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JSBSim Aerodynamics: Difference between revisions
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== Effects == | == Effects == | ||
* Stall - A 'stall' is generally regarded as a loss of lift due to flow separation over the top of a wing, however, examination of lift polar for an airfoil over a full 360 degrees shows that significant amounts of lift are NOT lost as the stall occurs. The biggest aerodynamic effect of a stall is a large and rapid increase in drag. | * '''Stall''' - A 'stall' is generally regarded as a loss of lift due to flow separation over the top of a wing, however, examination of lift polar for an airfoil over a full 360 degrees shows that significant amounts of lift are NOT lost as the stall occurs. The biggest aerodynamic effect of a stall is a large and rapid increase in drag. | ||
* '''Spin''' - Spins are caused loss of stability in the Yaw Moment axis. A stock [[Aeromatic]] [[FDM]] yaw section does not take alpha into account when calculating the yaw moment. | |||
* Spin - Spins are caused loss of stability in the Yaw Moment axis. A stock [[Aeromatic]] [[FDM]] yaw section does not take alpha into account when calculating the yaw moment. | * '''Faking lift polars''' - If we assume a symmetrical airfoil that stalls at +/- 15 degrees (0.26 radians) AoA and assume the lift is linear between the two we can create a table like: | ||
<syntaxhighlight lang="xml"> | |||
* Faking lift polars - If we assume a symmetrical airfoil that stalls at +/- 15 degrees (0.26 radians) AoA and assume the lift is linear between the two we can create a table like: | |||
<table > | <table > | ||
<independentVar lookup="row">aero/alpha-rad</independentVar> | <independentVar lookup="row">aero/alpha-rad</independentVar> | ||
| Line 58: | Line 57: | ||
</tableData> | </tableData> | ||
</table> | </table> | ||
</syntaxhighlight> | |||
Beyond +/- 22.5 degrees AoA we'll use 0.26 * sin(2*AoA) to approximate lift, and linear interpolate between 15 and 22.5 degrees AoA. (These numbers are rather arbitrary.) The resultant table returns the same value as alpha-rad for the "stable" flight regime so the function will accept the [[aeromatic]] coefficient. Outside of the "stable" flight regime a better number will be used allowing more realistic flight behavior at high alpha or beta angles. | Beyond +/- 22.5 degrees AoA we'll use 0.26 * sin(2*AoA) to approximate lift, and linear interpolate between 15 and 22.5 degrees AoA. (These numbers are rather arbitrary.) The resultant table returns the same value as alpha-rad for the "stable" flight regime so the function will accept the [[aeromatic]] coefficient. Outside of the "stable" flight regime a better number will be used allowing more realistic flight behavior at high alpha or beta angles. | ||