These seem to compete more in the helicopter realm than the airliner realm. That's likely to be true of the relative level of safety of this vs a helo vs an airliner. (I've sometimes quipped that helicopters are one of the primary predators of billionaires.)

While the stated/projected costs (which I doubt will be achievable), these would compete very favorably against a helicopter on a cost basis. Without the ability to auto-rotate (or a functional equivalent level of safety system), there's no way I'm getting in one nor recommending my family get in one [and I'm perfectly happy flying my family in single engine piston aircraft at night].

eVTOL have to be designed to the same safety standards as other aircraft; and in fact, they will be held to slightly higher design safety standards due to their novelty, required to meet safety standards that otherwise only apply to larger transport category aircraft.

You are right, eVTOL cannot autorotate, but electric motors can be far more reliable than internal combustion engines, with many fewer failure modes. Additionally, they are much lighter, and so you can have much greater redundancy. There is considerable redundancy in the lift motors on these aircraft, so one or in many cases more than one lift motor can fail while still providing safe and controllable flight. The exact level of redundancy needed is verified via probabilistic risk analysis, considering failure probabilities of different components, and as mentioned the target failure rate will be lower for these than for equivalent sized conventional aircraft due to their novelty.

While there's still a lot of design and development work to do, I'd be very surprised if these didn't end up much more reliable and less prone to failure than helicopters and single engine airplanes.

Note: I work for one of these startups, so I may be a bit biased, but I also have insight into the design process and safety and redundancy of systems are absolutely a top concern.

Oh, I should also say, for a helicopter autorotation is only particularly helpful if you have enough forward airspeed or height to initiate it. Helicopters come with an HV diagram indicating safe flight envelope, such that autoration could be initiated in case of an engine failure, or you are low enough for a crash to be survivable if you do not have enough height or airspeed for autoration.

https://en.wikipedia.org/wiki/Helicopter_height%E2%80%93velo...

In an eVTOL, if you have enough height or velocity, you should be able to glide on the wing. So you'll be wanting to keep yourself in the appropriate region of the HV curve, and your emergency engine out procedure will be much more like a conventional fixed wing aircraft, rather than a helicopter.

We shall see… I can make a strong counter argument for your first paragraph.

The EVTOL community has long lobbied for, and for some time, has gotten away with a whole new set of performance based standards not previously used to certify other aircraft of similar size and weight. This was, of course, until several weeks ago when the FAA made the abrupt rule change going from Part 23 to 21.17b for these vehicles. Much has been said about this in the industry, but I understand that questioning the performance based standards is at the core. We’ll see where the dust lands, but it’s clear that some in the EVTOL community are not interested in applying airliner safety standards to these vehicles.

Questions: is your firm following ARP 4754A and 4761 to the letter? What systems are being mandated to DAL A (requiring a 10 to the minus 9 failure rate?) Are these the usual components found in other jets, or new components that typically haven’t required the same level of safety criticality?

These are a whole new type of aircraft—there are so many unknowns that it’s impossible to compare safety standards to other aircraft, even if the intent is to meet something like Part 25.1309. Case in point: power distribution systems in airliners are rarely DAL A, but I’d recon they’re pretty damn safety critical in an EVTOL. No power distribution = no spinning propellers = no thrust, and all on a “powered lift vehicle…” cue the classic line about the V22, “a plane that can’t glide AND a heli that can’t autorotate—all in one!”

You're right, some other entrants in the eVTOL community seem to have strategies that rely on some kind of regulatory magic. The company I'm working for, Beta, is taking a very different strategic approach, with much less reliance on "then some regulatory magic happens;" we are focusing on cargo first, and a passenger variant later. We are not particularly concerned with the change to 21.17b, we're willing to work with the FAA on that rather than fighting it. And because our initial target is cargo, such as transporting organs between hospitals with existing helipad infrastructure or cargo from airport to distribution center, there are a lot fewer regulatory hurdles about where we operate than the air taxi market.

We are following ARP4754A and 4761, yes. We are still in the process of doing our safety assessments at the aircraft and systems levels and finalizing our type certified design, so I can't say which systems are going to be required to be DAL-A, but I expect that the pilot inputs, flight controller, battery systems, high voltage distribution system, low voltage distribution system, lift motors, and control surface servos will be designed to that level. Our strategy is to build ourselves the critical components for an electric aircraft, so we are doing the battery, high voltage distribution, and electric motors, while we are buying the other components (pilot inputs, flight control computer, control surface servos, primary flight displays, etc) from existing suppliers who already have experience in this space.

In the meantime, we are also learning a lot from flight test of our experimental proof-of-concept airframes, which we can feed into this process. We've already built one experimental eVTOL under a previous design, and then two proof of concept airframes with a design much closer to the type certified design that we're now working on; so while we go through the process of breaking down the requirements per 4754A and doing safety assessments per 4761 and working on our final type certified design, we're also learning a lot about operational concerns and refining our design on our experimental proof of concept airframes.

As for the V22 line, well, our aircraft can't autorotate, but it's not bad as a glider. That was a primary design criterion; it should mostly be a glider that happens to have electric power. We recently did a cross-country trip halfway across the country on our PoC aircraft in CTOL configuration (https://evtol.news/news/beta-alia-250-prototype-flies-cross-...), with a number of stops on the way, of course, our range is limited by physics, and the majority of that trip was done such that there was an airport within the glide cone of our aircraft; we did allow for a few legs in which that wasn't always the case, and we would need to ditch in the event of power failure, but for most of the trip there was an airport within our glide cone if we had a power off event.

Safety can be solved with a parachute that lands the whole aircraft in the event of a catastrophic failure. These are already fitted to high end GA aircraft like Cirrus.

Safety and weather are covered by certification requirements. Those will be somewhere between small aircraft and helicopters with some eVTOL specifics. If it gets certified those bases are covered.

Privacy: Regulated airspace is your friend, plis why wait for one those if you can have your own drone for the price of one Lilium ticket.

Crime: Regulations also cover airport operations, so that base will be covered as well.

For me the question is not if those aircraft are goong to fly (they will if it os technically possible and people fund development), but rather whether there is an actual market for those big enough to make the manufactirers and operators viable businesses. The last qiestion is hard (IMHO impossible) to answer without getting them to market first.

There are certification requirements for both the aircraft and Ops Spec approvals for Part 135 (on-demand charter) operations. I can see that these would be certified to fly (and thus eligible for Part 91 (private) operations) far more easily than the more stringent requirements for Part 135 charter operations.

The FAA thinking is that you have greater understanding as a passenger on a Part 91 operation and are better able to judge the risk yourself, whereas a Part 135 (charter) or Part 121 (scheduled airline) operation, the public cannot effectively judge the safety of the operation so the FAA holds them to a higher standard.

Single engine Part 135 is possible, but there's a large amount of focus on redundancy: https://www.aviationconsumer.com/industry-news/single-engine...

I work for one of these startups, Beta.

We are focusing on a slightly different market than the other entrants; we're focusing initially on cargo rather than passenger transit. One initial customer is United Therapeutics, for transporting organ transplants and artificial organs to hospitals. Another is UPS, for getting air freight from airports to distribution centers; cutting out the truck trip can save a ton of time there. We are also making a passenger variant, but since the regulatory and NIMBY concerns for the passenger air taxi market present a lot of risk, we're not betting solely on that market like a lot of the other companies are.

This helps with a lot of the concerns raised in this thread. In fact, another one that I'm not sure has been brought up is vertiport design and siting concerns; right now standards on vertiports are still a work in progress, and there are questions about whether it will be feasible to get them installed, because even with vertical takeoff and landing you generally need to keep approach angles of about 15° clear, which means once a vertiport is installed you need to limit the heights of any surrounding buildings to keep the approach clear.

To address a few of your other concerns: we're located in northern Vermont, we know cold weather. Actually, for our use case hot weather tends to be more of a concern; batteries and motors heat up when used, especially in the very high power vertical lift phase, so our limitations there tend to be thermal and cold air provides better cooling.

Our charging stations also include air for cooling and warming the batteries; so you should be able to avoid the issues with batteries being cold on startup with our air system.

All aircraft have limitations on weather that they can be flown in; crosswind limits for takeoff and landing, etc. As very lightweight aircraft, with high lift/drag, these will be somewhat lower than the limits for your big jumbo jets, but will be high enough to be useful in a lot of weather. All aircraft have requirements for design and testing for HIRF (high intensity radiated field/lightning), so these will all be certified to the same standard there. Aircraft can optionally be certified for flight into known icing conditions (FIKI); I believe our plan is to have the capability, but as an optional add on, as it requires a number of heating elements which add weight and complexity. But overall, the weather concerns shouldn't be too much different than for other small aircraft.

As far as safety goes, that's obviously a concern in any aircraft. One advantage of electric aircraft is that electric propulsion systems are far mechanically simpler, with far fewer moving and wearing parts. The only real wear item of concern are the main bearings on the motors, and the landing gear. So maintenance intervals can be much longer than with ICE aircraft, and I expect reliability to be considerably higher. Additionally, electric motors can be much smaller and lighter, and thus can be made redundant. Each propeller on our aircraft will be driven by multiple independent motors (probably can't say the exact configuration at the moment), so that motor failures can be tolerated without catastrophic consequences.

> crosswind limits for takeoff and landing

Most aircraft have a “maximum demonstrated crosswind capability” which is a required test flight item but is not a limitation. It has to be demonstrated during flight testing to a figure of not less than 20% of Vso, but once that’s hit, they don’t have to find a greater crosswind to determine an actual limit.

You're right. The maximum demonstrated crosswind velocity isn't a limit, but more of a guideline, based on what was tested for.

However, many aircraft do that testing to a higher level than is required. For instance, for a Cessna 172, 20% of Vso would be 8.2 knots, but it has a maximum demonstrated crosswind velocity of 15 knots.

Anyhow, all I'm saying is that at least for our aircraft, it looks likely that the maximum demonstrated crosswind velocity will be on the low side; at least the mandated limit based on Vso, possibly a few knots higher, but like most small aircraft, much much lower than what you have for big jets.

Pilots will care more about the aircraft’s capabilities than the demonstrated crosswind limits. My A36 was demonstrated to only 15knots IIRC, but easily handles a 25 knot direct crosswind. Whether Beech test flew it to 11, 15, or 20 knots I wouldn’t care the least bit about.

(In VTOL mode, could you wheel the aircraft into the prevailing wind for takeoff and/or land it pointed into the wind to reduce crosswind effects? [I’m a fixed wing guy with I think only 0.7 dual received in a helo.])

Yes, in VTOL mode you are generally going to want to land into the wind or wheel the aircraft into the wind for takeoff. I think that would probably be possible.

But we are also concerned with CTOL performance; in order to add more flexibility, CTOL performance is something that we are focusing on heavily, as if a runway is available you can do a takeoff and/or landing with lower energy use and thus get more range, so we're designing to be able to takoff and land either CTOL or VTOL. For example, one of our use cases is cargo, such as UPS getting packages from an airplane at the airport, to its distribution center. At an airport, you have a runway available for takeoff, so you might do a CTOL takeoff, and then a VTOL landing at the distribution center, and vice versa for the return trip.

And what I'm saying is that our aircraft, at least, won't have crosswind capabilities that are terribly high when doing CTOL takeoff and landing. It's pretty light and floaty and has a strong weathervaning tendency, and control surface sizes are kept limited in order to save weight and drag. It will be able to handle the minimum and maybe a bit more, but I wouldn't expect it to do well significantly above what the demonstrated crosswind velocity is. Ours is designed more as a glider that happens to have electric propulsion and lift capabilities, rather than a conventional powered aircraft, in order to be able to eke more range out of our batteries and provide a greater safety margin in the event of loss of propulsion power, but there are some tradeoffs to that design.

Also, I should say that I'm a software guy, this is my first aviation related job, and I only have about 2 hours in my logbook for dual received, and our certified design is not finalized and we are still doing some trades on things like control surface sizes, so anything I say here might be wrong now or in the future. But right now, we have a fairly limited crosswind envelope.

That might not be as big of a concern as it first appears. You’re rarely more than 50 miles from an airport with either a crossing runway or a taxiway better aligned to the unusual wind (naturally, airports tend to have a primary runway aligned with the prevailing winds when terrain permits).

In an emergency, landing on an aligned taxiway is probably not materially different in risk profile from a VTOL landing on an uncontrolled ramp or parking lot under those same wind conditions.

Yep, I'm not saying it's a big limitation, given the VTOL capabilities and availability of airports. Just that there will be few windy days in which we might not be able to fly, but that's the case for pretty much all small aircraft.