Studies of trims, stability, controllability, and some flying qualities of a tandem rotor helicopter

Two mathematical models for determining the trims of a tandem rotor helicopter were constructed separately using two technologies (momentum theory and vortex theory). A computational method for the stability and control derivatives was proposed based on the linear perturbation theory and the five-point central difference algorithm. The stability roots of a CH-47B tandem rotor helicopter in the uncoupled mode were calculated. As a verification, the calculated, referenced, and test data of comparable trims and stability roots were shown to have acceptable agreement. Analysis presented included stability and controllability features of the tandem rotor helicopter, based on the momentum theory model. According to ADS-33E-PRF, the flying qualities of the tandem rotor helicopter in hovering were studied mainly with respect to four aspects: bandwidth, attitude quickness, interaxis coupling, and disturbance of the lateral gust. Indications of all the work are summarized at the end of this article.