October 7, 2022, ©. Leeham News: Last week, we discussed the reality of mass fractions for certified aircraft. There is an abundance of statistics on projects that have gone through the arduous development and certification phase, which always turns out heavier than projected.

Using such statistics, we have a base from which to fly a typical hover and cruise eVTOL design and see what we get in terms of energy consumption and range.

Figure 1. The Vertical Aerospace VX4 in an early rendering with similar looks to the eVTOL we discuss. Source: Vertical Aerospace.

To capture the energy consumption of our typical four-passenger eVTOL, we need to look at how much energy the different phases of a mission consume. For this, we need to define a typical mission.

We operate our eVTOL in an air-taxi style feeder role to a larger airport, where regional airlines take over and fly the passenger to his destination or a major hub. We don’t set a defined range or mission time; instead, we discuss a feasible operational profile given the eVTOL design and whether we fly VFR or IFR due to weather. Then we discuss the resulting range and if it’s operationally suitable for this type of mission.

Let’s start with the easy parts first, the beginning of the mission:

Then we come to the more troublesome part of the mission, the descent and landing:

We now have the mission parameters we need for our energy consumption calculation next week. Funnily, the vertical part is the simple one. The more difficult calculation is the forward flight phase.

 Category: Aircraft Certification, Aircraft Development, Bjorn's Corner, Electric Aircraft, Future aircraft, VTOL

 Tags: eVTOL, Mission parameters, Mission range

20-30 Minutes flight reserves for aircraft that can hardly make their foreseen flights even with tomorrow’s hoped for battery capacity..

Apparantly the eVTOL industry is hoping for major exemptions and wavers from flight safety and ATC requirements?

Or lots of alternative heliports with an UAM industry standard autoland systems close to your intended destination. If the destination is an airport you don’t transition to vertical mode just make a rolling landing. Similar for T-O from an airport to use an available UAM short runway. In the cities you need vertiports and you need reserves, still you can always turn back to the city airport and make a rolling landing if battery juice is enough. If might be a US certification requirement to be able to make a rolling landing on baseball diamonds or football stadiums. Like interrupting a Yankees game during bad weather for a couple of UAM’s landings to be pushed off field by Linebackers after landing.

Linebackers at a Yankees game makes as much sense as anything else about electric air taxi’s. Maybe they will put that in the MLB/NFL collective bargaining agreements.

Fotball is MetLife stadium, sorry, still might work as well. Guess the Referrees will need another flag color to throw for UAM emergency landings.

Bad weather at one heliport is usually also bad at any other nearby. If these aircraft ever fly their range limitations mean they’ll be fair weather only.

Good lights at Yankee stadium for evening landings and good wind protection as you get close to ground. Well, the ATC will decide which landing site is best for the moment and which emergency landing spots to use. All of them preprogrammed into a RNP type of GPS WAAS precision landing. One would assume all UAM’s will have Automatic Dependent Surveillance – out and in boxes.

So build Yankee stadiums all across the country?)

Setting up Veriport will probably be similar to Heliports and it is non-trivial.

https://aviationweek.com/business-aviation/safety-ops-regulation/considerations-rooftop-heliports-part-2

https://aviationweek.com/aerospace/faa-releases-interim-vertiport-design-guidance

Since all these flights are bound to be short, there is very little risk of landing weather becoming a lot worse than what it was at the time of takeoff. Because of that, it may make sense for the lower (helicopter) times to be required, although it seems logical that it be in hover mode.

Surprising number of planes that flew and were very different but either not accepted more widely or only a very limited practicality These ‘vertical taxis’ will likely join these, including Goodyear Inflatoplane and Nasa flying Bathtub

https://www.pilotmall.com/blogs/news/20-of-the-weirdest-planes-ever-to-take-flight

Initial operations are meant to be short-duration and short-range. I highly doubt that there will be much consideration for IFR in the beginning. With short range/duration, localised weather prediction becomes less of a problem (still a problem, just maybe not as big as implied in the article).

However, limiting ops to VFR will definitely detract from the appeal of such a service, in terms of convenience and availability.

The heights they say they want to fly at indicate it will often be in cloud , in say Europe and US Northeast. It doesn’t have to be extreme weather for beyond VFR , just in cloud will cover that. And yet for the range they want to be at the extreme altitude for non pressurised cabins, now you suggest they can be VFR as well. It all doesn’t add up

Yes, at many locations the weather can switch very fast. I can think of Japan, Tasmania, Iceland, Newfoundland, Fairbanks Alaska, Denver as called in the US “weather whiplash”. It can be hard to notice as when moist air freezes to clear ice and would effect UAM’s quickly as few will be certified for flight into known icing conditions. After a few accients Rain and Ice protection systems ATA30 will be mandatory..

Maybe the electric vehicle can pick people up in front of their house/ office, it can be super silent, spacey, go in real bad weather & cost 10 times less to build and maintain. And you don’t need next gen ATC and pilot linceses. Name it EQ, Tesla or iX.. order thousands today for delivery within a year.

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