Checking the CG (the balance)
last updated 9-24-2004

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9-24-2004 There is some contraversy as to how the balance should be checked. Some say using the main shaft as a 'high point balancer' as indicated below does not give the correct result. They say lifting the helicopter by the flybar is the right way and will give a different result then the other technique. I have checked my helicopter and both techniques give the same result. Honestly I have never had a CG problem with any of my helicotpers because they are built stock as the engineer designed it for and they have always flown great. Because of this I have not put any time into the finer details of balancing the helicopter. So I leave the choice up to you. If you use the flybar technique make sure the blades are both straight out as that will effect the result. And also do not pay attention to the skids as they may not be 90 degrees to the main shaft.
Note: The reason most want to check the CG is because of a difference in elevator trim between hover, forward flight, and inverted hover. But keep in mind that wind will effect this too. And in addition to this also remember that slop in the elevator servo gears, slop in the control linkages, slop in the swashplate, and loose parts in the head can all effect the flight characteristics.
Check the balance with the tank half filled with fuel.
This is how to check the CG (the balance) of the helicopter. Grab the rotor grips and pick up the helicopter. Rotate it to its side so the main shaft is parallel to the ground and so is the tail boom. The helicopter should stay in this position if balanced right. This would indicate the CG (Center of Gravity) is directly under the main shaft. If the nose rotates down then it is nose-heavy. If the tail rotates to the ground then it is tail heavy. It is always better to be nose heavy then tail. If the nose rotates slowly downward that is fine but if it rotates quickly then the helicopter is too nose heavy. In most cases I find a tail heavy situation due to placing the tail servo at the back or using light weight lithium polymer battery packs. This can cause the symptom of the nose dipping down in forward flight. In this case you can use a heavier battery pack up front. Or make an extension to the platform to shift the battery further forward. Opposite of that you can have a nose heavy situation due to use large sub-c batteries on a R30/50. For this size helicopter the 'A' size packs work best.
Nose dipping in forward flight -
This is caused by an off balance situation, usually a tail heavy problem. In a hover the heavy tail end dips and causes the helicopter to drift backward. You can use forward elevator trim to fix this however when you go into forward flight you now have the rotor disk tipped forward with the trim. So you will find you constantly have to correct this all throughout the flight.