Dr. Michael Weigand, is a Professor at the Technical University University of Vienna, Austria, and Head of the Research Unit of Machine Elements and Transmissions for Aviation.
Prof. Weigand, can you explain what Geared Turbofan is?
Prof. Weigard: Conventional/classical turboshaft engines have two coaxial shafts: one for the high-pressure compressor/high-pressure turbine, and one for the low-pressure compressor/low-pressure turbine. The fan is connected to the low-speed shaft and operates at the same speed. The Geared Turbofan of Pratt & Whitney and the UltraFan® of Rolls Royce have a planatery gear stage between the low-speed shaft and the fan to reduce the speed of the fan.
What is the benefit of this design approach?
Prof. Weigard: By reducing the fan speed, larger fan diameters and thus a higher bypass ratio are possible, which increases the bypass ratio, reduces engine emissions by up to 20%, and drastically reduces noise emissions. This makes this design, both economically and ecologically, very interesting. This is highlighted by the following facts: Over 10.000 aircraft (especially the Airbus 320 Neo, – new engine option) have already been sold. To date, the GTF engine family has saved nearly 4 billion liters of fuel and avoided 10 million metric tons of CO2 emissions. Approximately 10% fuel savings lead to lower overall costs when operators change from aircraft with conventional engines to aircraft with GTF´s. The much lower noise is not only an ecological benefit but also reduces operating costs, for example, through lower landing fees at airports.
Why is this technology interesting with respect to actual developments in battery, hydrogen, and fuel cell technology?
Prof. Weigard: The Geared Turbofan Technology is already available today and is not only concerning ecology but also the economy. With respect to the climate goals and timeline, the Geared TurboFan technology will, in my mind, be the only one to contribute in time to these goals. In contrast to "disruptive technologies" like batteries, hydrogen, and fuel cells, the geared turbofan already contributes to lower emissions. New system concepts like ZERO-e by Airbus are announced for 2035 as prototypes; this shows that the new technologies will need at least 10 more years to have a positive effect on emissions and climate.
Why is this technology not the primary focus of technical development?
Prof. Weigard: Gears and gearboxes are underestimated, and decision-makers in politics and funding tend to prefer "hype topics" like batteries, hydrogen, and fuel cells. We work in both areas – in HEROPS as a Clean Aviation project on fuel cells, but also in the project "GREEN-by-GEARS", funded by our national research funding "TakeOff" in Austria. There, we explore the further potential of the Geared TurboFan technology together with our professorships in Thermal Turbomachinery and Aircraft Design. We expect to find further benefits in line with the timeline for climate neutrality in aviation.