Tail heavy rudder?

[1:1_Scale]

I'm going ot rivet the trailing edge of my rudder today, and was curious about how the rudder is supposed to be counter balanced. From what I understand, the elevators should balance at the hinge line so niether end should be lower than the other, but when I try to pick my rudder up at the leading edge of the spar, it's very "tail" heavy

Is counter balancing a vertical surface different than for a horizontal surface?

[cjensen]

It will be "tail" heavy. Don't know the exact physics of it, but there is a lot of metal in the big 7 rudder, and that little lead weight at the top is not enough to really balance the surface when it's held at the spar.

[svanarts]

Your legs are a lot stronger than your arms so it's good to not have the rudder too counter balanced, if that makes sense. If it was balanced like the elevators the least little push from your toe would deflect the rudder. Somebody more aerodynamically smarter than me could explain it better.

[captain_john]

I am willing to bet that the section forward of the pivot point on the top of the rudder contributes to aerodynamically stabilizing the control surface.

Think aboudit, kick the rudder one way and aft of the pivot goes one way, forward of the pivot goes the other.

...just this school teacher's opinion.

Am I at all correct?

CJ

[jakec]

Indeed you are correct. It's called aerodynamic balancing and it's a way to reduce the control forces necessary to move the control surface. The more the portion of the control surface ahead of the hinge line "pokes" out into the slipstream the more "assistance" you get. You can get the same effect by using the spades you see on some aerobatic aircraft.

However, I don't think that the weights are to reduce the control forces necessary to move the control surface. I believe they are to eliminate or reduce the possibility of flutter at high speeds. Someone please correct me if I'm wrong.

[Spike]

I believe you to be correct Jake.

[1:1_Scale]

That was my understanding also- weight for flutter resistance, area for control assistance or feel. That's why I thought it was interesting that the rudder is "tail heavy". Maybe it has something to do with it being a vertical surface If I asked on the other forum, I think 80% of the replies would be "don't question Van, or you'll make a crater"

Another type of aerodynamic control assitance are "servo tabs". Basically, they are similar to trim tabs, but they are anchored to the stabilizer. So in the case of an elevator, when the elevator goes up, the servo tab deflects down, pushing the trailing edge of the elevator up. The first time I saw them was on my aunt and uncle's turbine Porter. Not sure if I've seen them on any other plane.

[svanarts]

Another type of aerodynamic control assitance are "servo tabs". Basically, they are similar to trim tabs, but they are anchored to the stabilizer. So in the case of an elevator, when the elevator goes up, the servo tab deflects down, pushing the trailing edge of the elevator up. The first time I saw them was on my aunt and uncle's turbine Porter. Not sure if I've seen them on any other plane.

You'll see them on Grummans too.

[jim_geo]

I always kind of thought the weight was there to add mass to the set up adding to the aerodynamic effects.

[1:1_Scale]

I sent Joe Blank at Van's a message asking about it, and he said that the balance on the rudder isn't isn't as critical as the balance on the elevators. I guess this makes sense since the rudder doesn't have gravity trying to cause it to deflect one way or the other (in normal flight) like the elevators do