Principles of flight with drones
In this blog, I am going to explain the knowledge of what keeps an aircraft in the air without going into too much detail. I will explain both the theory of flight, the forces acting upon a flight and how they interact and play of one another. This blog will cover all types of aircraft, whether that be a fixed wing or propeller, they all work the same when it comes to the aerodynamics of the surfaces of the wings/propellers. As this blog is based on drones we will look at it as a propeller as opposed to a fixed wing.
The four forces
When an aircraft is in flight, there are four primary forces that act upon it, Weight, Lift, Drag and Thrust. Weight is the force applied to an object because of gravity pulling it to the centre of the earth. Lift is an aerodynamic force produced from the flow of air through a drone’s propellers. Drag is basically air resistance caused when the drone is flying through the air which opposes the movement of the drone and acts upon it on the opposite direction of flight. Thrust is the force produced by the propulsion system of the drone. The amount of thrust generated will all depend on the location of the propellers and in most cases, the direction of thrust will be at 90 degrees. Obviously with all this being said, for a drone to fly properly the lift must be greater than the weight and the thrust must be greater than the drag.
Factors that can help lift a drone
There are many factors that can help increase the lift when it comes to flying. This can be determined from both human corrections or the environment itself. Air density is something that will affect the lift of an aircraft and something that humans can control. If we fly in denser air, then more air molecules within the air flow through the propeller increasing the amount of lift. This all depends on temperature and altitude where if we increase either the air density decreases. On a hot day or in high altitudes the performance of the drone will be reduced. Airspeed is a massive factor when it comes to increasing lift, maybe one of the biggest. By increasing this you are increasing the downward flowing air and therefore the lift. Also, the design of a wing can affect the lift it generates. Without going in too much detail the wing area, shape and thickness can all affect how efficiently the air moves through the propeller.
Different types of drag
Drag is the resistance of movement of an object through the air such as a drone. Parasite drag is the term used and the drag created by the physical shape of an object. This means an object with a larger frontal face will be affected more by parasite drag. This is why propellers are made with a streamlined shape in order to decreased parasite drag. Obviously, every object will take some sort of skin friction but it is something that can be reduced. Induced drag is another form of drag which is formed due to a spillage of air around the propeller tip. This is caused by air flows colliding and causing strong voices, therefore creating drag.
Mass and Centre of Gravity
The CofG is the average location at which the weight of the drone is. An unbalanced centre of gravity can really affect the stability of the drone. For example, if the weight was heavier on the left-hand side of a drone then the propellers on that side would have to work harder as well as opposed to the other ones in order to maintain a centre of gravity.
Angle of attack
The angle of attack is basically the angle at which the wing or propeller attacks the air to generate lift. The bigger the angle the greater the lift however when the angle becomes too big the aircraft can go into aerodynamic stall. The propellers on a drone have introduced a twist along the length of the blade so that it has the same angle of attack throughout.