The analyzes of P. Langlois on "flying shuttles":
Electric shuttles, a convergence of technologies
Written by Pierre Langlois
The 23 / 01 / 2017
There are at least four different technologies, other than battery chemistry, that are expected to mature in the next decade and facilitate the advent of electric powered shuttles. A paradigm shift on the horizon.
Already, autonomous electric cars are a reality. The improvement of the sensors (radars, lidars, sonars, digital cameras), the very important decrease of their cost, the constant increase of the computing power of the processors, the precision of the GPS and the connectivity between the vehicles are at the origin of the rapid growth of robotic driving.
As road regulations allow, more and more segments of driving will integrate robotics. At first, highway driving and parking, then urban driving, more complex.
This same robotic driving will obviously apply to electric flying shuttles (NVE), and to reassure many readers, for the NVE to become a reality, there will be no question of allowing total freedom in the movements of these aircraft and to produce a cacophony above our heads. It is certain that we will create traffic corridors, a bit like virtual highways. There will be no intersection of trajectories because the movements in different directions will be at different heights in the sky. And the NVE will talk to each other to avoid potential collisions.
Moreover, to limit the number of NVEs in the sky, it will be important to focus on public transport for these aircraft, which makes sense also at the economic level, since these NVE will not be given and that we will be interested in using them for more than an hour a day.
Ultra-light and ultra-efficient range extender
Currently, the company Ehang is developing a NVE that can carry two passengers and fly at 100 km / h for about twenty minutes on a full charge of its battery. And, as we saw in my last post, for fast intercity transport, one would need NVEs capable of reaching 150 km / h for one hour.
It would therefore quadruple the energy density of the batteries if you fill up the 100 km, recharging or exchanging the battery in specially designed heliports. This recharge would be done during a stop of about 5 minutes to get up or down passengers.
A decrease of an 2 factor of the weight of the batteries seems achievable within ten years, but an 4 factor could take 20 years. Never mind, we can always add an ultra-lightweight and ultra-efficient range extender that consumes advanced biofuel (next section).
Such a range extender is currently under development by the company Liquid Piston, and I spoke about it recently in my 19 December 2016 ticket. Much lighter than a traditional combustion engine, this company's rotary engines are 30% more efficient than a diesel engine!
Advanced biodiesel emitting significantly less GHGs
The Finnish company Neste has developed a synthetic diesel fuel made from vegetable oils, very similar to petroleum diesel. This new advanced biodiesel can mix in all proportions with petroleum diesel, up to 100% biodiesel, and presents no problem in very cold weather, which is not the case of traditional biodiesel. In addition, no modifications must be made to the engines of the vehicles. This is called a "drop-in" biofuel in the English literature. Finally, this advanced biofuel Neste burns more cleanly and can reduce up to 90% greenhouse gas (GHG), according to a recent article by Green Car Congress.
Moreover, in the electronic magazine Les Affaires, François Normand told us, the 17 January 2017, of a $ 1 $ project to set up a biorefinery in La Tuque, Quebec, in 2023. It would produce advanced biodiesel from forest residues, using the Neste process, which is a partner. A non-profit organization, Bioénergie La Tuque (BELT) was set up to pilot this project.
Instead of using vegetable oil from oil plants or recycled vegetable oils (food industry), bio-oil would be produced using a portable pyrolytic reactor that would be moved over the countless kilometers of roadways. wood of the region (the city of La Tuque is as big as Belgium). The bio-oil would be sent to the biorefinery, greatly reducing the costs of collecting biomass. They are in preliminary studies that should lead to a pilot biorefinery eventually if the preliminary results are conclusive. Then we would build a commercial plant at La Tuque, for 2023 hopefully.
New ultra resistant and ultra light materials
If we manage to reduce the weight of the NVE structure, it is the equivalent of reducing the weight of the batteries. However, MIT researchers have just announced the discovery of a new graphene material structured in a three-dimensional network, which is 20 times lighter than steel and 10 times more resistant! If we manage to produce it on a large scale at a competitive price, it is a real revolution on the horizon, especially for aeronautics.
What MIT researchers knew at the beginning was the importance of the shape of materials to increase their mechanical strength, in addition to their intrinsic strength of course. For example, a sheet of paper offering very little structural strength, sees this resistance increase much if it is rolled. Similarly a flat sheet of steel is much less resistant than a corrugated sheet. So they looked for 3D shapes with the greatest resistance. To help them in this process, the researchers produced several plastic forms using an 3D printer and tested their resistance. The illustration below shows one of the most promising forms they have tested.
In summary, the use of a 30 range extender more efficient than a diesel engine, which would consume advanced biodiesel emitting much less GHG (over its life cycle), for 30% 50% of kilometers ( the rest of the mileage would be electric), is a solution that would make functional NVE with only a factor of two reduction of the weight of current Li-ion batteries, from 10 to 15 years. Especially if we use ultralight and ultra resistant materials.
Let's not forget also that we aim for fast inter-urban public transport and that consuming a little advanced biofuel for a part of the kilometers offers a transient alternative that is entirely acceptable. Not to mention that a range extender provides redundancy for the power source, which increases security.