기어드 터보팬 (Geared Turbofan) (GTF: Geared Turbofan)
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Definition
팬과 저압 터빈 사이에 감속 기어박스를 사용하여 각각 최적 속도로 회전할 수 있도록 한 터보팬 설계.
What Is a Geared Turbofan?
A geared turbofan (GTF) is an advanced turbofan engine that interposes a planetary reduction gearbox between the large front fan and the low-pressure turbine (LPT) shaft. This mechanical decoupling is the defining innovation: the fan and turbine can each rotate at their individually optimal speeds rather than being locked to the same shaft speed.
How It Works
In a conventional turbofan, the fan, low-pressure compressor, and low-pressure turbine are all mounted on a single shaft. Because the large fan must turn slowly to avoid supersonic blade-tip speeds, the LPT is forced to operate below its aerodynamically ideal speed — a fundamental efficiency compromise.
The GTF's gearbox, typically with a reduction ratio of approximately 3:1, allows the LPT to spin roughly three times faster than the fan. The LPT can therefore be designed with fewer stages (typically 3 vs. 7 in equivalent conventional engines), reducing weight and parts count. The fan, freed from shaft-speed constraints, grows larger — enabling bypass ratios of 12:1 or higher — while spinning at speeds that minimize aerodynamic losses.
Performance Specifications
- Gearbox reduction ratio: approximately 3.0:1 (Pratt & Whitney PW1000G series)
- Bypass ratio: 12:1 on PW1100G (A320neo), 12.2:1 on PW1500G (CSeries/A220)
- Fuel burn improvement: 15–20% over CFM56/V2500 predecessors
- Noise reduction: approximately 75% reduction in noise footprint vs. prior generation
- LPT stages: 3 (vs. 6–7 in ungeared equivalents)
Aircraft Examples
- PW1100G-JM on the Airbus A320neo — entered service 2016, rated at 120–147 kN (27,000–33,000 lbf)
- PW1500G on the Airbus A220-300
- PW1900G on the Embraer E195-E2
- PW1700G on the Embraer E175-E2
The geared turbofan concept, pioneered by Pratt & Whitney with over $10 billion in development investment spanning two decades, entered revenue service in January 2016. By 2025 the engine family had accumulated over 30 million flight hours across more than 1,500 aircraft.