The center of gravity on the Ultrasport 254 must be between 4.5" and 1.5" in front of the mast.

Assuming a slope of 15 degrees for the seat back, the pilot's center of mass will be about 10" in front of the back of his head. If the mast has a 2" diameter then the pilot's center of mass is 11" in front of the mast.

Origin (0,0,0) is the point where the centerline of the 2 masts would meet if extended downward below the gearbox. I.e. the base of the V. 

Note: The positive and negatives shown below are for weight and balance only. The signs are reversed when considering the helicopters axes system(s).

X-axis is for-aft (station). Positive is aft.

Y-axis is side-side (buttock). Positive is to port.

Z-axis is height (elevation). Positive is up.

At present, it is assumed that the center of the surface area weight coincides with the center of weight.

Look in book "Aircraft Inspection and Repair], chapter 13. 

In a side wind it will probably be best to have the center of rotation at the mast (datum 0). This way the side wind will not want to rotate the craft and all yaw control input can be used to rotate the craft and not fight the side wind. 

In forward flight it will probably be best to have the center of rotation behind the mast. This way the horizontal air will help in keeping the craft on course. 

It would appear that the best location would be a compromise, where the center of rotation is located slightly behind the mast. Say 12"  

A heavier person will move the center of gravity forward because this person will have greater depth at chest. longer legs and will weigh more. For a lighter pilot consider:-

1. Put a cushion behind pilot to move his center of weight slightly forward. Consider the relocation of pedals also.

2. Add weight to the front end of forward support tube, by the pedals. Assuming that the pedals are movable, this weight could be attached through the forward foot pedal crossbar hole, which is used by tall heavy pilots.

3. Move battery from extreme tail to extreme nose? The battery cable would be a permanent fixture running the full length of the spar and have connectors at both ends.

4. Re: Pilots of different weights: Normally the heavier pilots will be taller. Consider having an adjustable seat instead of the pedals. This will allow the balance arm length to increase as the balance weight decreases. The seat should move down slightly as it moves ahead (in-line with the tail tube?) so that the shorter person's ankle has the same angle with the pedals as the tall person. A problem with this is that the seat may no longer be a part of the structure.

There could be a drawing done for 0472. It would consist of an outline of the 3 views of the synchropter and on another layer a grid would be drawn based on the centerlines, and on another layer there would be 3 lines showing the centers of mass. 

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It looks now that the center of gravity is too far aft. If so, this could be corrected by;

1/ Make the distance between fuselage and power train origins 1/2 to 2" more. This would allow the seat back slope to get back to around 15 degrees. This 15 degrees will be better for forward flight when the helicopter is nose down.