We consider that use of SAF is mainly a question of its availability and price. For engineers, it is a matter of sourcing primary energy involved in producing SAF- not to forget that SAF is only sustainable, if the CO2 is really taken out of the atmosphere in fuel production, which is intended to be put back into the atmosphere during flight. LH2 requires new (or modified) aircraft that are less efficient than conventional aircraft. Calculations show about 40% more fuel consumption (by energy) for LH2. This adds to the demand of LH2 for sourcing more primary energy. Batteries for electric flights suffer from their weight (as we already know). In addition, there are interesting aircraft design questions arising from issues such as: higher number of propellers and propeller integration into the airframe. It is explained, why hybrid electric or turbo electric solutions have clear disadvantages. There are also the non-CO2 effects. Here we shall consider flying lower with LH2 and also kerosene/SAF aircraft.
