The aviation sector must undergo a revolution as commercial air travel is growing at an impressive pace and impact of emissions on climate change at high altitude are deemed very relevant. The targets set by ACARE of 75% CO2 and 90% NOx emission reduction respectively by 2050 relative to a baseline aircraft from the year 2000 are pushing the aviation industry to rethink the way aircraft are designed and operated.
Within the Clean Sky 2 framework a plethora of technologies are under investigation to enable the next generation of aircraft with new technologies to make them lighter, more aerodynamically efficient, quieter, and more fuel efficient.
Aircraft operators use these aircraft to make a profit, which implies that they will fly these aircraft on multiple routes at a combination of speed and altitude that maximizes their revenue. This implies that most transport aircraft fly at altitudes where contrail-cirrus formation is high resulting in a negative impact on global warming.
Also, to cater for network flexibility, most of the routes in the network have a mission range that is considerably below the maximum mission range, which implies that the aircraft is actually oversized in terms of weight, wing area, and engine power to fly these missions.
This results in more emissions and global warming impact on such missions than would be the case for an aircraft that is specifically designed for these missions.
The question is for what top-level aircraft requirements (TLARs) the next generation of aircraft should be designed such that their impact on global warming is minimized while network flexibility is still ensured.
In aircraft design optimization studies, fuel burn, maximum take-off mass or direct operation cost are used often used as cost functions. However, as shown by Vos et al., when an environmental-impact metric is used, such as equivalent CO2 emissions, the optimal aircraft has different wing-loading and thrust-to-weight ratio and flies at a different cruise altitude compared to an aircraft designed for minimal fuel burn.
It is therefore important that if we wish to design aircraft for minimal global warming impact that a Climate Function for Aircraft Design (CFAD) is defined that is sensitive to aircraft/engine design parameters as well as operational parameters.
Climate impact of aviation
More than 50% of the climate impact from aviation arises from non-CO2 effects. Hence it is essential to include these non-CO2 effects in a climate-optimised aircraft design. These non-CO2 effects, stemming, e.g., from NOx emissions and contrail formation, are largely independent from CO2 emissions, and their climate impact largely depend on the atmospheric state.
Therefore, complex climate-chemistry models were used in the past to evaluate the climate impact of aircraft cruise altitude and designs, which is far too computational demanding for a multi-disciplinary optimisation (MDO) process, requiring a multitude of climate impact evaluations.
Instead, climate functions are developed in GLOWOPT, to enable such an MDO process.
In five work packages ambitious challenges are addressed: