Flight principle and hardware configuration of multi-rotor UAV

Bernoulli effect: the air flow between two papers is large, the pressure is small, and the two papers are close to each other.

Bernoulli's principle was put forward by Swiss daniel bernoulli in 1726, and it is a dynamic equation of ideal fluid steady flow. It is explained that the sum of pressure potential energy, kinetic energy and position potential energy at any two points on the streamline of incompressible fluid remains unchanged when the viscosity loss is ignored.

Its essence is the conservation of mechanical energy of fluid, that is, kinetic energy+pressure potential energy+position potential energy = constant. When the fluid flows at the same height, the pressure is small when the velocity is large, and the pressure is large when the velocity is small. The wing is subjected to upward lift.

It can be seen from the shape of the cross section of the wing that the top is convex and the bottom is flat, which makes the airflow streamline above the wing dense, the velocity is large, and the streamline below is sparse and the velocity is small when the aircraft moves forward. According to Bernoulli's principle, the pressure above the wing is small and the pressure below is strong. In this way, the plane is lifted off by the pressure difference between the air and the plane.

However, the upward radian of aircraft airfoil is only within a certain range, and the greater the radian, the greater the lift-drag ratio. Once it exceeds this range, the resistance increases rapidly, but the lift-drag ratio decreases.

The control principle of quadcopter is that when there is no external force and the weight distribution is even, the four propellers rotate at the same speed. When the upward pull of the propeller is greater than the weight of the whole machine, the four axes will rise, and when the pull is equal to the weight, the four axes can hover in the air. When the front of the four axes is subjected to downward external force, the front motor speeds up the rotation speed to offset the influence of the external force so as to keep the four axes horizontal. Similarly, when it is necessary to control the four axes to fly forward, the front motor slows down and the rear motor accelerates, so that the four axes will tilt forward and fly forward accordingly. Similarly, We need to fly backwards, leftwards and rightwards, so that the four axes can fly in the direction we want to control. When we want to control the head direction of the four axes to rotate clockwise, the four axes will speed up the rotation speed of the left and right motors at the same time, and reduce the rotation speed of the front and rear motors at the same time. Because the left and right motors rotate counterclockwise, the rotation speed of the left and right motors is the same, so the left and right are balanced, while the front and rear motors rotate clockwise. But the speed of the front and rear motors is the same, so the front, rear, left and right can be balanced and the flying height can be maintained, but the force of counterclockwise rotation is greater than that of clockwise rotation, so the fuselage will rotate in the opposite direction, so as to control the direction of the nose. That's why we use two reverse paddles and two forward paddles.