Should Airlines Replace Short-Range Fleets with Huge Numbers of Electric Commuters?

A lot of small is also big

In a recent article about hybrid-electric short range aircraft, I pointed out that a A320-type of aircraft could have energy, emission and further cost benefits in the range of 20 % in a hybrid-electric form due to the way this type of aircraft is typically operated: While short range aircraft is typically designed range of >3000 nm, many airlines (in particular cheap airlines like e.g. Ryanair) fly much shorter distances with it. The shorter the distance, the larger the benefit of the hybridization as proportionally more energy is used from battery with zero local emissions and a powertrain efficiency of approximately 90 % with state-of-the-art technology.

Several people responded to this, that this segment will not exist in the future as it will be replaced by smaller aircraft, for instance eVTOLs and electric commuters. Indeed, this is an idea worth thinking of as it could have several potential benefits for customers if it is cost effective. In this article I would like to share some thoughts on this idea.

Customer’s darling: On-demand service

Let’s start with the most important thing for a successful business: The customer demand. What modern customers are used to in many businesses is what psychologist like to call instant-gratification. If you want something, be it a tasty phad-thai, watch the latest movies or crave for social attention, you can have it with just a few clicks on your phone.

In the transportation sector, ride-hailing services such as Lyft or Uber come closest to this (or simply owning a private vehicle - be it a car or bicycle - that one can use at any desired time). Train connections, or even more so flights, are at the opposite side of the spectrum, where travel times are fixed and you rather have to adjust your time schedule to the departure time than otherwise.

This paradigm established itself as it is more cost-efficient to transport many people in one large batch over large distances than few people in many small batches. This brings up the question, if electric commuters (such as shown in Fig. 1) can be cost-effective enough to break with this paradigm? Clearly, customers (and probably in particularly business travelers) would love to travel at their preferred time rather than being fixed to a given inflexible schedule.

Figure 1: Overview of (hybrid-)electric aircraft programs with capacities < 30 PAX. a) Faradair (UK) b) Ampaire (USA) c) Zunum Aero (USA) d) Eviation (Israel) e) VoltAero (France) f) e.SAT (Germany). Image courtesy of companies named.

A closer look at the cost structure

A typical cost breakdown for the total costs of ownership (TCO) is shown in Fig. 2 [1]: Typically, 36% are spent on purchase, 19 % on personal costs, 22 % on fuel and 23 % on maintenance (and other things such as insurance etc.). At this point, I would like to highlight, that the results shown later strongly depend on this breakdown and in other sources breakdown data can be found that deviates strongly from the cost structure shown in Fig. 2. For instance, in [2] the expenses for fuel are about 40 % while the purchase contributes only 13 % to the TCO. However, the presented cost structure in Fig. 1 seems to be consistent with many sources. Hence, it will serve as our starting point to analyze how the TCO will change if an airline would decide to transport the same amount of passenger from A to B with a fleet of smaller airplanes instead of putting them in one A320.

Figure 2: Breakdown of total cost of ownership of A320-type of aircraft. Data taken from [1].

Instead of buying one A320, the airline will have to purchase N = ceil(150/PAX) smaller airplanes at a purchase price of PriceGA. I assume here an A320 model with 150 passengers. PAX denotes the passenger capacity of the chosen electric commuter.

Further, instead of having 2 pilots for one single A320 aircraft, every smaller aircraft will require to have its own 2 pilots for its operation. Thus, the personal costs will proportionally increase by a factor of ceil(150/(2*PAX)). I assumed the factor 2 as I would think that for a smaller aircraft less service crew members would be required; and pilots for commuters are probably less expensive.

I assume that the proportion of the maintenance costs will roughly stay the same, as I would argue that smaller electric airplanes will require less overhaul but on the other hand, more planes have to be serviced. These two effects could well balance each other.

At last, a very important factor are the fuel costs. In Fig.3 the fuel consumption as a function of passenger capacity is shown for a plurality of state-of-the-art aircraft. Blue points are aircraft models with cruise speeds > 250 knots, red points with cruise speeds < 250 knots. The trend of lower fuel consumption per passenger (FCp) with higher capacity is apparent (that is one of the main drivers for the paradigm described in the previous section). Let’s assume a fit to the blue points of the form FCp(PAX) = A/(PAX +B) + C. It allows to estimate the fuel consumption per passenger depending on the aircraft size. The function is gauged by FCp(150) = FCp_A320, where FCp_A320 is the fuel consumption per passenger of an A320 on its design mission with 100 % occupancy.

Figure 3: Dependency of fuel consumption per passenger on passenger capacity for state-of-the-art aircraft. The fit function FCp has the form A/(B+PAX) + C. The raw data for the plot was collected from public sources.

Using these assumptions and the information given previously, we can calculate the TCO for a fleet of smaller electric aircraft, that have a passenger capacity PAX, a price PriceGA and a reduced fuel consumption compared to today state-of-the-art aircraft with piston engines (or gas-turbines) FCr. 

Now, the problem arises, that an electric aircraft has only been certified recently by Pipistrel ##link## [3] for the first time, so that there are hardly numbers available for real purchase prices apart from announcements here and there [4]. Even more so, there is no data available that allows to judge on the real operational fuel consumption reduction of two airplanes (one electric and one conventional) that were designed for the same mission.

Thus, I decided to take an inverse approach and look at what purchase prices and fuel consumption a fleet of small electric airplanes would be cost competitive with operating an A320, i.e. the total costs of ownership are equal. The result is shown in Fig. 4 (left) for different passenger capacities. I assumed here that the smaller aircraft can be built fully electric.

Wait, what? The price of the aircraft has to be negative to be cost competitive? That’s correct. If one has to fly, say, 15 small airplane each with 10 passengers, each airplane still requires a pilot, a co-pilot (and maybe one board-crew member), driving the personal costs beyond limits. However, we know that most of the times planes fly on autopilots and autonomous flying airplanes are technically feasible. Under the assumption, that the airplane is operated as a “RoboPlane”, the result looks more promising for smaller electric airplanes as shown in Fig. 4 (right).

Figure 4: Lines of equal competitiveness as function of SFC reduction and aircraft purchase price. Left: Including personal costs, Right: For autonomously piloted aircraft. Different colors represent different passenger capacity.

If personal costs for pilot and on-board crew can be omitted (both for the A320 and small electric airplanes), electric commuters can become cost-competitive if the fuel consumption can be reduced by at least 40 %. However, at this reduction level the airplane has to be a gift to the airline. At realistic prices for a 20 PAX aircraft (in the range of 5 M€), the fuel consumption reduction has to be in range of 60 %. For smaller aircraft the low price and fuel consumption reduction are even more stringent. To replace an A320 with 15 or 10 PAX airplanes, their fuel consumption has to be reduced by more than 70 %.

The requirements get even tougher if we assume that also the A320 is developed further and built for instance in a hybrid-electric design that would allow to reduce its fuel consumption by 50%; s. Fig 5 (left). In this case, electric airplanes with 20 PAX capacity would require reductions in the area of 80 % and airplanes with < 10 PAX, reductions in the area of 90 %.

One might ask if this a realistic goal. Remembering that a piston engine or turboprop (as typically used for this size of aircraft) has an efficiency well below 40 % but an electric drive train, an efficiency of 90 %, it looks good. Still, this effect is compensated to a significant amount by the additional battery weight that is required for the same flight range. Thus, increasing battery density is one key ingredient.

Two more effects could come into play in the future that are mainly controlled by government: For instance, in Germany, a high percentage of price for electric energy are taxes that are used to accelerate the decarbonization of the country. It is not unlikely that electric airplanes could be exempt from this tax (and maybe also from VAT), to encourage zero emission flight. This would sum up to a price reduction of 40 % per kWh of energy. This alone could lower the threshold in required fuel consumption reduction to about 40 % to 50 %. 

Secondly, taxes on emissions that are increased step-by-step could be an additional cost block that will eventually rise to a similar level as the costs for fuel. As electric airplanes have a zero emission carbon footprint, it gives them an advantage, that again lessens the requirements for fuel consumption as can be seen in Fig. 5 (right).

Figure 5: Lines of equal competitiveness as function of SFC reduction and aircraft purchase price. Left: Autonomous piloted aircraft, taking into account the SFC reduction of hybrid-electric A320 of 50 %, Right: Same scenario as left but taking into account taxes on emissions that have similar cost impact as fuel.

“Side-effects”

Before coming to the conclusions, I would like to point out two nice “side-effects” that could come with the discussed change in fleet composition.

Noise: Small electric airplanes have a significantly lower noise footprint than a A320. Even if several of them start and land at the same time (to enhance to passenger throughput), their perceived noise emissions are much lower. This is not only very nice for the people living close to airports but particularly interesting for airlines that could extend their flying hours and therefore their average utilization, which is a very critical quantity for an airline’s profitability. Even 24/7 flying may become feasible in some areas where this is deemed impossible with conventional transport aircraft.  

Regional airports vs. flight speed: When aircraft is more silent it opens more opportunities to use (or build) infrastructure in densely populated areas, where flying would be unacceptable otherwise at today’s noise levels. Furthermore, with small aircraft small size regional airports could become economically interesting again. This could compensate for the fact that the cruise speed of smaller electric aircraft would be lower than for an A320 as more people would have an airport in their proximity that offers short-range flights on-demand. In smaller airports also the time-to-departure is usually much lower, reducing further the door-to-door travel time. 

Conclusions

In this article, I discussed the viability of replacing A320-type jets with an equivalent amount of smaller size electric aircraft that could perform the same transport mission. The discussion is based on the typical cost breakdown of A320-type passenger jet operations. From a high-level perspective the following conclusion can be made:

-      The aircraft must be autonomously piloted. Otherwise the personal costs explode and make the concept non-viable.

-      If autonomy is given, a reduction in fuel (or equivalent electric energy) consumption in the range between 40 % to 80 % is required compared to state-of-the-art general aviation aircraft. The lower the passenger capacity, the higher the required fuel savings.

-      If it is taken into account that also the A320 is developed further (and eventually hybridized), so that its fuel consumption is reduced by 50 % compared to current state-of-the-art, the requirements are more stringent, i.e. in the range between 80% to 90 % of fuel consumption reduction.

-      If governments decide to support the growth of zero-emission aviation by reducing taxes on electric energy or increasing taxes on CO2-emissions, the requirements are less stringent, ranging from 50 % (for ~ 20 PAX aircraft) to 85 % (for ~ 5 PAX aircraft)

There are two more effect that were not discussed but will further favor small aircraft:  On the one hand customers are willing to pay a premium for shorter door-to-door travel times and flexibility. To which extent is a question of detailed market research and customer behavior. On the other hand airlines have to keep reserve aircraft and crew stationed in case of unforeseen issues. These costs could be significantly lower with small size aircraft.

References

[1] ICAO: “Airline Operating Costs and Productivity” (2017)

[2] planestats.com: “Cost per Block Hour” (2014)

[3] European Union Aviation Safety Association: “EASA certifies electric aircraft, first type certification for fully electric plane world-wide” (June 2020)

[4] Bye Aerospace: “Projects – eFlyer 4”

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