What is an air craft?
"All man made contrivances which fly, that is to say which are kept in the air by forces produced by the air are called aircraft".
Eg: balloons, kites, aeroplanes etc.
There are two kinds of air crafts, those which are lighter than air and those which heavier than air. The lighter than means their weight by volume is less than that of air. Heavier than means the weight by volume is heavier than that of air. The former includes balloons, airships etc. and the later comprises kites and aero planes.A heavier than air flying machine, supported by aerofoils, designed to obtain, when driven through the air at an angle inclined to the direction of motion, a reaction from the air approximately at right angle to their surfaces is known as aeroplane. The various forces which acts on the aeroplane when it travels through the air are lift force, drag force, thrust force and its own weight. For steady condition the weight should be balanced by the lift and drag by thrust. The lift is obtained due to the special shape of wings and thrust is obtained by propulsion systems.
"A heavier than air flying machine supported by airfoils , designed to obtain, when driven through the air at an angle inclined to the direction of motion, a reaction from the air approximately at right angles to their surfaces".
Four forces on an aeroplane
Weight is a force that is always directed toward the center of the earth. The magnitude of this force depends on the mass of all of the parts of the airplane itself, plus the amount of fuel, plus any payload on board (people, baggage, freight, ...).The weight is distributed throughout the airplane. But we can often think of it as collected and acting through a single point called the center of gravity. In flight, the airplane rotates about the center of gravity, but the direction of the weight force always remains toward the center of the earth. During a flight, the airplane's weight constantly changes as the aircraft consumes fuel.
To make an airplane fly, we must generate a force to overcome the weight. This force is called the lift and is generated by the motion of the airplane through the air. Lift is an aerodynamic force ("aero" stands for the air, and "dynamic" denotes motion). Lift is directed perpendicular (at right angle) to the flight direction. As with weight, each part of the aircraft contributes to a single aircraft lift force. But most aircraft lift is generated by the wings. Aircraft lift acts through a single point called the center of pressure. The center of pressure is defined just like the center of gravity, but using the pressure distribution around the body instead of the weight distribution.
As the airplane moves through the air, there is another aerodynamic force present. The air resists the motion of the aircraft; this resistance force is called the drag of the airplane. Like lift, there are many factors that affect the magnitude of the drag force including:
" shape of the airplane
" "stickiness" of the air
" speed of the aircraft