Hi OSTexo

Other than the fin for yaw damping the fuselage has little impact on the aerodynamics of the glider (its all about the wing).

Smooth lines do however reduce parasitic drag of the interface between the fus and wing and also look cool :-) . Practically speaking the fus is there to: provide a tail to mount a vertical stabiliser (fin) to , and provide a nose to add lead to balance the glider around its CG (centre of gravity). Longer the nose the greater the leverage, so less weight required.

Cheers & tnx again.