The term Dynamic Balance implies that this is involved with some sort of interaction with movement - perhaps Aero Balance or Aerodynamic Balance are more accurate terms You appear to understand Static Balance. So, let's edit the first three:
1. Aero balance is usually done to reduce pilot force input requirements and is achieved by having some area of the control surface in front of the hinge arm. There are other methods for achieving static balance.
2. Static balance is done to reduce the possibility of flutter by moving the aileron c of g closer to (or forwards of?) the hinge arm and is achieved with some ballast forward of the hinge arm.
3. A 100% statically balanced aileron would have a c of g on the hinge line.
Now 4, well, right concept but very wrong on execution. Aero balance gets complicated in a hurry.
First let's get the concept straightened out. If you put the hinge at 50% C', the ailerons would try to deflect hard over, called aileron snatch. This is because the lift produced at the aft end of all airfoils decreases pretty much linearly and toward zero as you go towards the trailing edge. Look it up in the v/V or (v/V)^2 plots on any airfoil. The lift looks like a triangle, and the centroid of lift on things like ailerons is about 33% C'. All other things having no effect, if you put the hinge line about 1/3 back along an aileron, it would have zero restoring moment.
There are other things in there too.
If you were to simply make the profile of the aileron a slice from the wing and put the hinge at 33% C', when you deflect the aileron, the part forward of the hinge protrudes into the airflow and adds more moment towards deflection. This is another type of aero balance added on top of what you already have and is capable of producing aileron snatch if too large. It can be tuned by changing the radii at the forward corners, narrowing the width of the forward portions, or rounding the whole thing over;
You can do what a number of aerobatic ships and the last of the muscle powered big airplanes did. Round off the part of control surfaces ahead of the hinge, which reduces the additional balance due to deflection into the air flow. This reduces but does not eliminate the issue.
Next up is that lift is distributed pretty much elliptically span wise, so the lift at the tip gets pretty darned small as you move towards the tip. A sheilded balance horn at the tip of wing is mostly to get mass balance at min weight while giving some aero balance when deflected. An unshielded balance horn will reduce on center feel, while a shielded horn tends to have better on-center feel but can have non-linear feel as deflection proceeds.
Extending the balance horn forward allows less weight to do the job. When the balance horn is at the wingtip, it does tend to have less aero balance than if the same area and arm effects were further inboard. Moving it inboard will increase the aero balance effect of the same horn. Placing the balance horn at the wing tip MAY also require more structure weight in the aileron as it is at one end so all of the moment from the surfaces has to be carried to one end. Min gage issues and designing ailerons to stiffness tends to make this last one moot in our little airplanes.
Most of us like to have some on-center feel for controls, and then nicely increasing control forces as the surface is deflected. The on-center feel allows you to put a hand on the control and not deflect it, and keeps the control from floating, which will make the airplane wander. The entire force vs deflection curve that starts low (but not on zero) and monotonically grows allows us to feel control surface is deflection. Aileron snatch is the opposite, with forces to hold a certain deflection decreasing and then going opposite the direction of travel, and needs to be avoided. Worst case is aileron lock, where it snatches, then has such high forces that you can not return the control to neutral... Hope you are wearing a parachute and can get out if this ever happens.
The task of balance is thus several fold:
If you are fast enough to need mass balance, you do it:
Aileron forces should be put into harmony with the other control forces. There are a variety of rules on the apparent forces for each axis. Ailerons should be lightest, and yet, they tend to be heaviest unless we do some aero balance and/or use very small aileron chords;
The forces should be progressive - that is higher as airspeed goes up, higher as the deflection increases, higher as response increases;
No force reversals are desired. Aerobatic pilots sometimes put in huge efforts to get their spades and thus control feel right over the whole range.
Have fun making all of that work...
Billski
