Investigation on propulsion of flapping wing with modified pitch motion

Purpose - With possible practical application in a micro aerial vehicle (MAV), propulsion characteristics of a flapping wing with modified pitch motion are investigated both theoretically and experimentally in this paper. Design/methodology/approach - Modified pitch motion is defined as a sinusoidal pitch motion with the pitch axis outside the wing chord line. Based on the momentum theory, an analytical model is developed to analyze the propulsion characteristics of the defined flapping wing. Following that, a water tunnel study of the effects of pitch axis distance, pitch frequency, and stream velocity on thrust generation is carried out. Thrust is directly measured using a 1-D load cell and the flow visualization is captured using a high speed video camera. Findings - It is found that shifting pitch axis outside wing chord line benefits the thrust generation significantly. Positive average thrust is produced at a relatively low frequency and increases almost quadratically with the motion frequency. The effect of stream velocity on the thrust time history is signified but has little effect on the average thrust magnitude. Practical implications - Compared to other types of flapping wing motions, the proposed flapping can be achieved with simple mechanism and thus has the edge in practicality for propelling MAV or other submarine systems. Originality/value - The paper provides useful aerodynamic characteristics of a type of flapping wing motion which possesses mechanical simplicity and relatively large thrust generation at low-flapping frequency. This flapping wing has the potential to provide propulsion for a MAV or other submarine systems.