Forces

To firmly understand how an airplane, you have to understand that upon an airplane there are constantly acting 4 forces:

• Lift: the upward acting force;
• Weight or gravity: the downward acting force;
• Thrust: the forward acting force;
• Drag: the backward acting force;

As you can see, lift opposes weight and thrust opposes drag.
When a plane:

• takes of: its thrust and lift must overcome its drag and weight;
• is flying: it's trust and lift equals it's drag and weight;
• is landing: it's thrust and lift must be safely reduced so that they are overcomed by the plane's drag and weight;

Lift

As you know lift is the upward acting force that opposes gravity and makes the airplane fly.
At the bases of lift are some very interesting principles of physics: when air moves quickly over an arched surface, the air pressure above the surface drops.
Most of an airplane's lift is created by its wings. An airplane wings ussualy has a special basic shape: the upper surface is curved and the lower surface is flat
When the wing passes through the air some of the air goes over the top: where its pressure is reduced, by the centrifugal of flowing accros the curved air, and it (the air) is accelerated downward as it leaves the trling edge of the wing.
The wing is forced upwars by:

• the higher air presure beneath the wing which forces the wing into the region of reduced air pressure above the upper surface of it (the wing);
• the downward acceleration of the air at the traling edge or downwash;

Also a planes lift is determined by:

• the size, shape and thickness of the wing;
• the velocity of the air moving past the wing;
• the air pressure/ the density of the air;

In order for a plane to get lift:

• the wing must be passing through the air OR
• the airmust be moving around a stationary wing OR
• both

Lift is also determined by the angle of attack, which is the angle that the wing makes with the airflow. As the angle of attack increases so does the lift of the airplane. But a high angle of attack can interrupt the flow of air over the wing and cause the plane to lose it's lift, to stall.
In our days this kind of stall is almst impossible becuase the planes are equiped with computers that control the angle of attack and lets he pilot know if the plane is stalling.

Drag

In order to understand drag you have to understand what drag is you have to understand that everytime an object passes through a fluid it encounters different types of resistance. For example, when a big rock sinks in water it encounters resistence from the water.
Even though the air is invisible, it is a fluid and like all fluids it has its own weight, mass and inertia. Drag is the resistance of the movement of an aircraft in the air.
Each time an aircraft moves through the air it pushes aside a volume of air, at a very high rate and in response the air pushes back in a form of drag.
Drag also influences the flight performences of the airplane, greater drag increases fuel consumption, affects acceleration, and degrades maneuverablilty.
There are 3 main types of drag that an aircraft encounters while flying.

Induced drag

Induced drag is the most important type of drag, it is direct result of lift.
In order for a plane to take off and fly it has to have a positive angle of attack, but when the wing has a positive angle of attack it collides with the air it is moving through, creating a backward force called induced drag force.
Because it is a direct result of lift, induced drag is always present when flying a plane at a positive angle of attack and it plays an important part in the aerodynamics of thr airplane.

Skin friction / parasitic drag

Skin friction drag or parasitic drag results from the wind resistence encountered by the plane due to the rought surfaces and protuberances of the airplanes.
It is important becuase it influenced the emont of weapons of an airplane. When we load a airplane with weapons we modify its aerodynamics and we create drag that effect the flight performance of the airplane. If airplanes have a full load of weapons sometimes they have to use their afterburners to take off.

Wave drag

This kind of drag is encountered only by jet fighters or supersonic airplanes. When a plane moves at supersonic speed it creates an enormous shockwave in front of it. The resistence encountered by planes that are moving through these shockwaves is called wave resistence and for a plane to pass through these waves it needs an enormous energy.
When the shockwave reaches the ground it produces a sound, called sonic boom, but the pilot of a supersonic plane never heares the sonic boom because the wave is always moving away from the airplane.

Thrust

Thrust is the force that actually moves the plane trough air. In order for a plaine to actually go somewhere its thrust has to overcome the airplane's aerodynamic drag and its inertia.
Thrust gives the plane a forward motion and it can pull or push the airplane. It is created by a powerful source of power, such as an engine. the engines can be: propeller engines or jet engines.

G forces

G forces are present in our every day life, without them there would not be any gravity and things would be imponderable.
On the Earth's surface the force of gravity encountered when we sit, stand or lie is 1G. When pilots fly there airplanes they encounter G forces up to 8 or 9 G, or higher, do to the high speed and the altitude.
G forces can be positive and negative, but both can have a dangerous effect on the pilots if they pass over a certain value.
The modern airplanes can easily produce G forces up to 9 G, and this increases your weight: For example: if you normaly have 50 kg at 9G your weight is about 450 kg.
If the G force increases the pilot can become lose his consciousness, when the G force is high than 10 G the blood in your body is pushed to your legs and the heart can't pump it back into your head and oxygenate your brain. And after a few minutes everythng will turn black and you will lose your consciousness.
In our days the pilots use the G suit to protected them from the positive G forces. The G suit is a suit that pushes the blood back into your head. They use compressed air to push the blood back into the pilot's brain.
Also fighter pilots can encounter negative G forces, these G forces are the opposite of positive G forces and they cause the pilot's weight to decrease. The negative G forces occure when the pilot pushes the nose of the plane downward. But when the negative G forces have a different effect on the pilot, they cause the blood to push in the head and so the blood vessels in his eyes will rupture. That's why the pilot' scan stand more than 2 or 3 negative G.
In order to avoid negative Gforces the pilot's came up with a very simple solution: instead of pushing the nose of the plane downward and creating negative G force's, they first rotate the plane 180 degrees and then and then pull back on the stick. By doing this the pilots will experience positive G instead of negatives ones.

Stalling

If a plane's speed drops under a sertain value, the plane loses its lift and consequintly it will fall. This kind of fall is called stalling.
Every airplane has to have a minimum speed in order for it to generate enough lift to stay airborne, this speed is called stall speed. There are more than one stall speeds due to the different air densitys.
The air has its maximum density on the surface of the Earth, but at a higher altitude the air's density is smaller and the air is thiner, so the plane creates less lift for the same emont of thrust.
As a plane's altitude increases so does its stall speed and in order for it to stay airborne, at a high altitude, it has to create more thrust.

Engines

Propeller engine

A propeller engine works exactly as a car engine: a mixture of air and fuel is compressed by the piston and an electric spark causes the mixture to explode, driving the piston downward. This motion is transferred by a series of connecting rods to a propeller.
A propeller is an airfoil, similar to the wing, that turns and accelerates the air, creating a propulsion force that gives the plane its thrust.

Jet engines

A jet engine ejects a jet or a fluid or a stream of gas in order to obtain thrust.
An aircraft's jet engines uses the oxygen from the atmosfere, which combines with the fuel, kerosen, and the new mixuture is ejected at a high speed.
There are many types of jet engines:

Turbojet

A turbojet engine uses a turbine-driven compresser to suck in and compresse the air needed for the fuel combustion. The exahaust from the combustion drives the turbine that compresses the airand creates thrust.

Turbofan

A turbofan engine works exactly like a turbojet engine. The only difference is that the turbofan has a portion of the compressor extended. This modification propels bypass air around the engine core providing additional thrust.

Turboprop

A turboprop engine works like a turbojet engine, but o portion of the exhaust engine isused to drive a propeller. This way the engine's thrust is a combination of the propellers thrust and the exhaust thrust.

Ramjet Engine

The ramjet engine is a jet engine that can give the airplane speeds of over 5 times the speed of sound. But in order for a ramjet to work it has to be traveling through at the speed of sound. So in order for a plane to use ramjets it has to get to the speed of sound through other means.

Scramjet

Scarmjet work exactly like the ramjets, but, while the ramjets slow the supersonic stream of air to subsonic speeds before combustion, the scramjes combust the supersonic stream of air without slowing it.

Control and manuevering

Manuevering

Every airplane flys along 3 imaginary axis of rotation, that run perpendicular to each other, through the center of gravity of the plane: a longitudinal axis, a lateral axis and a vertical axis.
The movements along these 3 axis are called: roll: the rotation along the longitudinal axis, whici is the axis from the nose to the tail of the plane; pitch: the rotation along thre lateral axis, whici is the axis from wingtip to wingtip; yaw: the rotation along the vertical axis, whici is the aixs from beneath the plan to above it;

Control

In order to control a plane you have to control it's movement along the 3 axis of movement. This contol is made by controling the plane's ailerons, elevators and rudder.

Ailerons

The ailerons controls the planes movement along the longitudinal axis, it's roll. The aileros are situated on the planes wings and they alter the lifting ability of the wing, when an aileron is:

• lifted: the lift of the wing decreases causing the wing to slightly drop;
• lowered: the lift of the wing increases causing the wing to slightly rise;

The 2 ailerons are controled by a wheel or a stick and they work simultanosly, but in opposite way: when one is going up the other is going down, this causes the airplane to roll.

Elevators

The elevators controls the planes movement along the lateral axis, it's pitch. The elevators are situated on the horizontal portion of the ail. They work simultanosly and they are controled by the stick or the wheel of the plane, when the stick is : pulled back: the elvators move upwards, causing the tail of the plane to go down and the nose to pitch upward; pushed forward: the elevators move downwards, causing the tail to go up and the nose to pitch downward.

Rudder

The rudder controls the planes movement along the vertical axis, it's yaw. The rudder is situated on the veertical portion of the ail and it is controled by the planes pedals, when we push the right pedal the rudder moves to the right, causing the planes tail to move to the left and it's nose to yaw to the right, and when we push the left pedal the rudder moves to the left, causing the tail to move to the right and it's nose to yaw to the left.