FlightGear Newsletter October 2019: Difference between revisions

→‎Support for transonic flow effects in YASim: Prandtl/Glauert plot and warning about supersonic use
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(→‎Support for transonic flow effects in YASim: Prandtl/Glauert plot and warning about supersonic use)
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YASim now supports [[YASim#Surfaces|transonic compressibility effects]] on flight surfaces. Aircraft that fly faster than Mach 0.6 often have supercritical airfoils, where the flow on the upper surface reaches supersonic speeds even if the aircraft itself is below mach 1. These airfoils are optimized for lower drag in this flight regime.
YASim now supports [[YASim#Surfaces|transonic compressibility effects]] on flight surfaces. Aircraft that fly faster than Mach 0.6 often have supercritical airfoils, where the flow on the upper surface reaches supersonic speeds even if the aircraft itself is below mach 1. These airfoils are optimized for lower drag in this flight regime.


YASim now has a parameter "flow" which is valid for wing, mstab, vstab and hstab. If set to "TRANSONIC", YASim applies a Prandtl/Glauert compressibility correction for each surface of the wing which results in more lift above mach 0.6 with a peak at Mach 1 (see figure). The default value is "SUBSONIC" which turns the behavior off and computes just like previous YASim versions. Use this parameter for all jets with supercritical airfoils or anything that flies faster than mach 0.6. The result is a more balanced lift/drag result from the solver.  
YASim now has a parameter "flow" which is valid for wing, mstab, vstab and hstab. If set to "TRANSONIC", YASim applies a Prandtl/Glauert compressibility correction for each surface of the wing which results in more lift above mach 0.6 with a peak at Mach 1 (see figure). The default value is "SUBSONIC" which turns the behavior off and computes just like previous YASim versions. Use this parameter for all jets with supercritical airfoils or anything that flies faster than mach 0.6. The result is a more balanced lift/drag result from the solver. Please do not use this parameter for supersonic aircraft!
 
[[File:Prandtl-glauert-transform.png|thumb|Plot of the subsonic and supersonic Prandtl/Glauert transformation.]]


Also you can specify a critical mach number for each wing (and mstab, vstab, hstab) using the parameter "mcrit". In aerodynamics the critical mach number is the flight mach number above which drag due to mach (also called wave drag) becomes relevant. If flow="TRANSONIC" is set, YASim looks for mcrit (default is 0.6) and adds exponential mach drag above that mach number. The estimation is done by a method according to Perkins and Hage. Future versions may tune and expand this behavior a bit.  
Also you can specify a critical mach number for each wing (and mstab, vstab, hstab) using the parameter "mcrit". In aerodynamics the critical mach number is the flight mach number above which drag due to mach (also called wave drag) becomes relevant. If flow="TRANSONIC" is set, YASim looks for mcrit (default is 0.6) and adds exponential mach drag above that mach number. The estimation is done by a method according to Perkins and Hage. Future versions may tune and expand this behavior a bit.  
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