronger spring on.
 
Servo to Rudder Cable?

The pix shows my tie-in to the rudder cable for the rear seat rudder peddles on my -4.
I’ve been thinking of mounting a trim servo and attaching a spring then a cable directly to the right rudder cable. Like I did for the peddles. Perhaps mounting it just aft of the baggage compartment.
 

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I was thinking of a pair of springs from the top of the rudder pedals pulling toward the firewall, with a bias lever, similar to the way the aileron trim springs work.

For me, there isn't room up there to do that, because I have the pedals all the way forward as far as they can be. But an added benefit would be keeping the rudder cables taught all the time.
 
Pman said:
Moe,
I see the spring is from McMaster, however, what about the other pieces of hardware? Where did you get the other pieces of hardware, of did you make them?

Thanks everyone for your replies!

Mike
Click to expand...

I made them
 
Linear actuator and spring on the right rudder cable

I fabricated a "bridle" (at least that's what I think it's called) to capture the right rudder cable forward of where it goes into the spar. Using the TLAR method (that looks about right) I selected a spring from my collection and used an Actuonix 12V linear actuator left over from another project.

The theory was that the spring would apply more or less (down to zero) right rudder pressure, which is what my RV-8A requires at various speeds. This conveniently allowed me to mount the actuator on the rear wall of the aft baggage compartment. I certainly don't have any room between the rudder pedals and the firewall for any kind of a rudder trim system.

It worked fairly well in the 2-3 test flights I flew. And when parked on the ramp I ran full right rudder trim so the rudder no longer banged on the stops.

But at low speed/high power it needed more right rudder, i.e. an actuator with more throw (100 mm vs. the 50mm I installed). I didn't feel it was worth the $90 it would have cost so so I haven't bought it (yet) and removed the components, at least for now.
 

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Thread is 5/8-11. Next time I'd go more course. No need for fine adjustment. Cut from 6061 1.5" round bar.

Overall there's 5" of thread there, you only need 3. Less if you use a stiffer spring.

Knurl nut is like 1.5" od.

It's a custom piece made on a 109 year old lathe and a 60s era Bridgeport knockoff. For the hours I have into it, I'd have to charge far more than anyone in their right mind would be willing to pay.

You could easily draw this up in solidworks and have it 3d printed.
 
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