# Basic Theory of Flight

## Basic Theory of Flight

The basic theory of flight. Flying is a human kind dream since a years ago. History of human race was recorded that many attempts has been trying to fly. Human are inspired by the birds, birds flapping its wings and gliding in the sky.

Birds can flap in a few gestures and convert it into distances with gliding, very good efficiency though. This video below contain brief description of how birds fly.

There are four major forces applied on aircraft during flight. First, lift force, this force is coming from wings surface upwards opposite to gravity forces. Second one is, gravity force, all things in the world that has a mass should be has this force. Gravity force always act to the core of the earth. Force that make aircraft moving is called Thrust force, thrust force pushing aircraft forward. Thrust force can be produced from power plant or rotor. Against of Thrust force is drag force, drag force act opposite way of the thrust force.

In take off phase, thrust and lift forces work together to make aircraft fly, the two forces must have enough amount to compromise with aircraft weight, from standstill. While cruising at constant speed, all forces on the same axis are equal. In landing phase aircraft even more complex since thrust is set to as minimum as possible but lift force remain high due to aircraft weight and gravity. Also the angle of attack of aircraft and elevation play big role during touching down.

## Aerofoil, cross-section of wings profile

Lift force is type of aerodynamic force that work against gravity and being the main reason why aircraft can fly. The main source of lift force is generated by wings surface due its shape. Refer to the image (aerofoil). In simple way, imagine air is a fluid or water, this simplification adhering same physical and math principle. Air that through in upper section of aerofoil is move slower than lower section of the aerofoil, equal to the pressure condition. Pressure difference makes force acting to top direction, this force called the lift force.

To be more details, since aircraft wings are specially shaped. Upper section of aerofoil are curved and the bottom section tend to be flatter, as air moves along two-sections of aerofoil, there are pressure reduction and increment. The pressure is reduced due to centrifugal force generated by curvy surface in upper section of aerofoil.

Then the air accelerated since downwards of the surface then leaves after trailing edge. At the results, wing is move into the lower pressure condition rather than higher pressure. As the velocity of air increases, lift force also increases and angle of attack as well. However, the higher angle of attack the more lift force can be generated, but at certain point lift force obviously loss, in aviation glossary we called it stall condition.

Those are basic theory of flight, it was simple, human are trying to imitate nature and modify it.