ターボプロップエンジン (Turboprop Engine)

ターボプロップエンジンとは？

A turboprop engine is a gas turbine powerplant where the majority of power extracted from combustion drives a propeller through a reduction gearbox rather than being converted entirely into jet exhaust thrust. This configuration is highly efficient at speeds between 250–450 knots and altitudes below 30,000 feet, making turboprops the preferred choice for regional and commuter aircraft.

仕組み

Like all gas turbines, a turboprop draws air in, compresses it, mixes it with fuel, and ignites the mixture. The key difference is the power turbine stage:

• Power turbine: Extracts 80–90% of combustion energy to drive the propeller shaft.
• Reduction gearbox: Reduces turbine speed (typically 20,000–30,000 RPM) to propeller speed (1,000–1,500 RPM). Without this, propeller tips would exceed the speed of sound, causing severe noise and efficiency losses.
• Residual jet thrust: The remaining exhaust provides a small amount of additional thrust, typically 10–15% of total output.

Turboprops deliver Thrust far more efficiently than pure jets at lower speeds because propellers accelerate a large air mass at low velocity — the most thermodynamically efficient thrust mechanism at subsonic speeds below Mach 0.6.

性能仕様

• Power output: 500–6,000 shaft horsepower (SHP) depending on size
• Cruise speed: 250–400 knots (compared to 460–490 knots for regional jets)
• Optimal cruise altitude: 15,000–25,000 ft
• Fuel efficiency advantage over jets: 25–40% lower fuel burn on short sectors (<400 nm)
• Break-even vs jet: Turboprops typically more economical on routes under 400–600 nm

航空機の事例

• ATR 72-600: Pratt & Whitney Canada PW127M, 2,475 SHP each — world's best-selling turboprop airliner
• Bombardier Q400: PW150A, 5,071 SHP — fastest turboprop airliner at 360 knots cruise
• Cessna Caravan: PT6A-114A, 675 SHP — iconic single-engine utility transport
• Lockheed C-130 Hercules: Allison T56, 4,591 SHP × 4 — military tactical transport workhorse
• Pilatus PC-12: PT6A-67P, 1,200 SHP — premium single-engine turboprop