Flight model

Finally! I managed to set the flight model to match the speed polar with acceptable accuracy. What it is acceptable? Well the L/D ratio of the flight model follows the speed polar with max 2.5% error. It means, for example if desired L/D = 43 @ 79 km/h then my flight model is in range +/-1 so the L/D equals say 42. For given speed of 79 km/h the glider should sink about 0.51 m/s. With L/D = 42 it will sink about 0.52 m/s. For now I'm fully satisfied with the result.
All tuning I performed with load of 490 kg (wing load = 28 kg/m2). X-plane flight model calculations seem to do a good job as I found the flight model matches the speed polar also for wing load = 42.8 kg/m2.
Here is the acheived flight model speed polar vs. real life* speed polar for wing load 28kg/m2

Speed polar 28 kg/m2