A Method of Reducing Blade Sailing through the use of Trailing Edge Flaps

During rotor engagement or disengagement operations of a helicopter there exists an imbalance between the aerodynamic and inertia forces which in severe wind conditions, typical of shipboard aviation, can lead to excessive blade excursions and/or structural loads. The phenomenon is widely known as blade sailing which in severe cases can lead to ‘tunnel-strikes’. The ability to control these blade excursions could lead to a significant increase in the operational envelope of the shipborne helicopter or alternatively could reduce the likelihood of damage to the aircraft. In recent years there has been a proliferation in the literature concerning the application of an actively controlled trailing edge flap for a wide range of applications during normal flight regimes. This paper considers the use of a trailing edge flap for the reduction of the blade sailing phenomenon. Results are presented using two helicopter blade dynamics methods to which aerodynamic models for the trailing edge flap have been applied. It was found that for a simplified wind model, significant reductions are available in the tip deflection and the structural bending moment if the flap is operated in opposition to the blade tip deflection velocity. Due to the low dynamic head at low rotor speeds the control effectiveness is increased by using the largest possible flap farther outboard and with the largest possible flap deflection, however the flap need only be actuated at rotor speeds well below 50% normal operating speed which could reduce the control power required. Although aspects of the model are under development (for example future work should consider the effects of a turbulent inflow) the current results are very promising.