From Wikipedia: The idiom “jumping the shark” or “jump the shark” is a term that is used to argue that a creative work or entity has reached a point in which it has exhausted its core intent and is introducing new ideas that are discordant with, or an extreme exaggeration of, its original purpose.

Welcome to https://siriusjet.com/

This is a project that combines several aspects of physics that are best left alone. I had thought that these types of projects had gone the way of Milli Vanilli and Moonboots but this looks like a fresh one.

Where does one start?

Powertrain

On their powertrain graphic, they claim to carry a tank of liquid hydrogen and to do this they will have a proprietary cooling system.

I like their bold mastery of physics. Carrying liquid hydrogen means that you swap the problem of storing at thousands of psi with storing at a very low temperature.

It also means that in order to maintain your hydrogen in a liquid state you need to consume power in order to operate the cooling system. Whenever people talk about hydrogen storage I go to this diagram:

This tells you that to keep hydrogen in a liquid state it has to be at around 20Kelvin, or -253C. Looking online for cryogenic cooling systems, I could not find a system that does not rely on an existing external source of liquid nitrogen. So let’s pretend that they have a system that can keep their tank at -253C without the need for an external source of liquid nitrogen and that it is reliable and light enough to put in an aircraft and let’s pretend it is both cost and energy-effective.

(Side note, with liquid hydrogen you can’t just park up, put the handbrake on, and walk away. If your cooling system is not running continually your hydrogen will turn to gas with the inevitable increase in pressure and will exit your storage system either through a pressure relief valve or by more kinetic means. This means that you have to run your cryogenic cooling system when you are parked on the ground in midsummer in Riyadh, fighting the 40C heat, creating a required temperature differential of 293C)

You also have to have access to a source of liquid hydrogen and a way to get it from where you think it might be (tank or truck) into the fuel tank in the aircraft. Let’s pretend that those problems have been solved and there is a low-cost readily available source of liquid hydrogen and a means to get it from ground storage to your aircraft.

Figuring out MTOW
Let’s look at some other metrics – they have 28 electric motors that weigh 9.6kg each and produce 100daN on thrust each, that is 225lb of thrust in real money. Each fan has a 300mm diameter.

So we can quickly work out that the maximum thrust is 225 x 28 = 6300lb. So assuming that they have a 1.5 thrust margin to nominal 1g thrust, their MTOW should be around 4200lb.

Power Requirement
When I want to look at disk loading I go to this graph:

The Sirius has a disk loading of around 190 (nominal) – 290 (peak) lb/sqft, using the graph above that puts them higher than is optimum and at an installed power loading (for good ducted fans) of around 2 – 2.5lb per HP.

Doing the simple math means that the power system needs to generate between 1.25 (nominal) to 2.3 (peak) MW or 1680 to 3150HP.

This compares to Lilium’s peak power requirement of 2.2MW so we are in the right ballpark.

Cruise Performance

We will overlook the misspelling of ‘noise’, I have made enough spelling mistakes of my own… cruising for 1150miles at 323 MPH gives a cruise endurance 3.5 Hours.

If they have a cruise L/D of 10 (Lilium claim a cruise L/D of 18, but let’s be real. Their peak L/D may be higher but high speed cruise L/D is never at the peak value).

Their power consumption in cruise flight will be 1.25MW / 10 = 125KW or 168HP.

When I want to look at Gravimetric density and Volumetric density I use this graph:

So cruising at 125KW for 3.5 hours. that is 438kWh.

Now we can work out the weight and size of the Hydrogen tank.

Liquid Hydrogen has a gravimetric density of around 32 kWh/kg, so assuming 100% efficiency you need around 14kg of Hydrogen. But let’s assume some powertrain inefficiencies: We will assume the combination of fan, wiring, controller, fuel cell, etc then you have a combined inefficiency of 75% – you need 18kg or 40lb of Hydrogen. Then you have to add the weight of the tank, the insulation and the cooling system – let’s say a total of 100lb

Similarly, the volume required will be around 250L or 50 Gallons.

Hovering Performance
For take-off and landing the vehicle will use batteries – the power required for take-off and landing we can assume to run at an average of 1.2 x one g of thrust. That is 1.5MW.

The Hydrogen power system will contribute the cruise power it is sized for, which is .125MW, this leaves 1.375MW to come from batteries.

If we assume take off and landing (and potential aborted landing, hold, and go around) lasts for 10 minutes that is 1375 x 10/60 = 230Kwh. We had to add some inefficiency and batteries to motors are better without a fuel cell so lets assume 80% overall efficiency 230 / 0.8 = 287.5Kwh.

Good installed battery energy density = 200Wh/kg.

The mass of batteries needed = 287,500/200 = 1438kg or 3162lb of batteries. Or 75% of MTOW.

Realistically this vehicle will only be able to hover (and maneuver while in hover) for less than a minute.

And, bear in mind that we are not considering any reserve requirements in the above calculation.

System Weights
So the total eight of the powertrain and fuel will be something like:

Fans (28 x 9.6 x 2.2) = 592lb

Fuel and Tank = 100lb

Batteries = 3162lb

Estimate for Wiring, power electronics and all the other stuff = 100lb

Total weight of powertrain and fuel = 592 + 100 + 3162 + 100 = 3954lb

Which is very close to our MTOW of 4200lb.

That is a no go.

Summary
In essence, this project has taken all of the impracticality, complexity and performance issues of the Lilium jet and has compounded them with the addition of a cryogenic storage hydrogen power storage system.

Maybe the founders of this program have just not been watching the eVTOL sector, the high consumption of investment for little progress, the immaturity of type and operation regulations, the lack of air traffic and power infrastructure, and the bored indifference of the traveling public outside of a small group of manic cheerleaders.

Nice website, shame about the aircraft.

A young engineer at a client sent me a question about bird strike requirements and the speed of the aircraft to consider for the bird strike condition. Explaining the rabbit warren of part 23 certification was interesting – so I have reproduced my response here :

Hey (Name Redacted), sadly the wording of the (new) regulations (23.2320) can be ignored in favor of the ‘standards’ (the old regulations). This makes it seem like the regulations are meaningless and the advisory standards carry more weight than the regulations themselves. This is the case, and in this recent and innovative inversion of reality you can ignore the wording of the regulations.

Even the FAA does not understand how the new regulations and standards work together (despite them driving the creation process and approving them) and we will have to lead the FAA through the process of interpreting their own mess.

Just to be clear, this aspect of the ASTM only applies to level 4 aircraft (4.7.6) and we are not a level 4 aircraft (kind of the old part 23 commuter category aircraft, but not really) so this will not apply to us, and in theory we do not have to consider bird strike in this manner in order to show compliance to FAA part 23 (although we have to consider it from a composite damage tolerance point of view for the airframe structures, but that is another thing altogether and there are no explicit means of compliance for that, but ignore that for now because it will get even more confusing if we don’t.)

To make things more exciting, the ASTM standard only applies to the windshield and no other parts of the aircraft. However EASA will not allow our aircraft to be certificated in Europe until we comply with a CRI (the EASA equivalent of a FAA special condition) which is usually applied to ‘high performance’ CS 23 aircraft – this “High Performance” category is something that EASA have created that they like to apply to a lot of part 23 aircraft and has nothing to do with pre amendment 64 commuter category aircraft or post amendment 64 level 4 aircraft. So that’s good.

This CRI contains a set of specific safety standards and compliance with the CRI will automatically allow us to comply with that part of ASTM F3114. To make things even more exciting we will not know the exact wording of the CRI until we start discussions with EASA, but they have applied the same CRI with the same wording to every relevant program in the last few years so we can be relatively confident about the wording (but not completely certain):

For all CS-23 high performance aeroplanes the following applies:

• Windshield panes directly in front of the pilot(s) in the normal conduct of their duties, and the supporting structures for these panes must withstand, without penetration, the impact of a 0·91 kg (2 lb) bird when the velocity of the aeroplane relative to the bird along the aeroplane’s flight path is equal to the aeroplane’s maximum approach flap speed.
• The windshield panels in front of the pilot(s) must be arranged so that, assuming the loss of vision through any one panel, one or more panels remain available for use by a pilot seated at a pilot station to permit continued safe flight and landing.
• Continued safe flight and landing is required after impact of a 0·91 kg (2 lb) bird when the velocity of the aeroplane relative to the bird along the aeroplane’s flight path is equal to the aeroplane’s maximum approach flap speed. This must be shown for any location prone to bird strike where a safety assessment reveals a vulnerable item of concern (e.g. cockpit, fuel tanks, empennage attachments, critical flight systems in the nose or canopy area) either through direct impact or shock wave effects.

You will notice that item (1) from the CRI mirrors the wording of the ASTM. Item (2) adds another visibility criteria – we can comply with this by design because we have separate LH and RH windshields.

(As a side note, this requirement (2) for visibility was applied to commuter category part 23 aircraft and was in amendment 63, and prior amendments, of the FAA regulations as 23.775 (h)(2). For very clever ‘reasons’ this was usefully moved into F3117-23a 4.3 so unless you are psychic or an obsessive anal retentive and search all of the ASTM standards to see if it was deleted or not you would not know it still existed. Thankfully it lives on in the CRI in the original comprehensible form as a traditional sequentially read paragraph of coherent prose – very old school)

Item (3) is the fun requirement to show compliance with – and this mirrors the same wording “after impact of a 0·91 kg (2 lb) bird when the velocity of the aeroplane relative to the bird along the aeroplane’s flight path is equal to the aeroplane’s maximum approach flap speed”

To summarize:

• The wording of the regulations has been very carefully ruined by amendment 64 and can be ignored as they are now vague, confusing and not fit for purpose.
• The partially incoherent ASTMs can be treated as if they are the regulations and must be followed (Despite this being technically illegal – long story – the FAA does not understand the legal issues despite being the government entity created with the statutory authority to enact the law so, errrr, meh)
• In this instance we can ignore the regulations (because they are rubbish) and the ASTM standards because the EASA CRI envelopes the ASTM requirements and exceeds them. We will show compliance to the standards defined by the CRI. (even though a similar CRI has not been formally applied to our program but we can safely assume that it will be at some point. Probably.)
• The likely wording of the probable CRI and the ASTM standards (and the original pre amendment 64 set of regulations) mirror each other. The same wording regarding the relative speed of the bird to the aircraft is repeated more than once in the CRI making this the ‘definitively definitive definition’ of the speed of impact of the bird.
• The people in charge of the regulations and standards might not actually be intellectually subnormal but they have a lot of training and practice and by working very hard together they emulate idiocy with unnerving accuracy.

Welcome to the wonderful world of compliance.

From one of our readers, Chip Haynes (reproduced with his permission, minor corrections for email speed typing):

I have a couple comments on your commentary that provide at least a partial rebuttal. Although I largely agree with your conclusions, there are some points that justify why we are where we are.

Mr. Haynes makes some good points, tempering my hyperbole. Thanks.

Boeing has secretly and very effectively been digging a deep hole for itself. Well, now it is not so secret but that is how these things tend to go.

We know that what we are seeing is not the problem, they are some of the results caused by the problem. The results we see are the low quality control of the final product. The problem is systemic. There has been a change to the operation of the company (the system of systems) that has decreased the quality of the product

The total ‘system’ is a combination of the company manufacturing engineering, manufacturing, quality control processes and all of the human actions and interactions that occur in the implementation of those processes.

It may be that the manufacturing engineering process has changed so it is purposefully no longer instructing manufacturing not to install critical hardware, but this is unlikely.

It may be that manufacturing system has changed so that they are purposefully not following the instructions from manufacturing engineering, but this is unlikely.

It may be that the quality system has changed so that they are purposefully not inspecting critical areas. Although this is also unlikely.

Whatever the cause, the system of systems has failed and it would be great to know why.

Boeing has put forward a “Product safety and quality plan” which describes how they are going to improve the quality of their products.

https://www.washingtonpost.com/documents/227ed543-2dc6-4739-af6d-62eabe062131.pdf

This document appears to contain no results of a root cause analysis and no reflection as to what has caused the degradation in company performance and why it happened. However there were some pleasing anodyne word salads, this is one of my favorites:

Page 10:

Safety culture. Boeing is undertaking actions to deepen leadership and employee alignment to a positive safety culture, conduct improved safety culture assessments, and enhance safety reporting mechanisms. Fundamentally, these actions focus on simplifying employee guidance and ensuring employees understand their part in Boeing’s safety culture, no matter their job role.

The whole document is basically a ‘Don’t worry guys – we’ve got this!’ with a total absence of self reflection or any analysis of the root cause.

This is not unusual in modern corporate culture and is a demonstration of the evasion of responsibility that is antithetical to aircraft development and manufacture.

Boeing have passed their peak and look like they will not be returning. Unless they wake up, the future is an easy downhill path of least resistance.

https://appliedcax.com/docs/femap/femap-symposium-2015-seattle-area/FEA-Validation-Requiremnents-and-Methods-Final-with-Transcript.pdf

https://www.easa.europa.eu/en/downloads/116479/en

I am getting into the subject of FEM validation with one of our clients. Finite element methods have been used in aerospace development for over half a century and are not new. So why has the FAA decided that a formal validation of finite element models is required now?

Let’s remind ourselves of how this used to work. Finite element modeling was one of a set of tools available to the analyst. From hand analysis to more complex excel, mathcad or matlab models and the linear and nonlinear finite element models.

All these methods were used at the discretion of the engineering organization and subjected to checks and reviews of the engineers and technical management based on their professional knowledge and experience. Where necessary, you would work with a Designated Engineering Representative or a Compliance Verification Engineer to validate to the level necessary for typically only the global finite element model.

Now, any Finite element model requires validation, no matter how simple or determinate.

Some years ago the certification agencies started to get nervous about the integrity of finite element models. The reason for this is not clear. I don’t know if it because of an actual or perceived drop in standards within the industry, an actual or perceived drop in confidence and specific technical competence of people at the FAA or the general creep we are seeing towards the slow adoption of all manner of judgment being transferred from non government entities (me and you) to government entities.

Will it make aircraft safer? – maybe. Will it make the process of development more expensive? – yes.

The problem has been outlined to me during conversations with people who have tried to go through the process already.

The problems encountered go something like this (and I am very broadly paraphrasing):

“The reason that the regulator wants greater oversight over FE modeling is because most people at the FAA do not really understand FE modeling. Getting a detailed plan agreed and approved for exactly how you are going to show validation of your FE models is very difficult and can take a very long time because most people at the FAA do not really understand FE modeling.”

You get into the circular logic of government oversight. The government wants more oversight because they do not trust you because of their lack of knowledge and experience. The oversight process is difficult and expensive to complete because the people at the government do not have the necessary knowledge and experience to make a decision.

Those of us in the engineering community know that hand analysis methods for load distribution and failure mode prediction have a set of issues and problems and that finite element models for load distribution and failure mode prediction have a different set of problems. This is why the unlimited use of any methods by a professional engineer subject to check and approval by their industry peers and betters is the best approach to take.

I am curious how far this creep is going to progress. If the regulator is getting nervous about FE models, I can’t wait to see the reaction when they find out how inaccurate hand analysis methods can be.

I wonder how long it will be before we have to validate all analysis methods to government controlled standards. Imposed with the best of intentions but without any nuance, wisdom or professional volition.

The way this is imposed as a mandatory element of the power of the regulator is not through law, or regulation, or advisory material, or policy, but through DER training.

This is an increasing problem. You will have noticed that the adoption of the ASTM standards have created a set of absolutely and definitely non mandatory proprietary commercial standards as the only possible way of certifying to part 23 regulations. In this way government departments can create what are in effect absolutely mandatory rules, not by changing the statue or even regulations but by using methods with much less consideration and accountability.

The regulator is now using DER training to create mandatory rules. Just like ‘independently developed industry standards’ (chuckle) such as the ASTM standards can have the weight of law, now DER training carries the mandate of statute.

Those who pay attention may have observed a gradual erosion of what were once cherished freedoms, now replaced not by statutory restrictions, but by rules masquerading as law, crafted within government departments without any accountability.

At least with the conversion of part 23 from open regulations into a horribly flawed pay to play system there was lip service to a public consultation process. The majority of the comments in the process which were against the change were completely ignored, but at least there was the fig leaf of a rushed and entertainingly pointless consultation process.

Using DER training is a new, much quicker and efficient process of creating mandatory rules without all that tedious mucking around in the actual rulemaking process

The links at the start of this document lead to the training and guidance material. The information in this guidance material is excellent and I have done similar studies on the different outcomes of different modeling methods, as a lot of other engineers will have as well. We are all naturally curious and want to understand the methods and techniques we employ.

But no need to worry! The government has done all of the curiosity for you and all you have to do is relax and comply to your heart’s content.

Will engineering be spending significant additional time to write detailed validation plans and enter negotiations with the regulator until those validations have been approved and then spend additional time to nuance FE models to strain gage results so they match close enough to satisfy the plan? Absolutely!

Anyone who has done a lot of testing will know that strain gauge results come with accuracy problems all their own – there is some good information here on the accuracy of ideally installed gages https://www.omega.co.uk/techref/pdf/straingage_measurement.pdf

The engineer has the challenge of selecting strain gage locations for correlation that meet the following criteria:

High enough strain to be read accurately

Low strain gradient

Accessible to allow gage installation

The engineer then has to pray that the gauge is installed correctly (perfectly) and endures for the duration of the test program giving perfect results.

The guideline is that deflection has to match with 5% and strains have to match within 10%

If the structural means of compliance depends on the FE model, failure to validate the FE model means that you do not get your type certificate.

The other amusing part is that if you fail to validate your model you are not allowed to improve your model and then show validation. Within the compliance process there is no possibility of improving the model, it is a one shot pass/fail single event.

Also, bear in mind that the FE model validation standards are to be applied regardless of the performance level and complexity of the aircraft. If you are dealing with a small stiff composite aircraft that does not allow buckling up to ultimate level that is inherently easy to predict, you are forced into the same level of validation as a non linear, buckling transport category aircraft.

When all you have is a hammer everything looks like an expensive compliance exercise of dubious value.

Rather than a technical article about the aircraft industry this month I will focus on the psychological and the commercial.

I work with a lot of startup companies and like all startup companies, the companies that I work with are generally pre-revenue and they have to go out into the world and convince one or more investors to part with a lot of money. The risk is high but the rewards are great and there is a lot of competition.

Most of the projects I work with are started by engineers. Career engineers. Why is this significant? Well, it usually means that the projects are based, in reality, in terms of performance, certifiability and commercial aspects. People who have spent a good deal of time in the field of engineering understand the crippling limitations of physics, legislation and the market. Non ‘career engineers’ tend to shy away from tackling the critical minefield of reality

Communicating the reality of the ‘crippling limitations’ that you will be laboring under does not make a persuasive case for investment. But unless you are intimately familiar with them and your project tackles them head on with utter pragmatism there is a very good chance that you will fail. Investors don’t seem to care about how good you are at avoiding almost certain failure, but they should.

Crafting your communications with potential investors around unvarnished reality is not a winning approach, no matter how good you are at managing the risks and communicating those management skills, and this is a trap that many projects fall into.

Engineers fail to appreciate that no one else appreciates the things that they appreciate. Everyone else could be wrong, but that ‘everyone else’ class of the population includes all of the people who are likely to invest in your project.

So the messaging needs to bifurcate. Internal messaging in development is around identifying, documenting and resolving every problem, external communication is all about a vision of the future.

I am going to very badly paraphrase Maya Angelou: People do not remember what you said, or what you made them think. People remember how you made them feel.

A finely honed financial model with stunning market justification for your revenue stream where all risks are identified and mitigated may bring engineers (and all analytical modelers) out in a hot flush of excitement. But it does not have that effect on anyone else, including investors. Even though you would think that is exactly the kind of thing they should care about.

The truth is that human beings can review as many positive flow forecasts that you can throw at them. It does not make them feel anything.

My projects often express their frustration that apparently impossible and certainly impractical eVTOL programs can pull in hundreds of millions of dollars in investment and they can’t get a dime. Well – investors buy into dreams, they buy emotional validation and they invest in visions.

Investors (mostly middle aged men similar to myself) are as prone to emotional purchases as women buying makeup or clothes. Although men are far less likely to admit it.

These emotional animals are the people that you have to get investment from.

You can see exactly what they emotionally react to in a positive way as these are the projects that get invested. Joby, Vertical, Wisk, Archer, Volocopter. So what emotions are those projects selling? You can see that by looking at what they are buying.

An individual’s emotional makeup is both simple and complex. It is formed in childhood and modified throughout a lifetime.

So what were all these investors exposed to growing up that would influence them all in one direction? They all grew up in an age where Star Wars, Star Trek and Blade Runner dominated the imagination of technical minded boys who looked to the future. They read Arthur C Clarke, Asimov and Heinlein, Frank Herbert and Harry Harrison. The same things I read and a lot of you probably read 30 years ago.

Deep in their mind they are still the 10 year old boy who watched as Luke Skywalker graduated from his old, rough landspeeder in the deserts of Tatooine to the X wing fighter. Or the pre teen who read Starship Troopers or Childhood’s End or the Foundation trilogy. That is what they are investing in: The imagined future of their childhood. They are trying to make it real.

They are no different from a woman investing in a pretty dress that they dreamed about as a little girl, or a lottery winner buying an E-Type or a Shelby Cobra. They are in part fulfilling a childhood dream. They are taking part in a shared fantasy that has the most flimsy fig leaf of a poorly conceived financial model to cover the secret that none of these programs are actually viable.

You can see symptoms of this. There is a great resistance to rational reassessment of the EVTOL field, this resistance is purely emotional – people will resist being woken up from a very pleasant dream. The petulant defense of the dream is almost childlike.

Reality does suck but in the end there is no escape from it.

You have to sell the dream and manage reality. The critical aspect is to sell a dream that, at least in part, is actually achievable.