Tandem Helicopter Trim and Flight Characteristics in the Icing Condition

This paper describes an established flight dynamic model with two rotor-icing models that are capable of studying CH-47B tandem rotor helicopter trim and flight characteristics in a rime icing condition. First, considering the ice-shedding phenomenon and the local temperature variation on the rotor blade, an engineering rotor-icing model is developed based on the empirical two-dimensional airfoil icing tunnel data. Second, using the principle of computational fluid dynamics, a theoretical rotor-icing model is set up for comparison with the engineering rotor-icing model. As verification, the results of two rotor-icing models are shown to have acceptable agreement. Analysis was made on the effects of icing on trims, stability, and some flying qualities of tandem rotor helicopters in terms of forward velocity, icing time, atmospheric temperature, liquid water content, and median volumetric diameter. The degradation of flying qualities of tandem rotor helicopters in hovering due to icing is studied mainly with respect to the following aspects: attitude quickness, interaxis coupling, and vertical axis control power. Finally, conclusions of all the work are summarized at the end of this paper.