The APM solver supports symmetry solutions across the x-z plane. When using the symmetry option the solver calculates the influence coefficients 2x faster and requires 2x less memory. To enable the symmetry option, set the symmetry option to 1 in the .conf file. Note that any motion that you prescribe (if performing an unsteady simulation) must honour the x-z symmetry requirements. This means no velocity components in the y-direction or non-zero sideslip angle! The image below shows the comparison of the wake between symmetric and non-symmetric solutions.
Symmetric and non-symmetric (not assuming) symmetry of a fixed-wing UAV.