The prowess of flapping. Semi-rigid rotor testing.
1,593 views · Published 4 April 2010 · 3:47 · Indexed 29 October 2026
Channel: RCmags · 2010 · Gaming
After more fiddling with the previous helicopter, performance was GREATLY improved when I became aware of the cause of a problem encountered during lateral flight. In the earlier version, the center of mass of the helicopter was above the center of drag of the airframe. Since the blades are almost unconnected to the airframe (and any force acting on them are overcome by flapping or sheer thrust, its effect is practically null) we can say it takes no part mayor part affecting the stability. Having a force offset from the center of mass of the helicopter will cause torque. Meaning that if most of the drag from the body is under most of the mass of the helicopter. The helicopter will start to roll into the direction of the drag (think of it as an inverted pendulum), this along with cyclic torque, means that if the natural resistance to motion of the rotor is overcome by these two forces, the helicopter will pitch forward into the direction of motion, so if the helicopter is moving forward it will start to DIVE, it will be NEGATIVELY stable. To adjust this one can move the center of mass of the helicopter. If it is close to the same position as the center of drag, the helicopter will be neutrally stable, so at most lateral speeds, there is very little force to overcome to change the angle of the helicopter relative to the motion. If the center of mass is UNDER the drag, it will positively stable. Meaning the helicopter will naturally have a tendency to pitch backwards into the direction of motion, so the faster it moves laterally, the harder it becomes to maintain current angle of the helicopter.
