Aerodynamics is the study of science which is related to flow of air. We are all surrounded by air and we live and also take breath in order to sustain our lives. We have made control on water and developed ships and boats in order to travel through water. Similarly we have made airplanes and spaceships in order to travel through air. So with respect to air we can say that it plays a leading role in order to fly in the sky and to travel. 

We all are surrounded by air and inorder to take its advantages as well as overcome disadvantages we need to know its characteristics. So we need to study the air, and it is aerodynamics. When an object is flying through the sky it is generating two forces, lift and drag. Lift is a force which makes the object fly in the sky, whereas drag opposes its forward motion. So in order to encounter or balance lift we have to weigh the object. In general Lift = Weight . In order to encounter drag, there is thrust which is created by the engine. So drag is countered by thrust or we can say that Drag = Thrust. 

On any vehicle including cars, it can experience all these four types of forces. When a car travels at a very high speed it is experiencing all these types of four forces. At slow speed, there is no such effect, however as the speed of the car increases, there is an increase in its degrading effect. 

First of all the most important is the drag, which has a very large effect on its speed itself. When there is a large speed, there is also a very large drag due to the large flow of air over its surfaces. So, in order to overcome the drag, there are some methods which can be implemented in order to reduce this. Once such a method is about making the body streamlined. A streamlined body has a smoother flow of air around its body, having less drag. So we generally see that the body of a car now has an oval shape rather than the blunt shape like in our earlier days. An oval shape is more streamlined than the blunt shape, so it is  reducing the drag and also increases fuel efficiency. When we have less drag it also means that we will have less fuel consumption so thereby increasing car or engine efficiency.  

Car Aerodynamics

Another way of improving the car aerodynamics is by using spoilers at the end, which is also called, the rear deck spoiler. The main purpose of this is to reduce the uplift force which is usually created at a very high speed due to flow of air beneath it. Active air dams are also used on the front side of the vehicle, in order to give the vehicle more stability, and also adjust and redirect the flow of air, in order to have greater fuel efficiency. Lowering of the car height at a large speed also can be used to improve aerodynamics, as it creates a downward force. 

Aerodynamics is the study of flow of air and its interaction with the body. Here the article is about how does aerodynamics work on cars and how does aerodynamics affect the speed of a car. This article is also about how to make a car more aerodynamic. Need of study aerodynamics is required to improve the performance of any vehicle. Car aerodynamics simulation in the wind tunnel as well as in simulation software are carried out to know the aerodynamic results. There are both advantages and disadvantages of aerodynamics in cars. There are two forces which are created by the flow of air on the vehicle. One is the drag force and the other is the lift force.

Car aerodynamics

Car aerodynamics engineers carry out the car aerodynamics test and car aerodynamics diagram to increase the car aerodynamics fuel efficiency and modify the car aerodynamics parts. Here the car aerodynamics is explained. The lift force can uplift the vehicle from the road when moving at a very high speed. The drag force provides resistance to the vehicle. Both forces need to be seen as they create detrimental effects on the car or any vehicle’s performance. So aerodynamics plays a very crucial role in vehicle design. The main use of aerodynamics is to optimize car performance by minimizing its fuel use, maximizing its stability, decreasing the sound inside the car – air whistling sound may be created otherwise, to remove the stucking of dirt from the road into the car.

In order to obtain a high aerodynamic efficiency in a car the body of the car should be of streamlined shape, a low frontal area and minimum opening in the body, these are also the features of race car aerodynamics. The car’s exterior body should be slippery so that there is very less drag. Spoilers and side skirts are there in order to manipulate air flow and improve downforce. Aerodynamics features are generally based on speed, however acceleration, yaw rate, steering wheel angle and brakes can also come into play. Tire vents in the car body allow the air to cool the tire and brakes, vanes and fins direct airflow which create a downward force and improve the stability of the car.

Aerodynamic car

Rear spoilers retract at a certain speed to give stability and reduce drag. Rear flaps in the car are used to increase air extraction capacity under the car while the front vertical flaps are used to generate downforce in order to balance each other. Flaps also direct air inside the car for engine cooling.

Aerodynamics means dynamics of air as the name suggests. Aerodynamics is the study of flow of air around an object. Where there is an atmosphere there is air. Like our planet earth there is atmosphere in Mars, Venus and other planets. Aerodynamics is an important field for aeronautics and aerospace engineering.

The basic concept for working of aerodynamics consists of 4 forces. These forces are Lift, Weight, Thrust and Drag. All these forces come into play when any object is in the air. Lift balances the weight of the object. So any body when it is in air either flying or thrown upward these two forces act in the perpendicular direction. Lift is in the opposite direction of weight and both forces balance each other when any object is flying. Lift in an airplane is generated by the wings.

Flying Airplane

Thrust and drag are the two forces which act parallel to the flying object. Thrust makes any flying object to gain forward motion or we can say to oppose the drag force. When any object is moving forward there is an equal and opposite force generated and that is the drag. So we can say that in order to move forward we need to overcome drag and this is achieved by engines of airplanes which produce the thrust.

A bird’s wing generates both lift and thrust in order to balance its weight and drag force and fly.

Flying bird

The aerodynamics of a cow will be as a blunt object. The air mostly sees the front of a body and then flows according to the shape pattern behind. Earlier the experiments were done in the wind tunnel to determine and know the flow pattern of air over the object. The experiment shows the streamline flow of air over an object whose shape is oval or streamline like the airfoil. These kinds of objects can generate lift if its shape is little bit changed making flow over the airfoil little faster than the flow down the airfoil. So by modifying the shapes a varying amount of lift can be generated. These types of bodies are known as a body of aerodynamic shapes.

Unlike the aerodynamic streamline bodies, a body which obstructs the flow of air is a blunt body. These types of bodies create the largest amount of drag and very less amount of lift. Blunt bodies are non streamlined bodies, like cuboid, spherical and cylindrical shapes. These bodies obstruct the flow of air. 

A cow

So any bodies which are blunt will not produce any streamline flow of air. Even cars and other vehicles are now designed to have an aerodynamic shape so that there is very less drag on a vehicle, making it to have an advantage of low consumption of fuel and higher speed. Animals like cheetahs which run very fast make their body streamlined to achieve a very high speed while running. Cows and other herbivorous animals do not run for prey, so their body need not be streamlined for a smoother, faster flow of air.

A running cheetah

Here, \[\alpha = 5^{\circ}=0.0873\,rad,\, M = 2.5\]From linearized theory, for a flat plate at an angle of attack \[c_{l}=\frac{4\alpha }{\sqrt{M_{\infty}^{2}-1}}\]Therefore, \[c_{l}=\frac{4\left ( 0.0873 \right )}{\sqrt{\left ( 2.5 \right )^{2}-1}}=0.1524\]\[c_{d}=\frac{4\alpha ^{2}}{\sqrt{M_{\infty}^{2}-1}}\]Therefore, \[c_{d}=\frac{4\left ( 0.0873 \right )^{2}}{\sqrt{\left ( 2.5 \right )^{2}-1}}=0.0133\]\[C_{p}=\frac{2\theta}{\sqrt{M_{\infty}^{2}-1}}\]Therefore,\[C_{p}=\frac{2\left ( 0.0873 \right )}{\sqrt{\left ( 2.5 \right )^{2}-1}}=0.0762\]

From isentropic flow properties table, for \(M_{\infty}=0.52,\frac{p_{0}}{p_{\infty}}=1.202\)
for, \(M_{\infty}=0.82, \frac{p_{0}}{p_{\infty}}=1.555\)
Coefficient of pressure is \[C_{p}=\frac{p-p_{\infty}}{q_{\infty}}=\frac{p-p_{\infty}}{\frac{\gamma }{2}p_{\infty}M_{\infty}^{2}}=\frac{2}{\gamma M_{\infty}^{2}}\left ( \frac{p}{p_{\infty}}-1 \right )\]\[\frac{p}{p_{\infty}}=\frac{\frac{p}{p_{\infty}}}{\frac{p_{0}}{p}}=\frac{1.202}{1.555}\]
Therefore, \[C_{p}=\frac{2}{\left ( 1.4 \right )\left ( 0.52 \right )^{2}}\left ( \frac{1.202}{1.555}-1 \right )=-1.199\]
Coefficient of pressure can also be calculated by using the formula,
\[C_{p}=\frac{2}{\gamma M_{\infty}^{2}}\left [ \left ( \frac{1+\left ( \frac{\gamma -1}{2} \right ){M_{\infty}^{2}}}{1+\left ( \frac{\gamma -1}{2} \right )M^{2}} \right )^{\frac{\gamma }{\gamma -1}} – 1\right ]\]\[\Rightarrow \frac{2}{\left ( 1.4 \right )\left ( 0.52 \right )^{2}}\left [ \left ( \frac{1+\left ( \frac{1.4 -1}{2} \right ){\left ( 0.52 \right )^{2}}}{1+\left ( \frac{1.4 -1}{2} \right )\left ( 0.82 \right )^{2}} \right )^{\frac{1.4 }{1.4 -1}} – 1\right ]=-1.1984 \]

The infrastructure of air traffic management is constituted by communication, navigation and surveillance of aircrafts.

Air traffic control

Communication: Communication refers to the exchange of voice and data in between pilot and air traffic controllers. Communication is done through high frequency, very high frequency and ultra high frequency systems and through communication satellites.

The function of air traffic controllers is to direct the aircrafts which are on the ground and also which are in controlled airspace. It also provides advisory services to aircrafts which are in non-controlled airspace.

ATC prevents aircraft collisions and organizes aircraft traffic. ATC monitors the aircraft through radars and communications are made with pilots with the help of radio.

Navigation: Navigation of aircraft means plan, record and control the movement of aircrafts from accurate and reliable determination of position. Navigation of aircraft is done through visual flight rules and instrument flight rules. In visual flight rules aircraft navigation is made by visual observations and dead reckoning using maps. Dead reckoning is the calculation of current position from previous determined position, and using speed, heading direction and time.

Instrument flight rules: Instrument flight rule uses instruments and radio navigation aids like beacons. Navigations aids like distance measuring equipment (DME), very high frequency omni-directional range(VOR), non-directional beacon (NDB) and global positioning system (GPS) and Global navigation satellite system (GNSS) are used.

GPS navigation system

Inertial navigation system uses computer, sensors like accelerometers and gyroscopes to calculate position, orientation and velocity of aircraft. Inertial guidance system is now also combined with satellite navigation systems.

Surveillance: Aircraft surveillance system is divided into two types, a dependent surveillance and an independent surveillance. In dependent surveillance or a cooperative system, the position of the aircraft is determined from on-board navigation equipment and then conveyed by the pilot to air traffic control through voice reporting.

Secondary surveillance radar on the ground communicates with transponders on the aircraft to find the position and other details of the aircraft. Position of aircraft can also be determined through global navigation satellite system (GNSS).

Automatic dependent surveillance – Broadcast(ADS-B) determines aircraft position from satellite navigation and other sensors and broadcasts periodically to the air traffic control ground stations. Other aircrafts can also receive the information (from ADS-B) which can be used for awareness and self-separation.

Automatic Dependent Surveillance - Broadcast

Independent surveillance or non-cooperative systems uses instruments on the ground such as primary surveillance radar or secondary surveillance radar measures range and azimuth of the aircraft from ground station by transmitting pulses of radio waves which then reflects off from the aircraft’s hull.

Pressure is defined as force per unit area. In fluid pressure on a surface is the normal force acting per unit area due to time rate of change of momentum of the gas molecules which is impacting the surface.

The pressure due to the pure random motion of the molecules of the gas is the static pressure. Whenever a body is in a flow, the fluid will get an obstruction at the surface of the body and the velocity of the gas molecule will be zero. If a body is a tube with one end closed, the fluid molecules will fill the tube and its velocity will be zero, that the fluid will stagnate.

A tube in a fluid flow

At the opening of the tube the fluid molecules sees obstruction. Therefore upcoming fluid molecules slows down and reduces to zero velocity. Any point in a fluid flow where flow velocity is zero is called the stagnation point. As velocity is decreased so pressure is increased. Therefore, pressure at stagnation point is larger than the static pressure.

The pressure at the stagnation point is called the stagnation pressure or total pressure.

Therefore, there are two types of pressure in a fluid flow, static pressure and total or stagnation pressure. Static pressure is the pressure which is felt when a fluid has a velocity and stagnation pressure is the pressure that is felt when flow velocity is reduced to zero.

If a flow is isentropic in between two points then the total pressure is constant at that points. An isentropic process is a process in which entropy remains constant. An isentropic process is both reversible and adiabatic.

The temperature of a gas is directly proportional to the average kinetic energy of the gas molecules. Therefore, a gas which has a high temperature, the molecules are moving randomly at a very high speed. A gas in low-temperature, there is a slow random motion of the molecules as compared to the high temperature gas.

The temperature of a fluid element when it is bought to rest adiabatically is called the total temperature. Stagnation temperature is the temperature when a moving flow is isentropically brought to rest. At the stagnation point total temperature and stagnation temperature have the same value.

High aspect ratio straight wing

Using Helmbold’s equation, for calculating the lift slope for straight wing, \[a = \frac{a_{0}}{\sqrt{1+\left ( \frac{a_{0}}{\pi AR} \right )^{2}}+\left ( \frac{a_{0}}{\pi AR} \right )}\] Lift slope for the airfoil \(= a_{0} = 0.15\,/degree = 8.5944\,/radian\).

Therefore,

\[a = \frac{8.5944}{\sqrt{1+\left ( \frac{8.5944}{\pi \left ( 6 \right )} \right )^{2}}+\left ( \frac{8.5944}{\pi \left ( 6 \right )} \right )}=1.4569\,per\,radian\]

Swept wing

Using Helmbold’s equation, for calculating the lift slope for a swept wing ,\[a = \frac{a_{0}cos\Lambda }{\sqrt{1+\left ( \frac{a_{0}cos\Lambda}{\pi AR} \right )^{2}}+\left ( \frac{a_{0}cos\Lambda}{\pi AR} \right )}\]Here, \(\Lambda = 30^{0}\), is the sweep angle of the wing referenced to the half-chord line.  Therefore,  \[a = \frac{8.5944cos30^{0}}{\sqrt{1+\left ( \frac{8.5944cos30^{0}}{\pi \left ( 6 \right )} \right )^{2}}+\left ( \frac{8.5944cos30^{0}}{\pi \left ( 6 \right )} \right )}=1.4436\,per\,radian\]On comparing the lift slopes of straight wing and swept wing, we can see that there is a reduction in  lift slope for the swept wing.

Wing sweep is decreasing the lift slope, and it affects lift slope to a larger degree for a high aspect ratio wings than for a lower aspect ratio wings.

Span is the wingspan of the airplane. It is the distance from one wing tip to other. It is measured in a straight line and is independent of the wing shape and sweep.  Lift per unit span produced by a wing is given as \({L}’ = \frac{1}{2} \rho _{\infty}V_{\infty}^{2} c\left ( 1 \right )c_{l}\). Here, \(\frac{1}{2} \rho_{\infty}V_{\infty}^{2} \) is called the dynamic pressure , \(q_{\infty} \).  Coffeicent of lift, \(c_{l}\), for this airfoil will be \[c_{l} = \frac{{L}’}{q_{\infty}c\left ( 1 \right )} \]\[\Rightarrow c_{l} = \frac{1400}{\left (\frac{1}{2} \times 1.225 \times 70^{2} \right )\left ( 2.3 \right )\left ( 1 \right )}\]\[\Rightarrow c_{l} = 0.203\]Therefore, coefficient of lift for this airfoil is \(0.203\). For, NACA \(0012\) airfoil from the lift curve -slope for this airfoil, the angle of attack is \( 2^{\circ} \).