Estimating the Economic Viability of Advanced Air Mobility Use Cases: Towards the Slope of Enlightenment

Round 1

Reviewer 1 Report

This research investigates the operating cost of an airline including capital, wage, crew, maintenance, terminal, and fuel in advanced air mobility market. Here, many subtle points have been mentioned in the article and interesting results have been obtained, which of course are similar to the results of the analysis of existing airline operations. Also, the effect of variation of flight cycles and load factor that influence the cost is studied by sensitivity analysis on flight cycle, load factor, and.

The idea is interesting, the best available papers are considered by the authors and the manuscript, especially the outlook section, is well-organized. However, it needs clarification of some matters before it could be considered for publication in the MDPI Drones.

-          The presentation of the unit cost in Eqn. (2) in its current form is a bit confusing. Please explain it in a better way.

-          Please clarify why the block Time is taken to be fixed (0.83hr)

-          What is P_OEM in the Eqn. 8? Please clarify Eqns. 7 and 8 by an example.

-          I believe that E-Hang 216 is not a good candidate for intra city, considering the travel distance and maximum payload.

-          Inspection cost may exist in the maintenance cost.  The authors are advised to take it into account.

-          Table 5 does not give a good overview about the benefit in the aspects of energy consumption and time saving of AAM in comparison to general aviation. It would have been better for the authors to use dimensionless numbers for comparison.

-          In aeronautical industry the profit margin, is usually less than 10%. Since this value affects economic viability, I suggest the authors to examine the profit margin more carefully.

-          The captions of some figures (3, 4, ..) are partially disappeared.

-          Please add ASK to your abbreviations.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The article estimates the direct operating costs of a short-range
electric aerial vehicles for urban and suburban mobility. Since this
type of transportation is expected in the relatively near future
(at least one company is preparing to begin operations in South
America), the results presented in the article will be of interest
to readers.   Nevertheless, there are some points that need to be corrected or
additionally explained:   1. In the manuscript, fuel consumption is calculated based on the
unit price per kilometer. This is unusual for aircraft, where
consumption is proportional to the mass of the aircraft. For
conventional aircraft, the Breguet equation is used because it takes
into account that the mass of the aircraft changes during flight.
Since the mass of electric vehicles does not change during the flight,
a simple energy consumption calculation based on the unit per mass
and kilometer can be applied. Therefore, the authors should estimate
the fuel price using the price per km per kg instead of just per km
or explain why the price per km is the better choice.   2. In line 189, the authors give C_energy=0.4 EUR/km without
explaining how this number was estimated. The authors emphasize
that the fuel consumption of this type of vehicle is not known.
However, a simple model evaluated from the general aviation case and
based on physical principles can be applied.   3. Equation (3) should simply be operating time/block time. The "operationtime-downtime" used by the authors is probably meant
as "operation time with maximum utilization-downtime". This should be
explained precisely, since "operation time" simply means the number
of hours the vehicle is in operation and already includes downtime. Similarly, block time is defined as flight time + ground time
(turnaround time). So the "flight time+block time" should be either
just "block time" or "flight time+ground time"   4. In equation (6) the distance term is missing   5. The landing charge (in equation (4)) and the estimated value of
6 EUR/passenger should be explained in more detail. Airports usually
charge fees for landing or takeoff (the use of the runways with all
the infrastructure), for passenger handling, for security, and for
the use of infrastructure (toilet cleaning, baggage handling, etc.).
Some of these fees are charged per passenger, some per unit of mass,
and some as a unit value. Which of these fees are included in the
"6 EUR/passenger" and how are the fees charged per unit of mass or
per unit only converted per passenger?   6. Can you please explain how eq. (7) is obtained, as this is not
usual term for annual depreciation cost (see for example eq 14.12
in https://www.fzt.haw-hamburg.de/pers/Scholz/HOOU/AircraftDesign_14_DOC.pdf9   7. Authors estimate that the utilization of the air vehicles will
be close to maximal possible (12 hours per day with shortest possible
turn around time and downtime). Nevertheless, it is evident from
aircraft schedules that only large aircraft have such utilization,
while smaller regional aircraft have lower utilization. Therefore it
would be interesting to include graphs showing how the price per km
changes with the utilization instead of just looking at three scenario
possibilities.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

General Comment

In the current paper, the authors perform an economic viability study for the envisioned Urban Air Mobility segment with a focus on the direct operating costs. I found the paper interesting and aligned with a current research theme. However, from my point of view a more detailed discussion on the assumptions made should be included, especially covering the implications on the results.

 

Comments and Questions

From my point of view, you should complete reference 1 to 5 for the interested reader to check them directly. The same applies to references 8, 11, 16-29, 31-33, 37-42, and 49.

What was the rationale behind the assumptions presented in appendix B? From my point of view a reference or a brief discussion on each assumption (namely what would be the implications of altering it) should be provided.

What was the drag model used for the mission profile? Did you assume a constant lift to drag ratio for each considered aircraft or just an airspeed for cruise?

Why have you assumed a landing fee of 6€ and not another value? I suggest to use values similar to those applied to helipads/heliports.

You use as basis of reference for some discussions and options the general aviation segment. However, rotorcraft/helicopter segment might be more adequate given the vertical rotors and provide more conservative cost estimations. Please not that some decades ago there was a service similar to UAM in New York operated by helicopters.

Why have you assumed a cleaning cost of 10€? Is it based on other means of transportation?

What does the OEW include? Does it include batteries for the VTOL aircraft? Please note that the OEW for general aviation aircraft running on conventional fuel does not include fuel, i.e., the energy source.

In section 3, it is worth noting that the Archer Midnight is not quite a multirotor. I would rather label it as a lift + cruise configuration since it also has a wing which allows it to fly faster.

I would suggest to add lines connecting the parts of the wheel chart to the values around it to help the reader.

What does it mean the parameter a in Table 4? What about parameter d? Are these parameters units (per year and per day, respectively)?

On page 11, you should note that a reduction of passengers alters the energy consumption of the aircraft since trimmed flight conditions are different.

In table 5, you present also information about the regional AAM. If you want to maintain it in that table, you should provide a description in text and adapt the caption. Furthermore, from my point of view, it would facilitate the comparison if you split in two the values of AAM.

I would suggest introducing a sub-section 4.6 with a comparison with other means of transportation for the 3 cases, for instance in terms of price and travel time.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors answered all my questions in a satisfactory way.

Author Response

Thanks for you feedback.

Best,
Jan Pertz