To achieve flight, an insect generates aerodynamic force by flapping its wings. However, this aerodynamic force acting on the wings has not been directly measured during free-flight. In this study, we fabricated an ornithopter modeled on a hawk moth, and attached a MEMS differential pressure sensor on its wing. Then, we measured differential pressure between upper and lower surfaces of the wing during free-flight. Reynolds number of the wing and wing load of the ornithopter were designed to be 4.2 × 103[–], and 7.5[N/m2], which were close to those of a hawk moth. The mass, wing length and flapping frequency were 6.8[g], 110[mm] and 13[Hz], respectively. The maximum differential pressures at the center of the wing were 39[Pa] and 18[Pa] during downstroke and upstroke, which were 5 and 2 times larger than the wing load. The differential pressure contributed vertical pressure of 38[Pa] during downstroke and horizontal pressure of 15[Pa] during upstroke. The time average of vertical differential pressure was 7.0[Pa], which was as large as the wing load of the ornithopter.
