Control Surface subsurfaces are unique to the OpenVSP Wing component and are used to define regions where ailerons, flaps, slats, etc. are placed in your model. The VSPAERO solver GUI and the API can also detect these types of subsurfaces and leverage them in vortex-lattice analyses. The region defined by a Control Surface may be tagged inside/outside as with any closed subsurface type and may also be defined on either the upper, lower, or both surfaces. Additionally, Control Surfaces may be tagged to attach at the leading edge rather than the trailing edge, if you wish.
Rather than define the subsurface with length and width in UW, Control Surfaces are defined in the chordwise direction as either a length or fraction of chord and in the spanwise direction by start/end U location. Note that by default, the Control Surface end angles will be automatically set to be aligned with the component X-axis.
The positive direction of control surface rotation will be about the +U axis along the wing. For a +U right-side wing, this means that trailing edge (TE) control surfaces will rotate TE down and leading edge (LE) control surfaces will rotate LE up on the RIGHT side and opposite this convention on the LEFT. It’s worth briefly noting here that the deflection setting in VSPAERO will therefore rotate the control surface in opposite directions like an aileron unless the gain for one surface is set to be negative e.g., VSPAERO > Control Grouping tab > Deflection Gain per Surface. Setting one of the gains to be negative will cause a negative rotation about the axis when a deflection is applied in VSPAERO.