The science behind how planes fly
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  • 1. The Science Behind How Planes FlyIntroductionTo understand how planes fly we need to understand the science behind flying because thebasic principles of flight apply to all planes. From the Wright Brother’s first machine tomodern Airbus, there has been no change in the science behind flying over the centuries.A plane will maintain its flight if it maintains its control surfaces, that are mainly the ailerons,elevator, rudder and the flaps. The elevators are located at the back of the plane and theycause change in lift with small changes in movement. The ailerons control the longitudinalaxis and maintain the plane’s rolling activity. The rudder gives direction to the plane and islocated at the back of the plane. The flaps or the wings are the main reason behind the lift ofthe plane and they are the most important for flight (Moore, 2008).This paper tries to enumerate the different forces and laws behind the science of flying.Aerodynamic ForcesSimply speaking, there are basically four forces that make flying possible for any plane.These four forces are known as aerodynamic forces and they are lift, gravity, thrust and drag.
  • 2. Thrust and lift are the forces that keep the plane flying in the air (Moore, 2008). Thrust isgenerated by the engine of the plane while the design of the plane gives them the required lift.Thrust is required to overcome the drag that slows the plane. Drag is the resistance of air thatis created against the lift. It is the friction that is generated by passing air (Phillips, 2004). Toreduce the drag, planes are generally in streamlined shape. The lift is created by the wings ofthe plane and it must be greater than gravity to keep the plane airborne. The gravity is theforce that is created by earth’s pull and the weight of the plane. During take-off, the planemust be in such a state so that the thrust is able to overcome drag and the lift must overcomegravity to make the plane fly (Phillips, 2004). Again, during flight, all the four forces must bein balance to keep the plane airborne. In such times, the thrust must be equal to the drag andthe lift must be exactly equal to the weight of the plane. Whereas during landing, the thrustmust be reduced compared to the drag and the lift should also be reduced in comparison tothe gravity (Phillips, 2004).Now, let us look at the popular and disputed principles behind lift and the science behindflying.Bernoulli’s PrincipleThe top surface of the plane is more curved than the bottom to generate more lift thanopposing drag. This shape is known as aerofoil and it significantly helps in creating lift.
  • 3. According to the principle of Bernoulli, when the air speeds up, a low pressure is created thatprovides the necessary lift for flying the plane (Anderson and Eberhardt, 1999). It is statedthat the wind goes faster over the top of the wings. The region of low pressure is therebycreated below the wings that in turn generate the lift necessary for the plane flight.However, these days, researchers believe that Bernoulli’s principle fails to explain liftappropriately as it ignores the fact that lift requires power. This power is measured as workper time.Newton’s Laws and LiftThe argument reaches Newton’s first and third laws. According to Newton’s third law, anopposite and equal reaction is generated against every action (Phillips, 2004). Thus, the airthat is deflected downwards by the lower surface of the wing creates an equal and oppositereaction that pushes the airplane wings upwards.The Wing as a PumpAccording to Newton’s principle, the lift of a wing is generated as a reaction against the airthat is pushed down by the wings. This change in momentum that is created by the wing is aproduct of mass and velocity. From Newton’s second law we know that Force (F) is equal toMass (m) into acceleration (a) - F=ma. Thereby we can derive the conclusion that more liftthe plane has to either increase its downward velocity or increase the amount of air that it
  • 4. diverts with its wings (Anderson and Eberhardt, 1999). The upward lift is known as upwashwhile the downward velocity is known as downwash. The following diagram shows the truepicture of the airflow over a wing that generates lift. True airflow over a wing with lift, showing upwash and downwashThe question that next arises is that how can the wing divert so much air to create therequired lift. The answer is that air while rotating around the wind creates a bound vortex thathelps the wing to generate enough power to lift the plane (Phillips, 2004).It is a known fact that air has viscosity. Thus, when air comes in contact with a movingsurface that is curved in any particular shape then it will follow that shape. This tendency ofair and water to follow any curved surface is known as Coanda effect and this too plays animportant role in helping the plane fly (Anderson and Eberhardt, 1999).Angle of AttackThe angle of attack is another important factor in lift generation. This angle is the pitch atwhich the wing is situated with relation to the horizontal airflow and as this angle increasesso does the lift of the plane (Schmidt, 1998). It has been proved that above 15 degree ofangle, the lift begins to decrease and at such point the pilot needs to correct the situation byincreasing the speed of the airplane to maintain its flight (Anderson and Eberhardt, 1999).
  • 5. Otherwise, the plane would be wing stalled due to the sudden loss in lift. It can be said thatthe angle of attack is more important than viscosity of air. It is required to understand thedynamics behind why planes fly.Lift Requires PowerFor a plane to sustain its speed and height there must be a lot of power involved. The wingscannot generate enough lift unless there are strong engines to supply the necessary power.The lift of a wing is proportional to the amount of air diverted down times the velocity ofsquared of that diverted air (Anderson and Eberhardt, 1999). Simple speaking, as the speed ofthe plane is increased, the amount of air that is diverted down by the wings also increases,providing a subsequent upward pressure to lift the plane. Drag of the plane is also dependenton power and it equals power divided by speed (Anderson and Eberhardt, 1999).Generally, the wings of the plane are designed to reduce the drag of the plane and increase itslift. During takeoff and landing, the flaps behind the wings extend to divert more air so thatthey would create more lift by generating air pressure.Controlling Flight of PlaneThe pilot of the plane has to control the flight of the plane. He uses special control to makethe plane fly and keep it airborne. By using the throttle the pilot increases or decreases thepower of the engine. This in turn increases the speed of the plane and helps it to maintainheight. The pilot also uses the ailerons of the plane to make the plane roll while he uses therudder to control the yaw of the plane. Yaw is the turning of the plane while pitch is to makethe plane descend or climb altitude (Schmidt, 1998). The pilot controls the elevators locatedat the back of the plane to maintain the pitch of the plane and he pushes the pedals to use the
  • 6. brakes of the plane. All these controls are important to maintain the flight of the plane(Schmidt, 1998).ConclusionIn conclusion, we can state that there are several important laws behind the science of flying.Firstly, the Newtonian principle describes that upward lift is derived by accelerating air massdownward. Secondly, the power needed to lift the plane is dependent on the vertical velocityof the air (Anderson, 1997). Thirdly, drag is incurred by accelerating the air mass forward.Lastly, forward propulsion is gained by the power generated by the engines. There are severalother reasons behind safe flight that have been described above (Anderson, 1997). Moving airhas power to lift things up that has been seen from hot air balloons and this theory alsoapplies to plane flight (Moore, 2008). Overall, it can be stated that Newtonian principlesbehind flight explains a lot of things but Bernoulli’s principle still holds true because withoutgenerating air pressure the plane cannot lift and without lift there can be no flight.ReferencesAnderson, J. (1997). A History of Aerodynamics. Cambridge University Press.Anderson, David. Eberhardt, Scott. (1999). How Airplanes Fly: A Physical Description ofLift Level 3. Retrieved December 9, 2011, from http://www.allstar.fiu.edu/aero/airflylvl3.htmMoore, Rob. (2008). Why Does It Fly? Cambridge Young Readers.Phillips, W. F. (2004). Mechanics of Flight. J. Wiley & Sons.Schmidt, L. (1998). Introduction to Aircraft Flight Dynamics. AIAA Press.