Hi Ilan,

Thanks a lot for the explanation, i hope i will understand better the relationship between the parameters and the polar, i will study the document you sent...

For the models i made, i used empirical methods like: the lift is in propotion to the wing surface, the drag is in proportion to the drag coefficient, the speed is in proportion to the weight... and so on and i started from one existing model you made, say the cirrus, and noted the stall speed and corresponding sink, the min sink, the ratio speed to sink for several speeds and then was able to draw roughly the polar (speed on x axis and sink on -y axis). Then with the empirical relationship, i tried to modify the parameters to reach a given polar. It's a quite long process. I applied this for the three sailplanes i made: emouchet, asw28 and asg29. I think the result is quite acceptable but i was not fully satisfied.

With your explanation, i will try to do better.

Sincerely