Pitching Moment Control Design for an Integrated Servo-Flap Rotor

An integrated servo-flap rotor has much better aerodynamic performance as compared to an external flap, because it has a higher lift to drag ratio. One of the key issues in an integrated servo-flap rotor design is to properly determine blade aerodynamic pitching moments using this type of design. What will be the required pitching moment and control loads on the control system when the pilots try to fly this rotor? In order to clearly answer this question, the design engineer must have wind tunnel test data to find out what percentage of the blade pitching moment can be generated when the flap is under certain controlled motion. Also, the size and location of the flap play an important role in determining the required pitching moment under the given target design conditions. Wind tunnel airfoil test data are acquired during the design process to verify the basic aerodynamics information such as Ci, Cd and Cm to determine whether they are adequate to fly the helicopter. The design requires the servo-flap to produce a blade pitching moment coefficient higher than 0.011 per degree of flap deflection. Wind tunnel test results indicate the blade/flap aerodynamic pitching moments are adequate for the present integrated servo-flap rotor design.