Servo/Control-Surface Loads

[chadtyro]

We have an interesting discussion on servo/control-surface loads started here:

http://www.rcgroups.com/forums/showthread.php?t=619018#post8077922

Instead of taking more away from the original intent of the thread, I figured we could continue here. I'm basically looking for more input regarding the following:

-Given two very different airplanes with similar-sized control surfaces, what factor(s) play a role in increasing loads on the control surfaces which translate into increased loads on the servos?

-Will these loads be different between the two? If so, how? If not, why?

-What loads, in general, are placed on control surfaces/servos?

Thanks,
Chad

[MarkusN]

Factors that will affect control surface loads:

Wing loading
Speed

To a lesser degree: Camber

[Brandano]

And how much of the load is counterbalanced aerodynamically or by counterweights. Full size acrobatic planes often have "blades" protruding in front of the ailerons that act as both aerodynamic balance and counterweight. The surfaces gain some inertia, naturally, and add to the overall weight of the plane.

[macboffin]

Aerodynamic and mass balancing are part of the design of nearly all aircraft, including light aircraft, on rudders and elevaters, and on many aircraft on ailerons also. They reduce pilot/servo loads, loads in the control circuit and hinges, and reduce flutter effects. The mass balance needs careful fitting to exactly balance the weight of the surface behind the hinge point. Another coat of paint on a full size aircraft necessitates re balancing the surfaces.
(For interest, the elevater balance weight on a 747 is around 230 lbs of depleted uranium.) D.Ur or lead are preferred since they only need a shorter lever arm than other materials. The amount of surface area ahead of the hinge line is between a quarter and a third of the area behind the hinges.
When pulling some G, a mass balanced surface also reduces the G feedback in the circuit due to the surface wanting to "sag", as well as reducing the force necessary to hold the surface against the air load.
For models, reducing servo load extends battery life as well as reducing work load.