Physics is the science that aims to describe and quantify natural phenomena. While some argue that physics is the science upon which every other discipline is built, there is no doubt that it is of predominant concern in aviation. In fact, every second of a flight can be modeled and described using the concepts of physics. If you are interested in aviation, this blog will prime you on some essential physics ideas on how engineered flight is achieved.
The concept of flight describes an interplay between four forces. Before trying to comprehend these topics, it is first essential to understand what force is. In physics, the most simple definition of a force is mass x acceleration, commonly written as F=ma. Mass is reported in kilograms (kg), with an average commercial jet being 80,000 kg. Acceleration, with regards to flight, may be experienced in 4 different directions. Tying these concepts together, we are left with the fundamental flight theory, which describes the relationship between thrust, lift, weight, and drag.
In order to increase altitude, the magnitude of an aircraft's lift must overcome that of its weight. Weight may be calculated using the aforementioned F=ma equation, with the numerical value for acceleration being 9.8m/s^2, which is the acceleration due to gravity. For an 80,000kg aircraft, the weight would be 784,000N, with "N" being the standard unit of force. On the other hand, lift is a more complicated force to quantify. Its equation is (1/2)(p)(v^2)(s)(CL), where "p" is the density of air, "v" is the aircraft's velocity, "s" is the area of the wings, and "CL" is the coefficient of lift. With this in mind, the optimal flight configuration would be an aircraft with large wings
moving fast through dense air while maintaining a high angle of attack.
Drag and thrust are the other crucial opposing forces to understand. T move forward, the force of thrust must overcome drag, similar to the previous variables. Therefore, the equation for drag is (Cd)(p)(v^2)(.5)(A), where "Cd" is an experimental coefficient, "p" represents density, "v" is for velocity, and "A" defines the overall area of the vessel. Interestingly, density and velocity, which one may assume would have a negligible impact on a backward force, play significantly into the magnitude of drag. Thrust, which must overcome forces produced by drag, is challenging to model because it varies between propulsion methods. For example, the general equation for a jet engine
is (m)(v2-v1), where "m" is the mass of air entering the intake area, and the two velocities represent the speed of air entering the engine and the speed of exhaust exiting it.
Another phenomenon to appreciate in aviation physics is the nature of air and how it changes under varying temperatures and altitudes. In this domain, density and pressure share an important connection. Particularly, density is inversely proportional to altitude due to the fact that air molecules are less concentrated at higher elevations, decreasing their mass over a given volume. This, in turn, ties directly into pressure because it increases or decreases linearly with density. Finally, due to the similar relationship between pressure and temperature, aircraft are exposed to much colder conditions as they climb.
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