By: John Martin Winther Andersen
Disclaimer: This article has no intention to point out any individuals nor companies professional mistakes, work or investments, but through examples of published infrastructure designs to point out a potential "sell-out" of safety barriers like in the Swiss Cheese model, that in our view has the potential of leading to avoidable accidents and incidents.
With the upcoming eVTOL's servicing local and regional communities all around the world in a network of short routes and flights within the largest cities and metropolis, city-to-city and to/from rural areas and islands, many landing facilities are needed to support the needed infrastructure, incl. in congested areas. Hardly any two places are geographically or physically alike, so at some level individual requirements must be expected to be met.
In congested areas some looks to rooftops of for example parking houses, high-rise buildings etc., because they invite to the usage of an often little to non used piece of property and away from the congested and costly land surface, clearing many obstructions by being high in the air. In theory a great idea.
But from an operational perspective, some of these designs and concepts out there of "High-Flying" Vertiports- and pads seems to have missed a very important element, which laws of physics does not change from its past, so we should learn from our past; The Weather !
Changed Business model, but The Physics of Weather has not
In the 1950-70's there where scheduled flights with helicopters from among different places, the top of New York Pan Am building, some 800 feet above ground level.
The business model has changed since the usage of 50-70's helicopters for shuttling and providing what we today define as UAM services, to the upcoming eVTOL aircrafts. eVTOL aircrafts are designed with a higher level of technical safety than a helicopter has, i.e. no fossil fuel, mechanically simplified (no axels, no gearboxes etc. that can fail), maintenance going to be a lot less, lowering cost and ticket price reaching out to a much larger customer base. There are a lot of redundancy in many electric motors and many rotors instead of 1-2 engines and 1-2 big rotors. All these are good technical inventions and integrations into an aircraft.
But eVTOL's are aerodynamically different than helicopters and does not keep a good property that helicopters has. Explanation follows below.
First a statement from former helicopter pilot of New York Airways, Deene Sanders, his wordings landing on the Pan Am building back in the days in this Bloomberg feature from 2017;
".. it was extremely challenging, especially at night in the weather. Probably the most challenging thing I've ever done, except for getting shot at in Vietnam ..".
That is a type of statement from an experienced helicopter pilot, that some architects, developers, investors and other non-aviators seems to have missed totally out on, when they are designing, building and/or investing in infrastructure some of the places for upcoming eVTOL's. At the end of the day, it is the pilot and his/hers experience, skills and knowledge who is going to takeoff and land on these Vertiports safely and successfully, not the architect nor the developers visions, ideas nor assumptions.
Expect many low-experienced pilots
In addition keep in mind that the average future pilot(s) being at command of an eVTOL in the future, will not be this highly experienced ex-military pilot as Mr. Deene Sanders. Many of the pilots we shall expect to be flying around, will just have passed the minimum legal requirement in experience, especially because in the beginning we will need A LOT of pilots til fill out the seats in all these eVTOL's we expect to buzz around above us, an amount of pilots that simply does not exist today nor tomorrow or the day after.
Even if there where enough highly experienced pilots available, due to cost an eVTOL with just 2-6 paying seats can not afford if the cost is to be kept low enough in competition with other eVTOL operators and land based modes of transportation, to have a highly experienced skipper pulling over $ 80.000 for approx. 700 flight hours per year.
Planners and investors should pay attention to the current status of lack of pilots on ordinary airlines airplanes after COVID19 has ended, how many thousands of flights are being cancelled due to lack of pilots and crew, because among other reasons they fired a lot of them during COVID19. Imagine adding thousands on thousands if not tens-of-thousands of eVTOL's to the stack in not that many years to come of other aircrafts already needing pilots. It takes 1-2 years to educate a newly graduated pilot with less than 200 flight hours training and zero flight hours of operational experience. As my first Chief Pilot said when hiring me right after Flight Academy, ".. now you have to learn to fly .." because one thing is Flight Academy training to pass minimum requirements to get your license, another is to get an operational mindset, knowledge and most importantly, operational experience.
So add another min. 3 years of operational experience in a non-complex environment to make an even medium yoke experienced pilot, and landing on highly elevated platforms is not a non-complex environment.
On top of that the vast vast majority of eVTOL's out there are designed single-pilot, no room has been designed for dual-control onboard like in airliners, small or large airplanes and helicopters, where a training captain can take a newly educated rookie pilot under his/hers wings where they can gain operational knowledge on the job in a safe environment. Not possible for single-pilot cockpit to be training on job with paying passengers onboard the vast majority of eVTOL's.
eVTOL's don't have the gyroscopic stability as helicopters does
Next topic to consider, a major aerodynamically difference between helicopters and the wast majority of eVTOL's. Remember your physics classes back in elementary- or high school ? - Remember if your teacher explained the phenomenon "gyroscopic precession" with a spinning bicycle wheel ? - if not, "Get Smarter Everyday" by clicking the link. On top of the gyroscopic precession the spinning wheel has, it's also hard by external force like your hand to move or tilt that spinning wheel due to its gyroscopic stability.
The main-rotor of a helicopter has similarly physical property as a gyroscope because 1: of its high mass and 2: its high rotation speed. The helicopters large main rotor really don't want to move out of its way, if an external force is pushing on it, for example a gust of wind, strong turbulence and alike wants to push a helicopter out of its path or position, the helicopters main-rotor has a lot of ability to counteract this external force of wind keeping the helicopter much more stable than for example an airplane of similarly mass, that in addition has big non-moving wings (read: large surface area) that the wind really can catch on to push, pull or tors around.
Many eVTOL designs are much more like a small airplane than a helicopter in this respect. Several but small low-mass rotors or propellers and large wing surfaces.
So architects, designers, builders and investors expects such eVTOL's to be able to land safely and comfortably on high-rise buildings on an everyday basis, what is in its essence of size, weight and wing surface of a small Cessna or Piper airplane with some low-mass rotors added to it for vertical lift capacity ? - Or are they fine with operations such places happens only those few days with clear sky and low wind and letting the passengers down on all other days ?
This is what it looks like when small light airplanes with relatively large wing surface untied to the ground are being exposed to strong winds, like here a wind of 55 kts ? - if not for the quick reacting pilots still onboard in each Piper plane and engines running and glider crew, they would have been tumblering around like tumbleweed.
And this happened on ground level on a big open clear unobstructed surface like an airport. Imagine this several hundreds of feet in the air with only the space needed for a few eVTOL's to land and park. No area beyond that and they would have felt to the ground on top of other buildings, pedestrians, cars, cyclists, trains etc..
As mentioned, eVTOL's as an aircraft type are being technically designed more safe with a lot of redundancy compared to any conventional current airplane or helicopter. But that type of safety has nothing to do with the aerodynamic challenge to land and takeoff when weather is blowing high winds, or turbulence, or rain-showers, at night or a combo of some or all of the above. What we refer to landing "in the weather".
If landing a big heavy helicopter on top of the Pan Am building in the weather was by grade of challenge only beaten by flying in the Vietnam War, despite having a large amount of gyroscopic stability and highly experienced helicopter pilots at the helm (often two pilots onboard these large helicopters), imagine a future landing a fairly light, low gyroscopic stable, relatively large wing surface eVTOL with probably one single low-experienced pilot at the helm (and later autonomous) on high-rise buildings as some designs and expectations suggest ...
High-rise Vertiport designs lack of operational perspective
In addition some high-rise designs seem to have very little operational consideration.
For example this concept design UBER Sky Tower by Pickard Chilton where landing platforms are also located midway on the structure right next to tall structures. Anyone who has driven on for example a large tall suspension bridge when passing by its pylons knows how bad in crosswind the turbulence can be and how much ones vehicle gets pulled/pushed from one vehicle lane to another and back again. Now imagine landing on such a spot next to such a structure in even just moderate crosswind in a light eVTOL aircraft with relatively large wing surfaces ...
Or this example of UBER Skyport from Humphreys & Partner, which has a clever thought of always having a pad straight into the wind for landing and takeoff. And that works on the rooftop clear of all surrounding obstructions, but at the lower level platforms, while the takeoff platform on one side is straight into the wind, the opposite landing platforms will be subjected to quite a lot of turbulence because of the way wind tends to act up or around a surface, in this case the building itself, just like aviators are being taught how wind acts behind a line of tall trees or a building, it creates rotors / vortices which can bring small aircrafts and helicopters down if they try to climb through these rotors / vortices in the attempt of clearing the tree line. And you can't land into the wind perpendicular to a platform neither, because your landing and/or takeoff path will likely conflict with the position of another nearby platform, or if need be and we need to plan for it, a missed approach (go-around) is needed.
Plus if we are to operate eVTOL's on elevated platforms on buildings or on the side of buildings, the demand will very likely be to operate them as we operate CAT A helicopters, meaning we can not land nor takeoff in any type of tailwind component, so that is even more limiting where and when we can use platforms designed such places.
Some designs also lacks proper proportions to what to be expected to land on the platform. For example this design from Paramount Miami World Center, a 700 feet tall high-rise. It's New York Pan Am building Heliport all over again, just more challenging due to a much smaller spot to land on vs. the Pan Am rooftop and in an eVTOL much less stable in windy conditions than a helicopter. Remember what the pilot Mr. Deene Sanders said about landing on top of the Pan Am building in the weather ? - ".. Probably the most challenging thing I've ever done, except for getting shot at in Vietnam ..".
Not to mention the potential downdraft from the eVTOL's propellers or jets the open lower floors sunbeds and people staying there is likely to be exposed to during final landing and initial departure. And does the glass fence surrounding the FATO and TLOF area even lower itself before landing and takeoff, so there is no risk for the eVTOL landing gear to catch it, because it doesn't in the advertising video ? - we know from history what happens if a landing gear catch a part of the landing area and the helicopter starts a dynamically rollover throwing the aircraft over board like on this video. Much the same would be expected to happen for an eVTOL depending on designs.
A commercial video like the one of Paramount Miami World Center and videos alike are only at best valid when the weather is sunny in no to calm winds, and does not at large even remotely reflect real life operations.
Vertiports- and pads with single-point-of-failure designs
This topic is not so much a safety matter as the above topics, but it boggles us that some vertiport and pad designs has apparently build in single-point-of-failure in the sense of all operations and business can be shut down if one single thing fails, breaks etc. for hours or days, despite the development of eVTOL's has been meticulously to incorporate redundancy in the upcoming eVTOL aircrafts.
For example a stuck elevator or lift for those designs incorporating this like the worlds "First Vertiport" in Coventry, UK. If we humans are to learn from our past, the US Navy learned not to only have inboard elevators in the middle of the ships flight deck where airplanes take off and land, if the elevator got stuck in anything than fully up position, why the deck edge elevator was tested and invented for their Aircraft Carriers during and after WW2 to not interrupt operations at large, if a faulty elevator happened.
In the Vertiport at Coventry it would have made sense to include a side platform at the same level as the FATO area in its up-position in case of stuck elevator / lift, AOG aircraft etc., so the aircraft could be towed to the side and keep business open on the FATO. Learning from the past, having a helicopter AOG and stuck on an elevated helipad for hours or even days is not unheard of. Don't expect it to happen much less for eVTOL's.
What boggles us: Is it that more important for some to design form over function rather than function over form ?..
The Swiss Cheese model for accidents
Seen from an operational perspective and experience, if more or all of previous mentioned sell-outs of safety margins happens at the same time, i.e.;
- Light aircrafts with relatively large surfaces medium-to-strong winds can grab on
- Elevated platforms in the weather often with stronger winds than at ground level
- Obstructions (pylons, building etc.) creating unpredictable turbulence near platform
- Small elevated platforms offers too little margin for other than flawless landing/takeoff
- Low hours in-experienced pilots
.. accidents and incidents are doomed to happen more than can ever be accepted, risking the same end-game for eVTOL's to land such places as what closed the helipad on the Pan Am building helipad back then and pushed for a closure for helicopter shuttles back then and a bad reputation for eVTOL's further on for a long time..
Keywords to the designers, developers and investors of infrastructure
What some, not all, but some drawn concepts of Vertiports- and pads out there seem to be missing for continuous, regularly, smooth and SAFE operations are:
- Design primarily based on Operational experience. Go with function over form, not form over function. This is aviation, not a furniture you design. People can get hurt or get killed if form over function wins. In a form over function designed chair, you might at worst only end up with a sore back.
- Days with poor weather conditions, like strong winds, turbulence especially mechanical turbulence due to surrounding buildings, structures and alike, venturi effects from nearby structures etc..
- eVTOL's should be expected to be like a similarly sized airplane more prone for wind gusts, sudden change of wind direction etc. due to lower level of gyroscopic stability in more small/tiny rotors/propellers and often large wing surfaces vs. a helicopters BIG spinning relatively heavy main rotor with large amount of gyroscopic stability and no wing surfaces the wind can catch and push, making landing in gusty winds etc. much more a challenge and less comfortable than in a helicopter. So design of Vertiports should instead be as close to ground level as possible with as much clear unobstructed areas around it as possible.
Developers of eVTOL's put a lot of thoughts, energy and capital into;
- Making their eVTOL aircrafts as safe as possible, in EASA to be as safe as an airliner and safer than small aircrafts and helicopters.
- Making usage of eVTOL as seamless as possible, integrating it into other land-based modes of transportation solving that last-mileage issue from Vertiport to customers address.
- Making the rides as comfortable and quiet as possible for both users and other citizens for the lowest impact and notice that it is even there.
- Making the cost per ride as low as possible to reach out to the widest audience as possible.
Therefore: Developers of the eVTOL's infrastructure need to perform at the same level of safety, customer comfort and stability as the eVTOL developers need to be to succeed.
If you need an operative perspective on your Vertiport- and pads plans so you don't fall into these above mentioned faults, we recommend to partner up with a local well experienced helicopter operator who is used to land off-airport and elevated structures - or we at Copenhagen Helicopter will be glad to help or guide you in the right direction.