Author: Richard

EVTOL White Paper – Section 1: Technical

This is an early draft of the first section of three sections – spit into technical, commercial and compliance – non referenced images are all AI generated.

Almost every eVTOL aircraft is based on an electrical distributed propulsion architecture. Typically, this is in the form of multiple propellers or rotors driven by multiple electric motors. This type of configuration is only possible with electric drive systems. Turbine or piston engines generally must be ‘in line’ with the propeller or thrust vector (this is not the case for helicopters where heavy, expensive and complex gear boxes are required). Turbine and propeller engines do not scale efficiently below a certain level and require complex mounting and fuel system arrangements. This makes piston and turbine engines inherently unsuitable for a distributed propulsion architecture that requires many small motors driving multiple rotors or propellers.

There is an old dictum in aircraft design – you design the aircraft around the engine. When your engine is new and unique the risk of technical failure is high. The aircraft is designed around a major system that is unique and there is no replacement.

If an electrical drive system in an eVTOL aircraft design is flawed for any reason it is very likely there are no similar and suitable alternative powertrain systems. These air vehicles that use distributed propulsion cannot be converted to traditional drive systems. These air vehicles are rendered useless and worthless.

This is why almost all conventional aircraft programs have an ‘A’ primary powerplant choice and an alternative ‘B’ engine that they can use with some adaptation. If your engine supplier lets down an OEM, they need a way to continue with their program and recoup the investment.

What are the technical risks inherent in a typical eVTOL power train?

There are two major risks that affect the technical and market viability of an electric powertrain.

Batteries

Batteries are a suitable energy storage medium in non-weight critical applications where low power output is required. Laptops, phones, flashlights, etc.

Batteries have low energy density compared to hydrocarbon liquid fuels[1]. This can be seen in the limited published range and endurance numbers published for eVTOL and other electrical aircraft. The image below shows the effect of converting a helicopter to a battery powered electric drive system[2].

With contemporary battery technology the range of a conventional helicopter is reduced by a factor of more than ten. With projected battery technology in thirty years’ time, the range is still less than half of a conventional helicopter today.

Modern batteries (lithium polymer) have an irreversible thermal failure mode that results in temperatures about twice that of burning aviation fuel and are effectively inextinguishable as burning batteries generate their own oxygen for the combustion process.[3]

This critical failure mode of batteries and the requirement for residual power for safe flight and landing after any failure creates additional system complexity and additional weight. Battery installations must be designed with a high degree of redundancy, separation, venting and thermal protection.[4]

The weight of these risk mitigations further degrades the already low performance of the aircraft.

Motor Certification

It is not widely known but as of writing there is no electric motor that is certified for commercial aircraft primary powertrain use. There is one motor that is certified for use in Light Sport Aircraft. This is the Pipistrel Velis powertrain[5]. There are several projects that may result in a certified aircraft electric drive system such as SAFRAN[6] who aim to have their motor certified by first quarter 2024, Rolls Royce[7] (who bought the business from Siemens[8]) who again target 2024 for certification and MagniX[9]. MagniX probably has the longest development program, having started in 2009 and they have not published a date for certification.

There will be a limited and uncertain choice of electric motors for eVTOL developers to choose from. However, vehicles have already been configured, developed, flown and certification programs have begun.

This is similar to running the first leg of a relay race while your teammates are at the sports store working out if they can afford to buy a pair of running shoes.

Certification of a new aircraft system does not guarantee reliability of that system in service conditions. Almost all complex systems when they are first put into service suffer from lower than planned reliability. Electric aircraft powertrains will be no different.

Other Powertrain Systems

There is a plethora of positive messaging and targeted investments for hydrogen powered aircraft. Hydrogen has a wide range of practical barriers in the way of aircraft powertrain applications. This subject will not be covered in depth here, but some of the more significant problems around hydrogen as a fuel are: Availability, delivery, ground storage and handling, refueling, storage on the aircraft (very low temperature, high pressure, off gassing and the inability to store on the aircraft for anything other than the very short term), the volume required to store the gas, the immaturity of hydrogen fuel cell technology and hydrogen embrittlement of storage and distribution (on and off the aircraft) and powertrain components.

Control Systems

Almost all eVTOL aircraft lack any form of natural aerodynamic stability. This is a fundamental difference compared to helicopters and fixed wing aircraft.

Helicopters have no stick free stability and always require active pilot input. They are stable enough that they do not require software control system to fly.

eVTOL aircraft require stabilizing software similar to quad copters and other small UAVs. This type of vehicle stabilizing software has not been used for any manned aircraft or been certified before.

Manned aircraft approaching this low level of natural stability have only ever been developed for military applications. The level of aerodynamic stability for military applications is still maintained at the highest level possible considering the required mission envelope.

The technical risk of the control system for most eVTOL exceeds that of a $40Bn[10] military development program. This is not to suggest that it will cost this amount of money to develop and certify an eVTOL control system.

However, it is true to say that the technical risk for eVTOL control systems is greater than that accepted by large military programs with very high budgets.

Technical Summary

It is normal for aircraft developers to minimize technical risk to those areas that are absolutely required for the required incremental commercial improvement to justify the investment necessary for a new product.

eVTOL OEMs have adopted a new paradigm of accepting very high technical risks and spending very large amounts of money to mature new systems and attempt adequate risk mitigation.

This approach is diametrically opposed to that which has been consistently successful.

  1. https://en.wikipedia.org/wiki/Energy_density
  2. https://ntrs.nasa.gov/api/citations/20205000636/downloads/2021-08-20-eVTOL-White-Paper-Final_V48.pdf
  3. https://www.sciencedirect.com/science/article/pii/S2542435118302800
  4. https://www.easa.europa.eu/downloads/136701/en
  5. https://www.pipistrel-aircraft.com/products/velis-electro/
  6. https://www.safran-group.com/products-services/engineustm
  7. https://www.rolls-royce.com/products-and-services/electrical/our-electrical-power-and-propulsion-portfolio.aspx
  8. https://press.siemens.com/global/en/pressrelease/siemens-sells-electric-aircraft-propulsion-business-rolls-royce
  9. https://www.magnix.aero/
  10. https://en.wikipedia.org/wiki/Lockheed_Martin_F-35_Lightning_II_procurement

The Death Of Commercial Art

For the white paper on eVTOL I put together I decided to use AI generated art. Finding copyright free images is always difficult and I did not want to use pictures of actual eVTOLs. This was to avoid singling out any particular project in what is a criticism of the whole sector. This led me down a rabbit hole of the astonishing (and slightly spooky) capabilities of AI art. Since I have done this I have started to recognize it being used occasionally in commercial journalism

The images below were all generated for free using Microsoft Bing AI Art generation (https://www.bing.com/images/create?FORM=GENILP) and Gencraft (https://gencraft.com/generate) I tried a lot of free generators and I found these two were the best for what I was doing.

Below are some of the more interesting and wilder examples – starting with the Gencraft set. I will show the text prompt that generated the image above the image. These are in general order of complexity.

Wide shot of silver eVTOL aircraft flying over a city at sunrise

And then those generated using Microsoft Bing

Very spacious manufacturing facility for a small sleek white aircraft “eVTOL aircraft”. Workers wearing neat black overalls. Big windows and a sunny day

eVTOL with very complex wires and systems being worked on by maintenance technicians, standing on a lake, surrounded by people. Photoreal, sunny day.

And finally a couple of fun things.

Very spacious manufacturing facility for a complex steam powered “eVTOL aircraft” full of wires and systems. Man in a top hat. Big windows, large open doors and a sunny day. Union Jack flags.

A hall full of the readers of the newsletter from Abbott Aerospace UK Ltd. Bright sunny day, refreshments being served Large aircraft hanging from the ceiling of the hall.

Lost In Scotland

One of my clients, ARC Aero Systems, has been part of a project to examine the use of Cargo UAVs as an infrastructure component in the north of Scotland.

ARC has a 440kg winged, transitioning UAV that has been flown full envelope overseas. This was designed and built (under our watchful eye) by our external team and a fine job they did for us.

We were based at the airport in Wick which is a beautiful town on the Scottish coast. I had overall responsibility, but it was more a figurehead role because of the competence of the team at ARC and I had the pleasure of watching the team operate like a well oiled machine and taking a measure of undeserved credit.

What was remarkable was the extent to which we have to mitigate all of the possible risks for the CAA (the UK version of the FAA). We did a very limited flight of 100m, we never left a hover and were tethered at all times.

To repeat – this aircraft has flown at full envelope. It is transitioned to wingbourne flight and back multiple times.

The caution of our airworthiness authorities is somewhat ridiculous, especially for a flight like this where we were in a remote part of Scotland with multiple mitigations (geofencing and kill switches) from a small (former world war II) airfield on a day without any scheduled flights. The flight took over six months to arrange permissions for.

We will not be able to make any use of commercial UAVs in the current regulatory situation. So if you are waiting for a cargo drone delivery system in your neighborhood don’t hold your breath – write to your politicians.

A final thought for August

I have been thinking about where our public policies originate.

In the last 25 years we have lived (i.e. taken up legal residency, rented or bought a home, put our kids in the local schools and really lived like a local) in the UK, US, Canada, Belgium and the Cayman islands. Despite the surface differences it is amazing how similar the tax, legal and public policy landscapes between these countries are – it is even more amazing how fast they are all moving towards identical public policy positions across the board.

The point of a representative democracy is that the policies of the government should represent the will of the majority of the voting public. In the western world the major public policies do not.

I am not making a moral judgment about mass immigration and tolerance of illegal immigration or the net zero policies, the coming restrictions on cars and freedom of movement, the removal of cash and the reliance on digital financial transactions and the expansion of the surveillance state, compulsory medical treatment and the sexualization of children. Well. Ok – I will make a moral judgment on the sexualization of children – that is objectively evil and everyone involved should be arrested and face criminal charges.

The majority of these policies may be morally right or morally wrong. My moral judgment of them is not relevant. These are policies that will have a huge effect on our societies and none of them have originated within the electorate that has to vote upon them.

Where do they come from? Why are they a part of the policy landscape? Why does every major political party in almost every western country (and many others) end up adopting the same position on these issues?

It is hard to ignore the fact that there is a coordinated set of global political policies that are oblivious to the will and desires of the local electorates that our politicians are presenting to us as a fait accompli.

In effect, all of our national parties are just divisions of the single international political party. Local (national) elections are cosmetic popularity contests to choose the most photogenic or charismatic mouthpiece of the same unchosen, relentless, largely unpopular policies. There is no point in having a democracy if it is not a representative democracy.

All of these policies are represented as an essential reaction to some existential moral or life and/or planet threatening crisis and are placed in opposition to some hateful and irrational ‘phobia’ or act of ‘denial’ and that any resistance to these policies is somehow reprehensible. I think I might be a phobia-denier or a denialophobe – am I beyond redemption?.

Each time we vote for a party with these positions it legitimizes a set of policies that we did not choose and do not want.

Who do you vote for? Do you feel that their policies originate from local desires and needs? What are your thoughts?

I would like to hear from you.

How to Present Data and Why it Matters

Those of you who have been conscious for any part of the summer will be aware that this is the hottest summer ‘ever’. I do not have any data to refute these claims. So let’s assume that this is true as far as the data can be interpreted and a conclusion can be drawn from the interpreted data.

I am not going to try and put this in a historical context – the only thing we know less about than the current climate is the historical climate. But we can put the temperature data in a more rational context.

I have seen the climate data quoted in the celsius scale and the fahrenheit scale. These are arbitrary scales based in part on the physical properties of water. They are useful everyday measures of temperature but they are not an absolute measure of temperature.

There is an absolute measure of temperature. Temperature is an expression of the thermal energy contained in a material. The scale of temperature measurement that starts at zero thermal energy is Kelvin. If we use the Kelvin system for expression of temperature we are using an absolute scale of thermal energy and it is contextually meaningful in an absolute sense.

Lets start crunching some data – this is the global temperature data that is publicly available https://datahub.io/core/global-temp

When you plot the ‘temperature anomaly’ in celsius against year you get this data

That has a large upwards gradient. The data available presents the temperature anomaly in the range of about -0.4 to 1.0 degC. First of all we should recenter this about the mean anomaly for the period to remove the ‘hot bias’ in the data presentation.

OK so now we are showing the data around the mean value of the data set from -0.7 to +0.7 degC – and we have the same upwards gradient.

From this reference https://earthobservatory.nasa.gov/world-of-change/global-temperatures the average global temperature for his time period is 14 degC. We can convert the temperature anomaly into a global average temperature. Showing this on a celsius scale starting at the freezing point of water we can reduce the gradient of the data.

But that is not really meaningful. What we are concerned with is the increase in the thermal energy being retained by the atmosphere. Using the Kelvin scale where 0 degrees Celsius equals 273 degrees kelvin the gradient of the graph now looks like this:

How much has the thermal energy content of the atmosphere increased? If we take the mean of the temperature in kelvin over the time period shown the percentage change in the heat content (min to max) of the atmosphere is around 0.5%

This is a change, but it is not very large.

How accurately can we measure the total thermal energy contained by the atmosphere? What is the confidence in the data?

There is a paper here:
https://www.science-climat-energie.be/wp-content/uploads/2019/07/Frank_uncertainty_global_avg.pdf

That shows that the total measured/interpreted change in temperature is roughly the same as the uncertainty in the measurement of the data.

Is a possible total increase of the thermal energy content of the atmosphere of 0.5% a cause for concern?

Maybe.

How accurately can we measure this metric anyway?

Shrill media driven rhetoric and exciting new verbiage from the United Nations declaring we have moved from “Global Warming” to “Global Boiling” is not convincing. Especially as we should all recall a few years ago when it had not warned for some time the climate situation was contemporaneously branded as ‘climate change’ and ‘climate disruption’. As we now might have a discernible warming trend we are back to an updated version of the original language.

When the language around the thing is more important than the thing itself, you are listening to marketing. Not science.

I think it is more concerning that the total heat energy of the atmosphere may have increased by 0.5% than ‘it is a bit warmer in Spain this summer’.

What do you think? What is the integrity of the current measuring methods and the historical data we use for comparison? How much are we fooling ourselves that we understand anything at all about what is going on?

Patents, Press Releases and Related Pronouncements

One of the most important things you learn about press releases and promotion is that if you give a journalist a piece of marketing written like a news article they will print it with little to no change. This was true thirty years ago when I was working in the music industry and it is even more true now where the amount of ‘journalism’ has multiplied across the internet into clickbait headlines and engaging CGI graphics with a thinner and thinner veneer of accuracy.

If you can provide a modern journalist with a nice headline, a nice picture and something approaching a grammatically correct piece of marketing you do not have to pay for an advert as you can get it printed for free.

eVTOL figured this out years ago and the leading eVTOL developers are masters of the fine art of the internet press release.

The latest to appear is the offering from Alef Aeronautics. This is an intriguing concept of a wheeled car like vehicle that on take off rotates around the road vehicle’s longitudinal axis to present the top of the car to the airflow. The sides of the car form the wings of a biplane and the body of the car is revealed as a grid that allows the air to pass through. In effect it is a tailless biplane – box wing design as is revealed by one of their patents

https://patentimages.storage.googleapis.com/07/c9/ea/75a02000c814e8/US20210300546A1.pdf

This means they must have a fly by wire control system as they have no practical aerodynamic stability in all parts of the flight envelope.

Little performance data is available on the company website (https://alef.aero/) but the patent does give some interesting data:

The most intriguing metric is the peak L/D of 22. This is the ratio of lift to drag and is a measure of peak aerodynamic efficiency. For comparison, a motor glider will have a L/D similar to this aircraft. This should allow us to draw the conclusion that the peak L/D shown is not likely to be achievable.

Examining the rest of the patent the following data is also available – MTOW = 480kg, payload weight = 120kg, cruise speed = 50m/s.

Putting these values in real money: MTOW =1000lb, Payload =265lb, Cruise speed = 97knots.

First of all this is a very light aircraft. A very, very light aircraft. You can search the database of VLA (Very Light Aircraft) here: https://www.aeroexpo.online/aeronautic-manufacturer/very-light-aircraft-203.html

There are no aircraft in this category with a weight this low. One of the lightest VLA aircraft is the Pipistrel Alpha (https://www.aeroexpo.online/prod/pipistrel-doo/product-171425-740.html) this is a 1200 lb MTOW aircraft and has a peak L/D of 15 at 64 knots (https://pilotweb.aero/aircraft/flight-tests/flight-test-pipistrel-alpha-bcar-s-6305456/)

Considering that the Alef product is also a roadable aircraft that will have road wheels, tires and suspension, the idea that it could be lighter than the lightest equivalent non roadable aircraft is not credible.

Examining the dense milk crate structure that this aircraft has to push through the air their L/D projection is very optimistic. The drag coefficient of this aircraft is going to be somewhere between ‘very high’ and ‘very, very high’. And will not support a L/D of anything over 20. I would be surprised if it was greater than 5.

We can also look at some other aspects of this program. They claim they have been granted a limited Special Airworthiness Certificate. This appears to be the direct press release (https://www.prnewswire.com/news-releases/alef-becomes-the-first-car-certified-to-fly-301863749.html) There are details on the limited Special Airworthiness Certificate here: https://www.faa.gov/aircraft/air_cert/airworthiness_certification/sp_awcert/limited

On this page the following information is given “A limited category special airworthiness certificate is issued to operate surplus military aircraft that have been converted to civilian use under the following conditions:” This definition is confirmed by the federal register: https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-21/subpart-H/section-21.189

The company is also projecting customer deliveries in 2025. This means that the company must achieve flight and road certification in around two years.

To summarize:

  • The Alef project has filed a patent that includes information that, to be very charitable, is excessively optimistic in terms of weight and aerodynamic performance.
  • The company has issued information regarding the certification status that, on the face of it, is definitionally false. They may have been awarded a special airworthiness certificate that is limited in some other way (other than definitionally).
  • They will not be delivering certified products in 2025. They will suffer from significant weight growth, a large degradation of aircraft performance and excessive complexity, excessive cost and excessive delay in their design, production, supply chain and related compliance activities.

And planning for a more credible future, some key points:

  • If you are a journalist check that basic feasibility of the information you are given.
  • The patent office does not check your work for credibility only for uniqueness. You will be published, wrong or right, as long as you are unique.
  • Avoid putting easily refutable/physically impossible data in publicly available documentation.
  • Basing a business on your own far fetched marketing rhetoric will always end in tears. (don’t believe your own B.S.)

This aircraft is a neat concept and thought experiment. If it is ever actualized it will be a terrible aircraft and car in one.

Lies, Damn Lies and Business Plans

One of my rules for getting involved in a program is that the product has to be real. It has to have a market and it has to meet the market need.

There are gray areas in this arena and it is up to each individual to make up their mind how far they can suspend their disbelief before they have to admit the truth to themselves.

The conundrum that a team has to face is that at the start of a project that is truly innovative, there may be nothing more than projections and predictions with little real life substance to back up the claim – because the technology creating the fundamental advantage is immature.

It follows that the more ground breaking a project is the more work you should do to establish integrity for your forward looking projections in schedule, technical and financial models.

It is common that project teams confuse integrity with group think. Removing challenges to the hypothesis by silencing dissenting voices is not the same as providing additional evidence that the hypothesis in question is strengthened. But it can feel the same if you can suspend just a little bit of disbelief.

It is also critical that absolute belief in the project is communicated in all interactions with potential investors.

At the point in time where a project should be challenging assumptions and questioning the existing positions there is an overwhelming pressure to reinforce the basic concept and do whatever you can to make it look as attractive as possible.

Early stage investment is often based on a narrative based on unsupported positions because of this problem.

And this is where the problem starts.

If your initial investment is based on a collection of assumptions and positions that later turn out to be incorrect, what do you tell your investors? Can you change the product, the business case and the narrative to something new that has the same or better return on investment as the original proposition and sell it to your existing and new investors?

It is very rare that an initial over-optimistic business proposition can be replaced with one based in reality that is as good or better than the original proposition.

So what starts out as optimistic exuberance and a dream that you are doing your best to chase ends up either in compromising the vision or sustaining the unobtainable vision by lying.

There is a fine line between a forward looking statement and a lie. You might imagine there is a gray area. There isn’t. Once you know that your forward looking statement is not true you are telling a lie.

A lie can get you rich or get you in court, or both. Somewhere in the rush to grab that sweet, sweet venture capital a whole bunch of people working through their internal risk benefit forgot that lying is wrong.

Something New

One of my long-time clients Arc Aerosystems has been working on a new project under the radar. This is based on an already type certified jump take off auto gyro and we are planning on developing this under the existing part 27 type certificate.

Because of the type certification and general configuration we will fit under existing operating regulations. This neatly sidesteps the type certification and operating regulation problems of eVTOL programs that are developing unique configurations based on new technology.

The updated design was created by Norman Wijker.

For those of you interested in aviation historical minutiae, the Avian Gyroplane was developed in Canada by a group of ex Avro Arrow engineers. Smart people.

The Ongoing Part 23 Saga

I am blessed to work with many talented people across many programs. They are critical for confirming or challenging my preconceptions. I am always hesitant about naming people in this newsletter even in a positive light. This is a strange time indeed, so I will not name the guilty party at this time.

I am helping one of my clients set up a part 23 certification program. This is using the much beloved post amendment 64 part 23 (sarc.).

The way that the old regulations were formulated you took each line of the regulations and addressed each with a compliance action. In that way the process was clear. You could give a junior engineer the opportunity to do the first draft of a section of the compliance plan because it was deterministic.

In latest amendments of the part 23 amendments (64 & 65) the wording of the regulations is entirely immaterial. The ASTM standards (ostensibly the acceptable means of compliance) are the requirements that you address line by line.

The part 23 regulations are not worth reading as they have become a generic list of aspirational qualities for an aircraft. They do not regulate so much as create a linguistic environment for the regulations (now called ‘standards’) to inhabit.

The realization of this aspect of the new regulations is critical to understanding how they should be used. I had tried for a time to address each line of the regulations, as if they were, well, regulations.

I had determined that this was an impossible task as the actual regulations (the ASTM standards) are not related in any way back to each individual line of the new regulations. I did not want to admit to myself that I could not crack the code and was unable to figure out a way to do this. So I was struggling through the same problem over and over again.

Enter my new favorite DER who took away my intellectual pain. He gave away the secret. It turns out that actual wording of the amendment 64 and 65 regulations is meaningless. The paragraph number of the regulations is related to the ASTM sections by this table.

After that you cheerfully discard the wording of the new part 23 regulations without a second thought and continue as if the ASTM standards are the regulations.

Some of you may point out that this is exactly what the new amendments were pretending not to do. The ASTM standards were only optional acceptable means of compliance and absolutely were not the amendment 63 regulations with some minor updates placed behind a paywall.

So, for me, the final piece of the puzzle is now in place. I was honestly approaching the new regulations as if they meant something. Now I know that belief was the source of my problems. The new regulations are essentially meaningless and I have to treat the ASTM as if they are the regulations.

While this makes my life much easier it is disappointing as the new regulations are exactly what I feared they would be. A poor excuse to put the real regulations to a more useful purpose – making money for the friends of Uncle Sam.

I am a cynic when it comes to how the government operates, but I do harbor a secret hope that I am wrong. I hate to be proved right.

Interesting News

One of my projects sent me this news article

NASA have decided to not fly the X57 technology demonstrator. The reason given was described as “As we got into the detailed analysis and airworthiness assessment of the motors themselves, we found that there were some potential failure modes with the motors mechanically, under flight loads, that we hadn’t seen on the ground,”

According to this article

The motors have been developed by Joby Aviation.

If you read the whole article on the X57 they have had problems with the power electronics as well. It is hard to say what is really going on but it is hard to spin this as good news for NASA or Joby.