Can you offer some advice about how I can tune out an annoying tail wag? Nothing I do seems to help. Here are my details.

I am seeing a tail wag when hovering. The tail wags 2-3 times per second.

The heli is a Goblin 700 Competition Gas Conversion.

The headspeed is 1800 RPM and I use the smaller 26T tail pulley that SAB recommends for lower headspeeds.

Currently I use a MKS HBL990 tail servo and KDE tail slider upgrade, but previously I used a BK BLS-8005 tail servo and SAB precision (2-pin) tail slider with the same result. The tail mechanics move very freely.

My Spirit parameters are:
Rudder end-points: Left limit: 146, Right limit: 165
Rudder Common Gain: 1.30x
Rudder Gain: I have tried 50%, 60%, 70% and 80% without seeing much difference.
Rudder delay: 0
Pirouette consistency: 190, but I have also tried lower values.

I am novice pilot, so any advice about how I can approach solving this problem would be appreciated.

Hello,

for goblin helicopter it is very important to move the tail center so that there is a slight angle (3-4°).
This can improve overal performance of the tail.

What frequency you have configured for the rudder servo?

Also make sure that ball linkages are moving without any friction. KDE upgrade should help a lot, but you can still verify the mechanics also while motor is spinning.

Unmount all blades, disconnect push rod from tail servo arm and then start the motor. Then you can try to carefully move with the push rod in the available travel (instead of servo). You should not feel any friction. This is very, very important. If there is no friction, then tail should work perfectly.

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Spirit System developer

Thanks for the advice.

I changed the tail offset with the rudder servo centered from 0° to 3°. This also changed the Rudder end-points: Left limit: 133, Right limit: 183.

The MKS HBL990 tail servo frequency is set to 560Hz.

I tested moving the tail push rod with the engine running (1000-1500 RPM headspeed) and the push rod disconnected from the tail servo. The result was not what I expected. The centrifugal force from the tail grip arms forced the slider to center. I took significant force to move the tail slider away from center, however it did feel that the tail slider mechanics moved smoothly even with significant force required to move it away from center. Without the engine running the tail slider will almost move under its own weight as I turn the heli from one side to the other.

I do not like that the tail push rod support causes a slight bow in the push rod. I have a different push rod support that will let the push rod stay straight. Hopefully this will eliminate any friction at this point.

It will be next week until I can fly again and see if there is an improvement.

You are right, anything that is touching push rod that causes additional friction has negative impact. Eliminating any of these will definitively improve it.

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Spirit System developer