Propeller slipstream model for small unmanned aerial vehicles

Propeller slipstream, or propwash, can significantly affect the aerodynamic characteristics of propeller driven aircraft by providing additional airflow over their aerodynamic and control surfaces. It is therefore essential to have a good knowledge of the induced velocity within the propeller slipstream to determine the aerodynamic forces and moments on slipstream-immersed components. Existing slipstream models based on simple momentum and lifting line theory have limited application since they consider only the acceleration of air within the slipstream and do not take into account the diffusion phenomenon. As such, they yield good results near the propeller where acceleration is dominant but fail to predict induced velocity accurately far behind the propeller where diffusion dominates. This paper presents a slipstream model that takes into account both the acceleration and diffusion phenomena via simple analytical and semi-empirical equations to predict induced velocity accurately up to ~ 8 - 10 propeller diameters downstream of the propeller plane.