October 21, 2022, ©. Leeham News: This is a summary of the article Part 42P, eVTOL range. It discusses the range of a typical eVTOL flying a feeder mission from a city center to an airport.
The 42P article details the energy consumption for each stage in the mission and the range we fly. We summarize the results here.
eVTOLs, like all battery-based air vehicles, are severely energy constrained. You, therefore, calculate the range for such vehicles by first listing all the mandatory energy consumption areas. Then you calculate the vehicle range with the energy which is left.
First, we must understand how much energy we can fit into our eVTOL. We defined a mass fraction for energy in Part 39, Figure 2.
We have 743kg to spend on our battery system. If we assume that 700kg is available for battery modules (the rest is Battery management with cabling and liquid cooling system for the 56 modules), we end up with 144 kWh of battery energy for a system delivered in 2025 (energy density on the system level 206 Wh/kg).
We have defined that the battery system has been in use for a while and that a full charge achieves a 90% SOC (State of Charge). Our hover landing requires about 750kW of battery power, and the battery can only deliver such power levels when above 10% SOC.
It might be that the minimum SOC shall be higher for a battery at the end of its life as the internal resistance increases and the maximum current capability decreases. It requires a long-time test to establish which is beyond our scope for the articles. We assume a minimum of 10% SOC is OK.
We now have 114kWh of useful energy to spend on our mission (80% of 144kWh), Figure 2. Not all power can go to propulsion; we need power for all the eVTOL systems and passenger convenience. For our mission, 2.8kWh is blocked for such use.
Before you start mission calculations, you block off regulatory reserves, in our case 35.5 kWh for 20 minutes holding time in forward flight before transition.
We now have 76.8 kWh to use for our flying. Our vertical takeoff and transition take 6,5 kWh, followed by the climb 31KWh. We climb to 8,000ft, which gives a few nm longer range than if we climb to 5,000ft.
Our descent, approach, and vertical landing consume 20.8 kWh. It leaves 11.7kWh for the cruise, which is not a lot. Our total distance covered is 53 nm. It’s when we count all distances. As airports practice arrival and departure procedures, we should only count 50nm or less as a useful range.
It works to fly passengers from a city center to a closeby airport IF the weather is good. We have not introduced any margins for bad weather or flying in icing conditions, however.
It’s not useful for general air taxi services. It will seldom be that travel distances are below 50nm; in such cases, it’s faster to stay in the car and drive the distance. The city center to airport case has the city traffic speed as a motivator for the eVTOL services, the air taxi not.
In the next Corner, we will introduce more variables like non-ideal weather, normal landing instead of hover landing, etc., and see what happens.