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Flight Model modification for Jane’s WWII Fighters
by Joe Hong
Knowing the aircraft’s Alpha allows one to directly compute the Lift/Drag forces from the Axial/Normal forces, and vice versa. The FLT files define CZ as downwards and CX as forwards, while standard aerodynamic practice uses CL upwards and CD opposite the direction of flight.
CL = -CZ cos a CX sin a
CD = -CZ sin a – CX cos a
Conversely
CX = CL sin a – CD cos a
CZ = -CL cos a – CD sin a
Going back to the CX and CZ tables, we see 5 rows of coefficients in each. Let’s take the center rows and perform the computations. (It’s easy when you have a spreadsheet!)
Click to Enlarge Table 1
We then graph the results. The first graph shows the CX/CZ curves, straight from the table, and then the computed CL/CD curve. (CZ has been inverted to provide more clarity in the graph). The second graph is known as the Drag Polar, showing the relationship of drag to the lift being generated by the aircraft’s wing.
P-51D CX/CZ and CL/CD curves
P-51D Drag Polar
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