quorneng
Master member
I suspect the oversize fin area is a result of the plane having a low wing loading, a big span and being slow flying which results in a turn having a proportionally smaller radius than would be considered normal. This results in a more pronounced lift differential between the inboard and outboard wings. The inertia from the weight of solar panels spread all over the wing is likely to exacerbate this tendency. Unless the wing has significant dihedral (not ideal with solar panels) this can lead to a turn "auto tightening". The big fin and rudder are required to overcome this effect rather than for the needs of straight line lateral stability.
Just my own conclusion from my past full size glider flying.
Just my own conclusion from my past full size glider flying.