Turboprop Engines: How It Work

Can you combine the power of a jet engine with the fuel efficiency of a propeller feature? The answer is— at certain speeds, yes. Yes, you can. Turboprop engines combine the functionality of a jet engine and a propeller unit to create a unique propulsion system. Most jet engines use the thrust of high velocity exhaust, but turboprops use the exhaust of a gas turbine core to drive a propeller that powers the aircraft. How does this work? The engine utilizes the tech of reverse flow.

The turboprop engine has the same basic components of a standard jet engine: a compressor, combustor, and turbine. However, the turboprop design features a reverse flow combustor in a more compact engine.

Instead of standard air intakes, reverse air flow is achieved through large air intakes near the propeller that move air backwards toward the opposite end of the aircraft. When the aft limit of the intake is reached, the air reverts at 180 degrees, in a snake-like bend back towards the front of the engine, bends 180 degrees again to enter the combustor, and once more to flow to the turbine. In a standard turboprop engine, the same turbines that power the compressor pump air flow directly through an additional shaft to the reduction gear box, creating thrust and thus powering the propeller. The overall RPM is controlled by the reduction gear box, which is a collection of reduction gears that will slow the propeller to the desired speed.

Some turboprop models are referred to as a free power turboprop engine. Free power turboprop engines incorporate a reduction gear box that is attached to its own separate power turbine and power shaft. In this case, the compressor turbine does not directly provide power to the propeller. Instead, airflow moves through a secondary series of power turbines. Airflow moves through the airfoil blades and travels through the shaft powering the propeller. A very small amount of exhaust is expended during this process and is diverted from the engine to the exhaust pipes.

The features of the turboprop engine design make it incredibly fuel efficient for low speed, low to mid-altitude aircraft. An aircraft equipped with a turboprop also requires less runway for takeoff or landing, allowing access to remote locations that a jet engine could not reach. For this reason, many rescue and emergency aircraft utilize turboprop technology. In the right scenario, the turboprop is a compact, fuel-efficient option worth considering.

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