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Page 4

Flight Model modification for Jane’s WWII Fighters
by Joe Hong

So to make the flight models in WW2F more realistic, we need to make corrections to each aircraft’s lift/drag characteristics. All we have to do now is find the real lift/drag curves for each aircraft, then encode them back to the FLT files, right?

Unfortunately, this data for all WW2F aircraft is almost impossible to find anywhere. There is a lot of test data that is available for the Mustang, but they are not comprehensive. For instance, the data of the P-51D wind tunnel tests do not cover much of the range in the FLT file tables. This problem only increases for the British and German aircraft.

Therefore, any modification of the FLT tables will rely on some educated guesswork. The best anyone can do is to benchmark the flight parameters by concentrating first on the Mustang, and then applying the same procedures to the other planes and comparing performance. As an example of this difficulty, let’s take again the basic lift/drag curve for the Mustang.

We can correct this curve, either by copying the wind tunnel lift/drag coefficients straight then extrapolating the values at other alphas, or by merely scaling up the existing drag values. Once we do the correction, we can compute the CX/CZ coefficients for the center row. Now, what do we do with the four other rows? Multiple approaches are possible, but there is little data out there to guide us to the correct procedure.

My suggested procedure is this: keep the current Lift coefficients as they are. The lift values are generally in agreement with actual flight data. (I will prove this below.) The drag values indeed are too low. The only consistent and reliable procedure to use here is to multiply all the CD values in the curves, except for the min CD value, by some scale factor to produce a steeper parabolic curve. (A simple program can be written to process the CX/CZ tables in the FLT files to increase the drag values. We’ll see what magic programs the flight model experts out there come up with.)

We can prove that the max CL in the original FLT file is comparable to the max CL of the real aircraft. This allows us to accept the CL curve in the FLT file and focus on the CD curve. We know the stall speeds of the actual aircraft, plus a lot of their stats like wing area and basic weight. We can compute the max CL as follows. For a one-G stall condition (clean), Lift = Weight, therefore:

W = 0.5 r v2 S CLreal

Thus, CLreal = 391.162 W / (V2 S) where W is in pounds, V is in mph, and S is in square feet.

Numerical example: P-51D at 8000 lbs. One G stall speed clean w/ wing racks) is 94 mph, and S = 235 sq. ft.,

CLreal = 391.162 * 8000 / (942 * 235) = 1.5

The max CL from the P51.FLT file is about 1.55, which is acceptably close to the above number. Computations using the P-51’s 2.5G stall and 4G stall produce basically the same max CL. Similar results can be obtained with the other WW2F aircraft as well.

 

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