Centre of gravity
The centre of gravity is on 30-33% chord position by a normal airplane. The wing is 140mm width divided by 3 is 46,6mm, so the centre of gravity is on 46,6mm from the leading edge, bud with a bi-plane the centre of gravity lies just behind the leading edge of the lower wing. Support the model at the centre of gravity, which is indicated on the drawing. The correct centre of gravity has been found when the model sits horizontally, with the noise pointing down slightly. If the tail points down, add lead at the front. If the nose points down too much, add lead at the back. But it is better to move the battery to achieve the right centre of gravity. 


Pre flight tests
First check the equipment and perform a radio range test. Check if the rudders move the right way and don't have to much tolerance. It is easier to have a helper who can launch the model by hand. Choose a day with very little wind, for easier take-off and landing. Stalling occurs when the model climbs straight up immediately after take-off, it loses speed, the wings no longer give the necessary lift and the model drops to the ground. Countermeasures: compensate with the elevator immediately and land. Check the centre of gravity or change the angle of incidence of the wings to prevent excessive climb. Diving occurs when the model goes into a nose dive immediately after take-off. The speed increase and the danger of breakage is high. Countermeasures: compensate with the elevator immediately and land. Also check the centre of gravity or change the angle of incidence of the wings. Test the stalling characteristics only on high altitude before you throttle the e-motor back and raise the elevator carefully and keep them raised. This way you know how the model handles when you fly to slow (for landing). Avoid this at all times, a stall when landing certainly cost you your plane. Be sure the centre of gravity isn't to far back when you start testing the stalling characteristics, because the plane can  go to a spin from which you probable can't recover in time. When flying horizontal switch the power to the motor off, if the model dives then the motor camber and the angle of incidence must be increased slightly. This also applies for the opposite.