Research On Key Technologies Of Helicopter Flight Simulator

In recent years, the helicopter has achieved an irreplaceable role due to its uniqueperformance and mobility in military and civil fields. Our government, especially, hasalready opened airspace at low altitudes allowing private helicopters to fly. So,training helicopter pilots becomes more urgent. On the other hand, with thedevelopment of virtual reality technologies, flight simulator has already become anindispensable emulation test equipment for pilot training and aircraft-developmentowing to its safety, energy saving, low cost and high fidelity advantages. To meet theneed of practical research project, this paper has made a deep and systematicalresearch on the key technology of helicopter simulator and some innovativecontributions are enumerated as follows.(1)Aiming at simulation application, the main rotor aerodynamic model of thehelicopter flight has been set up. When the main rotor blade of the helicopter rotatesabout the hub, it also flaps around the level hinge. In this case, the calculation of mainrotor thrust will become quite complex. In addition, few literatures at home andabroad discussed iterative computation process of main rotor thrust. When theaerodynamic force acting on main rotor is analysed in this paper, the formulas tocalculate main rotor thrust in hovering, vertical climb and descent are deduced usingmomentum theory and blade element theory. Futhermore, blade natural-flap motionequations are derived in the general flight state and in the vertical climb and descentstate. When considering flapping motion of blades, the force on the blade element isanalysed and eight-site-occupancy method is put forward to calculate upward force,lateral force and backward force on the airframe from main rotor using blade elementtheory. And then, main rotor thrusts from ideal-twist and linear-twist blades areworked out based on Blade Element Momentum(BEM) theory. Iterative computationprocesses of main rotor thrust produced by the two different blade profiles areproposed, which are applied to simulation application.(2)Dynamics model of airframe which applied to both flight and landingsimulation has been established. In the existing dynamics models of helicoptersimulator, two different dynamics modules were adopted separately when flight andlanding, which made it difficult for simulator to accurately reflect the dynamic natureof helicopter at landing and liftoff moment. On base of the aforementionedaerodynamic model of helicopter flight, each tyre is regarded as a suspension, whichconsists of three-dimensional linear springs and viscous dampings in this paper. The Lagrange equation including dissipation function has been chosen as our modelingfoundation. Treating micro displacements and rotating angles of airframe in minutetime interval as generalized coordinates, we have given6-DOF dynamics equation ofairframe which involved flight as well as landing. Based on the fourth-orderRunge-Kutta method, concrete compute process about airframe position and attitudeangle was put forward.(3)Combined with the newly constructed experiment platform of helicoptersimulator, the dynamic and visual simulation software of the helicopter has beendeveloped. Via Software Multigen Creator,3D visual models of terrain and thehelicopter were established. Adopting technical framework HLA as datacommunication module, we have effectively realized data transfer between flightsimulation subsystem and visual simulation subsystem. Using time advancemechanism from HLA, this paper has effectively prevented the retardance of visualsimulation scene. According to position and orientation parameters of the helicopterand using view drive software OpenGVS, real-time drive of the helicopter has beenrealized on platform VC++6.0. Simulation scene showed this system had excellentfollowing performance and it could meet the requirement of real-time andverisimilitude in the respect of visual simulation for helicopter simulator.Aerodynamic theories of main rotor outlined above have been simulated and verifiedon the experimental platform of helicopter flight simulator. The simulation results andactual flight data have been compared to verify the correctness and practicality ofaerodynamic model and airframe dynamics model presented in this paper. Finally, thetypical flight and landing behaviours of the helicopter have been simulated on thisexperiment platform.The other works of this paper are summarized as follows:(1)The otheraerodynamic forces on the airframe have been modeled. The antitorque andgyroscoopic torque arisen by main rotor, aerodynamic force deriving from tail rotor,aerodynamic drag from the surrounding air on the airframe in the hovering state,vertical climb and descent state have been discussed in detail.(2)The whole planningscheme of simulator has been formulated and scene display subsystem as a part ofvisual simulation system has been designed. According to the design requirements ofsimulator, the overall planning of simulator was given. After the scheme of visualdisplay subsystem was determined, the ball-screen projection system was designed.