What is a Turboprop?

The turboprop engine is one of the most famous types of jet engines. This article explains the turboprop engine working, components, and applications.

The turboprop is a type of jet engine that delivers jet thrust and drives the aircraft propeller. This is different from a turbojet or turbofan, where the jet exhaust provides most or all of the thrust.

The working of a turboprop engine is the same as a turbojet engine, except that a turbine is added behind the combustion chamber and the propeller at the engine front, which rotates through a speed regulating gear and a shaft. A turbofan engine is used in small commuter aircraft and slow transport aircraft.

This type of engine has a propelling nozzle, a turbine, a combustion chamber, a compressor, a reduction gear, and an inlet. In this engine, firstly, the air is introduced into the combustion, where it is compressed. After air compression, fuel is drawn into the chamber where it mixes with air, and the fuel-air mixture ignites.

The hot ignited gas expands through the turbine. Some amount of the energy generated by the turbine uses to run the compressor. After this process, the combusted gas exhausts from the back of the engine.

Turboprop engines normally have more efficiency at lower speeds and altitudes than turbojets. Turboprop engines are most commonly used in cargo planes, smaller commuter planes, and other aircraft that don’t need the high-speed running of a jet.

Working of Turboprop

The working of the turboprop engine is very similar to the gas turbine. A turboprop works in the following way:

Turboprop Engine Working

Firstly, the engine sucks air from the atmosphere into the compressor of the engine.
A turbofan engine uses a centrifugal compressor for air compression.
As the air reaches the compressor, it compresses the air up to high temperature and pressure.
As the air is compressed according to the requirements, the compressor sends it into the combustion chamber.
When the compressed air is reached into the combustion chamber, a fuel injector injects fuel into the comber, which mixes with the air.
Due to the high compression of air, the fuel-air mixture ignites itself.
The ignition process increases the temperature and internal energy of the air-fuel mixture.
After the combustion process, the combusted fuel-air mixture is transferred into the turbine area, where it is expanded.
As the high-speed air-fuel mixture strikes the turbine blades, the blades extract maximum power of the air-fuel mixture to drive the compressor, and a very small amount of exhaust gas energy is discharged into the atmosphere.
When the compressor receives power from the turbine, it further drives the propeller of the engine (as you can see in the above diagram). As the engine propeller starts rotating, it generates thrust, which helps the airplane to move forward.

For a better understanding, watch the following video:

Components of Turboprop Engine

The turboprop has the following major components:

Air inlet
Compressor
Combustion chamber
Fuel Injector
Turbine
Propeller
Exhaust

1) Air Inlet

A turboprop engine needs an air inlet section from where it can suck air. This part of the engine uses to transfer air from the atmosphere into the engine. If a turboprop engine will not have this part, it can’t run.

2) Compressor

A turboprop engine uses an axial centrifugal compressor. In this compressor, the air enters and discharges in the axial direction to the shaft.

A centrifugal compressor uses an impeller and diffuser to compress the air. After suction, when the air strikes the blades of the impeller, the blades supply K.E. to the air and increase its velocity. After increasing the air speed, the impeller transfers this air to the diffuser.

The diffuser also has multiple blades. It slows down the air and transforms the air speed into pressure. In this way, a compressor increases the pressure and temperature of the air. After this process, the high-pressure air is delivered to the combustion chamber.

Read More: Different Types of Compressors

3) Combustion Chamber

When the pressurized air reaches the combustion chamber, a fuel pump injects fuel into the combustion chamber. As the fuel is mixed with compressed air, the ignition process occurs due to the high pressure and temperature of the compressed air.

When burning occurs in the combustion chamber, the temperature of the air-fuel mixture becomes very high. During this process, the pressure of the mixture remains constant.

4) Turbine

The turboprop uses a gas turbine that has multiple blades. These blades use to extract energy from the working fluid. When combusted air-fuel mixture comes into the turbine, it strikes the turbine blades. These blades extract the maximum power of the air-fuel mixture.

The turbine is used this extracted power to turn the shaft. This is the same shaft that links with the compressor and all other engine parts.

5) Reduction Gearbox

This is a type of transmission system used in turboprops. A gearbox is linked with the same shaft that runs the compressor. It links the engine and propeller. This part of the engine is utilized to decrease the engine rpm. The higher the rpm output, the faster the propellers will turn.

If a reduction gearbox is not installed, the propeller will turn with high rpm, and the engine will consume a very high amount of fuel. Therefore, a speed-reduction gearbox uses to improve the fuel efficiency of the engine.

Read More: Bad Gearbox Symptoms and Causes

6) Propeller

It is the most major part of the turboprop engine. It is connected to the gearbox, which is further linked with the compressor. When the turbine sends delivers rotational power to the compressor, the compressor turns and further sends its rotational energy to the reduction gearbox.

The gearbox adjusts the speed received by the compressor and drives the propeller. When the propeller gets power, it generates thrust by pushing the surrounding air backward. Due to this produced thrust, the airplane moves forward.

The propeller works well until the aircraft’s airspeed is high enough for air to flow through the blade tip to reach the sound speed. Beyond this speed, the ratio of the force driving the converted propeller to the propeller thrust drops sharply. Therefore, turboprop engine is not depleted in aircraft flying at speeds above Mach 0.6-0.7.

Advantages and Disadvantages of Turboprop

The advantages and disadvantages of the turboprop engines are given below:

Advantages of Turboprop Engines

Turboprop engines have low weight than turbojet engines due to that they perform well during takeoff.
This engine has more efficiency.
It provides more output power than a jet engine.
The turboprop airplane has the capability to land on non-concrete and shorter runways.
A turboprop has low cost than a turbojet engine.
These engines burn less fuel.
It has more reliability due to fewer moving parts.
It has a low maintenance cost.
A turboprop engine is more efficient than a turbofan engine at a flight speed less than 725 km/h.
It has unwavering mechanical property due to few moving parts.
It has a simple operation.

Disadvantages of Turboprop

These engines have a low cruising speed.
Turboprop engines can’t fly at high altitudes.
The slower speed of this engine makes the flight time longer.
These engines are not best for long-distance travel.
At high altitudes, the propeller loses efficiency.
It has a high vibration level which makes the passengers uncomfortable.
Due to the working height, climatic turbulence on the road can cause problems and additional inconvenience for travelers.

Turboprop VS Jet

The main difference between a turbofan engine and a jet engine is given below:

Turboprop Engine	Jet Engine
A turboprop uses a propeller to generate thrust.	A jet engine produces thrust by using a propelling nozzle.
They have low cruising speed.	These engines have high cruising speed.
These engines can’t fly at high altitudes.	These can fly at high altitudes.
These are best for low and medium-distance travel.	They are best for high long-distance travel.
Turboprop engine consumes low fuel.	Jet engine consumes high fuel.
It has a low cost.	It has a high cost.
These engines have low maintenance costs.	These engines have high maintenance costs.
It has fewer moving parts than a jet engine.	It has many moving parts.
A turboprop engine has low weight.	A jet engine has a high weight.
The airplane having turboprop can land on non-concrete and shorter runways.	Airplanes having jet engines cant land on non-concrete and shorter runways.

Turboprop Applications

General Aviation and Commercial Aircraft: Turboprop engines are most commonly used in cargo and smaller passenger planes.
Unmanned Aerial Vehicles (UAVs): Turboprops are also employed in a few larger drones or UAVs
Military Aircraft: They are employed in various military applications, such as surveillance aircraft, transport aircraft, and some other light attack aircraft.
Agricultural Aircraft: They are employed in agricultural aircraft that need good low-speed performance for various jobs like crop dusting.
Maritime Patrol Aircraft: Turboprops are also used in maritime patrol aircraft because of their ability to fly for a long time at lower speeds.
Helicopters: Turboprops are also used in some helicopters where these engines are usually denoted as turboshaft engines.

FAQ Section

Does turboprop have a mechanical compressor?

The turboprop engine has many compulsory components for generating thrust. A turboprop has a centrifugal compressor for the compression of air. Without a compressor, the ignition process can’t occur in a turboprop.

Who invented turboprop?

The engineer György Jendrassik invented the first turboprop. He patented his invention on 12 March 1929.

Is N1 the same as Ng?

Rather, the torque and speed of the propeller are utilized to adjust power, and N1 uses to observe system operation and control engine starting.

Note: NG and N1 are usually interchangeable values for turboprops.

Is turboprop better than piston?

The piston or reciprocating engine has a very simple design, but the turboprop or propeller engine has far fewer rotating parts, and the vibration-free, smooth operation of the turboprop engine generally provides more extraordinary longer service and intervals than reliable piston airplanes.

Is turboprop louder than a jet?

The cabin of a turboprop aircraft has 10 to 30 decibels higher noise than the noise level of a commercial jet aircraft. In contrast to jet noise, the noise spectrum of a turboprop engine is dominated by some low-frequency noises.

What is the purpose of turboprop?

The main function of the turboprop is to deliver propulsion to the aircraft. This propulsion helps the aircraft to achieve lift and maintain flight.

Who are the best turboprop aircraft manufacturers?

Daher
Cessna
Piper
Pilatus
Piaggio
Beechcraft

How is a turboprop engine so fuel efficient Powered by?

The turboprop is so fuel efficient because of its method of transforming fuel into thrust. In the turboprop engine, the maximum fuel energy is utilized to run a propeller, which further runs a large amount of air at slower speeds, compared to a turbojet, which transfers a small amount of air at high speeds. This feature enables turboprop engines to be more efficient at lower altitudes and slower speeds.