Archer vs Joby: who has the better motor?

| Description |
This video examines the electric motors by Archer and Joby, the two frontrunners in the eVTOL industry. We start with a high-level analysis of their relative benefits and drawbacks, scoping our analysis to their torque and power densities. The intention is to open a broader and more detailed technical discussion. Finally, we conclude with an answer to the question: who has the better motor?
| Timestamps |
0:00 Introduction
0:48 Analysis of Archer's motors
11:52 Analysis of Joby's motors
18:15 Conclusion
| Disclaimer |
For an aircraft engineer like myself, the advent of the eVTOL industry is exciting. The industry's current state is that many companies are exploring different aircraft designs and innovations. Some will work, but many will fail because they will ultimately be less economical or technically inferior. I aim to be an independent analyst, educator, and commentator about what aircraft concepts are sensible and feasible and what could be more challenging. I want to share those insights, hoping that they will accelerate the learning curve that the industry is on.
It is important to note that I do not provide investment advice. I am not telling you to buy or sell a particular stock. Instead, I provide opinions on the aircraft design. Whether or not companies will be successful depends on numerous factors, of which the aircraft design is only a fraction. With teaching as my priority, I aim to boost our understanding of maths, physics, and engineering by using this exciting industry as the motivating context.
My research and reports express my opinions, which I have based upon generally available public information, field research, inferences and deductions through my due diligence and analytical process. To the best of my ability and belief, all information contained herein is accurate and reliable, and has been obtained from public sources I believe to be accurate and reliable. I strive for accuracy and completeness to support my opinions, and I have a good faith belief in everything I write, however, all such information is presented “as is,” without warranty of any kind - whether express or implied. I make no representation, express or implied, as to the accuracy, timeliness, or completeness of any such information or with regard to the results to be obtained from its use. You agree that the use of my research is at your own risk. In no event will I be liable for any direct or indirect trading losses caused by any information available on this report. Think critically about my opinions and do your own research and analysis before making any decisions.
I am entitled to my opinions and to the right to express such opinions in a public forum. I believe that the publication of my opinions about public companies that I research is in the public interest. This report and all statements contained herein are my opinions and are not statements of fact. You can publicly access any piece of evidence cited in this report or that I relied on to create this report. All expressions of opinion are subject to change without notice, and I do not undertake to update or supplement any reports or any of the information, analysis and opinion contained in them.
| References |
(see the comments section below)

[@williambunting803]

Thanks for that very detailed expose, John. Very helpful.

[@PuLSe980]

Great videos, John. I'd love to see a high level video on what architectures you think are best for different business models. Also love to get your thoughts on Overair's butterfly

[@harryseagar]

Thanks again, fascinated to see the gen 2 VX4 aft rotors at work and in transition! With any luck that will be early - mid 2024. Also, if I could request more VX4 content, I would appreciate it!

[@zhihenglou]

Hi Harry! Sure, I'll keep that in mind! I haven't found a lot of public data on the VX4 yet, but I'm eager to report on them, too😄

[@faluffel]

Thank you for yet another great analysis! I really enjoy your in-depth videos. I'm really curious to hear, did you see Liliums recent battery webinar, and what did you think of it?

[@zhihenglou]

Hi! I'm glad you like these kinds of videos; thank you for your viewership! Yes, I've seen Lilium's recent battery webinar. Overall, I think it's an excellent presentation with clear and concise explanations. And it's positive to see Lilium's leadership team address some of the industry's concerns and engage with the public. However, in terms of content, I haven't seen anything in the presentation that would change my previous conclusion. Information about Lilium's batteries was already released more than a year ago (e.g., lilium.com/newsroom-detail/liliums-battery-strategy), so the battery webinar didn't bring new perspectives in this regard. Whilst batteries with high silicon content in their anodes can have outstanding performance, their adoption has been historically limited by numerous problems. I imagine Ionblox has invented a clever way to mitigate these problems - a goal that many other battery startups are aspiring towards. But, in the context of achieving a high aviation safety standard, I wonder if it is pragmatic to use novel batteries in a novel propulsion system as part of a novel aircraft concept? I think that's a risk any observer has to assess for him or herself, weighing it against the potential upsides. Best wishes, John

[@zhihenglou]

| References | (Anton, 2019) www.bbaa.de/fileadmin/user_upload/02-preis/02-02-preistraeger/newsletter-2019/02-2019-09/02_Siemens_Anton.pdf (Archer, 2022a) kzbin.info/www/bejne/hp61fJemfreaZtk (Archer, 2022b) archer.com/news/what-is-urban-air-mobility (Archer, 2022c) kzbin.info/www/bejne/sGO4fHqlod5njpo (Archer, 2023) archer.com/news/stellantis-to-build-electric-aircraft-with-archer-and-provide-strategic-funding-for-growth (AvBuyer, 2023) www.avbuyer.com/articles/ga-buyer-europe/what-to-know-siemens-hybrid-electric-propulsion-systems-112417 (AviationWeek, 2021) aviationweek.com/aerospace/urban-unmanned-aviation/archers-evtol-designed-early-market-entry (EASA, 2020) www.easa.europa.eu/en/downloads/114474/en (Electric VTOL News, 2022a) evtol.news/news/new-evtol-galleries (Electric VTOL News, 2022b) evtol.news/news/jobys-patents-reveal-new-details (Emobility-engineering, 2023) www.emobility-engineering.com/magnix-magni350-650-and-magnidrive-100/ (EMRAX, 2019) emrax.com/e-motors/emrax-268/ (Evolito, 2023) evolito.aero/media/2023/09/Evolito-D1500-2x3-Datasheet-V2.pdf (Flyer, 2020) flyer.co.uk/pipistrel-offers-type-certified-electric-motor-to-others/ (Gudmundsson, 2022) www.sciencedirect.com/book/9780128184653/general-aviation-aircraft-design (Joby, 2023a) kzbin.info/www/bejne/p2qQc6qIjK2UZqs (Joby, 2023b) twitter.com/jobyaviation/status/1678771583475929089 (NASA, 2022) www1.grc.nasa.gov/beginners-guide-to-aeronautics/size-effects-on-drag/ (Safran, 2023) www.safran-group.com/products-services/engineustm (Shankland, 2022) www.cnet.com/roadshow/news/archer-reveals-its-electric-air-taxi-for-10-minute-flights-to-the-airport/ (Stoll, 2015) nari.arc.nasa.gov/sites/default/files/attachments/Stoll-TVFW-Aug2015.pdf (The Air Current, 2023) kzbin.info/www/bejne/aYbbo5aeo8qZhdU (VFS, 2022) gallery.vtol.org/image/1D6eX

[@sakshammishra8291]

Excellent analysis videos, like the other ones on your channel. Really informative. Based on your previous videos comparing propulsions of Joby Aviation and Vertical Aerospace, and now the comparision between motors of Archer and Joby, I wonder what you think about Alia eVTOL by Beta and where it fits along with the other three.

[@zhihenglou]

Hi there! I think Beta's Alia eVTOL is a simpler design, so it could get certified and come to the market first. However, this advantage could be temporary, as it depends on the certification of eVTOL aircraft with better performance. On the other hand, other eVTOL aircraft may not get certified at all. So, I think Beta's eVTOL is a product with lower risk but also lower potential. Best, John

[@sakshammishra8291]

@@zhihenglou Hmm, interesting point. Thanks

[@rossnolan7283]

Flying the BETA without lift props is significant - it makes a mockery of the wing booms and weird ultra swept tail though --their props are also 'unusual' and unlikely to be efficient (2 blade scimitars ) --the sheer SIZE of these monsters is only apparent when somone walks under a wing with a foot or more to spare --and these are only four seaters (the other dozen or so 'stowaways' are in the battery compartment ...)

[@NevinChung]

I’m also interested to see how both compare in noise levels. Nasa did acoustic testing back in 2022 for Joby. Very impressive stats for Joby especially when compared to many other aircrafts. I haven’t seen any acoustic validation for Archer yet. Would love to see Archer’s and how they compare at take off/ landing and full transition flight.

[@amazingdiyprojects]

Again, great content, thanks! Interesting how the leading companies with such similar design requirements comes to two completely different conclusions. Jobys numbers sure seem to good to be true, I do hope they match reality, that would be great for the development of all future electric manned flight vehicles! Time will tell. I like the idea of dual winding (split stator?). If the dual winding also comes with dual esc, that might provide a sort of esc-motor redundancy within a single motor housing. Kind regards/Axel

[@zhihenglou]

Hey Axel, great to see you again :)!

[@yujack1766]

Thanks for your detail video, that's really helpful. I just wonder how could you get the conclusion that Joby is using an axial flux design?

[@NevinChung]

Great analysis. You validated my points I’ve been saying about Archer as Joby seems to be the winner when compared against each other. I believe the drag of the rear motors and extra weight alone is enough to rule out archer. I have never seen a full transition of flight in any released video from archer. Which been a RED flag for me as I do like there cockpit design but see many negative factors to their design choice and choice to use a gearbox. I have some electric motor experience since 2005 and I can tell you, a gear box is a negative for electric motors as those gears will need constant maintenance and eventually a full replacement.

[@skyloveglobalnelsonbarbonc8009]

❤ for me its nice to both are in servece 2:14

[@brianb-p6586]

Why would the graphic ask "are there 6 or 12 gearboxes" in the Archer design? Since the Archer presentation clearly implied a 6:1 reduction gear ratio, the rear rotors clearly cannot be effectively driven without reduction gearing - the torque to the rotor would be far too low.

[@evandrodaolio]

I have archer joby lilium evtl and evex❤

[@SwordOfApollo]

The speaker at the Joby presentation mentioned that their direct drive motor had been patented. I imagine you could perhaps answer some of your questions about it, if you were able to find that patent. I did some brief searching online, but the closest thing I found was a Joby patent on Justia for an "Aircraft propulsion unit." This doesn't seem to be for the motor itself. Perhaps the patent has been filed, but not published, yet? Or I just wasn't looking in the right place....

[@TheBagOfHolding]

That guy was a charlatan

[@user-gv4co6gc1h]

수치로 비교하면 정확하지만 저처럼 비 전문가입장에서 볼때는 아처 미드나잇 기체 프로펠러 숫자 9개 조비 s4기체 프로펠러 6개 ... 이것만 봐도 조비 모터가 더 힘이 쎄다는걸 추측해봅니다...

[@nottelling41]

Archer is very focussed on redundancy for safety and their presentation was very open. More motors means more weight. It appears that both companies chose the wrong motor!

[@ricksimmons1947]

This video has a lot of good information and data, however, the constant use of "rotor" where it should be " propeller" makes one question the validity of the rest of the data. These props are either constant speed (collective pitch only) or fixed pitch. There was not "cycle" control introduced in the video, which would be a characteristic of a rotor..

[@TheBagOfHolding]

mutli rotor evtols

[@ricksimmons1947]

NO! Multi Prop eVTOL . . @@TheBagOfHolding

[@brianb-p6586]

They're still rotors, even without cyclic pitch control. The tail rotor of a conventional helicopter has collective but not cyclic pitch control... and it's a *rotor*

[@davidgallefoss1254]

Are you familiar with h3x and their claim of 12,5kW/kg?

[@956870733]

I just checked h3x, including their latest megawatt class aircraft application. Those are great motors but keep in mind that they are only great for aircraft (or maybe boat) companies that prefer a less integrated approach. Because H3X is not a propeller or turbine blade or water impeller company so they are not responsible for handling aerodynamic and hydrodynamic loads on the spinning body. Another way to think about it is: in both EV and combustion cars, a lot of road loads go through the suspension system and vehicle chassis without being dumped onto the engine or electric motor. To use H3X's motor, a less integrated aircraft have to re-route the propeller load (or any large spinning body) elsewhere (separate structure, additional mass) to protect the motor. Aircraft companies that decide to design and build their own motor optimized for their own aircraft can sometimes choose to let the load go through the electric motor's structure instead. A motor company's business model usually focus on packaging their product to provide convivence to many audiences while a motor developed by an aircraft company focus on designing motor specifically for their own aircraft without worrying how their motor fit into the market. If one were to start up a car company with hub/wheel motor at each wheel, the founder will not use Lucid or Tesla electric motor even if the founder receives motors from these two brands for free.

[@g.zoltan]

I wonder what was the reason for re-uploading this video twice. I suppose you found some mistakes and wanted to have maximal informational accuracy?

[@zhihenglou]

Hi there! Yes, this is the second upload. I found the audio on my first attempt to be too quiet, so I went back to video editing and turned up the entire volume level. Hopefully, the audio is now more audible and in line with other KZbin videos now!

[@brianb-p6586]

It's loud engouh,@@zhihenglou , but your narration is so muffled it sounds like you are speaking through a barrier of rubber foam.

[@rossnolan7283]

A good comparison but limited first by the accuracy and honesty of the respective firms data. there has to be a major flaw in the calculation for Joby hover power (cited as '100 kw" -that is only 134 HP , and the basic idea that much less power is going to be used in hover than in wing borne flight is just wrong ( I suspect a decimal point problem -ie 1000 kw in hover perhaps -the level flight L/D might be around 15 or more and hovering requires thrust equal to weight with at least a 25% margin to get some useful work to climb and accelerate -plus a further margin to cover an engine failure (doubled to maintain thrust symmetry --more in the case of Joby which loses 1/3 of power or thrust versus 1/6 for Archer ) Whether peak power IS acheived at peak torque (never the case with ICE) is another questionable assumption - and the use of "continuous' torque rather than "peak" torque at this critical case seems in error - you need all the horses pulling as hard as possible in take off and vertical landing - less so in cruise. (MUCH less -this is the first Achilles heel for 'e' VTOL since the power is sized for the hover/climb and too much and too heavy in cruise . We need partial power figures rather than max everything but I realize that they are not publishing real engineering papers (No SAE etc and the latest Janes's is just advertising fluff ) -a critique is handicapped by the secrecy and disinformation put out. There is something amiss with Gudrunson's thrust curves --all reaching zero thrust at 250 is a bit strange -- without knowing the variables and constants it cannot be evaluated -- the eVTOL case needs as much blade area and disc area as feasible --with the rear props being fixed pitch (even if 'clocking' to fold flat in cruise as for VX4 ) they are going to be woeful in transition and in the wake of the front props -- a dog's breakfast of turbulent air and 'non optimum' orientaion etc -- how they expect to 'balance' a variable pitch five blade front prop with a fixed pitch rear prop in the 'engine out' case is a mystery - it has to be by software manipulation a la 737 Max MCAS..... how many failure modes are there ? Joby bad mouthing planetary gearboxes is a bit rich -just about every automatic car has multiple planetary (even the model T...) and smooth electric power is the ideal case -- again, propaganda aimed at Archer - both of them are like two bald men fighting over a comb in any case --the diseconomies and failings of the whole eVTOL fiasco are yet to play out ( I just purchsed some 1940s and 50s "Aeroplane' and "Aircraft Engineering " Aircraft Production " magazines at the local flea market and it is interesting to see the arguments for and against the huge passenger flying boat playing out on their pages together with pictures of the HUGE Saunders Roe Princess flying boats (they built THREE simultaneously so confident were they -none ever served..) the gigantic Hughes (Hercules) flying boat and the Bristol Brabazon are other examples of irrational exuberance and folly -literally dwarfing the current eVTOL madness but a similar affliction. Look behind the curtain. PS I will do a better analysis as time permits.

[@rossnolan7283]

The cross outs are some computer glitch -not intentional,sorry

[@zhihenglou]

Hey Ross, glad to see you back 😃! So for the hover power at 15:22 I meant the required power per rotor during hover flight. For the entire aircraft, I estimated a hover power of 600kW using a MTOW of 2700kg and a figure of merit of 0.7. On this slide, I wanted to estimate the blade tip speed during hover flight, so I started with an assumption for the power per rotor. Joby has six propulsion units, so the power per rotor during hover flight would be 100kW. (I should have probably not called it 'hover power' and just gone for the more wordy term). From what I have seen, peak power approximately occurs at peak torque. For example, take a look at this data, which closely matches Joby's needs: evolito.aero/media/2023/09/Evolito-D1500-2x3-Datasheet-V2.pdf For some motors, you can get more torque by sacrificing rotational speed and power. In terms of sizing the propulsion system, I reasoned that the motor's peak power is matched with a scenario where one rotor is inoperative, and another rotor is throttled down to trim the aircraft. The propulsion system's continuous power is matched with nominal take-off. I did not like the idea of matching peak power with nominal take-off. I could be wrong on the points above and would be eager to be corrected and learn! Best, John

[@rossnolan7283]

OK that seems a bit closer to reality ( I did consider if it was per rotor but that seemed a bit too low in total --the Lilium hover power still takes the cake for overkill , I'll take a look at your link in the morning (near midnight here --- no pun intended !) I just did my usual IN sanity check of the VFS register and note the latest entry is a virtual Joby clone from China but with the difference that the two inner front rotors are NOT tilters but fixed horizontal lifters that stop and fair fore and aft in cruise -this relieves those two tractor rotors in cruise on Joby and will help with the excessive blade area in cruise (Mark Moore and Joby itself pointed out the poor cruise efficiency with using all lift rotors as propellers in their S2 dissertation then convenientkly forgot that with S4 .... Those tilting hinges are obvious weak points and more so on Archer or Wisk or VZ4 et al --the destruction of the VX4 following blade assymetry (as predicted) shows this flaw - propeller whirl flutter caused catastrophic failures on the Lockheed Electra for the same root cause and is lurking still (blade icing etc can trigger it with those spindly booms on Midnight in particular - much more prone than VX4 . As to accounting for an 'inoperative' proprotor -- such 'inoperation' might well be instantaneous and total requiring full 'throttle down' on the corresponding 'good' prop -- runaway pich control has been a failure mode on earlier VTOL eg Curtiss X 19 Dynavert et al and actuator failure (tilters included) or resultant assymetry particularly in transition would be interesting (those hordes of fresh faced grads peering intently into screens on their promos have to be doing something -- this is much more accident prone than the model quadcopter case with extremely low inertias and rate gyros as the front line stability . more soon , cheers Ross . ATOL is the way.😋@@zhihenglou

[@brianb-p6586]

Peak power and peak torque _can_ occur at the same speed for an internal combustion engine, but only if the engine speed is limited (typically for fuel economy or reliability reasons) to that value. For instance, the 7.3 L gas engine in a Ford F-650 is rated at 468 lb.-ft. of torque and 335 HP, both at 3,750 RPM; the same engine in a much lighter-duty Ford F-350 can produce a similar 485 lb.-ft. of torque at 4,000 rpm, but is allowed to turn faster to produce up to 430 horsepower at 5,500 rpm.

[@brianb-p6586]

@@zhihenglouelectric motor peak torque occurs at zero speed, and from there up to the point that the motor and controller are no longer current-limited. Peak power speed depends on multiple factors including heat management and available drive voltage. In a typical automotive application, peak motor power is limited by the controller - not the motor itself - and the controller "cuts the top off of the power curve", so the same power is available all the way from about the speed where current is no longer the limit (e.g. about 2,700 RPM for a Nissan Leaf) to the point that voltage is the limiting factor (about 10,500 RPM for the same Nissan Leaf), with more speed allowed with lower torque (up to about 12,000 RPM for the Leaf). Since electric motors for aircraft don't need a wide speed range, in direct-drive applications they are typically designed to operate in a narrow speed range not far above the current-limited speed (so a Leaf motor would be used at about 3,000 RPM; other EV motors might have substantially higher corresponding speeds).

[@skyloveglobalnelsonbarbonc8009]

Its realy needed a quit 18:58

[@brianb-p6586]

The narrator's audio is really muffled - not low in level, but not clear.

[@CNCAddict]

it's odd how archer is calling motors engines. These are definately electric motors...no need to try to call them something else.

[@TheBagOfHolding]

At least they don't call them electric jet engines

[@brianb-p6586]

While "motor" is the current conventional word usage, "engine" is also technically correct. They must be aware that "motor" is conventional; I'm not sure why they consciously chose "engine", but it may be for familiarity in the aviation world.

[@keepmovn8039]

Its marketing, for common people to easily understand.

[@jeffbertuleit5848]

Now if Joby wants to generate some now cash, sell some motor and systems to the Experimental market.

[@TheBagOfHolding]

They don't have special motors that other people couldn't make without licensing. There isn't an experimental market. There are scam startups and they will not sell their insufficient components and blow the whole scam.

[@TheSecondWitness]

I’m a pilot, and I believe that Archer has a design flaw which is going to come back to be their ruin.

[@user-jc2we4sn1i]

I have designed better motors, jet engines, and rocket engines along with a bibliography of technical sources.

[@TheBagOfHolding]

I don't even think motors matter at all. Its all about the battery. Thats why they are all bunk.

[@brianb-p6586]

Everything matters, but I agree that at this point battery weight is more important than motor weight.

[@SeanWhite]

Pretty bad when your engineer does not know the difference between an engine and a motor.

[@brianb-p6586]

Pretty bad when people correct other people who are not wrong. Go to a dictionary such as Merriam-Webster (presumably online, but the still print them) and look at the definitions of the two words.

[@brianb-p6586]

I don't see any justification for the assumption at 7:38 that Archer's front and rear rotors are required to produce the same lift force. If the centre of mass is closer to the front row of rotors than the rear, which is likely, the front rotors will need to produce more lift.