Small flaps on rotor blades for high lift

Gurney flaps have been implemented on a variety of aerofoils from aeroplane wings to helicopter rotor blades to air turbines and race cars. Active gurney flaps (AGFs) are a key objective of the EU's Clean Sky aerospace research programme.

Adding an active component provides the ability to adapt to changing conditions and a system that significantly outperforms its passive analogue. It could provide important vibration damping at less weight than current solutions as a system that addresses vibration at its source, the blades.

The EU is funding the project 'Gurney flap actuator and mechanism for a full scale helicopter rotor blade' (PT656) to evaluate the capabilities of a helicopter main rotor blade incorporating an AGF. The AGF system will first be tested in a wind tunnel test of a helicopter main rotor blade held in a fixed position. It will then be evaluated on a ground-based whirl tower subjected to realistic conditions for a flying helicopter's main rotor blade.

Within the first period, scientists produced preliminary designs for the flap structural components and the actuation system. Electromechanical actuation was chosen for its reliability, high power density, high bandwidth capability, and robustness to extreme conditions of temperature, vibration and acceleration.

The actuation system was manufactured and preliminary testing to validate the performance of the electromechanical actuator in the operational environment has begun. In particular, preliminary stress analyses evaluated performance under various operational loads, whereas thermal analyses investigated heat transfer from the motor and moving parts of the actuator to the blade.

In the upcoming project phase, scientists plan to conduct the wind tunnel test campaign to enable evaluation of the capabilities of the AGF under controlled conditions. They will also continue with more comprehensive stress and thermal analyses. By project-end, PT656 expects to have demonstrated both the technological feasibility and performance capabilities of a helicopter main rotor blade incorporating an AGF. Benefits include greater lift, lower fuel consumption and fewer emissions. Implementation into rotorcraft will make a major contribution to the EU's Clean Sky programme and reduce the environmental impact of air travel.