DRAG AND LIFT FORCE

                           DRAG AND LIFT FORCE

IN our daily life we can feel drag when you walk in a swimming pool, water pulls us and a fisherman feels the drag on his lure as he pulls it through the water. In the Aerodynamics an airplane flies there is also concept of drag and lift force is use while designing the parts of airplane. Kites can fly because of the forces acting on the parts of the kite these force nothing other than drag and lift force. Though kites come in many shapes and sizes, the forces which act on a kite are the same for all kites. In this blog we are going to see what is drag and lift force and how it is acting on the body.

Lift is a force that acts at a right angle to the direction of motion through air. Lift is created by difference in air pressure. Thrust is the force that propels a flying machine in the direction of motion. Engines produces thrust. Drag is the force that acts opposite to the direction of the  motion.               

fig. fisherman feels the drag on his lure as he pulls it through the water

Fluids drag and lift force :

Fluids flow over solid bodies frequently occurs in practice, and it is responsible for numerous physical phenomena such as a drag force acting on automobiles, power lines, trees and underwater pipelines and the lift force developed by airline wings.

fig. drag force acting on body during swimming

                                       

What is the relationship between lift and drag?

Thrust is a force that pushes the object forward. It can be generated by a propeller, a rocket, a catapult--anything that makes the object move. But lift and drag can only arise as air moves past an object. Lift pushes the object upward, and drag, a type of air resistance, slows it down. The lift should balance the weight while the thrust should balance the drag for the plane to keep itself in the air. For an airplane flying, we can see the forces that are acting on the airplane (weight and drag) and generated by the airplane (thrust and lift)

Technically, drag is not necessary for flight to be achieved. However, it is impossible to completely eliminate drag during flight without eliminating air. Air is needed to generate lift, so although drag is not completely necessary for flight, an airplane that achieve's lift will always experience some form of drag.

Drag equation and Lift equation :

1.Drag Equation -In fluid dynamics, the drag equation is a formula used to calculate the force of drag experienced by an object due to movement through a fully enclosing fluid. The equation is ,

Equation of Drag Force

                                                                    

Where,

FD = Drag force

Cd=Coefficient of drag

ρ =Mass density of fluid

V= Flow speed of the object relative to the fluid

A= Frontal area.

This drag equation derived to within a multiplicative constant by the method of dimensional analysis. If a moving fluid meets an object, it exerts a force on the object. Suppose that the fluid is a liquid, and the variables involved under some conditions such as velocity of fluid U, density of fluid ρ, kinematic viscosity of fluid V, frontal area A, drag force FD.

2. Lift Equation -In fluid dynamics, the drag equation is a formula used to calculate the force of drag experienced by an object due to movement through a fully enclosing fluid. The equation is ,

Equation of Lift Force

                                                                          

 Where,

FL = Lift force

Cd=Coefficient of drag

ρ =Mass density of fluid

V= Flow speed of the object relative to the fluid

A= Frontal area.

This lift equation also derived same as that of drag equation by using dimensional analysis under same condition.

Applications of Drag and  Lift force :

We all know that gravity is a force that pulls everything towards the Earth’s surface. This pull is called the weight force. Planes and birds have to be able to provide enough lift force to oppose the weight force. Lift is caused by the variation in air pressure when air flows under and over an airplane’s wings. It acts upwards against weight and must be greater in order for the aircraft to fly.

Propulsion - Thrust and Drag 

The power source of a bird or plane provides the thrust. Thrust is the force that moves the object forward. Thrust is provided by:

• Muscles — for birds and other flying animals
• Engines — for flying machines
• Gravity — for gliders that actually fly by always diving at a very shallow angle (birds do this too when they glide).

Roll of Drag and Lift Force during flying of Birds 

fig. Birds and Biomechanics 

                                                                                 

fig. Drag and Lift force acting on birds body

                                                        

The four forces of flight are weight, lift, drag and thrust. These forces affect all flying things, including birds and kites! A force is a push or pull acting upon an object. Forces can help with flight, or make flight more difficult. Lift and Thrust are the forces that help flying things get off of the ground. Lift is a push upward and Thrust is a push forward. Birds get lift and thrust from flapping their wings and taking advantage of wind in a similar way to kites. The other forces of flight acting on objects are Weight and Drag. These forces pull objects down toward the ground (weight) and backward from the direction of flight (drag). In order for something to fly, its Lift and Thrust must be stronger than its Weight and Drag.

                                            .   .   .   

The force working against thrust is called drag. It is caused by air resistance and acts in the opposite direction to the motion. The amount of drag depends on the shape of the object, the density of the air and the speed of the object. Thrust can overcome or counteract the force of drag.

An object in flight is constantly engaging in a tug of war between the opposing forces of lift, weight (gravity), thrust and drag. Flight depends on these forces whether the lift force is greater than the weight force and whether thrust is greater than drag (friction) forces.

Lift and drag are considered aerodynamic forces because they exist due to the movement of an object (such as a plane) through the air. The weight pulls down on the plane opposing the lift created by air flowing over the wing. Thrust is generated by the propeller (engine) and opposes drag caused by air resistance. During take-off, thrust must counteract drag and lift must counteract the weight before the plane can become airborne.

How Drag and Lift force works :

If a plane or bird flies straight at a constant speed:

• lift force upwards = weight force downwards (so the plane/bird stays at a constant height)
• thrust force forwards = opposing force of drag (so the plane/bird stays at a constant speed)

If the forces are not equal or balanced, the object will speed up, slow down or change direction towards the greatest force.

If the forces are not equal or balanced, the object will speed up, slow down or change direction towards the greatest force.

fig. Force acting on Airplane

                                                                   

For example, if a plane’s engine produces more thrust, it will accelerate. The acceleration increases air speed past the wing, which increases lift so the plane gains altitude. Then, because the plane is moving faster, drag (air resistance) is increased, which slows the plane from speeding up as quickly until thrust and drag are equal again. The plane can now remain at a constant but greater height.

A plane can lose altitude by reducing thrust. Drag becomes greater than thrust and the plane slows down. This reduces lift and the plane descends.

Airplane wings are designed to take advantage of lift. They are shaped so that air has to travel farther over the top of the wing than underneath it. The reason for this is explained in Bernoulli’s Principle, which states that an increase in the velocity (speed) of air or any fluid results in a decrease in pressure. When the air has to travel farther over the top of the airplane wing, it must also travel faster, which results in lower pressure. The shorter distance under the wings results in higher pressure, causing the airplane to move upward.

• CONTRIBUTERS :

       1. DIPAK KHATALE

       2. ROHAN KHEKADE

       3. KAUSTUBH BORSE

       4. YUKTA KHAIRNAR

       5. SHARAYU KHANDAGALE