The Wright brothers’ maiden flight in 1903 introduced aircraft propelled by a gas-powered reciprocating internal combustion engine. British pilot Frank Whittle created and patented the first turbojet engine in 1930. In May 1941, the Whittle engine made its successful maiden flight. This engine included a nozzle, a single-stage turbine, a combustion chamber, and a multistage compressor. While Whittle was fine-tuning his invention, Hans von Ohain developed something similar in Germany. Hans built the German Heinkel He 178, the first aircraft to deploy a gas turbine engine successfully. In fact, it was the first flight propelled by a turbojet in history.
Since then, technological advancements have led to the production of many types of engines. As of today, most airplanes across the world use five main types of engines. Each has advantages, disadvantages, and ideal application scenarios. Read on to learn more.
How the Aircraft Engine Operates
Before getting into the engine types, we need to understand how it works. The basic operation of all jet engines and gas turbines is the same. A fan at the front of the engine draws air in. A compressor that has several blades increases the air pressure. As a result of the blades’ rapid rotation, the air compresses. A nozzle sprays fuel into the compressed air, and an electric spark ignites the combination. The expanding, burning gasses erupt at the nozzle on the back of the engine. As the gas jets fly backward, they propel the plane forward.
The turbine is a different set of blades that the hot air goes through on its way to the nozzle. The compressor and turbine mount on the same shaft. So when the turbine spins, the compressor also spins.
Types of Aircraft Engines
Let’s go through the five main types of aircraft engines.
These airplane engines are the lightest available and have no moving parts. The craft’s speed forces air into the aircraft’s engine. A ramjet functions similarly to a turbojet but without the revolving components. However, ramjet engines’ use is limited because the compression ratio is speed-dependent.
In contrast to conventional engines, the ramjet creates minimal push below the speed of sound instead of static thrust. That means a ramjet-powered aircraft needs assistance during takeoff, which can sometimes be another plane. Several guided missile systems and spacecraft use ramjet engines.
Turbofan engines have a huge fan attached to the front to draw in air. The airflow surrounding a turbofan jet engine’s exterior increases the plane’s thrust even when flying at low speeds and reduces noise.
Turbofan jet engines power most modern airplanes. In a turbofan jet engine, the air entering the intake surrounds the hot air generator, which comprises the turbine, compressor, and combustion engine. Only a small amount of air that flows through the engine makes it to the combustion chamber. The remaining air is compressed at low pressure before being combined with the generated gas or being expelled directly. This system aims to increase thrust while keeping consumption at the same level. The turbofan engine reduces the velocity while maintaining the same power output and increasing the total air mass flow to achieve this.
Compared to turbojet aircraft engines, turbofan engines are quieter and use less fuel. They also have a stunning design. The major drawback to these engines is that they are less effective at high altitudes and have a higher frontal area than turbojets, which adds to their weight.
The concept of a turbojet engine is straightforward. It entails drawing air into the engine and compressing it. But the fuel must be injected and burned in the combustion chamber to get the fluids mixture temperature up to roughly 1000 degrees. The resulting hot air forcefully goes into a turbine, which turns the compressor. The turbine’s discharge pressure has to be twice as high as the atmospheric pressure, but that depends on how efficient an airplane engine is. All the extra pressure then travels to the nozzle, producing gas streams that create a thrust. Turbojets use an afterburner, a second combustion chamber between the turbine and the nozzle, to boost thrust significantly. The afterburner heats the gas before it reaches the nozzle. During takeoff, an increase in temperature causes a 40% increase in thrust. Thus, when the aircraft gets airborne, the push increases rapidly.
A turboshaft engine is a gas-powered turbine that functions similarly to a turboprop engine but with minor differences. The turboshaft engine does not operate a propeller. It mostly powers the rotor in helicopters. The speed of a helicopter rotor rotates independently of the gas generator’s speed, thanks to the turboshaft engine’s design. As a result, even if the gas generator’s speed decreases, a helicopter’s rotor can maintain its speed. Additionally, it controls how much power a helicopter produces.
The fact that turboshafts use a large portion of their power to turn a turbine instead of generating thrust is the only distinction between them and turbojets. Compared to a turbojet engine, the turboshaft engine has an enormous shaft connecting the front and the back.
The turboprop engine uses the gearing system to connect to the aircraft’s propeller. An aircraft’s gearbox has a turbojet that rotates its connected shaft. The gearbox lowers the rotating shaft’s speed to enable the gear to engage with the propeller. The propeller revolves through the air to provide thrust, just like in a Cessna 172.
The mid-range rotational speed of turboprop aircraft engines, which can be between 250 and 400 knots, makes them fuel-efficient. Turboprop engines are effective at intermediate altitudes, but their weight makes their gearing system prone to failure. Their airspeed is also constrained.
The air and gas pressure produce the power that runs the compressor. At flight speeds under 500 knots, turboprop aircraft engines outperform turbojet engines in propulsion efficiency. In addition, modern turboprop engines have small propellers with several blades, which keep the plane stable at high altitudes despite its small diameter.
These scimitar-shaped blades are efficient at high speeds thanks to the swept-back edges of their tips. Propfans are the name given to aircraft engines using these kinds of propellers. Like the turbofan engine, the turboprop engine generates its propulsion by converting the energy of the gas stream into mechanical power. It generates enough power to operate the compressor, accessories, and propeller load. These engines have a shaft.
These engines are reliable and powerful enough to fly aircraft from one continent to the next. Over the coming years, we expect cutting-edge aircraft engine architectures like hybrid electric propulsion systems, open fans, and other revolutionary compact engine core designs. But for now, let’s enjoy these.
The image featured at the top of this post is ©frank_peters/Shutterstock.com.