Aerodynamics is a field of knowledge that studies the movements of air currents and their effects on solids. It is a subsection of hydro and gas dynamics. Research in this area dates back to antiquity, to the time of the invention of arrows and planning copies, allowing further and more accurately send a projectile at a target. However, the potential of aerodynamics was fully revealed with the invention of vehicles heavier than air, capable of flying or planning over considerable distances.
From ancient times
The discovery of the laws of aerodynamics in the 20th century contributed to a fantastic leap in many fields of science and technology, especially in the transport sector. On its achievements, modern aircraft have been created, which made it possible to make virtually every corner of the planet Earth public.
The first mention of an attempt to conquer heaven is found in the Greek myth of Icarus and Daedalus. Father and son built bird-like wings. This indicates that thousands of years ago, people thought about the possibility of breaking away from the earth.
Another surge in interest in the construction of aircraft arose in the Renaissance. Passionate researcher Leonardo da Vinci devoted much time to this problem. His records are known in which the principles of the operation of a simple helicopter are explained .
New era
A global breakthrough in science (and aeronautics in particular) was made by Isaac Newton. Indeed, aerodynamics is based on the comprehensive science of mechanics, the founder of which was an English scientist. Newton was the first to consider the air as a conglomerate of particles that, running on an obstacle, either stick to it or are elastically reflected. In 1726, he presented to the public the theory of air resistance.
Subsequently, it turned out that the medium really consists of the smallest particles - molecules. The air reflective ability to count was learned quite accurately, and the effect of “sticking” was considered an invalid assumption.
Surprisingly, this theory has found practical application after centuries. In the 60s, at the dawn of the space era, Soviet designers were faced with the problem of calculating the aerodynamic drag of descent vehicles of a "blunt" spherical shape, upon landing, developing hypersonic speeds. Due to the lack of powerful computers, calculating this indicator was problematic. It suddenly turned out that it is possible to accurately calculate the resistance value and even the pressure distribution over the frontal part using the simple Newton formula regarding the effect of particles “sticking” to a flying object.
Aerodynamics development
The founder of hydrodynamics, Daniel Bernoulli, described in 1738 the fundamental relationship between pressure, density and speed for an incompressible flow, known today as the Bernoulli principle, which is also applicable to calculations of aerodynamic lift. In 1799, Sir George Cayley became the first person to identify the four aerodynamic forces of flight (weight, lift, drag and thrust), as well as the relationship between them.
In 1871, Francis Herbert Wenham created the first wind tunnel to accurately measure aerodynamic forces. Invaluable scientific theories developed by Jean Le Rond Dalamber, Gustav Kirchhoff, Lord Rayleigh. In 1889, Charles Renard, a French aeronautical engineer, became the first person to scientifically calculate the power needed for a stable flight.
From theory to practice
In the 19th century, inventors looked at the wing from a scientific point of view. And thanks to studies of the flight mechanism of birds, aerodynamics in action was studied, which was later applied to artificial aircraft.
Otto Lilienthal succeeded particularly in studies of wing mechanics. The German aircraft designer created and tested 11 types of gliders, including a biplane. He made the first flight on the device heavier than air. For a relatively short life (46 years), he made about 2000 flights, constantly improving the design, which looked more like a hang glider than an airplane. He died during a regular flight on August 10, 1896, becoming both the pioneer of aeronautics and the first victim of a plane crash. By the way, one of the gliders, the German inventor personally handed over to the pioneer in the study of the aerodynamics of aircraft Zhukovsky Nikolai Egorovich.
Zhukovsky did not just experiment with aircraft designs. Unlike many enthusiasts of that time, first of all, he considered the behavior of air flows from a scientific point of view. In 1904, he founded the world's first aerodynamic institute in Kachino near Moscow. Since 1918 he headed TsAGI (Central Aerohydrodynamic Institute).
First planes
Aerodynamics is a science that allowed a person to conquer the sky. Without studying it, it would be impossible to build aircraft stably moving in air currents. The first aircraft, in the usual sense of the word, was made and lifted by the Wright brothers on December 7, 1903. However, this event was preceded by a thorough theoretical work. The Americans devoted much time to debugging the design of the airframe in a wind tunnel of their own design.
During the first flights, Frederick W. Lanchester, Martin Wilhelm Kutta, and Nikolai Zhukovsky put forward theories that explained the circulation of air currents that create lift. Kutta and Zhukovsky continued to develop a two-dimensional theory of the wing. Ludwig Prandtl is credited with developing the mathematical theory of subtle aerodynamic and lift forces, as well as working with boundary layers.
Problems and Solutions
The importance of aircraft aerodynamics increased as their speeds increased. Designers began to face problems associated with compressing air at a speed close to or greater than the speed of sound. Differences in flow under these conditions led to problems in controlling the aircraft, an increase in resistance due to shock waves, and the threat of structural failure due to aeroelastic flutter. The ratio of the flow velocity to the speed of sound was called the Mach number by the name of Ernst Mach, who was one of the first to study the properties of supersonic flow.
William John McQuorn Rankin and Pierre Henri Gugoniot independently developed a theory of the properties of air flow before and after a shock wave, while Jacob Akeret conducted the initial work on calculating the lift and drag of supersonic aerodynamic surfaces. Theodor von Karman and Hugh Latimer Dryden coined the term “transonic” to describe speeds at Mach 1 (965-1236 km / h) when resistance increases rapidly. For the first time, the sound barrier was overcome in 1947 on a Bell X-1 aircraft.
Main characteristics
According to the laws of aerodynamics, to ensure flight in the atmosphere of the earth of any vehicle, it is important to know:
- Aerodynamic drag (X axis) provided by air currents on an object. Based on this parameter, the power of the power plant is selected.
- Lifting force (Y axis), which provides climb and allows the device to fly horizontally to the surface of the earth.
- Moments of aerodynamic forces along three coordinate axes acting on a flying object. The most important is the moment of lateral force along the Z axis (Mz), directed across the aircraft (conventionally along the wing line). It determines the degree of longitudinal stability (whether the device will “dive” or lift its nose up during flight).
Classification
Aerodynamic characteristics are classified according to the conditions and properties of the air flow, including speed, compressibility and viscosity. External aerodynamics is the study of the flow around solid objects of various shapes. Examples are the assessment of the lift and vibration of an airplane, as well as the shock waves that form in front of the nose of a rocket.
Internal aerodynamics is the study of air flow moving through openings (passages) in solid objects. For example, it covers the study of flows through a jet engine.
Aerodynamic performance can also be classified according to flow rate:
- Subsonic is the speed lower than the speed of sound.
- Transonic (transonic) - if there are speeds both lower and higher than the speed of sound.
- Supersonic - when the flow rate is greater than the speed of sound.
- Hypersonic - the flow rate is much greater than the speed of sound. Usually, this definition means speeds with Mach numbers above 5.
Helicopter aerodynamics
If the principle of flight of an aircraft is based on the lifting force during the translational movement exerted on the wing, then the helicopter itself creates a lifting force due to the rotation of the blades in the axial blow mode (i.e., without translational speed). Thanks to this feature, the helicopter is able to hang in the air in place and perform vigorous maneuvers around the axis.
Other applications
Naturally, aerodynamics is applicable not only to aircraft. Air resistance is experienced by all objects moving in space in a gas and liquid medium. It is known that aquatic inhabitants - fish and mammals - have streamlined forms. On their example, aerodynamics can be traced in action. Focusing on the animal world, people also make water transport pointed or teardrop-shaped. This applies to ships, boats, submarines.
Vehicles experience significant air resistance: it increases with increasing speed. To achieve the best aerodynamics, cars are streamlined. This is especially true for sports cars.