How a wing helps airplanes fly. Short Course in Aerodynamics
Remember Lilienthal, who sacrificed his own life, opening a huge path to aviation. Many engineers and inventors before him had tried to conquer the air by imitating the movement of birds. These parts have been given a scientific name: ornithopters. Despite the inconsistency of the theory of “flapping wings”, the first rudiments of aerodynamics of aircraft were laid. Nowadays, all aviation is built on the principles of flight thanks to aerodynamics, so in this article I will explain in the most accessible way what rules an airplane flies.
First there were gliders and airplanes. The founder of this theory was the Englishman George Cayley, who guessed that it was more rational to use a flat and fixed wing to separate the lift and push force. Externally, it was a simple plywood sheet, which was located at a certain angle to the incoming stream. This angle was called the angle of attack. He also expressed the idea that for the stability of the flight, the airplane would need horizontal and vertical tails.
A little later, it became clear that a completely flat wing has minimal lift. Moreover, such a wing was highly susceptible to bending, so the following designs of airplanes had a convex upper part and a concave lower part. And the leading and trailing edges of the wing began to be rigidly fastened so that in flight the structure was in the same position, with a zero angle of attack.
In 1884, another Englishman, Horatio Phillips, came up with the idea of scientifically studying various sections of the wing, for which, in the same year, he received his first patent. Its wing was already similar to the modern one: a rounded leading edge of the wing, a thickened central section and a sharp trailing edge.
By the 1930s, it had become clear that Horatio Phillips’s idea was the dominant and most rational one. In pursuit of an increase in lift, aircraft designers began to detach not one, but two. This is how the first biplanes appeared. However, too many bearing surfaces reduced the speed of the aircraft. This is due to the “increased friction force” of the leading edges of the wing, so the idea of biplanes began to be abandoned in favor of monoplanes (“mono” – one), having only one wing.
Now that we’re done with the story, let’s move on to the topic of the aerodynamic operation of the wing. In an ideal airflow, the molecules move uniformly and in a straight line, but the behavior of the air changes dramatically as it approaches the leading edge of the wing. Due to the peculiarity of the wing profile, the air from above (the convex part of the wing) passes at a higher speed than from below. The air flow, by virtue of its peculiarities and by virtue of Bernoulli’s laws, has a constant pressure at each of its points.
At high speeds, air acquires the properties of a liquid. When the airflow line shifts (or, in simple words, when it meets the leading edge of the wing), the air changes its pressure. At the leading edge of the wing, the air pressure drops as the air molecules are somewhat inhibited, forming a rarefied zone. The air from below moves more slowly, but at the same time almost does not change its pressure, so the pressure from below is higher than at the upper edge of the wing, so the air below pushes the wing up. This force is called lifting. All the resulting force vectors are called the total lift.
In future articles, I will talk in more detail about how wing mechanization tools work, which not only increase lift, but also increase the load-bearing properties of the wing. In short, these include: slats, flaps, spoilers, brake flaps (air brake), ailerons, flaperons, etc. And many thanks to the excellent teacher of aerodynamics of the aircraft: Nosov Arkady Vasilyevich.