In the case of unsteady loading conditions at a rotor, the induced velocity response lags the thrust coefficient at the rotor. The two parameters that are responsible for unsteady loading conditions are rotor thrust (due to blade pitch, or rotational speed) and incoming wind speed. The induced velocity response to these two sources of unsteadiness have been compared in a free wake vortex ring model. It was found that a varying wind speed has a non-negligible dynamic inflow effect, and the effect is different from varying rotor thrust. Additionally, current engineering models are incapable of capturing this difference. Recently a new engineering model was proposed at the TU Delft by Wei Yu, and this model is extended such that it is able to distinguish between the response to dynamic wind and to dynamic thrust.