Flying a drone is great fun you can take off, you can hover(float) it turn on any axis you want. But have you ever thought about how the flight dynamics of the drone actually work? 

If you ever found yourself wondering how drones or quadcopters fly, then you are in the right place.

Drones use BLDC (Brushless) motors which are outrunners types, the propeller blades are attached to the cover of the motor. They have three motions Pitch, Roll Yaw.

Airfoil Principle

The propeller blades are the most important part of the drone each cross-section of the blade produces a lift force when air flows over the blade due to the Airfoil principle. The blade is designed in such a way that the lift force produced along the length will be in the same direction on both parts of the blades allowing us to represent the total lift force produced by the drone blade. 

The controller is used to modify the motor speed it is as simple as the greater the Blade Speed, the greater the lift force. 

What makes a drone fly?

During takeoff, just increase the rotor speed as the collective lift force produced by the blades overcomes the weight of the drone. It will lift from the ground this is known as a climbing stage. 

When you have achieved the necessary height you can reduce the rotor speed until the lift force exactly balances the drone weight that doesn't wait there we have it levitation. 

Drone Hovering

Levitation is technically known as Drone hovering in both the drone takeoff and hovering stages all four propellers rotate at the same speed. One diagonally opposite pair of propellers rotates in one direction and the other pair rotates in another direction, it might look strange but if all the propellers were spinning in the same direction then the drone body would have rotated in opposite direction.

Let's see why this is the case, this is because the stator of the motor is attached to the Drone body the rotor of the motor turns because it receives torque from the stator. If we enter Newton's third law of motion, if the motor is receiving torque from the stator, the stator will also receive an equal amount of torque but in the opposite direction of the rotor. If all the rotors are spinning in the same direction the Drone body will receive reaction torque. 

What happens if rotors are spinning in the same direction?

The net effect of these four reaction's torque would force the drone body to turn in the same direction as the reaction torque or in the opposite direction of the propeller rotation. By spinning the propeller pairs in the opposite direction, we make the net reaction torque zero.

Yaw Motion

Interestingly the same physics is used to achieve YAW motion in normal conditions all the blades will be spinning at the same speed, the yaw motion is produced by rotating one diagonal per at one speed and the other pair at a different speed. 

In this case, the reaction torque will not cancel out and the drone body will spin. when you control the yaw stick of the remote control its motion is circular.

Pitching and Rolling

Let's learn about the other two angular motions of the drone Pitch and Roll, the Pitch and Roll of a Drone are controlled by this same yaw stick and they worked based on the same physics.

Pitch Motion

To pitch the Drone forward the front propellers are spun at a lower speed and the back propellers at a higher speed. This creates a different lift force at the front and back and does a net torque the net torque causes the Drone to pitch.

Roll Motion

To roll the drone the same trick is applied but one side pair is spun faster and the other slower. Once again the net torque forces the drone to for a roll motion but to the side pair here.

One interesting thing to know, in both roll and pitch operation even though you are changing the speed of the propellers when you add the reaction torque produced by the motors it becomes zero.

This is the beauty of quadcopter drone design. They make way for stable Drone operation.

How does a drone fly forward?

At the beginning of this article we saw how to climb a Drone, now let's see how the Drone is flown forward or sidewalk. Assume you are facing the Drone forward after you achieve the desired pitch angle you brought the propeller speeds to the same value so that it won't pitch further, the Drone cannot balance at the tilted angle. 

To balance the drone we have to first balance the gravitational force suppose the propeller speed is such a way that the vertical component of the propeller force balances the weight, here comes the issue the propeller force has a horizontal component as well even though the vertical forces are balanced. 

The  unbalanced horizontal force will move the drone horizontally which will cause a drag force on the drone's body, the Drone will increase its speed horizontally until the drag force matches the horizontal force, 

In short, to fly the Drone forward you just pitch down the Drone and balance it vertically the Drone does the rest automatically moving forward. To get the side motion the same mechanics are used roll the drone toward one side and balance it vertically.

Is it possible to move the Drone in a perfect circle?

The answer is yes the answer lies in the physics of circular motion, Let's brush up on the basic principles Consider an object moving in a straight line when acted on by a force that is always perpendicular to its velocity the object will turn in a circle. 

For example, you can make the Drone move straight by pitching it down, now if you roll the Drone down you can easily produce a force perpendicular to the Drone's velocity, this will make the drone turn in a circle. 

I hope you have enjoyed learning about the interesting flight dynamics of the quadcopter drone.

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