Lesson 1 - Trimming The Helicopter

The following information is mainly for gas driven helicopters, but the basics can also be applied to electric R/C helicopters.

Here's the difficult part. Getting the helicopter properly trimmed. A helicopter which is trimmed means that during a hover, all the control trims on the Transmitter is at centre. 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, 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 helicopter. 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, 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, 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 centre, 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 fully low, 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:

Lastly, CENTRE 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 helicopter.

Rev up the throttle, and wait until you get a good constant sound from the engine. Then increase the throttle slowly until the helicopter is very light on its feet. At this stage, your helicopter will start to move in all directions. Counter the helicopter 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 big cross sticks with balls at the end to save $$$$ in case anything happens. Trying to be macho here won't gain points :)

Natural movements of the helicopter will be as such.

For a clockwise turning rotor, your helicopter 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 helicopter (head) will swing left, but the gyro should counter it slightly, and on decreasing throttle, the helicopter will swing right

If your helicopter behaves in this manner, then you got a properly trimmed helicopter.

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 helicopter 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 helicopter is a counter-clockwise rotation rotor, then the effects will all be opposite of the above.

Happy hovering.