HOW DO PLANES FLY?
Wingardium Leviosa!! Not surprising, that’s not how planes fly although that would be cool. It was the Wright brothers in 1903 to build the first plane and now we have come a long way from 12 seconds to intercontinental flights now but the overall concept of equating forces and maintaining equilibrium is the same.
(Structure of a plane, source- https://www.grc.nasa.gov/www/k-12/airplane/airplane.html)
There are 4 forces acting on a plane the weight acting downwards, the lift(upwards) due to the pushing effect of wind on the plane, the thrust created by the turbine/propeller of the plane which helps moving the plane forward and opposing the thrust is the drag force which is produced by the fluid(air) on any object moving through it.
(forces acting on a plane, sources- https://www.grc.nasa.gov/www/k-12/airplane/forces.html)
In a balanced flight, all the forces, cancel each other out and the plane is in equilibrium.
AIRFOIL
The cross-sectional shape of the wing is called an airfoil.
(Structure of an airfoil; source- https://web.mit.edu/2.972/www/reports/airfoil/airfoil.html)
Chord: line joining the leading and trailing edge
Camber Line: halfway between camber and upper wing surface
Angle of attack: Angle between direction of airflow and the chord
Wing creates lift by creating pressure difference between the upper and lower surfaces of the wing with low pressure above and high-pressure underneath.
One of the most important aspects that helps create lift is the viscosity of the medium as it creates vortices that produce lift conditions.
LIFT
In order for an aircraft to rise into the air, a force must be created that equals or exceeds the force of gravity. This force is called lift. In heavier-than-air craft, lift is created by the flow of air over an airfoil. The shape of an airfoil causes air to flow faster on top than on bottom. The fast-flowing air decreases the surrounding air pressure. Because the air pressure is greater below the airfoil than above, a resulting lift force is created.
The Bernoulli’s theorem is the main cause explaining lift(it has been explained later in the blog)
(source-https://web.mit.edu/16.00/www/aec/flight.html)
(source- https://web.mit.edu/16.00/www/aec/flight.html)
CL =>lift coefficient
0.5*rho*v^2=> dynamic pressure
S= surface area
Although along with lift, some drag is induced also called as induced drag (I will talk about this in this blog)
EQUAL TRANSIT THEORY:
It is a false theory explaining lift that states “because aerofoils are shaped with the upper surface longer than the bottom, air molecules that pass over the top of the aerofoil have further to travel than underneath.” The theory states that the air molecules have to reach the trailing edge at the same time, and in order to do that the molecules going over the top of the wing must travel faster than the molecules moving under the wing. Because the upper flow is faster, the pressure is lower, as known by Bernoulli's equation, and thus the difference in pressure across the aerofoil produces the lift.
BERNOULLIS THEOREM:
Given by Daniel Bernoulli, states that total mechanical energy of the flowing fluid (fluid pressure, the gravitational potential energy of elevation, and the kinetic energy of fluid motion) remains constant.
ASPECT RATIO
It is the ratio of the wingspan to the mean chord
(source- https://www.grc.nasa.gov/www/k-12/airplane/geom.html)
For example, the aspect ratio of a Schleicher ASH 31 glider is 33.5 and that of a piper Cherokee is 5.6. Wings with higher aspect ratio produce a lot less induced drag due to lower wing tip area since lesser amounts of vortices. But as we go on increasing the wingspan, it causes bending of the wing as more mass moves away from the fuselage. To nullify this effect, we need to make the wing structurally stronger which means more material must be added which increases the induced drag. Planes with higher aspect ratio have longer wings which means they have a higher moment of inertia therefore they have lesser manoeuvrability for example when an ice skater pulls in their hands closer to their body to increase their angular speed. The F-14 can change its aspect ratio based on the need as we could see in ‘Top Gun: Maverick’.
The Boeing 787 dreamliner has a huge wingspan and the wings bend a lot, which in a regular aluminium based aircraft would be structurally dangerous but the 787 dreamliner is made out of a special carbon fibre- plastic composite that without increasing the weight by a lot provides a lot of structural support to the jet.
VORTICES:
(SOURCE- https://www.boldmethod.com/learn-to-fly/aerodynamics/how-winglets-reduce-drag-and-how-wingtip-vortices-form/)
Wingtip vortices are circular patterns of rotating air left behind a wing as it generates lift. One wingtip vortex trails from the tip of each wing. Wingtip vortices are sometimes named trailing or lift-induced vortices because they also occur at points other than at the wing tips. This type of turbulence is significant because wing tip vortices decay quite slowly and can produce a significant rotational influence on an aircraft encountering them for several minutes after they have been generated. The origin of counter-rotating wing tip vortices is a direct and automatic consequence of the generation of lift by a wing. Lift is generated by the creation of a pressure differential over the wing surface. The lowest pressure occurs over the upper wing surface and the highest pressure under the wing. This pressure differential triggers the roll up of the airflow aft of the wing resulting in swirling air masses trailing downstream of the wing tips. The vortex strength increases proportionally to weight. The potential for hazardous wake vortex turbulence is greatest where aircraft follow the same tracks - i.e., are 'in trail' and closely spaced. This situation is mostly encountered close to the ground in the vicinity of airports where aircraft are on approach to or departure from runways at high frequencies. Sudden uncommanded roll moments.
GROUND EFFECT:
The positive influence on the lifting characteristics of the horizontal surfaces of an aircraft wing when it is close to the ground. This effect is a consequence of the distortion of the airflow below such surfaces attributable to the proximity of the ground. I know it sounds very complex but what it really means is that there is some “extra lift” generated by an aircraft as it approaches landing due to reduction of the induced drag. The increase in lift created by ground effect comes primarily from a reduction in the amount of induced drag generated which improves the lift/drag ratio. When generated in proximity to the ground, the form of the wing tip vortex, which is always generated when an aerofoil moves through the air, because pressure beneath a wing is always higher than that above it, is modified. Instead of being circular, vortices in proximity to the ground become elliptical as the airflow is pushed outwards. This causes the effective aspect ratio of the wing to become greater than the geometric aspect ratio and reduces induced drag. The direct effect on lift arises because a reduction in both upwash and downwash, as the air beneath a wing is compressed by ground proximity, creates a cushion effect.
ANGLE OF ATTACK:
(SOURCE- https://skybrary.aero/articles/angle-attack-aoa)
The Angle of Attack is the angle at which relative wind meets an aerofoil. It is the angle formed by the Chord of the aerofoil and the direction of the relative wind. An increase in angle of attack results in an increase in both lift and induced drag, up to a point. Too high an angle of attack and the airflow across the upper surface of the aerofoil becomes detached, resulting in a loss of lift, otherwise known as a stall.
CENTRE OF PRESSURE:
As an object moves through a fluid, the velocity of the fluid varies around the surface of the object. The variation of velocity produces a variation of pressure on the surface of the object. Integrating the pressure times the surface area around the body determines the aerodynamic force on the object the average location of the pressure variation the centre of pressure in the same way that we call the average location of the weight of an object the centre of gravity. Determining centre of pressure of an aircraft is very important as it is used for stabilising the aircraft.
(SOURCE- https://www.grc.nasa.gov/www/k-12/airplane/cp.html)
FLAPS:
Flaps consist of a hinged panel or panels mounted on the trailing edge of the wing. When extended, they increase the camber and, in most cases, the chord and surface area of the wing resulting in an increase of both lift and drag and a reduction of the stall speed. These factors result in an improvement in take-off and landing performance
There are various types of flaps:
Wing flaps are a significant part of the take-off and landing process. When the airplane is taking off, the flaps help to produce more lift. Conversely, flaps allow for a steep but controllable angle during landing. During both, efficient use of flaps help to shorten the amount of runway length needed for take-off and landing. Wing flaps change the sape of the airplane wing. They divert the air around the wing as necessary. The settings of the flap determines whether they are used to increase lift (as on take-off) or increase drag (used on landing.) When the airplane’s flaps are up, the camber of the airplane is such that the wings can produce more lift. Depending on the aircraft, the flap settings are usually between five and fifteen degrees. After lift-off, the wing flaps are retracted completely so that they do not begin to produce drag.
Conversely, extending the flaps of the airplane creates a “broken wing,” which increases drag. This also lower’s the airplane’s stall speed. It helps the airplane to slow down.
THRUST:
It is the mechanical force that opposes drag and needs some sort of a propulsion system to push the aircraft forward. Thrust is generated most often through the reaction of accelerating a mass of gas. Since thrust is a force, it is a vector quantity having both a magnitude and a direction. The engine does work on the gas and accelerates the gas to the rear of the engine; the thrust is generated in the opposite direction from the accelerated gas. The magnitude of the thrust depends on the amount of gas that is accelerated and on the difference in velocity of the gas through the engine.
DRAG
Drag is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid. For drag to be generated, the solid body must be in contact with the fluid. If there is no fluid, there is no drag. Drag is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid. The magnitude depends on the viscosity of the air and the relative magnitude of the viscous forces to the motion of the flow. There is an additional drag component caused by the generation of lift. Aerodynamicists have named this component the induced drag. It is also called "drag due to lift" because it only occurs on finite, lifting wings. Induced drag occurs because the distribution of lift is not uniform on a wing but varies from root to tip. For a lifting wing, there is a pressure difference between the upper and lower surfaces of the wing. Vortices are formed at the wing tips, which produce a swirling flow that is very strong near the wing tips and decreases toward the wing root. The local angle of attack of the wing is increased by the induced flow of the tip vortex, giving an additional, downstream-facing, component to the aerodynamic force acting on the wing. The force is called induced drag because it has been "induced" by the action of the tip vortices.
Also, I found this really cool video on drag: https://www.grc.nasa.gov/www/Wright/podcast/Podcast_Forces_Drag.m4v
BIBLIOGRAPHY:
https://www.youtube.com/watch?v=edLnZgF9mUg
https://ocw.mit.edu/courses/16-687-private-pilot-ground-school-january-iap-2019/video_galleries/class-videos/
https://www.boldmethod.com/learn-to-fly/aircraft-systems/how-does-aspect-ratio-affect-a-wing/
https://www.grc.nasa.gov/www/k-12/airplane/geom.html
https://www.grc.nasa.gov/www/k-12/airplane/airplane.html
https://www.grc.nasa.gov/www/k-12/airplane/forces.html
https://web.mit.edu/2.972/www/reports/airfoil/airfoil.html
https://web.mit.edu/16.00/www/aec/flight.html
https://owlcation.com/stem/Aerodynamics-The-Theory-of-Lift#:~:text=%22Equal%20Transit%22%20theory%2C%20also,further%20to%20travel%20than%20underneath.
https://skybrary.aero/articles/induced-drag#:~:text=Induced%20Drag%20is%20an%20inevitable,pressure%20outside%20the%20wing%20tip.
https://www.britannica.com/science/Bernoullis-theorem
https://www.grc.nasa.gov/www/k-12/airplane/geom.html
https://www.boldmethod.com/learn-to-fly/aircraft-systems/how-does-aspect-ratio-affect-a-wing/
https://skybrary.aero/articles/wake-vortex-turbulence
https://www.boldmethod.com/learn-to-fly/aerodynamics/how-winglets-reduce-drag-and-how-wingtip-vortices-form/
https://skybrary.aero/articles/ground-effect#:~:text=Ground%20effect%20is%20the%20name,the%20proximity%20of%20the%20ground.
https://skybrary.aero/articles/angle-attack-aoa
https://www.grc.nasa.gov/www/k-12/airplane/cp.html
https://calaero.edu/wing-flaps-function-and-purpose/
https://calaero.edu/wing-flaps-function-and-purpose/
https://www.grc.nasa.gov/www/k-12/airplane/thrust1.html















