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JSBSim Aerodynamics: Difference between revisions
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== Forces == | == Forces == | ||
For purposes of the Aerodynamics section the entire aircraft creates a single, unified aerodynamic force. This force is split into three component vectors. The most common way of splitting this force into vectors is the Lift Drag Side method. Another, potential better way from the perspective of generating a full 360 degree capable [[FDM]], is the Normal, Axial, Side method. | For purposes of the Aerodynamics section the entire aircraft creates a single, unified aerodynamic force. This force is split into three component vectors. The most common way of splitting this force into vectors is the Lift Drag Side method. Another, potential better way from the perspective of generating a full 360 degree capable [[FDM]], is the Normal, Axial, Side method. | ||
* '''Lift: CL''' Lift is the portion of the aerodynamic force that is at a right angle to the relative wind, | * '''Lift: CL''' Lift is the portion of the aerodynamic force that is at a right angle to the relative wind '''and''' lies within the aircraft's symmetry plane (body x-z-axis plane) '''and''' is oriented towards the aircraft's upside. (During inverted flight, it points to the ground). | ||
** Lift is a function of QBar * Wing Area * Cl<sub>lift</sub>. Cl<sub>lift</sub> is generally derived from a 2D table as a function of AoA. In the real world it is also a function of the Reynolds and Mach Numbers. | ** Lift is a function of QBar * Wing Area * Cl<sub>lift</sub>. Cl<sub>lift</sub> is generally derived from a 2D table as a function of AoA. In the real world it is also a function of the Reynolds and Mach Numbers. | ||
* '''Drag: CD''' Drag is the portion of the aerodynamic force that is parallel to the relative wind. | * '''Drag: CD''' Drag is the portion of the aerodynamic force that is parallel to the relative wind. | ||
** It is important to ensure all coefficient functions in the drag section remain positive. When drag coefficient functions are negative, drag is effectively acting as thrust opposite the relative wind. | ** It is important to ensure all coefficient functions in the drag section remain positive. When drag coefficient functions are negative, drag is effectively acting as thrust opposite the relative wind. | ||
* '''Side: CY''' Side is the portion of the aerodynamic force that is at a right angle to the | * '''Side: CY''' Side is the portion of the aerodynamic force that is at a right angle to both the Lift and the Drag vector. It usually points to the aircraft's right side. | ||
This system was developed by and for people using wind tunnels. Lift is to the top of the wind tunnel, drag is out the back and side is to the side. As a real aircraft in free space yanks and banks it | This system was developed by and for people using wind tunnels. Lift is to the top of the wind tunnel, drag is out the back and side is to the side. As a real aircraft in free space yanks and banks it may become ambiguous which direction the forces are applied. If an aircraft's body-x-axis is oriented exactly perpendicular to the relative wind, the definitions given above cannot be applied. | ||
Enter the Axial, Normal, Side system. | Enter the Axial, Normal, Side system. | ||