Types of Aircraft Engines

Since the first aircraft took off in Kitty Hawk, North Carolina in 1903, much progress has been made on aircraft and engine design. The two World Wars in particular helped to dramatically spur progress when it came to aircraft engine designs. By 1945, 42 short years later, aircraft engines were unrecognizable from the one that the Wright Brothers had first flown.

Today, there are many types of aircraft engines used across the world. Over time, these engines have been tweaked, reengineered, and fitted in everything from aircraft, to missiles, and even spacecraft. Let’s take a look at the four most common types of aircraft  engines in operation today and dive a little bit into their downsides, and advantages.

 

Why Turbine Engines Are So Common

Turbine engines, or jet engines, are sometimes referred to as gas engines or combustion engines. They consist of several parts: a combustion chamber, a rotating compressor that directs hot gasses upwards, and a turbine that moves downstream. These engines work by mixing combusting air and fuel over very high temperatures. The resulting gasses are then directed at blades located in the engine. These high-pressure gasses cause the blades to spin and thus efficiently create power in the compressor.

Within the category of turbine engines there are four types of popular engine designs

1) Turbojet Engines

Turbojet engines came into existence at the start of the second world war. One of the first aircraft to be fitted with a turbojet engine was the German Heinkel He 178.

The turbojet engine is a reaction engine. In a reaction engine, expanding gasses push hard against the front of the engine. The turbojet sucks in air and compresses it. The gasses flow through the turbine and make it spin. These powerful streams of superheated gasses are directed backward, thrusting the aircraft forward. Turbojet engines are capable of very high speeds and power. However, they also consume vast amounts of fuel, making them unsuitable for the profit conscious commercial aviation industry.

Advantages

• Turbojet-powered aircraft can achieve incredible speeds and power, making them ideal for military purposes. Most high-speed military aircraft before the ’70s used turbojet engines to achieve their incredible speeds and maneuverability. However, they have been replaced by after-burning turbofan engines .

Disadvantages

• High fuel usage means these aircraft engines cannot be used for commercial purposes. The only exception to this is the discontinued Concorde jets which were operated by Air France and British Airways. They were powered by four Rolls-Royce/Snecma Olympus 593 turbojet engines.
• Turbojet engines produce a lot of noise, which means they are not ideal for highly populated areas. This is why Concorde flights faced criticism over the noise they produced when flying over cities. Among many factors, this is one reason why this type of aircraft never caught on among airlines.

 

2) Turboprop Engines

A turboprop engine is a turbine engine that drives a propeller.These types of engines work on the same principle as piston engines. A turboprop consists of an intake, reduction gearbox, compressor, combustor, turbine, and a propelling nozzle. The turbine engine is directly connected to the propeller through a gearbox. The hot combustion gasses expand through the turbine stages, generating power at the point of exhaust. Turboprop engines have the following advantages and disadvantages.

Advantages

• These engines are relatively lightweight when compared with other types of turbine engines. This means they tend to be very fuel efficient, especially at low altitudes.
• Landing and take-off flexibility – turboprop engines do better than most other types of turbine engines in areas with limited runway spaces. The lightweight nature of the engines and the drag created by the propeller all combine to ensure that the aircraft can stop very quickly, an advantage on short runways.

Disadvantages

• Aircraft powered by turboprop engines tend to have lower cruising speeds and altitudes. This can make for very uncomfortable flights, especially in bad weather. The slow speed also means that journeys take longer, making them unsuitable for long flights.
• Some of the power generated by the turbine is used to drive the compressor and electric generator. The gasses are then exhausted from the turbine. In contrast to a turbojet or turbofan, the engine’s exhaust gasses do not provide enough energy to create significant thrust, since almost all of the engine’s power is used to drive the propeller.

 

3) Turbofan Engine

Turbofan engines are the mainstay of the commercial airline industry, as they combine power with fuel efficiency. Turbofan engines combine the best features of turboprop and turbojet engines to produce a hybrid. Unlike a turbojet that sucks in all the air inside the engine, a turbofan engine sports a large fan at the front which sucks in most of the airflow around the outside of the engine.The objective of this sort of bypass system is to increase thrust without increasing fuel consumption by increasing the total air-mass flow and reducing the velocity within the same total energy supply.

Advantages

• Turbofan engines are very fuel efficient, thanks mainly to their bypass mechanism. This is the main reason these engines are found in most commercial airliners.
• Turbofan engines allow for high-speed, long-range cruising, thus making international travel much easier and economical.
• They are also very quiet, which makes them ideal for aircraft flying in overpopulated areas.
• Another advantage of these engines is that they can generate immense thrust even when operating at low speeds. This makes aircraft landing safe and smooth, a critical factor when operating commercial airliners.

Disadvantages

• Compared to turboprop and turboshaft engines, these engines require a considerable runway allowance to land and take off. This, largely, limits their use to very specific, if common, use areas.

 

4) Turboshaft Engine

These engines work on the same principle that turboprop engines operate on. The main difference is that the power generated turns a transmission that drives a rotor. As the description suggests, they are primarily found in helicopters, where they help drive the rotor system. This, in turn, creates the lift necessary to operate the helicopter.

Advantages

• Their ability to land and take off vertically means they can be used in ways other aircraft cannot. For example, helicopters are critical for search and rescue operations, as they do not need any runway to land or take off.

Disadvantages

• Aircraft that are powered by this type of engine generally have limited cruising speed and altitudes. This, in turn, limits their use to specialized tasks and short journeys.

 

 

Propeller Engines & the 5 Most Common Types

Propeller engines consist of two or more blades that are connected to a central hub. That hub, in turn, is connected to the engine of the plane. The role of the propeller is to give the aircraft thrust, thus helping move the aircraft forward. The blades of a propeller are typically shaped like the wing of the aircraft, thus allowing the rotational speed of the propellers to produce lift (sometimes referred to as thrust).

Propellers are based on the third law of motion, as proposed by Isaac Newton. He held that there is an opposite and equal reaction to every action. Propellers produce thrust by pushing air behind them. This, in turn, creates an equal counter-reaction which pushes the plane forward. The more air displaced and pushed backward by the propeller, the greater the forward thrust.

Having discussed how propeller engines work, let us now look at various propeller engines commonly found in aircraft today.

1) Fixed-Pitch Propeller

These are propellers that have a built-in pitch or angle that cannot be adjusted. The idea behind such engines is that they work optimally under optimum conditions. The aircraft’s performance is also affected if these conditions are varied. Such propellers are typically found in single-engine, light aircraft that fly at low altitudes and speeds. Such aircraft also tend to have very limited ranges. However, the simple design makes repairs and maintenance fairly easy.

2) Ground-Adjustable Propeller

Unlike fixed-pitch aircraft, the angle of the propellers can be adjusted, but only when the aircraft is on the ground. Once it is in motion, the set pitch is maintained throughout the flight. These kinds of aircraft offer slightly better performance than fixed-pitch aircraft. However, ground adjustable propeller aircraft are not very common these days.

3) Constant-Speed Propellers

These are sometimes referred to as controllable pitch propellers and feature propellers whose pitch or angle can be adjusted mid-flight. This makes them ideal for flying in variable conditions, as the pilots can change the pitch to suit the flying conditions. They tend to offer greater range, speed, and altitude than the other aircraft that we have mentioned.

4) Feathering Propellers

This is a variant of the controllable or constant speed propeller, where the propeller’s pitch can be angled up to 90 degrees. This type of propeller is typically found in multi-engine aircraft. The pitch is used when the engine does not have sufficient power to turn the propeller.

5) Reverse-Pitch Propellers

This is a type of controllable pitch propeller where the pilots can adjust the propeller to produce a reverse or negative thrust. This means that the aircraft produces a reverse thrust, unlike the typical forward motion thrust that is typical in propeller aircraft.

 

Single-Engine Planes vs. Multi-Engine Planes

As the name implies, single-engine planes are powered by one engine, while multi-engine planes have two or more engines. Single-engine aircraft can operate at significantly lower cost levels when it comes to aircraft parts and maintenance, as you only have a single engine to deal with. With multi-engine aircraft, this is multiplied by the plane’s number of engines. However, multi-engine aircraft can fly faster and can generally handle much more weight than single-engine aircraft.

Apart from operating costs and efficiency, another factor that weighs in favor of a multi-engine aircraft is the redundancy factor. If an aircraft has two or more engines, the failure of one engine does not compromise the safe flying of the aircraft. Large passenger aircraft have been known to fly and land safely even when one of their engines has failed completely, or not -infrequently, sometimes even on fire. This is a significant factor for an industry that tends to be very conscious of safety.

 

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