In the paper, we present a linearized mathematical model of a small scale coaxial helicopter with Bell-Hiller stabilizer bar, which is extracted from numerical linearization of a non-linear mathematical model with small perturbation theory. Stability and control derivatives calculated by numerical method are compared and analyzed for stability and control analysis on coaxial helicopters equipped with different type stabilizer bar. The study indicates that the coaxial helicopter with stabilizer bar fixed on the upper rotors has better capability on stability and control.

Based on the engineering reality, a calculation model of the rotor unsteady aerodynamics of the small-scale coaxial helicopter had been set up. An airfoil unsteady aero- dynamic model was established by introducing a set of Leishman-Beddoes semi-empirical indi- cial response formula. The induced velocity of the aerodynamic interaction between upper and lower rotors of a coaxial helicopter was set up based on the rigid wake model, free wake model and the dynamic inflow model with interference factors. Considering the teetering rotor＇s particular flapping dynamic formula, the Runge-Kutta method was used to obtain the numerical solution of the rigid blade flapping angle. According to the calculation and analy- sis, the thrust response to a rapid collective pitch increase in both the hovering and forward flight states were obtained, and the blade＇s hinge moment of the upper and lower rotors were compared.

Based on the traditional method,a calculation method of electric-powered helicopter flight performance was proposed,which combined with the features of electric-power system and the characteristics of helicopter preliminary design.The influence of different variables and parameters on flight performance was analyzed.By taking a small-scale helicopter as an example,the flight performance before and after was calculated and compared.The calculated results and analysis show that electric-powered helicopter with short endurance due to battery technology limitation has higher ceiling.Compared with light and medium helicopter,micro and small-scale helicopter have a lot of advantage and latent capacity.This method is applicable to electric-powered helicopter preliminary design and parameter selection,which is also significant for helicopter.

Using perturbation approach,a linearized flight dynamics model was formulated for the non-linear coaxial helicopter flight control problem.Based on mathematical parametric model of the rotorcraft,the system identification model was obtained by utilizing the input and output data of longitudinal and lateral channel in flight test.The analysis and validation of the above two models in the time domain was given by computer simulation.The stability derivatives,control derivatives and the system eigenvalues were computed for the stability analysis of the helicopter.Results show that the mathematical model can reflect the dynamic characteristics of the longitudinal and lateral channels,based on which the system identification model can be a mathematical model for autonomous flight control system design.