# Aviation propulsion: Engineering methods

Turbofan, geared fan, open fan, propeller or rotor

Source page: https://www.materialinsights.org/energy/e_aviation/methods/

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)**^[6](https://www.geaerospace.com/news/articles/product/french-connection-air-france-klm-will-use-fuel-efficient-leap-engines-power-new)^[3](https://theicct.org/publication/fuel-burn-of-new-commercial-jet-aircraft-1960-to-2024-feb25) | 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](https://www.rtx.com/prattwhitney/products/commercial-engines/gTF) | 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)**^[8](https://www.rolls-royce.com/media/press-releases/2023/13-11-2023-rolls-royce-announces-successful-run-of-ultrafan-technology-demonstrator-to-maximum-power.aspx)^[9](https://www.rolls-royce.com/~/media/Files/R/Rolls-Royce/documents/others/ultrafan-80-demonstrator-fact sheet.pdf) | 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)**^[10](https://www.geaerospace.com/news/articles/shape-things-come-open-fan-technology-championed-airbus-summit-2025)^[1](https://www.nationalacademies.org/read/23490/chapter/6) | 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)**^[12](https://www.atr-aircraft.com/?p=33934)^[17](https://www.atr-aircraft.com/presspost/atr-powers-its-aircraft-into-a-sustainable-future-with-the-new-pratt-whitney-canada-pw127xt-engine/)^[1](https://www.nationalacademies.org/read/23490/chapter/6) | 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](https://www.safran-group.com/company/safran-helicopter-engines) | 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

1. [Commercial Aircraft Propulsion and Energy Systems Research, chapter 2: Aircraft-Propulsion Integration and gas turbine engines](https://www.nationalacademies.org/read/23490/chapter/6) National Academies of Sciences, Engineering, and Medicine, 2016
2. [Fuel burn of new commercial jet aircraft: 1960 to 2024](https://theicct.org/publication/fuel-burn-of-new-commercial-jet-aircraft-1960-to-2024-feb25) ICCT, 2025
3. [French connection: Air France-KLM will use fuel-efficient LEAP engines](https://www.geaerospace.com/news/articles/product/french-connection-air-france-klm-will-use-fuel-efficient-leap-engines-power-new) GE Aerospace, 2022
4. [GTF engine: the most fuel-efficient engine for single-aisle aircraft](https://www.rtx.com/prattwhitney/products/commercial-engines/gTF) Pratt & Whitney (RTX), 2026
5. [Rolls-Royce announces successful run of UltraFan technology demonstrator to maximum power](https://www.rolls-royce.com/media/press-releases/2023/13-11-2023-rolls-royce-announces-successful-run-of-ultrafan-technology-demonstrator-to-maximum-power.aspx) Rolls-Royce, 2023
6. [UltraFan demonstrator fact sheet](https://www.rolls-royce.com/~/media/Files/R/Rolls-Royce/documents/others/ultrafan-80-demonstrator-fact sheet.pdf) Rolls-Royce, 2023
7. [Shape of things to come: open fan technology championed at Airbus Summit 2025](https://www.geaerospace.com/news/articles/shape-things-come-open-fan-technology-championed-airbus-summit-2025) GE Aerospace, 2025
8. [The most responsible regional aircraft by design](https://www.atr-aircraft.com/?p=33934) ATR
9. [Safran Helicopter Engines: the world's leading manufacturer of helicopter engines](https://www.safran-group.com/company/safran-helicopter-engines) Safran
10. [ATR powers its aircraft into a sustainable future with the new Pratt & Whitney Canada PW127XT engine](https://www.atr-aircraft.com/presspost/atr-powers-its-aircraft-into-a-sustainable-future-with-the-new-pratt-whitney-canada-pw127xt-engine/) ATR, 2021

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_aviation/index.md)
- [Overview](https://www.materialinsights.org/energy/e_aviation/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_aviation/correlation/index.md)
- [Science and limits](https://www.materialinsights.org/energy/e_aviation/science/index.md)
- [Value chain](https://www.materialinsights.org/energy/e_aviation/valuechain/index.md)
- [Unit economics](https://www.materialinsights.org/energy/e_aviation/economics/index.md)
- [Equipment and suppliers](https://www.materialinsights.org/energy/e_aviation/equipment/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_aviation/links/index.md)