Rasio Bypass (BPR: Bypass Ratio)
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Definition
Rasio massa udara yang mengalir di sekitar inti mesin terhadap udara yang mengalir melalui inti, indikator utama efisiensi bahan bakar.
Apa Itu Bypass Ratio?
Bypass Ratio (BPR) is the ratio of the mass airflow bypassing the engine core to the mass airflow passing through the core in a Turbofan Engine. A BPR of 10:1 means ten kilograms of air flow around the core for every one kilogram that passes through it. Higher bypass ratios generally translate to greater fuel efficiency and lower noise.
Cara Kerja
The fan at the front of a turbofan accelerates both bypass and core airstreams. The bypass air, expelled at moderate velocity through the fan duct, provides the bulk of thrust efficiently. The core air undergoes combustion and exits at very high velocity, contributing the remainder. The efficiency gain comes from the physics of momentum:
- Low BPR (1–3:1): High exhaust velocity, high noise, lower efficiency. Typical of older jets and military aircraft.
- Medium BPR (4–7:1): CFM56 family, older 737s and A320s. Good efficiency balance.
- High BPR (8–13:1): LEAP, GE9X, Trent XWB. Maximum commercial efficiency and minimum noise.
Spesifikasi Kinerja
- CFM56-7B (737 NG): BPR ~5.1:1
- CFM LEAP-1B (737 MAX): BPR ~9:1 — 15% fuel saving vs CFM56
- PW1100G (A320neo): BPR ~12:1 — geared turbofan architecture
- GE9X (777X): BPR ~10:1 with 134-inch fan diameter
- GE90-115B (777-300ER): BPR ~8.7:1, previously world's most powerful engine
Contoh Pesawat
- Airbus A220: Pratt & Whitney PW1500G, BPR ~12:1 — quiet regional operations
- Boeing 787 Dreamliner: GEnx-1B, BPR ~9.6:1, or Rolls-Royce Trent 1000, BPR ~10:1
- Concorde (retired): Olympus 593 turbojet, BPR 0:1 — pure core thrust for supersonic flight
BPR directly affects Specific Fuel Consumption (SFC). Higher BPR reduces SFC, extending aircraft range. Engine Fan Blades grow larger as BPR increases, requiring wider Nacelles.
Related Terms
Bilah Kipas
Bilah aerofoil berputar besar di depan mesin turbofan yang mempercepat udara untuk menghasilkan daya dorong bypass dan memasok inti mesin.
Konsumsi Bahan Bakar Spesifik
Ukuran efisiensi bahan bakar mesin: massa bahan bakar yang dikonsumsi per unit daya dorong per jam, dinyatakan dalam lb/(lbf·h) atau kg/(kN·h).
Mesin Turbofan
Jenis mesin jet paling umum dalam penerbangan komersial, menggunakan kipas besar untuk menghasilkan sebagian besar daya dorongnya.
Nacelle
Selubung aerodinamis yang mengelilingi dan melindungi mesin pesawat, mengurangi hambatan dan kebisingan sambil mengarahkan aliran udara.
Propfan
Desain propulsi hibrida yang menggabungkan efisiensi turboprop dengan kecepatan seperti turbofan menggunakan bilah baling-baling tersapu dan berbeban tinggi.
Tahap Kompresor
Sekumpulan airfoil berputar dan stasioner di dalam mesin jet yang secara bertahap memampatkan udara masuk sebelum pembakaran.
Turbofan Bergerigi
Desain turbofan yang menggunakan gearbox reduksi antara kipas dan turbin bertekanan rendah, memungkinkan masing-masing berputar pada kecepatan optimal.
Turbofan Bypass Tinggi
Mesin turbofan dengan rasio bypass di atas 5:1, yang mengalirkan sebagian besar udara masuk mengelilingi inti mesin untuk efisiensi bahan bakar maksimum dan kebisingan minimum.