ORIGINAL: wsmalley
Maybe I posed the question the wrong way. Assuming the pivot point is on the scale 20% MAC, would-or should- the stab be 'balanced' at that point with no linkage connected. That is, would it 'sit' level. Indeed, I recall most jet stabs hang tail heavy. I assume full size, and models too, are attempting to put the least strain on the actuator, or servo. Maybe there are other reasons aerodynamically for their design and balance-or being purposely weighted to hang aft.
I just checked and the scale pivot location for the Su-27 stab is 21% MAC.
I'm not an aeronautical engineer, nor do I play one on the internet. But, as I understand it, it has something to do with the static margin of balance. With the stab balanced aft of the pivot point, it wants to "rotate" around it's own CG. Since the pivot is located ahead of the CG, it physically prevents this "rotation" from occurring, thus preventing the surface from fluttering. Or something like this.
I used to have a more scientific explanation, but can't seem to put my fingers on it right now. Charles at Yellow Aircraft has explained this, too and says that it is unnecessary to balance the stabs on any of his jets. Says you can if you really want, but it really doesn't matter. Says that all you're doing is relieving the servo load on the ground.
It's not that they're purposefully balanced tail heavy. Rather, the CG is aft of the pivot point, so they naturally hang down once the hydraulic pressure is removed.
('leading edge devices'?)
Dick,
I understand what you're describing and you're right about hinged controls like ailerons, elevators and rudders. I agree that those should be static balanced.
I know what I call them and have heard many different names including elevons, tailerons, flying tails, flying stabs and even ailervators. (Yes, Futaba does use that term in the manual to one of their radios, or so I'm told)
I just call them elevons because I'm too lazy to say taileron.
