INSTRUCTIONS AND PROPHECIES OF THE Blessed MOTHER ALIPIA GOLOSEEVSKY, Kyiv...
1. The movement of the vehicle is associated with the movement of air particles, which consumes part of the engine power. These costs are made up of the following:
2. Drag, which appears due to the pressure difference in front and behind a moving car (55-60% of air resistance).
3. Resistance created by projecting parts - rear view mirror, etc. (12-18%).
4. Resistance arising from the passage of air through the radiator and engine compartment.
5. Resistance due to friction of nearby surfaces on air layers (up to 10%).
6. Resistance caused by the pressure difference between the top and bottom of the car (5-8%).
To simplify the calculations of air resistance, we replace the resistance distributed over the entire surface of the car with the force of air resistance applied at one point, called sail center car.
It has been established by experience that the force of air resistance depends on the following factors:
On the speed of the car, and this dependence is quadratic;
From the frontal area of the car F;
From the coefficient of streamlining K in, which is numerically equal to strength air resistance created by one square meter frontal area of the vehicle when moving it at a speed of 1 m/s.
Then the air resistance force .
When determining F use empirical formulas that determine the approximate area of resistance. For trucks F usually: F=H×B(the product of height and width), similarly for buses. For cars accept F=0.8H×B. There are other formulas that take into account the track of the car, the probability of changing the height of the vehicle, etc. K in ×F called streamlining factor and denote W.
To determine the streamlining coefficient, special devices are used or the coast-down method, which consists in determining the change in the path of a free-rolling car when moving at different initial speeds. When a car moves in an air stream, the force of air resistance R in can be decomposed into components along the axes of the ATS. At the same time, the formulas for determining the projections of forces differ only in coefficients that take into account the distribution of force along the axes. The streamlining coefficient can be determined from the expression:
where C X is a coefficient determined empirically and taking into account the distribution of the air resistance force along the "x" axis. This coefficient is obtained by blowing in a wind tunnel, 
;
r - air density, according to GOST r \u003d 1.225 kg / m 3 at zero.
We get 
.
The product is a velocity head equal to the kinetic energy cubic meter air moving at the speed of the car relative to the air.
Coefficient K in has dimension .
Between K in and C X there is a dependency: K in \u003d 0.61С X.
The trailer on the vehicle increases the drag force by an average of 25%.
All components of air resistance are difficult to determine analytically. Therefore, in practice, an empirical formula has been used, which has the following form for the range of speeds characteristic of a real car:
where With X - size free airflow coefficient, depending on the shape of the body; ρ in - air density ρ in \u003d 1.202 ... 1.225 kg / m 3; BUT- midsection area (transverse projection area) of the car, m 2; V– vehicle speed, m/s.
Found in the literature air resistance coefficient k in :
F in = k in BUTV 2 , where k in = with X ρ in /2 , - air resistance coefficient, Ns 2 /m 4.
…and streamlining factorq in : q in = k in · BUT.
If instead With X substitute With z, then we get the aerodynamic lift force.
Midsection area for cars:
A=0.9 B max · N,
where AT max - the largest track of the car, m; H– vehicle height, m.
The force is applied at the metacenter, creating moments.
The speed of air flow resistance, taking into account the wind:
, where β is the angle between the directions of the car and the wind.
FROM X some cars
|
VAZ 2101…07 |
Opel Astra Sedan | |||
|
VAZ 2108…15 | ||||
|
Land Rover Free Lander | ||||
|
VAZ 2102…04 | ||||
|
VAZ 2121…214 | ||||
|
truck | ||||
|
trailer truck |
Lift resistance force
F P = G a sin α.
In road practice, the magnitude of the slope is usually estimated by the magnitude of the rise of the roadbed, related to the magnitude of the horizontal projection of the road, i.e. the tangent of the angle, and denote i, expressing the resulting value as a percentage. With a relatively small slope, it is permissible to use not sinα., and the value i in relative terms. For large values of the slope, the replacement sinα by the value of the tangent ( i/100) is not allowed.
Overclocking resistance force
When the car accelerates, the progressively moving mass of the car accelerates and the rotating masses accelerate, increasing the resistance to acceleration. This increase can be taken into account in the calculations, if we assume that the masses of the car move forward, but use some equivalent mass m uh, a little bigger m a (in classical mechanics this is expressed by the Koenig equation)
We use the method of N.E. Zhukovsky, equating the kinetic energy of a translationally moving equivalent mass to the sum of energies:
,
where J d- moment of inertia of the engine flywheel and related parts, N s 2 m (kg m 2); ω d is the angular velocity of the engine, rad/s; J to is the moment of inertia of one wheel.
Since ω to = V a / r k , ω d = V a · i kp · i o / r k , r k = r k 0 ,
then we get 
.
Moment of inertiaJcar transmission units, kg m 2
|
Automobile |
Flywheel with crankshaft J d |
driven wheels (2 wheels with brake drums), J k1 |
Drive wheels (2 wheels with brake drums and axle shafts) J k2 |
Let's replace: m uh = m a · δ,
If the vehicle is not fully loaded: 
.
If the car is coasting: δ = 1 + δ 2
Vehicle acceleration resistance force (inertia): F and = m uh · a a = δ · m a · a a .
As a first approximation, we can take: δ = 1,04+0,04 i kp 2
We are so used to being surrounded by air that we often do not pay attention to it. We are talking here, first of all, about applied technical problems, in the solution of which at first it is forgotten that there is a force of air resistance.
She reminds of herself in almost every action. Even if we go by car, even if we fly by plane, even if we just throw a stone. So let's try to understand what the force of air resistance is on an example simple cases.
Have you ever wondered why cars have such a streamlined shape and a flat surface? But everything is actually very clear. The air resistance force consists of two quantities - the frictional resistance of the body surface and the resistance of the body shape. In order to reduce and seek to reduce irregularities and roughness on external parts in the manufacture of automobiles and any other Vehicle.
To do this, they are primed, painted, polished and varnished. Such processing of parts leads to the fact that the air resistance acting on the car is reduced, the speed of the car increases and fuel consumption decreases when driving. The presence of a resistance force is explained by the fact that when the car moves, the air is compressed and a local area is created in front of it. high blood pressure, and behind it, respectively, the rarefaction region.
It should be noted that at increased speeds of the car, the main contribution to the resistance is made by the shape of the car. The resistance force, the calculation formula of which is given below, determines the factors on which it depends.
Resistance force \u003d Cx * S * V2 * r / 2
where S is the area of the front projection of the machine;
Cx - coefficient taking into account ;
As it is easy to see from the reduced resistance, it does not depend on the mass of the car. The main contribution is made by two components - the square of the speed and the shape of the car. Those. Doubling the speed will quadruple the resistance. Well, the cross section of the car has a significant impact. The more streamlined the car, the less air resistance.
And in the formula there is another parameter that simply requires paying close attention to it - air density. But its influence is already more noticeable when flying aircraft. As you know, as altitude increases, air density decreases. This means that the force of its resistance will decrease accordingly. However, for an aircraft, the same factors will continue to influence the amount of resistance provided - the speed of movement and shape.
No less curious is the history of studying the effect of air on shooting accuracy. Works of this nature have been carried out for a long time, their first descriptions date back to 1742. The experiments were carried out in different countries, With various form bullets and projectiles. As a result of the research, the optimal shape of the bullet and the ratio of its head and tail were determined, and ballistic tables of bullet behavior in flight were developed.
In the future, studies were carried out on the dependence of the flight of a bullet on its speed, the shape of the bullet continued to be worked out, and a special mathematical tool was developed and created - the ballistic coefficient. It shows the ratio of the forces of aerodynamic resistance and those acting on the bullet.
The article considers what the force of air resistance is, a formula is given that allows you to determine the magnitude and degree of influence various factors on the value of resistance, its effect in different areas technology.
When any object moves on the surface or in the air, forces arise that prevent it. They are called forces of resistance or friction. In this article, we will explain how to find the resistance force and consider the factors that affect it.
To determine the resistance force, it is necessary to use Newton's third law. This value is numerically equal to the force that must be applied to make an object move uniformly on a flat horizontal surface. This can be done with a dynamometer. The resistance force is calculated by the formula F=μ*m*g. According to this formula, the desired value is directly proportional to body weight. It is worth considering that for the correct calculation it is necessary to choose μ - a coefficient depending on the material from which the support is made. The material of the object is also taken into account. This coefficient is selected according to the table. For the calculation, the constant g is used, which is equal to 9.8 m/s2. How to calculate resistance if the body does not move in a straight line, but along an inclined plane? To do this, you need to enter the cos of the angle in the original formula. It is from the angle of inclination that the friction and resistance of the surface of bodies to movement depend. The formula for determining friction on an inclined plane will look like this: F=μ*m*g*cos(α). If the body moves at a height, then the air friction force acts on it, which depends on the speed of the object. The desired value can be calculated by the formula F=v*α. Where v is the speed of the object, and α is the drag coefficient of the medium. This formula is only suitable for bodies that move at low speed. To determine the drag force of jet aircraft and other high-speed units, another one is used - F = v2 * β. To calculate the friction force of high-speed bodies, the square of the speed and the coefficient β are used, which is calculated for each object separately. When an object moves in a gas or liquid, when calculating the friction force, it is necessary to take into account the density of the medium, as well as the mass and volume of the body. Drag significantly reduces the speed of trains and cars. Moreover, two types of forces act on moving objects - permanent and temporary. The total friction force is represented by the sum of two quantities. To reduce resistance and increase the speed of the machine, designers and engineers invent a variety of materials with a sliding surface from which air is repelled. That is why the front of high-speed trains has a streamlined shape. The fish move very quickly in the water thanks to the streamlined body, covered with mucus, which reduces friction. The resistance force does not always have a negative effect on the movement of cars. To pull the car out of the mud, it is necessary to pour sand or gravel under the wheels. Thanks to the increase in friction, the car copes well with swampy soil and dirt.Air resistance is used during skydiving. As a result of the resulting friction between the dome and the air, the speed of the skydiver is reduced, which allows parachuting without damage to life.
