Trimming an RC Helicopter

Lesson 1 : Trimming The Helicopter
Here's the difficult part. Getting the heli properly trimmed. A heli which is trimmed means that during a hover, all the control trims on the Tx are at center position. This is ideal, but this is not always the case.
To begin, make sure that your servos center point is neutral with the control surfaces. ie: With your swashplate level, your aileron and elevator servos should be at center position, with the control sticks also at center position. Rudder is difficult, so follow your instruction manual on pre-setting the rudder. Only during your first hover would you know how much rudder trimming you need.
Setup your gyro, and pay careful attention to the way your gyro moves in conjunction with the way you swing the heli. You would want the gyro to counter your movement.
Set up your throttle and pitch curve the way you want it. How I normally set mine (using a Futaba) is to set the throttle first, then the pitch.
With the Throttle stick at 50% Center, open up the throttle lever on your engine to 50% (approx), and then fit the horn into the servo gear. Next, push the throttle trim to minimum, and the throttle stick to minimum as well. Your throttle should be fully closed. Make sure the linkages do not buckle. If your throttle is not at the fully closed position, there should be a pot (or computer) setting to adjust the Low end travel. Adjust this until the throttle fully closes without buckling the linkages.
Now push throttle stick to high position, and the throttle should fully open. As before, if the throttle is not fully opened or the linkage is buckling, then adjust the throttle pots (or computer) for the high end travel.
This setting should make your throttle quite linear. Re-adjust later if you find your head speed to be off.
For the pitch setting, set your throttle stick to the center position, and with a pitch gauge, set the pitch for hovering (5 to 6 degrees), and mount the linkage to the servo gear. Push the throttle to the fully low position, and then check the pitch. Adjust your pot (or computer) to give you the pitch you want. If you are unable to attain the pitch you desire, use a longer servo horn. Do the same for the high side. Normally, for starters, -1 to 10 degrees is ideal.
Therefore, we can summarize it as follows:
STICK POSITION
THROTTLE
PITCH
Low Position
0% (trim at min)
-1 degree
Middle Position
50%
5 degrees
High Position
100%
10 degrees
Lastly, CENTER OF GRAVITY (CG) has to be right in the middle of the rotor mast! If it's not, use weights to adjust the position till it's there.
Once you have completed the preliminary setup, it's time to fuel up and trim up the entire heli.
Rev up the throttle, and wait until you get a good constant sound from the engine. Then increase the throttle slowly until the heli is very light on its feet. At this stage, your heli will start to move in all directions. Counter the heli movements by controlling your cyclic and rudder. For the first timers, this may be impossible, so get someone to help if necessary. Also, put the training gears on to save $$$$ in case anything happens. Trying to be macho here won't gain points :)
Natural movements of the heli will be as such.
For a clockwise turning rotor, your heli will tend to drift to the left, due to the tail rotor pushing to counter the torque. This is normal, and I normally just push my aileron trim 2 to 3 clicks right.
Pushing the aileron right to counter will cause the tail to rise, because of the slight angle, and this is countered by a little back elevator.
During the hover, your tail should be rock steady
On increasing throttle, your heli (head) will swing left, but the gyro should counter it slightly, and on decreasing throttle, the heli will swing right
If your heli behaves in this manner, then you got a properly trimmed heli.
If the tail drops during lift off, your CG is too far back. Use a heavier battery or some weight to counter it. Same goes for the opposite. But if the CG is correct, check the swashplate. It might not be level.
If your heli drops severely left or right, the swashplate is probably not level. Check direction, and readjust.
Tail swings left (head right) during hover. Rudder linkages too much positive degree. Adjust the linkage to reduce the rudder pitch.
Tail swings right (head left) during hover. Rudder linkages too little degree. Adjust the linkage to increase the rudder pitch.
Tail starts to wag. Your gyro gain is too high. Reduce.
Note: If your heli is a counter-clockwise rotation rotor, then the effects will all be opposite of the above.