Aviation propulsion: Engineering methods
Turbofan, geared fan, open fan, propeller or rotor
What this tab covers The engineering methods that can do this conversion, compared on efficiency, scale, economics, limitations and reliability.All commercial aircraft engines share a gas-turbine core; they differ in how they turn core power into thrust: a directly driven fan, a geared fan, an unducted open fan, a propeller or a rotor.
Comparison
| Method | Efficiency | Scale | Economics | Limitations | Reliability |
|---|---|---|---|---|---|
| Direct-drive high-bypass turbofan (e.g. CFM LEAP)63 | 15% lower fuel use than the CFM56 it replaced (company claim) | single-aisle jets (A320neo, 737 MAX); more than 20 million engine flight hours by 2022 | the default for 150-240 seat aircraft | fan diameter limited by ground clearance and fan speed | mature; durability of hot-section parts in hot, sandy climates is the main issue |
| Geared turbofan (Pratt & Whitney GTF)7 | up to 20% fuel saving per trip on the A320neo family; up to 25% per seat on A220 and E2 (company claims) | 13,000 engines ordered, 2,730+ aircraft in service, 51 million hours (company figures) | lower fuel cost; durability problems have raised maintenance costs and grounded aircraft for inspections | gearbox heat and weight; hot-section durability | GTF Advantage upgrade promises longer time on wing (no figure given) |
| Large widebody turbofan and geared UltraFan (Rolls-Royce)89 | UltraFan 10% better than Trent XWB and 25% better than the first Trent (company claims for the demonstrator) | 25,000-110,000 lb thrust family | not yet in production | large fans add weight and drag for widebody installation | demonstrator ran to maximum power in 2023 |
| Open fan (CFM RISE)101 | target about 20% better than current engines (company target) | single-aisle successor, flight demonstration planned later this decade | unknown | noise, blade-off safety, cabin installation | 250+ critical tests and 300+ hours of wind tunnel tests so far |
| Turboprop (e.g. ATR with Pratt & Whitney Canada PW127XT)12171 | about 30% less fuel than a similar-size regional jet (ATR claim); ATR also quotes 69 g per seat-km without saying of what (probably CO2) | 30-78 seats; 1,900 ATR aircraft sold | lowest fuel cost per seat on short routes | slower, cabin noise | PW127XT claimed to stay on wing 40% longer, cutting engine maintenance cost by 20% (company claims) |
| Helicopter turboshaft (e.g. Safran Arriel)13 | much higher fuel per passenger-km than aircraft because power is needed just to hover | 21,500 Safran engines in service with 2,500 customers in 155 countries | justified where runways are absent (offshore, rescue, medical) | speed and range | gearbox and rotor fatigue drive inspection schedules |
Efficiency gains come mainly from bigger, slower fans (propulsive efficiency) and hotter, higher-pressure cores (thermal efficiency). Turboprops beat jets on fuel but not on speed; geared and open fans push the jet towards turboprop-like propulsive efficiency. ICCT finds that new-aircraft fuel burn improvement has stalled since 2020, with fewer than one new type certified per year and no new narrowbody planned before the mid-2030s. IATA reports fleet fuel efficiency stopped improving in 2024 and 2025 because of aircraft delivery shortages.
How each method works
Direct-drive high-bypass turbofan (e.g. CFM LEAP)A low-pressure turbine drives the fan on the same shaft, so fan and turbine speed are a compromise. LEAP added ceramic matrix composite parts and higher temperatures.
Geared turbofan (Pratt & Whitney GTF)A gearbox lets the fan turn slower and the turbine faster, each near its best speed, allowing a bigger fan and fewer turbine stages.
Large widebody turbofan and geared UltraFan (Rolls-Royce)Three-shaft Trent engines power long-haul jets; UltraFan adds a power gearbox of over 50 MW and a 140-inch carbon-titanium fan.
Open fan (CFM RISE)An unducted fan of very large diameter, with fixed guide vanes behind, gives a bypass ratio of about 60:1 against 11:1 today.
Turboprop (e.g. ATR with Pratt & Whitney Canada PW127XT)The gas turbine drives a propeller through a reduction gearbox; the propeller moves a large mass of air slowly, giving high propulsive efficiency at moderate cruise speeds.
Helicopter turboshaft (e.g. Safran Arriel)A small gas turbine sends shaft power through a main gearbox to the rotor, which must produce both lift and thrust.
Sources
- Commercial Aircraft Propulsion and Energy Systems Research, chapter 2: Aircraft-Propulsion Integration and gas turbine engines National Academies of Sciences, Engineering, and Medicine, 2016
- Fuel burn of new commercial jet aircraft: 1960 to 2024 ICCT, 2025
- French connection: Air France-KLM will use fuel-efficient LEAP engines GE Aerospace, 2022
- GTF engine: the most fuel-efficient engine for single-aisle aircraft Pratt & Whitney (RTX), 2026
- Rolls-Royce announces successful run of UltraFan technology demonstrator to maximum power Rolls-Royce, 2023
- UltraFan demonstrator fact sheet Rolls-Royce, 2023
- Shape of things to come: open fan technology championed at Airbus Summit 2025 GE Aerospace, 2025
- The most responsible regional aircraft by design ATR
- Safran Helicopter Engines: the world's leading manufacturer of helicopter engines Safran
- ATR powers its aircraft into a sustainable future with the new Pratt & Whitney Canada PW127XT engine ATR, 2021