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Introduction
Aviation is considered as amalgamation of various other disciplines. The major disciplines for aviation are mathematics, geography and various physics laws which constitute meteorology branch. Well meteorology plays very important role in weather forecasting which help out the pilot to carry out safe flight. Aircrafts have always inspired me a lot. Especially what really fascinated me as a child was seeing an aircraft or an aero plane flying. I always wondered about the relation between the weather, aircraft and conditions required for a safe flight. So let us first consider here the atmosphere which is the medium connecting the pilot and his/her aircraft. Review Of Literature Today with help of technologies, there has been constant improvement in aviation and reduction in accidents .Thus aviation plays a major role in contributing towards economyThere are many factors that effect aviation, although due to discrepancies in these factors accidents occur, causing huge loss.Thus to understand this we need to talk about the atmosphere first.

The Atmosphere
The atmosphere is nothing but an envelope surrounding the Earth. We need to find out average value of variables like pressure, temperature, density and water vapor etc in order to provide appropriate condition for aviation. Weather is caused by unequal heating of Earth’s surface which causes an imbalance in temperature, if the Earth would stop spinning there won’t be any weather. An atmosphere differs from land to that of water where it has composition of Nitrogen, Oxygen and other gases including Argon which are 78%,21% and 1%. Other gases are trace whose composition is Carbon Dioxide, Neon, Helium, Krypton, Ozone, Hydrogen, average dry air and water content. The Earth spins so the temperature at equator is more as compared to that of poles. The atmosphere is been divided into four regions vertically -the troposphere, the stratosphere, the mesosphere and the thermosphere. Further there is a region called exosphere which is around 500 km above from the surface of earth. The lowest part of our atmosphere contains the Troposphere which contains most of the weather like rain, snow and clouds etc. contributing to around 75% of the atmospheric air and water vapor. As the distance increases above the Earth’s surface the temperature gets colder. Every day the temperature varies. The reason for decrease in temperature is connected with that of reduction in pressure with height. When the pressure is low, air parcel expands while moving upward and as due to low pressure when expansion of air occurs ,the cooling process happens. Thus higher up the air is, cooler it will be as compared to lower air. Boundary layer is the lowest part of the troposphere, the place where motion of air is determined by properties possessed by the surface of Earth. This is the place where when wind blows over Earth’s surface and as the sun heats, thermal rising from the land occurs which gives rise to a phenomenon known as turbulence. Due to this phenomenon redistribution of heat, pollutants, moisture and other constituents happens. Troposphere’s top known as the tropopause is about 10km above the Earth’s surface .This is lowest at the pole and highest at the equator.

Layers Of Atmosphere
The stratosphere is about 50 km from troposphere which contains ozone layer that protects us from harmful UV radiations by absorbing them. Aircrafts fly in this layer. This layer is quite stable due to little convection and less stratification of temperature. This layer is dry and air contains little water vapor that is why very less clouds occur in this region. Air in this layer is very thin by which the aircrafts reach maximum supersonic altitude. Lack of convection in vertical direction causes the materials in stratosphere to stay there for longer time. That is the reason why harmful chemicals like chlorofluorocarbons stay there for longer time. Mesosphere is above Stratosphere where the temperature decreases with height upto 90 degree Celsius at its top layer called Mesopause. Thermosphere is the regions where temperature increases with height due to absorption of UV rays plus X rays from the sun. Above is the ionosphere region above about 80km from the atmosphere where charged ions and electrons are present. Above 500km is the region called exosphere where hydrogen and oxygen atoms collide and enter right into the space.

Principles Involved In Flight And Forces Affecting It
In a flight equilibrium occurs when these four forces are in balance. Let us first define lift. Lift occurs when air acts on Airfoil and it is perpendicular to the relative wind. Its is produced in wings, slats and flaps. Lift is always opposite to the direction of gravitational force. Also lift is irrespective of the reference to that of earth. That means even if the aircraft is inverted lift is perpendicular to wind and not to that of earth. Second factor is weight of an aircraft which consists of aircraft, cargo, fuel and crew members. Weight varies where weight actually acts vertically downwards towards the center of gravity. There is a relationship between weight and lift. where when the weight of an aircraft is equal to that of its weight we say that the aircraft is in equilibrium. Lift acts perpendicularly upwards whereas weight acts perpendicularly downward. Thus if lift is more than weight the vertical speed of an aircraft decreases. Similarly if lift is more than that of weight, the vertical speed of an aircraft increases. In both of these cases, we say that the aircraft is unstable. Third is the drag which is the resisting force caused by disruption of air flow. Fourth is the thrust is the force that acts forward to propel the aircraft and it opposes the drag .Its due to excess or scarce amount of thrust only by which there is acceleration or deceleration occurs. When the thrust equals drag, at this point the aircraft stabilizes. When engine power of an aircraft is increased thrust also increases and aircraft accelerates till the time thrust is greater than drag whereas when thrust equals drag the aircraft is supposed to be in same air speed .Similarly when the power of an aircraft engine is reduced drag is less and aircraft decelerated.

Bernoulli’s Principle And Newton’s Laws Of Motion Affecting Flight
The reason why lift is produced can be explained by Bernoulli’s principle and Newton’s laws of motion. Where Bernoulli’s principle says that as the pressure of fluid increases the velocity must decrease. Thus in wing of an aircraft as the pressure above wing is decreased the relative pressure which is below the wing is higher. This causes the difference in pressure which is known as lift. Secondly according to Newton’s laws in motion, the first law with lift is that - an aircraft at rest or at motion continues to be in same until an unequal and unbalanced inertia is applied on it. The second law is connected with the speed and direction. And the third law can be associated as the propeller of an aircraft moves, air is pushed backward and thus the airplane moves in forward direction. Thus based on above laws we say that lift is dependent on density of air(P), surface area of wing of an aircraft(S), velocity(V) and lift coefficient(C) which give rise to equation L=C*P*V^2*S/2 Here from this equation we derive the following results- 1.If density of air is decreased, then there must be an increase in surface area of wing, wing velocity, air density or lift coefficient in order to keep the aircraft in flight. 2.Secondly the area of wing, which is directly proportional to lift. Thus lift increases or decreases with increase or decrease in area of wing. 3.Thirdly, the lift is directly proportional to the square of the velocity, thus if velocity of an aircraft doubles, the lift becomes four times. 4.The coefficient of lift is a constant number.

External Factors Affecting Aviation
Apart from that we also have the other factors which determine the aviation(Waitz et.al, 2004).. These are the external factors which are- =VISCOSITY= Viscosity which is been considered as the fluid’s property of fluid. Air is fluid where fluid means something which don’t resist deformation, where we call the slightest resistance we call as viscosity. Therefore, viscosity causes resistance to flow. Liquids with high viscosity are thick and flow resistant whereas liquids with low resistant are thin and flow easily. Thus air with low viscosity flow easily. =FRICTION= Another factor is friction. If we consider surface of an aircraft’s wing at macroscopic level, where air molecules resist the motion near the surface of wing due to friction. Further the resistance of flow is caused by viscosity. These two factors together causes a phenomena known as drag of a wing of an aircraft. Whereas when it comes to atmospheric pressure, it is the topmost concern of pilots as it is one of the prominent factor of weather changes which are important flight instruments. =TEMPERATURE= As we know that the generation of lift is dependent on density of air where density of air depends on temperature an elevation where high level of temperature and high elevation, both lowers the density. Thus if the temperature is low, the lift is more, whereas if the temperature is high the lift is low. Thus during the hot days the density of air is low, that is why weight restrictions are been put on an aircraft. An aircraft flies at a distance of 20 km above with the standard temperature of about 76 degree centigrade. =PRESSURE= The pressure is an essential variable which is defined as the force acting over an area. A perfect theoretical level for pressure altitude is been considered as 29.93 Hg in standard setting(Waitz et.al, 2004).. When we consider the major problem in aviation industry, it is the accidents which occur during the takeoff phase and landing phase of an aircraft. Thus density which is defined in layman words as the ratio of mass is to volume is been considered as an important fact. Here in aviation we consider air density. So we see that when the density effects engine, which in turn effects the performance in aerodynamics. Thus decrease in air density lowers the performance of engine. The reason can be contributed as when the density is low the molecules are away from each other. Density is dependent on various other factors such as pressure, humidity ,temperature and altitude. Now when we consider the relation, we see that when the altitude is high, temperature is also high, pressure area is low and humidity is also high, all these factors lead to decrease in air density. =HUMIDITY=

As humidity increases the air pressure goes down this means there will be less number of air molecules present in these molecules less lift. Consider the example of jet engine which are built on humid here, which is both cold and dry that means the no. of molecules of oxygen present to burn per unit volume will be few. The engine does less combustion and thus puts less amount of thrust by which the performance of jet plane decreases due to hot humid high and heavy air. The above factors lead to lowering of density of air. Thus humidity causes the reduction in performances of air crafts. As it not only affects wings of the air craft but also causes the reduction in efficiency of engine. =TURBULENCE= can be defined as the disturbance which can be compared with that of experience in the movement of waves of the sea. When an aircraft flows over any structure which can be manmade building or a natural mountain, there is disruption in the flow of air which causes turbulence. There is increment in turbulence at higher altitudes due to the difference in the pressure which again leads to disruption causing up or down or side to side turbulence. The person may feel either lifted or being pressed in seat .Thus to avoid any accident due to turbulence, the pilots are been trained to understand the causes of turbulence and measure to avoid ,also the aircraft is also been designed in such a way that these risks can be reduced.

Psychological Factors Affecting Pilots:
There are other factors such as psychological factors affecting pilots. Many pilots often face motion sickness which is also called as the air sickness in which brain receives messages which are conflicting according to body’s state in which the body feels nausea, sweating, vomiting and discomfort. Along with this pilots often experience stress and anxiety which can also contribute towards motion sickness. To overcome this problem flight instructors normally takes different measures for pilots like asking to focus on objects outside the flight, avoiding unnecessary movement of body or giving medicines in small doze to relax the pilot. Apart form this the pilots also face the problem of poisoning caused by carbon monoxide which is been produced by engines of aircrafts and gets attached to the hemoglobin which prevents hemoglobin to carry oxygen to the various cells of body. Thus this poisoning is dangerous and pilots must be aware of any leakage. Another factor is stress which releases adrenaline hormones that increases levels of heart rate, blood pressure and heart rate etc that causes burden which is intolerable due to that this chronic stress causes a rapid fall in performance of an individual. Also if the pilot is suffering from fatigue ,this influence the decision making ability of a pilot. This fatigue which is caused due to physical ,deficiency in oxygen, psychological stress etc causes fight and flight .The reserved energy in the body is depleted which causes fatigue at a severe level again reducing the performance of pilot .Here pilots are advised to eat proper diet and a good amount of rest, so that the body doesn’t eat away its own cells during the time of fatigue .This is the only way as training really doesn’t help in overcoming acute stress. Only rest helps.

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