Last month we wrote about the possible return of supersonic passenger flight in the next few years. United Airlines is betting on supersonic startup Boom under the caveat that their upcoming planes will run on Sustainable Aviation Fuel (SAF).
The big question that raises is, if SAF is viable, why aren't we using it for every passenger flight?
The simple answer is that the fuel and the engines that run on it aren't quite there yet technology wise. Boom is making promises about the fuel that the Overture supersonic plane will run on, but those are based on an assumption that the fuel tech will mature enough before the plane reaches a final production stage to be able to deliver on them.
Although it might no be ready for commercial use yet, SAF, which is made up of used cooking oil and other waste fats, is getting there.
If you skim through some recent news headlines then you might notice that the largest passenger plane in the world, the Airbus A380 made a test flight last month running completely on SAF. If you actually read a little deeper then you will realise that actually only one of the giant plane's four engines was running on the sustainable fuel with the other three using conventional aviation fuel.
That doesn't diminish the achievement, or the ambition, though. This is not the first time that Airbus has tried flying planes with 100% sustainable fuel powered engines, they have also done it with A350 and A319neo planes over the last year.
Airbus might be hitting the news with their adventures in SAF right now, but actually the idea of using it is far from new. The important part of what Airbus is doing is the '100%' part, at the moment many of their planes are certified to use up to 50% of SAF mixed with traditional fuels but the plane maker is aiming to have models that are certified to run entirely on the new fuel by 2030.
Some major international airlines, like KLM, are already using a blend of regular jet fuel, with up to 50% SAF on some of their international flights.
Using SAFs in jet fuel isn’t new with airlines such as KLM currently using a blend of traditional jet fuel and up to 50% SAF on some international flights. There are plenty of barriers along the way though, apart from the lack of certification, there is also the cost of the fuel itself, which is up to four times more expensive than fossil-based jet fuel.
The Scandinavian airline SAS has come up with an interesting solution to the cost problem. Scandinavians are among the most climate aware and climate guilty customers in the world, so the airline is giving them the option to pay extra for biofuel. It's an option that can be selected at the time of booking a flight or added on at any time up until departure, with the airline saying they aim to "give travelers the option to reduce their climate impact."
Plane makers and airlines are in a race to try and make flying carbon neutral. The aviation industry as a whole has set a target to reach net zero carbon emissions by 2050, which seems a few decades too late to be honest. On top of that some countries have set far more ambitious targets, like Denmark which plans to have all domestic flights fossil fuel free by 2030.
To achieve the goal of carbon-neutral, the aviation industry isn’t putting all of its eggs in one basket.
SAF is the cheapest and easiest to implement for existing fleets of planes because existing engines can be relatively easily converted to run on the fuel, but other options are being actively explored as well.
Pure battery electric options are being used for small short-distance flights, but they are not likely to make the transition to longer flights anytime soon, due to the weight-power ratio of batteries. Keeping a plane in the air and moving forwards needs a lot of energy, and adding enough batteries to deliver that power for a long flight means adding huge amounts of weight, which means more energy is needed, which... It's a vicious circle.
Hydrogen might seem like an obvious solution, planes that run on a fuel where the only waste product is water, with no carbon emissions at all. The drawbacks of that are the fact that the vast majority of hydrogen currently on the market has been produced using fossil fuels, and that it is hugely expensive compared to other fuel options.
Despite those downsides, Airbus is teaming up with Delta Airlines to develop the world first zero-emission hydrogen aircraft called ZEROe. There are currently three different designs in development; the first two look like current turbo prop and turbofan planes but feature hybrid-hydrogen engines. The third design is a futuristic designed Blended-Wing plane with liquid hydrogen storage tanks stored underneath the wings and two hybrid-hydrogen turbofan engines to provide thrust. Airbus claims that it is planning to bring these planes to the market by 2035