Josselson Robert. Introduction to 6-DOF Simulation of Air Vehicles

Visual Solutions, Inc, 1997. – 24 p.A 6-DOF simulation has 6 degrees of freedom: three rotations and three translations. Since a vehicle both translates and rotates through the air, two coordinate systems keep track of the
vehicle. The first is a known or fixed reference system, referred to here as a local-level coordinate system. The local-level system is a standard, right-hand, three-axis coordinate system with the x-y plane representing the horizontal ground plane; the z-axis is positive down. This is a fixed system that does not translate or rotate. It is commonly thought of as fixed to a flat, non-rotating earth for short duration flights.
The second coordinate system is fixed to the body of the simulated vehicle, referred to here as the body-fixed coordinate system. The x-axis is positive out the nose of the vehicle; the y-axis is positive out the right hand side looking forward; and the z-axis is positive looking down. The origin of the body-fixed coordinate system is located at the center of gravity of the vehicle. Its position is known with respect to the origin of the local-level coordinate system. The attitude of the vehicle is obtained relative to the local-level coordinate system orientation through three rotations known as Euler angles. Direction cosines (or quaternions) keep track of the Euler angles (or attitude) of the vehicle (the attitude of the body-fixed coordinate system) relative to the locallevel coordinate system.Coordinate System and Transformations
Derivation of the Equations of MotionKeeping Track of the True Body Attitude
Euler Angle RatesAerodynamic Forces and Moments
Aerodynamic Coefficients
Gravity
Angles of Attack and Side Slip
Sensed Accelerations
Local-Level Velocity and Position
Environmental Model
Graphical Simulation
Simulation Organization
6-DOF Simulation Implementation in VisSim
Simulation Example
Simulation Enhancements
Monte Carlo Simulations