This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift, as well as in cars with aerodynamic wings that redirect air to cause downforce. Samuel Langley noted that flatter plates with a higher aspect ratio had higher lift and lower resistance, they were put into circulation in 1902. Without the invention of the aerodynamic quality of an aircraft, modern aircraft design would have been impossible.
Lifting and moving
The total aerodynamic force acting on the body is usually considered to consist of two components: lifting and moving. By definition, the force component parallel to the oncoming flow is called displacement, while the component perpendicular to the oncoming flow is called lifting.
These basics of aerodynamics are of great importance for the analysis of the aerodynamic quality of the wing. Rise is made by changing the direction of flow around the wing. A change in direction leads to a change in speed (even if there is no change in speed, as is seen with uniform circular motion), which is acceleration. Therefore, changing the direction of flow requires that a force be applied to the fluid. This is clearly visible on any aircraft, just look at the schematic image of the aerodynamic quality of the An-2.
But not so simple. Continuing the theme of the aerodynamic quality of the wing, it is worth noting that the creation of an air lift under it is at a higher pressure than the air pressure above it. On the wing of the final gap, this pressure difference causes air to flow from the root of the lower surface wing to the base of its upper surface. This span airflow combines with flowing air, causing a change in speed and direction that twists the airflow and creates vortices along the trailing edge of the wing. Created eddies are unstable, they quickly combine to create wing eddies. The resulting vortices change the speed and direction of the air flow behind the trailing edge, deflecting it down and thereby causing the valve behind the wing. From this point of view, for example, the MS-21 aircraft has a high level of aerodynamic quality.
Air flow control
Vortex flows, in turn, change the airflow around the wing, reducing the ability of the wing to generate lift, so that it requires a higher angle of attack for the same lift, which tilts the total aerodynamic force back and increases the drag component of this force. Angular deviation slightly affects the rise. However, there is an increase in resistance equal to the product of the lifting force and the angle due to which it deviates. Since the deviation itself is a function of the elevator, the additional resistance is proportional to the angle of elevation, which is clearly seen on the example of the aerodynamic quality of the A320.
Historical examples
The rectangular planetary wing creates stronger vortex vibrations than the conical or elliptical wing, so many modern wings are narrowed to improve aerodynamic quality. However, the elliptical plan shape is more effective, since the induced flushing (and therefore the effective angle of attack) is constant over the entire wingspan. Due to manufacturing difficulties, few planes have this planned form, the most famous examples: Spitfire from the Second World War and Thunderbolt. Conical wings with straight front and rear edges can approach the elliptical distribution of the rise. As a rule, straight wings cut off without a cone produce 5%, and conical wings produce 1-2% more induced resistance than an elliptical wing. Therefore, they have the best aerodynamic quality.
Proportionality
A wing with a high coefficient of proportionality will produce less induced resistance than a wing with a low aspect ratio, since there are fewer air disturbances at the tip of a longer, thinner wing. Consequently, the induced resistance can be inversely proportional to proportionality, however paradoxical it may sound. The distribution of the lift can also be changed by leaching, twisting the wing in a circular fashion to reduce the fall to the wings and by changing the aerodynamic profile near the wings. This allows you to get a greater rise closer to the root of the wing and smaller to the wing, which leads to a decrease in the force of the vortices of the wing and, accordingly, to improve the aerodynamic quality of the aircraft.
In the history of aircraft engineering
On some early aircraft, fins were mounted at the tips of the tails. Later aircraft have a different wing shape to reduce vortex intensity and achieve maximum aerodynamic quality.
Impeller roof fuel tanks can also provide some benefit by preventing the creation of a chaotic airflow around the wing. Now they are used in many aircraft. The aerodynamic quality of the DC-10 in this regard was deservedly considered revolutionary. However, the modern aviation market has long been replenished with much more advanced models.
Aerodynamic formula: simple words
To calculate the impedance, it is necessary to take into account the so-called stray resistance. Since the induced resistance is inversely proportional to the square of the airspeed (for a given rise), while the stray resistance is directly proportional to it, the general resistance curve shows the minimum speed. A plane flying at such speed works with optimal aerodynamic qualities. According to the above equations, the speed of the minimum resistance occurs at a speed at which the induced resistance is equal to the stray resistance. This is the speed at which the optimum sliding angle is achieved for non-operational aircraft. In order not to be unfounded, we consider the formula on the example of an airplane:
The continuation of the formula is also very curious (in the photo below). If you fly higher, where the air is thinner, the speed at which the minimum resistance occurs will increase, and thus, it will allow you to travel faster on the same amount of fuel.
If the plane flies at the maximum permissible speed, then the height at which the air density will provide it with the best aerodynamic quality. Optimum altitude at maximum speed and optimal speed at maximum altitude may vary during flight.
Endurance
Speed for maximum endurance (i.e. time in the air) is speed for minimum fuel consumption and less than speed for maximum range. Fuel consumption is calculated as the product of the required power and specific fuel consumption per engine (fuel consumption per unit power). The required power is equal to the drag time.
History
The development of modern aerodynamics began only in the 17th century, but aerodynamic forces have been used by people for thousands of years in sailing boats and windmills, and images and stories about flights appear in all historical documents and works of art, such as the ancient Greek legend of Icarus and Daedalus. The fundamental concepts of continuum, resistance, and pressure gradients appear in the works of Aristotle and Archimedes.
In 1726, Sir Isaac Newton became the first person to develop a theory of air resistance, making it one of the first discussions of aerodynamic qualities. The Dutch-Swiss mathematician Daniel Bernoulli wrote a treatise in 1738 called Hydrodynamica, which described the fundamental relationship between pressure, density and flow rate for an incompressible flow, known today as the Bernoulli principle, which provides one method for calculating aerodynamic lift. In 1757, Leonard Euler published the more general Euler equations, which can be applied to both compressible and incompressible flows. Euler equations were expanded to include viscosity effects in the first half of the 1800s, which led to the appearance of the Navier-Stokes equations. Aerodynamic performance / aerodynamic performance of the polar was discovered at about the same time.
Based on these events, as well as on studies conducted in their own wind tunnel, the Wright brothers flew on their first plane on December 17, 1903.
Types of aerodynamics
Aerodynamic problems are classified by flow conditions or flow properties, including characteristics such as speed, compressibility and viscosity. They are most often divided into two types:
- External aerodynamics is the study of the flow around solid objects of various shapes. Examples of external aerodynamics are the assessment of lift and drag on an airplane or shock waves that form in front of a rocket’s nose.
- Internal aerodynamics is the study of the flow through passages in solid objects. For example, internal aerodynamics covers the study of air flow through a jet engine or through a pipe for air conditioning.
Aerodynamic problems can also be classified according to the flow rate below or near the speed of sound.
The problem is called:
- subsonic if all speeds in the problem are less than the speed of sound;
- transonic, if there are speeds both lower and higher than the speed of sound (usually when the characteristic speed is approximately equal to the speed of sound);
- supersonic when the characteristic flow rate is greater than the speed of sound;
- hypersonic when the flow rate is much greater than the speed of sound.
Aerodynamics do not agree with the exact definition of hypersonic flow.
The effect of viscosity on flow dictates a third classification. Some problems can have only very small viscous effects, in which case the viscosity can be considered insignificant. Approaches to these problems are called inviscid flows. Streams for which viscosity cannot be neglected are called viscous flows.
Compressibility
An incompressible flow is a flow in which the density is constant both in time and in space. Although all real liquids are compressible, the flow is often approximated as incompressible if the effect of a change in density causes only small changes in the calculated results. This is more likely when the flow rate is much lower than the speed of sound. Compressibility effects are more significant at speeds close to or faster than the speed of sound. The Mach number is used to evaluate the possibility of incompressibility, otherwise compressibility effects should be included.
According to the theory of aerodynamics, the flow is considered compressible if the density changes along the streamline. This means that, unlike an incompressible flow, density changes are taken into account. In general, this is the case when the Mach number in part or in the whole stream exceeds 0.3. The value of Mach 0.3 is rather arbitrary, but it is used because the gas flow with a mark below this value shows a density change of less than 5%. In addition, the maximum 5% density change occurs at the stagnation point (the point on the object where the flow rate is zero), while the density around the rest of the object will be significantly lower. Transonic, supersonic and hypersonic flows - all of them are compressible.
Conclusion
Aerodynamics is one of the most important sciences in the modern world. It provides us with the construction of quality aircraft, ships, cars and comic shuttles. It plays a huge role in the development of modern weapons - ballistic missiles, accelerators, torpedoes and drones. All this would have been impossible if it were not for modern advanced ideas about aerodynamic quality.
Thus, ideas about the subject of the article changed from beautiful, but naive fantasies about Icarus, to functional and really working aircraft that arose at the beginning of the last century. Today we cannot imagine our life without cars, ships and planes, and these vehicles continue to improve thanks to new breakthroughs in aerodynamics.
Aerodynamic qualities of gliders in their time became a real breakthrough. At first, all discoveries in this field were made by abstract theoretical calculations that were torn off from reality by French and German mathematicians in their laboratories. Later, all their formulas were used for other, more fantastic (by the standards of the 18th century) purposes, such as calculating the ideal shape and speed of future aircraft. In the XIX century, these devices began to be built in large numbers, starting with gliders and airships, the Europeans gradually switched to the construction of aircraft. The last first time was used exclusively for military purposes. Ases of the First World War showed how important the issue of air dominance is for any country, and engineers of the interwar period discovered that such aircraft are effective not only for the military, but also for peaceful purposes. Over time, civil aviation has firmly entered our lives, and today not a single state can do without it.