Dişlili Turbofan (GTF: Geared Turbofan)
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Definition
Fan ile alçak basınçlı türbin arasında bir redüksiyon dişli kutusu kullanan; her birinin optimum hızda dönmesine izin veren turbofan tasarımı.
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.
Related Terms
Baypas Oranı
Motor çekirdeğinin etrafından geçen hava kütlesinin çekirdekten geçen havaya oranı; yakıt verimliliğinin temel göstergesi.
Nasel
Bir uçak motorunu çevreleyen ve koruyan, sürtünmeyi ve gürültüyü azaltırken hava akışını yönlendiren aerodinamik muhafaza.
Özgül Yakıt Tüketimi
Motor yakıt verimliliğinin ölçüsü: saat başına üretilen birim itme başına tüketilen yakıt kütlesi; lb/(lbf·h) veya kg/(kN·h) olarak ifade edilir.
Türbofan Motor
Ticari havacılıkta kullanılan en yaygın jet motor tipi; itmesinin çoğunu üretmek için büyük bir fan kullanır.