Forces of Flight



The flight of any airborne machine is the result of several forces. The four main forces, commonly referred to as the four forces of flight, are thrust, lift,  weight, and drag. The combined effect of these forces enables an aircraft to fly in the air. It is much easier to describe and understand the four forces of flight using the example of an airplane. We will first use an airplane to describe these forces before returning to quadcopters to explore their similarities and differences. To comprehend how a flying machine operates, it is essential to understand these forces and how they are controlled in various types of flying machines.


1. Thrust


Thrust is the forward-pushing force generated by the airplane's engines. In the case of jet engines, it is generated through the expulsion of air or exhaust gases at high velocities. And, in propeller-driven aircraft, propeller blades are responsible for generating thrust. This expulsion of gases, for example, in jet engines, creates a reactionary force, pushing the airplane forward. It is necessary for overcoming drag and achieving or maintaining forward motion. Thrust can be explained by Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction. In the context of an aircraft's jet engine, the action is the expulsion of gases at high speeds, and the reaction is the generation of thrust, pushing the aircraft in the forward direction. It is important to understand that thrust does not directly generate lift, but it does affect airflow patterns around the aircraft, indirectly assisting the wings in generating lift. Generally, thrust is directly proportional to aircraft speed, which in turn increases aerodynamic forces, i.e., lift and drag. Thrust is opposed by drag, which we will be discussing in a moment.


2. Lift


Lift is the force that allows flying machines to overcome gravity and stay aloft. Most of the lift is generated by the wings of an aircraft, but it is not true to say that lift is only generated by the wings. The entire aircraft generates lift to some extent, but the main and essential components that generate lift and keep an aircraft aloft are the wings. When an aircraft's engines produce thrust, and the aircraft begins to move forward, the airflow over the wings increases as a result. As the aircraft moves through the air, the wings create an area of lower pressure above and higher pressure below. This happens due to the purpose-built shape of the wings. The air passes faster over the top of the wings compared to the lower side of the wings, resulting in lower pressure above. This lower-pressure area above the wings effectively "sucks" the aircraft upward. This suction effect is a crucial component of lift generation. The faster the aircraft moves through the air, facilitated by thrust, the more pronounced this effect becomes.