Tail Rudder setup question

[Andrew]

When I set up my tail rudder linkage and servo, the tail blades are both completely straight. Should this be set up so that the midpoint will compensate for the main blade rotation, or is straight ok for a midpoint?

[darren_uk]

Hi Andrew,

Flat blades = no blowing = no anti-torque. Therefore your helicopter's nose will twist in the opposite direction to the main rotors.

Mid-point will need to be whatever angle-of-attack on the tail rotor blades it takes to keep the nose of the helicopter straight in a hover.

However, here's the tricky bit:

When you rise from the ground, more lift is required, and more torque is generated. Therefore more anti-torque from the tail rotor is required.

When you decend towards the ground, less lift is required, and less torque is generated. Therefore less anti-torque is required.

The gyro will compensate to a certain degree, and you may find you'll have to use a little left and right rudder in the ascend/descend (or vice versa, depends on which way your main blades rotate).

There is something that may help: Revo Mixing. This is where the radio will apply more rudder above a certain pitch stick position (it's the mid position on my radio) and less rudder below this position.

I personally quite like playing with full up and down pitch to watch the different effects between full power and minimum power. I'm not into forward flight yet so it's about the only excitement I get :-)

(Full-sized helicopter pilots do have to do some dancing with the pedals depending whether they're raising or lowering the collective. And in an engine-failure-in-the-hover it's full pedal on one side because the torque from the engine is suddenly lost hence the tail rotor will suddenly blow the tail around.)

[Andrew]

Originally posted by darren_uk
Hi Andrew,

Flat blades = no blowing = no anti-torque. Therefore your helicopter's nose will twist in the opposite direction to the main rotors.

Mid-point will need to be whatever angle-of-attack on the tail rotor blades it takes to keep the nose of the helicopter straight in a hover.

However, here's the tricky bit:

When you rise from the ground, more lift is required, and more torque is generated. Therefore more anti-torque from the tail rotor is required.

When you decend towards the ground, less lift is required, and less torque is generated. Therefore less anti-torque is required.

The gyro will compensate to a certain degree, and you may find you'll have to use a little left and right rudder in the ascend/descend (or vice versa, depends on which way your main blades rotate).

There is something that may help: Revo Mixing. This is where the radio will apply more rudder above a certain pitch stick position (it's the mid position on my radio) and less rudder below this position.

This would be great, except that my gyro manual specifically says to turn off revo mixing because it messes up the tail servo midpoint reading that the gyro takes on startup. I'm thinking I may have to just set the best midpoint I can for a decent hover and correct as needed with the stick when moving up and down.

I personally quite like playing with full up and down pitch to watch the different effects between full power and minimum power. I'm not into forward flight yet so it's about the only excitement I get :-)

Me neither. I'm still just hovering. The simulator is another story (I do full forward flight and simple stunts on it), but I'm a little more cautious when money is on the line.

(Full-sized helicopter pilots do have to do some dancing with the pedals depending whether they're raising or lowering the collective. And in an engine-failure-in-the-hover it's full pedal on one side because the torque from the engine is suddenly lost hence the tail rotor will suddenly blow the tail around.)

This is good to know. I quite enjoy having a real heli pilot participate on this forum.

[colin]

Originally posted by Andrew
When I set up my tail rudder linkage and servo, the tail blades are both completely straight. Should this be set up so that the midpoint will compensate for the main blade rotation, or is straight ok for a midpoint?

You sound like you got a heading lock gyro? Personally, I have never used a heading lock gyro, but traditionally, the tail blades are set to the angle (for midpoint stick), that will keep the heli facing in one direction.

Pushing the rudder (stick) fully right should increase the tail blades to the maximum angle that the push rods can take, and rudder to the left would do likewise. (for clockwise rotating main blade).

At mid point, your rudder should not be at 0 angle. If this was so, you wouldn't have enough angle for any authority over the tail.

[Andrew]

Originally posted by colin
You sound like you got a heading lock gyro? Personally, I have never used a heading lock gyro, but traditionally, the tail blades are set to the angle (for midpoint stick), that will keep the heli facing in one direction.

Pushing the rudder (stick) fully right should increase the tail blades to the maximum angle that the push rods can take, and rudder to the left would do likewise. (for clockwise rotating main blade).

At mid point, your rudder should not be at 0 angle. If this was so, you wouldn't have enough angle for any authority over the tail.

I have a GY401 which is an AVCS hold gyro. It can switch between heading hold and normal gyro mode. I think I'll set up the midpoint with the transmitter (or the linkage if it's off by a lot) while in normal mode, and then try using it in AVCS heading hold mode. From all the replies I've gotten, I don't think I want to leave it straight up and down at the midpoint. Thanks all for helping out with this question.

[darren_uk]

Just to throw a bit more at the complete picture:

" There is something that may help: Revo Mixing. This is where the radio will apply more rudder above a certain pitch stick position (it's the mid position on my radio) and less rudder below this position.


This would be great, except that my gyro manual specifically says to turn off revo mixing because it messes up the tail servo midpoint reading that the gyro takes on startup. I'm thinking I may have to just set the best midpoint I can for a decent hover and correct as needed with the stick when moving up and down."


My heli was setup by a professional model heli flyer. I've noticed that when I up collective, my tail rotor is altered, and vice versa. I have a gyro (non heading hold) on the heli. It look like there's revo mixing on my heli even though I had a gyro attached. I can't confirm it now: The batteries in the radio wore down, and because the radio's more than 5 years old, the lithium backup battery is also gone - hence I lost my data. I thought something was strange when I noticed the collective servo and throttle servo both rotating in the same direction (in other words, at low collective, the throttle was at 100% - classic mistake).

Not sure if this info is useful, but thought I'd throw it in.