You’re building a new road to a city – except that the city does not exist yet.
Once you’re done building the road, you’ll have to build the city too.
You’re quite sure that this city – built from scratch, will be much better than any city built before – since it can be designed carefully and use the best of previous methods.
The creation of this city is quite important – as it may be the only refuge for billions of people.
This metaphor describes the pursuit of building electric aircraft.
The Things Needed to Make Electric Aircraft Physically Possible
Better electric propulsion using air (fans)
Better electric energy storage (battery)
Better aircraft efficiency (lift/drag)
It is straightforward to calculate the base requirements to make a useful (5+ hrs) aircraft.
Independently, you would need,
Aircraft Efficiency Lift/Drag Ratio of ~55
Energy Storage Density of ~1100 Wh/kg
NOTE : Constants used above are based on current “standard” technology :
L/D = 10, Energy Density=205 Wh/kg, & Efficiency = 15 N/kW, when not optimization
The above analysis only uses 2 assumptions: straight-level flight & battery mass fraction = 0.5
Each one of the above numbers is significantly beyond the current technology horizon!
In fact, some of them may be argued to be a physical impossibility! Particularly energy density, which has a feasible maximum of ~850 Wh/kg due to the amount of electrons which can be bound in an atom. Also a lift/drag of 55 is unheard of, with the best aircraft ever attaining ~37.
As each individual technology gets better, however, there will come a time when electric aircraft are possible. Nothing in physics prevents this from occurring.
In other words, the balance of better numbers in each area can lead to electric success.
For instance! Let’s say that,
Batteries can bottle 400 Watt-hours per kilogram,
A propulsor can do 20 Newtons per Kilowatt at 95% efficiency,
Aircraft can attain L/D of ~20 in level flight.
With these (doable) numbers, a 5hr electric aircraft is both possible and feasible!
How long will it take to get 400 Wh/kg?
At 5% – 8% improvement per year? 20 – 12.5 years
How long will it take to get 20 N/kW @ 95% efficiency?
20 N/kW is around what Cessna propulsors do at sea level, but not near 95% efficiency.
Electric propulsion is 90% + efficient today.
Therefore with the right engineering, we can already do this.
How long will it take to get to 20 L/D ratio aircraft?
So where does that leave my project of the last 6 months, Propulsor Zero?
The thesis of Propulsor Zero:
Dramatic increases in propulsion will make electric aircraft possible, in sooner than 10 years.
The organizing principle of Propulsor Zero:
Utilizing open innovation challenges brings the best minds, ideas and methods to the table.
For the foreseeable future I will continue to study, prototype, and test methods of outrageous propulsion efficiency for electric aircraft as part of Propulsor Zero. The path is not quite clear, but the fundamental tenets remain strong.
In building the road to the city, I am not quite sure where the city will actually be.
Only in the open-minded exploration of many places, can it be found!