HOW AN AIRPLANE FLIES?

Introduction

The sight of an airplane in the sky or a huge airplane taking off or landing at an airport make us wonder about the technology involved in it. It is simply marvelous.

Don’t you wonder how such a huge metal bird effortlessly takeoff, flies to your destination, and land safely?

Do you know how an airplane flies? How many controls does an airplane have? What is the weight of an airplane?

Keep reading to know more about the fascinating world of airplanes.

This article takes you through the subtopics of how an airplane flies, forces experienced by an airplane, major parts of an airplane, how airplane wings lift the airplane, three axes of airplane flight and pitch, roll, and yaw, what is the speed of an airplane, and what is the weight of an airplane.

How does an airplane fly? Forces experienced by an airplane

When an airplane is in the air doing a level flight, it undergoes four forces viz. lift, gravity, thrust, and drag; ‘lift and gravity‘ and ‘thrust and drag‘ are the forces opposing each other.

The thrust is created by the jet engine or the propeller of an airplane and this is the force that moves it forward.

Drag is the air resistance experienced by the airplane when it tries to move forward and drag tries to slow down the airplane’s forward movement.

Gravity is the earth’s gravitational pull/force that pulls all objects down towards the earth.

Lift is the upward force created by the movement of air above and below the aircraft wings and the cross-section of the wings is designed in such a way that this movement of air creates a difference in pressure resulting in a lift force that is higher than the gravity.

Newton’s third law of motion states ‘for every action or force in nature there is an equal and opposite reaction or another force’. So, the thrust created by the jet engine to move the airplane forward in the air is resisted by the air resistance that drags the airplane. The thrust created should be high enough to overcome the drag to move the airplane forward.

When the airplane climbs to its altitude, it reaches the level flight and at this point, the thrust and drag and lift and gravitational force gets balanced and the airplane continues on a leveled flight.

Major parts of an airplane and their functions

Airplanes are designed for the transportation of people or cargo from one airport to another airport and they come in different sizes, shapes, and designs.

The pilot of an airplane has different controls for maneuvering it on land as well as in the air. The Aileron, Elevator, and Rudder are called the three primary control surfaces of an airplane and they are mandatory in all airplanes.

The major parts of an airplane are:

Wings

While flying in an airplane, you must have observed how large the wings of an airplane are and how they are constructed. The work of the wings is to provide the lift force to lift the airplane into the air and make it fly.

Yes, you are correct!! The wings of an airplane are not made from a single solid piece, on the contrary, the wings have many movable parts. The complete wing together with the movable parts on it forms a special shape in fluid mechanics and this special shape is called the airfoil shape. It is the airfoil shape that produces the lift for the airplane by using the air moving around it. The shape of the airfoil can be marginally altered by using the movable parts (slat and flap movements) to vary the lift force.

The wings generate most of the lift required by the airplane to hold it in the air. The airplane has to move through the air to enable the wings to generate the lift force. The air surrounding the airplane resists the forward movement of the airplane and this resistance force is called aerodynamic drag. Some airplanes have winglets on the tip of both wings for minimizing aerodynamic drag. The jet engines placed below the wings generate the thrust to overcome the drag.

The moving parts on the wings are discussed below and the pilot controls all these moving parts from the cockpit.

Ailerons: Ailerons are the hinged parts located at the trailing end of the wing (rear side) and there is one on each wing. Ailerons help the pilot control the roll of the airplane and the pilot uses it for the side-to-side roll of the airplane.

When the pilot turns to the left, the left aileron moves up (lift is reduced on the left wing) and the right aileron moves down (lift is increased on the right wing) and the result is the airplane rolls to the left and begins a turn.

When the pilot turns to the right, the right aileron moves up (lift is reduced on the right wing) and the left aileron moves down (lift is increased on the left wing) and the result is the airplane rolls to the right and begins a turn.

Flaps, slats, and spoilers:

Flaps, slats, and spoilers are called the secondary control surfaces of an airplane and their function is to improve the performance characteristics of an airplane and aid in flying the airplane. Unlike the primary control surfaces, the secondary control surfaces are not mandatory for all airplanes.

Flaps: Flaps are hinged parts and like ailerons, they are located on the rear side of the wing; but, unlike ailerons, flaps move symmetrically and this movement produces additional lift and drag. Flaps are normally used during takeoff and landing when the airplane speed is low. Flaps help generate additional lift. Flaps can only move downwards from its normal position and it can be deployed in angular increments.

Slats: Slats are hinged parts positioned on the front of the wings and when deployed slats temporarily change the shape of the wings and enhance the lift during takeoff. Slats enhance lift during low-speed maneuvers viz. takeoff, initial climb, and also during approach and landing. Slats can only move downwards from its normal position and it can be deployed in angular increments.

Spoilers: Airplanes are designed to minimize drag and increase fuel efficiency. An offshoot of this is that an airplane does not slow down immediately even at idle thrust and this is more so during descending.

Spoilers are the movable panels mounted on the top surface of the wing and when deployed, it will increase the drag and decrease the lift by distracting the flow of air above the wings.

Spoilers are deployed during the airplane’s descent and their function is to reduce the lift and allow the airplane to lose altitude (descend) without an increase in airspeed. Spoilers are also deployed during landing to reduce the speed of the airplane and they work against the flaps when the airplane is on the ground. Spoilers can be deployed only upwards.

When you are flying next time, take a window seat and watch how the different movable parts on the wings are manipulated during takeoff, leveled flight, turning, and landing.

The tail

The tail of an airplane offers stability to the airplane and helps enhance the lift in combination with the wings.

You can see the vertical and horizontal stabilizers at the tail and they are like small wings fixed at the tail of the airplane. The fixed horizontal part at the tail is called the horizontal stabilizer and the fixed vertical part at the tail is called the vertical stabilizer. The vertical and horizontal stabilizer helps control and maneuver the airplane, provides steadiness for the airplane, and keeps the airplane on a leveled flight. The horizontal stabilizer avoids pitching of the nose (up and down movement) and the vertical stabilizer prevents the nose of the airplane from yawing (side-to-side movement).

The horizontal stabilizer and elevator: The horizontal stabilizer controls the nose from moving up and moving down (pitching). An elevator is the hinged part on the horizontal stabilizer and is one of the three primary flight controls (the other two are the aileron and rudder). The pilot can move the elevators up or down. When the elevators are moved up, the tail is pushed down, and the nose of the airplane is tilted upwards. In the nose-up position the angle of attack on the wings changes and more lift is created; this is used during takeoff. When the elevators are moved down, the tail is pushed up, and the nose of the airplane tilts downwards: this is used during descending.

Vertical stabilizer and rudder: The vertical stabilizer controls the yaw or sidewise movement of the airplane. The rudder, another primary control of the airplane is hinged to the vertical stabilizer and the pilot can move the rudder to the left or right. The pilot pushes the left pedal to turn the rudder to the left, and with this, the tail is pushed to the right and the nose yaws to the left. Similarly, when the pilot pushes the right pedal, the rudder turns right, and the nose yaws toward the right. The pilot uses the ailerons in combination with the rudder for a smooth turn.

More about rudder and rudder pedals: There are two rudder pedals for the pilot to operate, left and right, and the rudder pedals control three things:

• Nose wheel (for turning when taxiing on the ground)
• Rudder
• Brake (operated only when the airplane is on the ground).

The rudder pedals have two parts, the bottom part controls the rudder (and the nose wheel when on the ground) and the top part controls the brake (when on the ground). Each side of the pedal controls the respective side of the control viz. the top left pedal activates the left brakes and the top right pedal activates the right brakes.

Fuselage

The fuselage is the body of the airplane and it holds the cockpit in the front and passenger and cargo space in the rear. Airplanes normally carry aviation fuel in the wings and many airplanes may use the space in the fuselage for carrying the aviation fuel.

The construction and design of the airplanes differ from manufacturer to manufacturer as also the purpose of the airplane. The aircrafts built for wars like fighter aircraft have a very different configuration compared to a passenger or cargo airplane. A fighter airplane has very different needs viz. quick functions, manipulations, reaching very high altitude, speed, and other things and hence its configuration is completely different from a commercial airplane.

Whatever the design, the forces acting on an airplane remain the same and the airplane has to work with three axes when it is in the air.

Engine

The engine can be of propeller type or a turbine/jet engine. In a propeller-type engine, the fuel and the compressed air are burnt in an internal combustion engine to spin the propeller and the spinning propeller generates the thrust required for forward movement of the airplane.

In a jet or turbine engine, the air enters the engine, gets compressed, mixed with the aviation fuel, ignited, and the high-pressure exhaust moves out from the rear. All these processes are happening in line.  In this, the thrust for the forward movement of the airplane is generated by the high-pressure exhaust.

Landing gear

The landing gear is positioned under the belly of the airplane and includes one set of wheels at the front and two sets of wheels at the rear. These wheels have the necessary arrangements to absorb the shock of landing and moving the airplane at high speed on the ground. The pilot has the hydraulic controls to deploy the landing gear before landing and retract it into the fuselage after the airplane takes off. The landing gear needs to be retracted into the fuselage to eliminate the additional drag it can create.

How do airplane wings lift the airplane?

Air is a fluid medium (just like water), and it has molecules and weight (remember the experiment of weighing an empty balloon and a balloon filled with air). But, the density of air is 1/800 that of water. Air is constantly moving around the objects open to it and air can push the objects or make the objects lift in the air including an airplane.

Objects lighter than air are buoyant in the air (they float), but heavier objects like an airplane need an upward force to keep afloat. This upward force is called the lift. The lift force for an airplane is mostly developed by its wings. Let us discuss how an airplane gets lifted into the sky and keeps flying in the air.

The cross-section of an airplane wing has a curved shape at the top and is comparatively flat at the bottom. This shape makes the air move faster over the top of the wing compared to its movement at the bottom. As per the theory, the reason for the faster movement of air at the top is it has to cover more distance compared to the air moving at the bottom and the time for both movements are same. The result is the pressure of air on the top of the wing is less than the pressure exerted by the air at the bottom of the wing.

The difference in pressure increases with the increase in the ground speed of the airplane, and at a particular speed, the pressure difference is capable of lifting the airplane into the air. The take-off speed for a light aircraft Cessna 150 can be around 62 MPH and jetliners use a takeoff speed of 149 to 177 MPH or more. This take-off speed is possible with the airplane’s nose pitched up at an angle of 5° to 15° (5° to 15° nose up enhances the lift from the wings).

Many people do not accept this theory and offer the following explanation.

When the airplane is in the air, the cross-section of the wings affects the air moving around the wing. As the air meets the metallic surface of the wing, a thin layer of it sticks to the surface of the wing and this thin layer drags the surrounding air with it. Now the air is divided into two pathways (above and below the wing) keeping with the contour of the wing.

The air moving above the wing moves around the nose of the wing and experiences a centripetal force or centripetal acceleration (this is the same force that throws you out of your seat when your bus makes a sharp and fast turn). Due to this incidence, the air that moves above the wing moves at a higher velocity than the air that moves below it.

The increase in velocity above the wing is always coupled with a decrease in pressure. On the other hand, the air moving below the wing does not experience a significant change in direction or speed and so, the pressure below the wing is higher than the pressure above it. This difference in pressure results in a positive upward force and this is the lift. As the ground speed of the airplane increases, the lift or the pressure difference also increases and when the lift force is more than the gravitational force the airplane takes off.

The three axes of an airplane’s flight and pitch, roll, and yaw

The three axes of flight for an airplane are the lateral axis, longitudinal axis, and vertical axis. The pitch implies the rotation of the airplane around the lateral or side-to-side axis, the roll implies the rotation of the airplane around the longitudinal axis and the yaw implies the rotation of the airplane around the vertical axis.

What are pitch, roll, and yaw?

Pitch

Pitch refers to the rotation of the airplane around the lateral or side-to-side axis and you can imagine this motion as the up and down or nose-up and nose-down position of an airplane. The axis of the pitch or the lateral axis rests above and along the airplane wings.

The pilot uses the elevator located at the tail of the aircraft to pitch the airplane up or down (nose-up or nose-down). The elevator has two functions (i) It provides stability to the airplane by creating a downward force on the tail; airplanes are normally built with a heavy nose and the downward force created by the elevator compensates for the heavy nose. (ii) To direct the airplane nose either upwards (nose-up) or downwards (nose-down) and this is called pitch.

The nose-up is used during climbing and the nose-down is used during descent.

When the elevators of the airplane are tilted upwards or skywards, the airplane gets more lift on the wings and less on the tail, so the airplane pitches up (nose-up). When the elevators are tilted downwards or earthwards, the airplane gets less lift on the wings and more on the tail, so the airplane pitches down (nose-down).

Roll

There are two ailerons located at the back of the aircraft wing, one on each wing and these ailerons are operated for roll. The ailerons work opposite to each other, hence when one aileron is raised, the other is lowered.

The work of the aileron is to increase the lift on one wing simultaneously reducing the lift on the other wing. This makes the airplane roll sideways, and the pilot uses this for turning the airplane.

The pilot controls the roll of an airplane with its ailerons. Ailerons have a hinged construction and are located at the trailing edge of each wing.

The Yaw and roll of an airplane can be confusing so it is important to distinguish between them. Yaw refers to the ‘left and right’ motion of the airplane and roll implies the rocking motion of the airplane (back and forth).

Yaw

The rudder is located on the tail of an airplane and has a hinged construction and it functions similarly to the rudder of a boat. However, unlike a boat, an airplane uses both rudder and ailerons for making a smooth turn.

The major purpose of the rudder is to offset the drag produced by the lowered ailerons while making a turn.

Yaw is the rotation of the airplane around the vertical axis and it moves towards left or right depending on the rudder position. The pilot controls the yaw of the airplane with the rudder that is located at the tail with hinges. Jointly with the ailerons of the airplane, the rudder moves the tail to the left and the right and directs the airplane movement along the vertical axis.

The pilot does not use the rudder to turn the aircraft during a flight, but it is most efficiently used for controlling the roll axis while making the airplane turn.

What is the speed of an airplane?

The speed of commercial jet airplanes is in the range of 350 to 650 MPH. Supersonic planes fly above the speed of sound (767 MPH) and the speed can be in the range of 760 to 1350 MPH. However, there are no commercial supersonic airplanes at present.

What is the weight of an airplane?

The weight of the airplane built by the Wright brothers in 1903 was 274 kilograms. But the average weight of the present-day commercial jet airplane ranges from 150 to 230 tons and mind it, this is the weight of the empty airplane. The airplane becomes heavier when it is filled with fuel, people, and luggage.

The weight of an airplane filled with fuel, people, and luggage is called the maximum takeoff weight or MTOW. If the airplane is loaded beyond its MTOW, the airplane may not be able to take off.

The maximum takeoff weight of an Airbus A380 is 575 tons and its takeoff speed is 315 KMPH or 196 MPH.

The weight of an airplane affects its fuel efficiency and also the environment since heavier airplanes consume more fuel and give out more emissions.

Conclusion

The airplane is simply fascinating and it is a delight and wonder to watch how a huge metal bird smoothly takes off and lands in an airport. Hope this article was able to answer some of your questions about it.

Caution: The purpose of this article is simply to satisfy the curiosity of a common person about the general construction of an airplane and how it flies in the air. This is not training material for a person to learn to fly an aircraft, small or big. Flying an airplane needs skill and experience. If you are interested in learning how to fly an airplane, contact a training institute near you.

References

https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/airplane-parts-function

https://www.flyaeroguard.com/learning-center/parts-of-an-airplane

https://www.grc.nasa.gov/www/k-12/UEET/StudentSite/dynamicsofflight.html

https://calaero.edu/aircraft-axes-pitch-yaw-roll

https://howthingsfly.si.edu/sites/default/files/2020-06/pitch-roll-yaw_0.gif