FUNDAMENTALS OF FLIGHT?

When we study how forces act on something that is moving, we call these dynamic forces.

Aerodynamics is a branch of fluid dynamics that deals with the study of the motion of air (or other gases) and the forces acting on objects moving through it. It involves understanding how air flows around solid bodies, such as aircraft, vehicles, and buildings, and how this flow affects their movement, stability, and performance.

Since we are learning about forces acting on a body moving through air, like an airplane, we call these aerodynamic forces.

At any moment, there are four main forces acting on an aircraft:

1. Lift 

What is Lift?
Lift is the aerodynamic force that acts upward, allowing an aircraft or drone to take off, climb, and stay in the air. Lift is generated mainly by the wings or propellers when they move through air.

How Lift Works 

Lift is produced due to two main principles working together:

1. Wing Shape (Airfoil Design)

Aircraft wings are designed in a special curved shape called an airfoil:

• The upper surface is curved

• The lower surface is flatter

When air flows around the wing:

• Air on the top surface travels faster

• Air on the bottom surface travels slower

According to Bernoulli’s Principle:

Faster-moving air has lower pressure, and slower-moving air has higher pressure

This creates:

• Low pressure above the wing

• High pressure below the wing

The pressure difference pushes the wing upward, creating lift.

2. Angle of Attack (AoA)

The angle of attack is the angle between:

• The wing’s chord line

• The direction of the oncoming airflow

When the wing is tilted slightly upward:

• It deflects air downward

• According to Newton’s Third Law, the downward deflection of air results in an equal and opposite upward force (lift)

Both Bernoulli’s principle and Newton’s laws explain lift together.

Factors Affecting Lift

Lift depends on:

1. Air speed – Higher speed = more lift

2. Wing area – Larger wings produce more lift

3. Air density – Denser air gives more lift

4. Angle of attack – Proper angle increases lift

If the angle becomes too high, stall occurs and lift decreases.

Example 

Kite Example:
When wind flows over a kite:

• Air moves faster over the top

• Pressure above decreases

• The kite is pushed upward

Drone Example:
Drone propellers act like rotating wings. As they spin, they push air downward, and the reaction force lifts the drone upward.

2. Weight (Gravity) 

What is Weight (Gravity)?
Weight is the downward force acting on an object due to Earth’s gravity. In aviation, weight includes the total mass of the aircraft, such as the structure, engines, fuel, payload, batteries, and equipment. Gravity constantly pulls the aircraft toward the center of the Earth.

How Weight Affects Flight

For an aircraft or drone to fly safely, lift must balance or exceed weight.

• Lift > Weight → Aircraft climbs

• Lift = Weight → Aircraft flies level (cruise or hover)

• Lift < Weight → Aircraft descends

Weight never disappears during flight; instead, pilots and systems manage lift and thrust to counteract it.

Factors That Increase Weight

Weight depends on:

1. Aircraft structure – body, wings, landing gear

2. Fuel or battery load – heavier fuel = more weight

3. Payload – passengers, cargo, cameras, sensors

4. Equipment – avionics, safety systems

More weight means the aircraft requires more lift and more thrust, increasing fuel or battery consumption.

Effect of Weight on Performance

• Takeoff: Heavier aircraft need longer runways or more power

• Climb: Increased weight reduces climb rate

• Stall speed: Heavier aircraft stall at higher speeds

• Landing: Requires higher landing speed and longer distance

Example 

1.When you drop a ball, gravity pulls it downward until it hits the ground.

2. If a drone carries too heavy a payload, it may fail to take off because lift is less than weight

3. Drag 

What is Drag?
Drag is the aerodynamic force that opposes the forward motion of an aircraft or drone as it moves through the air. It acts in the opposite direction to thrust and tends to slow the aircraft down.

How Drag Works

When an aircraft moves through air, it must push air molecules out of the way. This interaction between the aircraft’s surface and air creates resistance, which is called drag.

Drag occurs due to:

• Friction between air and the aircraft surface

• Disturbance and turbulence of airflow

• Pressure differences around the aircraft body

The faster the aircraft moves, the greater the drag.

Types of Drag

1. Parasite Drag

This drag comes from any part of the aircraft that does not produce lift, such as:

• Fuselage

• Landing gear

• Antennas and sensors

Parasite drag increases rapidly with speed.

2. Induced Drag

This drag is created as a result of producing lift.

• When wings generate lift, air spills around the wing tips, forming vortices

• These vortices create resistance called induced drag

Induced drag is high at low speeds and during takeoff and landing.

Factors Affecting Drag

Drag depends on:

1. Speed – Higher speed = more drag

2. Shape of aircraft – Streamlined shapes reduce drag

3. Surface smoothness – Rough surfaces increase drag

4. Air density – Denser air increases drag

Aircraft are designed with smooth, aerodynamic shapes to minimize drag.

Example 

Extra payloads or exposed wires increase drag, reducing flight time and efficiency.

     4. Thrust

Thrust is the force that moves an object forward by pushing air or gas backward. It is the force that allows aircraft, rockets, and drones to take off, fly, and change direction.

In simple words, when air is pushed backward, the vehicle moves forward. This is based on Newton’s Third Law of Motion: For every action, there is an equal and opposite reaction.

Example of Thrust

Drone Example:
When a drone’s propellers rotate, they push air downward. In response, the air pushes the drone upward, creating thrust. If the thrust is greater than the drone’s weight, the drone lifts off.

Rocket Example:
A rocket expels hot gases downward at high speed. The backward force of gases creates forward thrust, pushing the rocket upward.

How Thrust Works 

1. Energy Source:
   The motor (in drones) or engine (in aircraft/rockets) provides power.

2. Air/Gas Acceleration:

   • In drones: Propellers spin and push air downward.

   • In jets/rockets: Engines expel air or gases backward.

3. Reaction Force:
   The backward movement of air/gases creates an opposite forward force (thrust).

4. Movement:
   The object moves in the opposite direction of expelled air or gas.

Thrust in Drones 

• • More thrust than weight → Drone goes up

  • Equal thrust and weight → Drone hovers

  • Less thrust than weight → Drone comes down

               Role of Thrust in Drone Flight Operations

Background

A quadcopter drone used by Air Divit Udan Academy for training purposes was observed to have difficulty lifting off during practical flight sessions. The drone was carrying a camera payload for aerial inspection and training demonstrations.

Problem Identified

During pre-flight checks, it was noticed that:

• The drone was taking longer to lift off

• Battery voltage dropped quickly

• Motors were producing uneven sound

This indicated insufficient thrust generation.

Analysis

Thrust is the upward force produced by drone propellers when motors rotate them at high speed. According to the principle of Newton’s Third Law, when propellers push air downward, an equal and opposite force (thrust) pushes the drone upward.

In this case:

• One propeller was slightly damaged

• Motor RPM was lower due to battery degradation

• Payload weight was close to maximum limit

As a result, the total thrust produced was less than the drone’s weight, causing unstable flight.