Need some help on an Aero question

[Mel Duval]

I have had a couple of rudder/elevator planes that seem to be VERY sensitive to the rudder. Just tap the rudder and BANG it turns, let go and it immediately neutralizes. They fly fine, you just have to be REAL easy with the rudder. I suspect it is a sign of too much dihedral, but cannot confirm it. Took out a buddies plane Saturday and it did the same thing which is why I am asking the question. BTW, the planes were all high wing, flat bottom/foamy curved airfoils with fairly forward balance points.

Anyone got an idea what is happening?

thx,
Mel D>

[Ollie]

Make the rudder horn longer. Make the rudder servo arm shorter. Make the tx rudder low Dual rate/expo if you have it. You must make rudder throw much lower but not too much.

[Mel Duval]

Hi Ollie,
Understand about reducing the throw (which is what I ended up doing--twice). My main question is why it self neutralizes so harshly when you let go of the rudder.
thx,
Me D.

[Ollie]

"My main question is why it self neutralizes so harshly when you let go of the rudder."

Do you hold the rudder with your fingers or do you hold the rudder TX stick with your fingers but not put your fingers on the rudder?

If you just hold of the TX stick and let go of the stick, you have a very good servo. Letting go of the stick is a wrong technique in flying. Control the stick without letting go of it.

Self neutralizes so harshly is good not bad. I am quessing that you are using a rudder servo that it is a super fast, powerful, digital and a new servo. The old analog servos were less harsh.

[Sparky Paul]

Lots of di-polyhedral will do that rapid return (actually overshoot) to neutral.

[Ollie]

If you have di-polyhedral that overshots like Paul says, the overshoot can be reduced with along tail moment length, reducing the mass of the tail and wing tip mass. The yaw damping improves with the square of the tail moment length. The yaw damping is improved in proportional to vert. tail area but no tail mass increase.

[BMatthews]

Pictures of the models would help determine if there's too much dihedral. Or at least give us the span and amount of dihedral per side.

Speed also plays a part in the equation. I've got a couple of old time free flight designs with lots of dihedral but with RC in them (1/2A Texaco event models). Under power or in a dive they respond strongly. In the glide they are easy to fly with "normal" response. Both require very little rudder throw to work well. About 1/2 inch each side of neutral is plenty.