Please do not take me too serious when I say it is not really a longbow. Therefore I put a smiley after that statement. For all that shoot 3D tornaments I found an interesting rule in the IFAA rule book:
7. Longbow - (L.B.)
a. A one piece straight ended bow of any material, which when strung displays one
continued unidirectional curve, which is measured as follows:
When the strung bow is placed with the bowstring in a vertical position, the angle
as measured between the tangent of any point on the limb and an imaginary
horizontal line must always decrease as this point is moved further away from the
bow grip.