Turbo-prop vs. turbo-jet turbines: The power turbine of a turbo-prop engine (which must drive a propeller) is generally ________ the turbine of a turbo-jet engine.

Introduction / Context:
Gas-turbine layouts differ depending on whether thrust is produced by jet exhaust (turbo-jet) or by a propeller driven through a turbine and gearbox (turbo-prop). The fraction of enthalpy drop extracted by the turbine determines its size and work output.

Given Data / Assumptions:

• Turbo-jet: turbine extracts only enough power to drive the compressor and accessories; most exhaust kinetic energy provides thrust.
• Turbo-prop: turbine must also deliver shaft power for a propeller via reduction gearing.
• Similar overall compressor pressure ratios for a given era of design (conceptual comparison).

Concept / Approach:
A turbo-prop diverts a larger enthalpy drop in the turbine to produce substantial shaft power. More stage work extraction generally requires additional turbine stages and/or larger flow areas and blade heights to handle the work and mass flow at acceptable tip speeds. Therefore, the turbine section of a turbo-prop is typically larger (physically and in stage count) than that of a comparable turbo-jet.

Step-by-Step Solution:

Verification / Alternative check:
Cutaway comparisons show turbo-props often have a free power turbine downstream of the gas generator turbine, increasing overall turbine hardware compared with pure turbo-jets.

Why Other Options Are Wrong:

• Same as / smaller than: Conflicts with the added propeller power requirement.
• Identical blade count but smaller diameter: Neither blade count nor diameter is fixed; both scale with design targets.

Common Pitfalls:
Assuming nozzle thrust dominates in all gas turbines; for turbo-props, shaft power is primary, so more energy is extracted in the turbine.

Final Answer:
bigger than