An investigation of the global effects of the actuation system on the flow field over the NACA-4412 foils has been done as part of our effort to implement real time closed loop separation control using zero net-mass flow actuators. Our approach involves an application to the NACA-4412 foils of the method develop by Honohan et al. (2003) in which Particle Image Velocimetry (PIV) data coupled with the Reynolds Averaged Navier Stokes (RANS) equations to obtain the effect of the flow control actuation on the averaged pressure field. We have demonstrated (Andino et al.2005) the utility of this approach on the NACA-4412 hydrofoil to help us understand the global effects of flow control. A major effect of the actuation on the mean pressure field was backed out from the PIV/RANS approach.