What is the principle of insect flapping-wing flight?

The lower membrane wing is used to encourage air to fly, the leather wing is used to protect the wing, and the two pairs of membrane wings flap their wings in waves to ensure the direction of air flow, that is to say, their front wings and rear wings will never be at the highest point or the lowest point at the same time when flying. The structures related to insect flight mainly focus on the chest wing: one or two pairs of wings are attached to the chest wing, which is driven by the backboard to flutter up and down, and the rest muscles control the wings to twist around the torsion axis (the straight line radiating from the wing root to the wing tip), thus generating sufficient lift and thrust. Insect wings are membranous, and tubular veins are hard and elastic, supporting and strengthening the wings. Insect motor receptors are various. In order to control the speed and direction of flight, as well as the attitude of flight, insects need to change the way of wing movement, and some insects can control their own flight by changing the relative positions of their own parts.