The reduction gearbox reduces the RPM of which turbine?

• A. Gas turbine
• B. Power turbine
• C. Compressor
• D. Fluid turbine

Answer: (B)

The key idea is that a turboprop or similar engine uses a reduction gearbox to slow down the turbine that actually provides thrust power to an external load. The power turbine spins very fast to extract energy and drive the propeller, but propellers (and many other loads) run best at a much lower speed with higher torque. The reduction gearbox takes the high-speed power turbine output and reduces its RPM to a suitable pace for the propeller, delivering usable torque.

The other part of the engine—the gas generator turbine (which drives the compressor) runs at its own high speed and isn’t limited by the gearbox for the load-facing work. That’s why the gearbox is associated with the power turbine, not the compressor.