Last time I came to some wrong conclusions about force position relationship with airfoil shape/type. Moving the wing so that its 25% of chord will match approximately plane's CoG did not help much. Due the wing's shape and x-plane's internal calculations other than lift (induced drag etc) I still had to do some guessing on exact distance to shift the wing, including moment coef. Thus I did a little research and found something (http://wright.nasa.gov/airplane/ac.html). In general ALL airfoils for subsonic speeds are considered to have their liftforce at 25% plus a moment the airfoil produces. It is called Aerodynamic Center. And this is exaclty what x-plane expects user to enter. So I moved the wing back to its original position and continued with tuning the lift, drag and moment characteristics of the airfoil.
Based on wing area, desired speed and sink for every 5 km/h step of the speed polar range I calculated desired lift and drag coeficients I want the x-plane to end up. Then I started adding/reducing lift and drag coeficients of the airfoil based on actual results I got from stable glide at given speed. However this is still too much time consuming and I didn't reach my desired accuracy this way so far. As there are not all internal calculations of x-plane's flight model known (at least for me) I cant use exact math here. But I would be satisfied with some approximation of the unknown making difference between wing's lift and drag coefs vs. x-plane's lift and drag coefs. I assume that these differencies will be always same (approximately) at same angle of attack representing the unknown x-plane flight model calculation. I will play with these differences whether as percentages or constant numbers and hopefully get some expected results :)
Thanks for the update. Accuracy is so important especially in a time where most developers are pushing it as never before in X-Plane.
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