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How does an airplane engine work?

In aviation discussions, the engine of a flying device has always turned this machine into an attractive subject due to its complexity and benefit of advanced technologies, and most aviation fans call the airplane engine one of their favorite components.

The public’s perception of an airplane engine is a device whose function is only to push the plane forward and has no other use, while only one of the functions of the engine is to create propulsive force. But did you know that the power of all electrical and electronic systems, including the communication and lighting systems of the aircraft, is supplied by the engine?

Or did you know that the air you breathe inside the airplane cabin is provided by the engine compressor?

Or even when the plane lands, the most braking force and reduction of the plane’s speed is the responsibility of the plane’s engine? Did you also know that the engine is responsible for powering the aircraft’s hydraulic systems to open and close the wheels and move the control surfaces? And these are only a part of the named tasks of the aircraft engine. Maybe now you can consider the engine as the beating heart of the plane and realize its high importance in the plane.

In order to get to know the engine, we must first introduce you how the engine generates the driving force and then we will discuss each of the engine components and their roles.

Creating a driving force

Newton’s third law can help us understand how propulsion is created. This law states that if some amount of air is pushed back by an object, that object will be pushed forward in proportion to the amount and speed of the air that has been pushed back. The simplest example is a balloon full of air that we release from the end, as a result, it is observed that the air is released at a high speed at any moment and its reaction causes the balloon to be pushed forward (thrown). Like the balloon in the example, the airplane engine pushes back a significant amount of air at a high speed, and its reaction causes the airplane to move forward. Therefore, the more air is pushed back by the engine at a higher speed, the more forward force we will have, which is called creating momentum.

Types of air engines

Air engines are designed in several ways based on different applications, which include:

Turbo-Jet: Turbo-jet engines provide most of their momentum production from the exhaust gases of the engine. These engines can create high speeds, but due to noise and high fuel consumption, their production is stopped for commercial passenger planes and nowadays they are used for military purposes.

Turbofan: Commercial passenger aircraft engines often use turbofan engines. These types of engines have a relatively large fan in front of them, which provides almost 80% of the driving force of the engine, and the rest of the driving force is provided by the reaction of the exhaust gases from the engine.

Turbo Prop (Turbo Prop): Turbo prop engines, in fact, use propeller power to produce propulsion power, and it includes about 90% of the production power. These engines produce much lower thrust and speed than jet engines, but the fuel consumption of turboprop engines is much lower (about two-thirds of turbofan engines). These engines are often used in light aircraft and passenger planes for short distances.

Turbo Shaft: Helicopters are the most users of these engines. The components of this engine are not different from other jet engines, but their mechanism is not the production of propulsive force, but the creation of torque, which leads to the turning of the helicopter propeller.

Engine components

Common engines in commercial passenger planes usually have the same structure and consist of three main parts:

Compressor: Increasing the pressure and temperature of the air entering the engine and transferring this air to the combustion chamber is done by the compressor.
COMBUSTION CHAMBER: provides a chemical reaction between air and fuel to create an energetic mixture and transfers it to the turbine.
Turbine (TURBINE): Its task is to take energy from the mixture of air and fuel produced by the combustion chamber in order to turn the compressor, the fan and the auxiliary components of the engine.

Engine side components

These components are mounted on a gearbox and the gearbox is powered by a shaft connected to the compressor.

These components are:

Generator (GENERATOR): Its task is to produce electricity consumed in the plane, such as communication systems, lighting systems and entertainment systems, etc.
Hydraulic pump (HYDRAULIC PUMP): It provides the necessary pressure to move the plane’s control surfaces and also to open and close the wheels.
Starter (STARTER): Its task is to rotate the shaft of the aircraft engine to start it, which is usually pneumatic in turbofan engines, because the size and mass of the shaft is so large that electric starters cannot rotate it.
THRUST REVERSER: It is another side component of the engine whose task is to change the direction of the air pushed back by the fan and as a result it reverses the direction of the forward force to create reverse thrust and reduce the speed of the aircraft. This device is used by the pilots when the plane lands on the ground, and passengers often notice the increase in the sound of the engine during landing, which is caused by the activation of the engine reverser.

Systems using compressor air

The hot and high-pressure air produced by the engine compressor (so-called bleed air) is one of the most useful aircraft fluids, and several examples of its applications can be mentioned:

The pneumatic system of the plane, which includes the engine start system for its initial start-up, uses this air.
The air conditioning system (Air Condition System), which has the task of providing fresh air to the passenger cabin, uses this high-pressure air.
The Anti-Ice system, which prevents the formation of ice pieces on the edge of the wing and the engine, uses this air when necessary.

Sina Behari – Flight Qualification Continuity Expert of Kamotech Flight Company

How does a plane fly?

Otherwise, it is considered a big advantage in just a few hours. A privilege that only a century has passed since its creation. Inspired by nature, mankind has been thinking of inventing a tool to achieve the dream of flight since centuries ago. So that in the past, many people were trying to achieve the dream of flying by using designs similar to the wings of birds. Finally, after many years, the Wright brothers succeeded in inventing the airplane, an event in which they did something that today nearly 10,000 airplanes take to the sky in America alone in one day. The airplane is certainly one of the greatest human achievements.

But how does a plane fly?

If you think that the main reason for the airplane to fly is its engine, you are very wrong, because many flying devices such as gliders or even paper airplanes fly easily without an engine. Aircraft engines provide power for forward movement, but do not lift the aircraft off the ground. These are the wings that create the pressure difference necessary for the plane to take off from the ground. With the increase in the power produced by the engines, the air flow quickly hits the wings and by using the aerodynamic features, the necessary pressure difference is created by the wings for the plane to take off. But how does this happen?

By doing a very simple experiment, we can easily understand why the plane flies. Place a sheet of paper according to your mouth and blow on the upper surface. By blowing air on the paper, the air pressure above the paper is reduced and as a result the air pressure at the bottom of the paper is greater than its pressure at the top and due to this pressure difference, an upward force is applied to the paper and lifts it up. .

So easily by using this knowledge, scientists were able to design the wing of the plane and the plane has the power to fly.

Airplane wings have a curved upper surface and a smoother lower surface. This mode creates a shape called an aerodynamic section (Airfoil).

Imagine that two air molecules reach the front of an airplane wing and separate. One of these molecules is thrown upwards and the other remains slowly on the floor. These two molecules must reach the end of the wing at the same time. As a result, the air above the wing has a higher speed than the air below the wing and causes a pressure difference at the top and bottom of the wing and creates a net upward force. This force can even exceed the gravitational force on the plane and move it upwards.

Now let’s define the main forces entering the plane:

Lift: The force created by the impact of the air with the upper and lower surfaces of the wing and causes the plane to rise or continue its flight.

Drag: It is a force that resists the movement of the plane while advancing.

Thrust: It is the force that drives the plane forward, which is provided by the engines.

Weight: It is the gravitational acceleration applied to the mass of the plane by the earth and pulls it towards itself.

These are the four main forces entered into the plane, the flight of the plane depends on their performance: Weight, Thrust, Drag and Lift. The force of gravity opposes the lifting of anything from the ground and its flight. Propulsion or thrust also comes from the very fast rotation of the airplane propeller or in jet engines, from the expansion of the gases caused by combustion and the rotation of the turbine blades, which has the task of pushing the plane forward. In fact, this is the same power that household fans produce. The drag force or resistance is applied to the plane in the opposite direction of the propulsion force and pushes it back. If you put your hand out the window of a moving car, the air resistance that pushes your hand back is the drag force. But the fourth force is the force that pushes the plane straight up and makes it fly. This force is so strong that it can lift a monster like Boeing 747 with more than 370 tons of weight from the ground.

In a smooth, direct and non-accelerating flight, all 4 mentioned aerodynamic forces are in balance. This means that the opposing forces are equal to each other 2 to 2. That is, Thrust equals Drag and Lift equals Weight.

In this article, we tried to explain how the plane flies in the simplest possible way. In the next issue, we will discuss how to guide and control the plane.

Seyyed Hamid Grossi

Vice President of Daneshbanian Camotech Flight Company