I have many variables for the CG Calculation from aircraft.cfg and the calculated Total Weight and Total Arm for the B737-800 (FSX default).

Now the question is, what is the fsx ( or AirWrench ) internal formula for the CG % MAC value? I have tried a lot of formula find via Google. But I never have the same resulat as FSX or AirWrench ( B737-800 with EmptyWeight 35.95 % CG MAC).

Also I have try this formula in the AVSIM Documentation "

*fs_flight_dynamics_v1.0"*, but not with the same result as FSX or AirWrench.

As I understood in the "flight dynamic document" is the challange to get the LEMAC ( leading edge MAC ). The basic formula for the CG % is:

Distance to CG - Distance to LEMAC = Distance CG to LEMAC

and

(Distance CG to LEMAC / MAC) * 100 = CG % MAC

For Example Default B737-800, variables given:

wing_span = 117.42 ft

wing_sweep = 27.2°

wing_root_chord = 21.0 ft

wing_area = 1344.0 ft

MAC 14.10 ft ( calculated, same result as AirWrench )

The Calculation:

OK 14,41 ft LEMAC, then I will calculate the CG % MAC from empty weight of the B737-800

Arm = 9 ft

Then the formula for CG% MAC: 9 ft - 14,41 ft = -5,41 ft

And: (-5,41 ft / 14,10 ft) * 100

= -38,64 CG % MAC

This result is not the same as FSX and AirWrench empty weight CG ( 35.95 % ).

Can anyone see the mistake in the calculation ? Thanks in advance for your help !

Best regards

Sebastian