Christian Grassmann

Thanks a lot Stefan - that helps me to understand and that agrees with a feedback I got from another community. They gave me the advise to make a best estimation via Raymer cause especially in low speed, the simple mathematic model from xfoil struggles. I will try to find the way how to work with that Raymer. best regards Christian

Hello I m Christian, I design an microlight airplane and I use Xflr5 to get the necessary data for lift, velocity etc...in my design I wish to use laminar profiles. I started with the Wortmann FX71 150/30. The stall speed without flaps is 27,67m/s with 16° alpha. When I calculate with 15° flaps, the stall speed reduces only down to 26,81 m/s. Thats marginal and I cannot believe. When I try to calculate with flaps 30° ther comes no calculation result. Then I took another profile, which is used bey...