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EVTOL news and progress - do we need a new dedicated section?

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EVTOL news and progress - do we need a new dedicated section?

Old 29th Jan 2024, 21:17
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Originally Posted by petit plateau
Thanks.

To be fair with a 76 tonne aircraft they themselves come up with a 35 tonne battery, so your 42-tonne calc (including reserve) seems to be in wild agreement.

As to the reserve fraction that is where they go with a gasturbine genset and liquid fuel so as to minimise emergency ordinarily unused weight. That is exactly the strategy I use when designing similar energy systems so I am not surprised by it. So that leaves 7 tonnes (your figure 42 - 35 = 7) of not-required reserve battery & liquid fuel. If you look at Fig 3 that looks to be about a 5% mass fraction, or 3.8 tonnes for emgy turbine + fuel, so a useful saving on your 7 tonne estimate. It seems your numbers are directionally in agreement with their numbers.

Are there any numbers that are identifiably plain wrong ?
The best energy burn/passenger-km for conventional aircraft I could find was 259 wh/passenger-km (2.78L/100 passenger-km) and that number does account for inefficiencies of the engine, so I'm not sure how they arrive at the 167wh number; that's a massive improvement in flight energy consumption. An aircraft is an aircraft and a fuel burning machine will obviously reduce its weight as distance is traveled.
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Old 29th Jan 2024, 23:59
  #82 (permalink)  
 
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Guys help out this math challenged Biology major. So 76 tonnes = 167,000 lbs so even with a reasonable 10 lbs/hp power to weight ratio that is in round numbers 16,000 hp or 12,000kw of thrust. So assume 400 kph, 800 km no reserve requires a battery that can produce 24,000kw/ hr.

Is that even remotely possible even if the battery weighs 35 Tonnes ?

Finally how many electric cars can you make with 35 Tonnes worth of batteries?
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Old 30th Jan 2024, 03:10
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Originally Posted by Big Pistons Forever
Guys help out this math challenged Biology major. So 76 tonnes = 167,000 lbs so even with a reasonable 10 lbs/hp power to weight ratio that is in round numbers 16,000 hp or 12,000kw of thrust. So assume 400 kph, 800 km no reserve requires a battery that can produce 24,000kw/ hr.

Is that even remotely possible even if the battery weighs 35 Tonnes ?

Finally how many electric cars can you make with 35 Tonnes worth of batteries?
That's an interesting point. What is the power deliverable from a discharging battery looking at a charge/rate factor? If the battery is below say 25% charge, can it deliver at the same rate as a fully charged battery? What are the consequences for aircraft? Would it be necessary to look at a battery with 25% (number drawn out of the air) as less able to deliver energy to electric motors? How would this affect things such as reserve power and ability to do a go around?
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Old 30th Jan 2024, 10:53
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Originally Posted by Big Pistons Forever
Guys help out this math challenged Biology major. So 76 tonnes = 167,000 lbs so even with a reasonable 10 lbs/hp power to weight ratio that is in round numbers 16,000 hp or 12,000kw of thrust. So assume 400 kph, 800 km no reserve requires a battery that can produce 24,000kw/ hr.

Is that even remotely possible even if the battery weighs 35 Tonnes ?

Finally how many electric cars can you make with 35 Tonnes worth of batteries?
I will stay in metric for my sanity.

They do charge and discharge rate considerations in the paper, and it all looks plausible to me. Let us try some very crude ratio checks.
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There are 8 x 1.4MW electric motors on this design (continuous rating), which looks about right, so 11.2MW in toto.

For the 2nd gen aircraft they are using 440Wh/kg at pack level (table 3). So 35,000 x 440 = 15,400 kWh = 15.4 MWh

So at full throttle these motors could drain that pack in just over 1 hour (1.35h more precisely). That is entirely plausible and is similar to running a BEV automotive at max throttle.

For comparison a Tesla Model 3 has approx 82kWh and the motor in one variant is 137 kW, so at max power that could empty its battery in half an hour (0.59h).

So the aircraft is treating its batteries more gently than a typical automotive.
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15,400 kWh / 82 kWh = 188 cars worth of batteries.

For a 90 seater aircraft that looks about right, given the typical vehical seat occupancy fraction, and typical aircraft seat occupancy fraction.
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Old 30th Jan 2024, 13:50
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I've done some further analysis after a colleague has kindly supplied some historical data. I can combine that with my own database to figure out the energy density improvement trends vs cumulative cell production, which is a fairly standard way of analysing learning curves.

We can say that as an approximation the pack level automotive mainstream energy density in high volume commercial use is approximately half of the most advanced individual cell level density released for purchase.

So today the cutting edge cell is at ~700 Wh/kg (cell) and the leading mainstream use is ~ 300-350 Wh/kg (pack). Clearly one can pay extra and push up the price/performance curve at any given moment. The aircraft designers themselves make that point.

Looking ahead the technology improvement slope on energy density seems fairly linear trend. That is likely because power density is the priority mainstream performance metric that is being pursued, and (without looking at data) that is likely a power law trend. The current energy trend appears to be approx. 133 Wh/kg per 1 TWh cumulative increase. So the current 2.5TWh cumulative corresponds to the 700 Wh/kg peak cell or the 350 Wh/kg avge pack. Therefore the 10 TWh cumulative corresponds to 1700 Wh/kg peak cell, or 850 Wh/kg avge pack. The 2.5 TWh is 2023, and the 10 TWh is likely to be 2028.

So the proposed design is indeed sensible in the context of the 2030s timeline they have in mind. They have done this cell learning curve analysis themselves even if it is not explicitly written down in their paper.
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Old 30th Jan 2024, 15:55
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188 electric cars would presumably replace 188 ICE cars. Wouldn’t the net environmental benefit be much higher than replacing one 90 seat short haul airliner powered by fossil fuels with an electric version ?
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Old 30th Jan 2024, 17:00
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Originally Posted by Big Pistons Forever
188 electric cars would presumably replace 188 ICE cars. Wouldn’t the net environmental benefit be much higher than replacing one 90 seat short haul airliner powered by fossil fuels with an electric version ?
It is possible to do both. It is beneficial to do both. And in this instance doing both in parallel is approximately equally environmentally beneficial. (There are no constraints apart from $$$capital and solving the 10 or so challenges that the paper sets out - there seems to be no unobtainium in there)

From an aviation industry perspective it is better to get such an airliner into service as soon as possible. Absent such an airliner the high speed rail networks will expand to cover a greater network than if such an airliner exists. Once high speed rail networks exist, then the ability of an airliner to get back into competition on those routes is very much more difficult. So for the benefit of both the operating part of the industry (airports, flight crews, etc) and the manufacturing part of the industry (airframers etc) it is better to push ahead with such projects faster rather than slower. Especially given that this airliner is aimed at the edge of the viability zone of the high speed rail network (4h rail vs 2-3h flight + airport).

(This is an entirely different commercial segment than the airtaxi EVTOL one, which requires a new business model to become viable, as well as new products. This aircraft satisfies an existing viable business model. That is a huge risk reduction).

That is why this is such a fascinatng paper.
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Old 30th Jan 2024, 18:01
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Originally Posted by petit plateau
This aircraft satisfies an existing viable business model. That is a huge risk reduction).
True. But if you take the current business model and existing aircraft but utilize 100% SAF fuels in those aircraft then there would basically be no risk. So how would that compare to this new electric airliner in your opinion?
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Old 30th Jan 2024, 18:14
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Lots of interesting formulas in this Thread, but the most applicable formula for battery-powered-airliners is probably:

PONZI = number of investors x average contribution
1/no. of years it can be dragged out

I might be wrong, but time will tell.
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Old 31st Jan 2024, 09:28
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While I believe the design is technically possible, I see few issues:
800km still does not make the aircraft versatile enough for most airlines. It can only serve a limited number of routes, compared to the already lacklustre Q400, which has more than twice the range. Also see Dassault Mercure.
Fully draining the batteries will wear them out very quickly. Normally you should not drain them below 20%, leaving the rest only for reserve.
Charging them to 100% means a turnaround of at least 1.5 hours. Not ideal for scheduling or crew planning. Making 36 tonnes of batteries in the wing replacable on the stand is not realistic.
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Old 31st Jan 2024, 12:37
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Originally Posted by wrench1
True. But if you take the current business model and existing aircraft but utilize 100% SAF fuels in those aircraft then there would basically be no risk. So how would that compare to this new electric airliner in your opinion?
The paper does look at that. Drop in liquids are in my opinion an illusion being deployed for distraction. But even if they were to become available at quantity then they are very costly. I expect them to get reserved for long range transoceanic and military, and other niche applications - driven largely by high costs. So whilst capex of running on existing design types with dropins is low, the opex is high. So first mover takes the risk but gets a good reward, unless of course simultaneous first movers emerge in the airframers.

Originally Posted by procede
While I believe the design is technically possible, I see few issues:
800km still does not make the aircraft versatile enough for most airlines. It can only serve a limited number of routes, compared to the already lacklustre Q400, which has more than twice the range. Also see Dassault Mercure.
Fully draining the batteries will wear them out very quickly. Normally you should not drain them below 20%, leaving the rest only for reserve.
Charging them to 100% means a turnaround of at least 1.5 hours. Not ideal for scheduling or crew planning. Making 36 tonnes of batteries in the wing replacable on the stand is not realistic.
The study looks at the cyclic life and charge times, both of which fit with 45-min turnarounds and 1/year hangar maintenance.

Routes and flexibility would be an issue if up against an unconstrained opposition. But if up against expanding TGV network (and EV users) at bottom end; and drop-in liquids at the top end, then it begins to look very advantageous.

The technology growth curve graph for battery energy density doesn't need to hit a brick wall in 2030 at 10TWh cumulative, further improvements are possible. LHR-ATH is realistic in that timeframe, which serves a lot of the market.
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Old 31st Jan 2024, 16:55
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Originally Posted by petit plateau
Drop in liquids are in my opinion an illusion being deployed for distraction. But even if they were to become available at quantity then they are very costly. I expect them to get reserved for long range transoceanic and military, and other niche applications - driven largely by high costs.
Interesting, except you have to put this into context. SAF mixtures have been commercially flying for a number of years. However, only 50% SAF mixtures are currently approved with 100% SAF usage currently in the approval process to include its use on revenue flights.

As to cost, yes its currently about 2x the cost Jet A but the full market won’t be realized until 100% SAF usage is certified. Once that happens then you see both production increase and cost lower as projected. For example, SAF now accounts for about 2% of the Jet fuel market, up from .01% in 2019. And the yearly SAF production increase forecasts are now about 3% higher than Jet fuels yearly increases at 1%.

Plus those numbers are mainly for Part 121 ops. The Part 135, rotorcraft, and hybrid markets are still working out details as there is no feasible route forward until SAF achieves 100% certification. So while it may appear as an illusion, SAF has been flying in the real world for quite some time vs a drawing on paper.

In my experience, I believe SAF usage and hybrid ICE aircraft will fill the “void” vs a true e-aircraft at the “mass” transport level for years to come. At the UAM and RAM levels it’s a different dynamic and more fits the e-side of the equation.
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Old 31st Jan 2024, 20:26
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Pushing up against the edge of what is predictably possible in battery technology gets you a short haul Regional airliner. Its effect on the reduction global emissions will so low as to be negligible. It is purely an exercise in green virtue signalling, hence my comment that using the rare earth metals on 200 cars per airplane actually makes more sense.

Yes commercial aviation has to do its part and the obvious way is with SAF, that is where development money should go, not on electric airliners.

I have a part time gig working on electric airplanes for flight training. They are IMO the future of flight training not because they are green, although that’s nice, but because the typical training duty cycle fits the capabilities of electric power and because their fly over noise footprint print is 10 db less than a typical ICE training aircraft and most importantly they will succeed because the economics are going to favour them. Not using expensive Avgas creates huge savings and the running maintenance cost are about %20 of an ICE airplane.

So what is the cost per seat mile of this electric 90 seat airliner and how does it compare to an equivalent Turbo Prop airliner ?
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Old 1st Feb 2024, 09:33
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Originally Posted by wrench1
Interesting, except you have to put this into context. SAF mixtures have been commercially flying for a number of years. However, only 50% SAF mixtures are currently approved with 100% SAF usage currently in the approval process to include its use on revenue flights.

As to cost, yes its currently about 2x the cost Jet A but the full market won’t be realized until 100% SAF usage is certified. Once that happens then you see both production increase and cost lower as projected. For example, SAF now accounts for about 2% of the Jet fuel market, up from .01% in 2019. And the yearly SAF production increase forecasts are now about 3% higher than Jet fuels yearly increases at 1%.

Plus those numbers are mainly for Part 121 ops. The Part 135, rotorcraft, and hybrid markets are still working out details as there is no feasible route forward until SAF achieves 100% certification. So while it may appear as an illusion, SAF has been flying in the real world for quite some time vs a drawing on paper.

In my experience, I believe SAF usage and hybrid ICE aircraft will fill the “void” vs a true e-aircraft at the “mass” transport level for years to come. At the UAM and RAM levels it’s a different dynamic and more fits the e-side of the equation.
Valid points.

Yes, I appreciate that SAF has been around is working its way through the approvals process. I mean at scale and at an economic price. That means that bio-SAF is excluded as that cannot scale sufficiently (imho). Leaving e-SAF from renewables for large scale utilisation. The ins vs outs table is pretty clear where that is likely to go. I fully accept that small amounts of bio-SAF will be flying but personally I am sceptical regarding large scale adoption. We will see.



Originally Posted by Big Pistons Forever
Pushing up against the edge of what is predictably possible in battery technology gets you a short haul Regional airliner. Its effect on the reduction global emissions will so low as to be negligible. It is purely an exercise in green virtue signalling, hence my comment that using the rare earth metals on 200 cars per airplane actually makes more sense.

Yes commercial aviation has to do its part and the obvious way is with SAF, that is where development money should go, not on electric airliners.

I have a part time gig working on electric airplanes for flight training. They are IMO the future of flight training not because they are green, although that’s nice, but because the typical training duty cycle fits the capabilities of electric power and because their fly over noise footprint print is 10 db less than a typical ICE training aircraft and most importantly they will succeed because the economics are going to favour them. Not using expensive Avgas creates huge savings and the running maintenance cost are about %20 of an ICE airplane.

So what is the cost per seat mile of this electric 90 seat airliner and how does it compare to an equivalent Turbo Prop airliner ?
Valid points.

The research paper is pretty silent on the seat mile cost issue. The Capex side of the equation is not mentioned, nor is the maintenance opex. The only thing one can directly inspect in the paper is the relative fuel (energy) usage. Given that fuel is a large cost driver it does not look impossible. Crew etc would be approximately equal in most cases. Regarding maintenance most things would be fairly equal, but combustion engine/fuel system (etc) maintenance costs would be almost entirely eliminated, and annual battery replacement costs would need to be factored in. How that might all net out I do not know. Maybe that is the 3rd paper in the series, but perhaps one has to sign an NDA to read it. Certainly it is critical as you point out.




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Old 1st Feb 2024, 21:28
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Originally Posted by Big Pistons Forever
So what is the cost per seat mile of this electric 90 seat airliner and how does it compare to an equivalent Turbo Prop airliner ?
That will depend almost entirely on fuel cost assumptions:
  • Battery electric: the battery will probably be semi-consumable, with a limited number of cycles, so it's "fuel" of a sort. How many cycles/years?
  • Fuel-cell electric: cost of hydrogen fuel - I don't think anyone has now a clear view of the likely costs of bulk supplies of green LH2 in the 2030s & 2040s
  • Hydrogen-fuelled turboprop: cost of hydrogen fuel (see above)
  • SAF conventional turboprop: will the SAF be 1.5x, 2x, or 3x the 2024 cost of fossil fuel?
  • Fossil-fuelled turboprop: cost of fossil fuel. I expect this will probably be still available until 2050-ish, but I expect carbon taxes to make this more and more expensive, then eye-wateringly more expensive, at least in "Western" nations.
Electric propulsion aircraft should be a bit cheaper in maintenance costs than turboprop aircraft, because there a so many fewer components - particularly rotating components - in their engines, but I doubt this will be significant in the whole picture.
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Old 1st Feb 2024, 22:29
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Originally Posted by petit plateau
I fully accept that small amounts of bio-SAF will be flying but personally I am sceptical regarding large scale adoption. We will see.
While you may be skeptical, the industry is scaling up with a projected increase of 40-50% by 2030. SAF demand is outstripping current production even at the 50% certification level, so there are about 18 new SAF production projects in progress in the US alone with the majority of that future production already under contract.

Regardless, even if 100% SAF approval stays on schedule, the one limiting factor will be SAF production capacity for the next decade. However, as you stated, we will see.



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Old 3rd Feb 2024, 19:10
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Originally Posted by kiwi grey
That will depend almost entirely on fuel cost assumptions:
  • Battery electric: the battery will probably be semi-consumable, with a limited number of cycles, so it's "fuel" of a sort. How many cycles/years?
  • Fuel-cell electric: cost of hydrogen fuel - I don't think anyone has now a clear view of the likely costs of bulk supplies of green LH2 in the 2030s & 2040s
  • Hydrogen-fuelled turboprop: cost of hydrogen fuel (see above)
  • SAF conventional turboprop: will the SAF be 1.5x, 2x, or 3x the 2024 cost of fossil fuel?
  • Fossil-fuelled turboprop: cost of fossil fuel. I expect this will probably be still available until 2050-ish, but I expect carbon taxes to make this more and more expensive, then eye-wateringly more expensive, at least in "Western" nations.
Electric propulsion aircraft should be a bit cheaper in maintenance costs than turboprop aircraft, because there a so many fewer components - particularly rotating components - in their engines, but I doubt this will be significant in the whole picture.
A couple of comments. Re hydrogen fueled turboprops, the issue with hydrogen is storage; tankage, whether liquid or gaseous will require a pressure vessel as normal wing tanks are sealed areas in the wing structure. Volume is a huge (ha ha) issue also, as the energy density of hydrogen/volume is low compared to jet fuel. Yes, n a weight/energy analysis hydrogen is great, but on a volume analysis it falls down vs jet fuel.

Also, hydrogen production is and issue; most hydrogen is now produced by a steam process breaking down natural gas, this requires more energy input than the fuel produces when used. Yes, if there were a large infrastructure of solar cells hydrogen could be produced by electrolysis, but if there weren't (and there isn't) electrolysis would require electricity generated by some sort of power plant, again negating any energy advantage of hydrogen. I won't go into the numbers here, but hydrogen fueled passenger aircraft just don't pen out.
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Old 4th Feb 2024, 19:03
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Maybe Gold Hydrogen is the answer?

https://www.newscientist.com/article...ss-clean-fuel/
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Old 5th Feb 2024, 13:36
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Latest Archer e-VTOL test flight video..


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Old 15th Feb 2024, 10:22
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Joby Aviation press release about Dubai operation

​​​​Santa Cruz, CA, and Dubai, UAE, Feb 11, 2024 —Joby Aviation, Inc. (NYSE:JOBY), a company developing all-electric aircraft for commercial passenger service, today announced it has signed a definitive agreement with Dubai’s Road and Transport Authority (RTA) to launch air taxi services in the Emirate by early 2026, with Joby targeting initial operations as early as 2025.​​​
Whilst I fully agree that this is a bit “showcasing” by Dubai it will, nevertheless, give Joby a real world test of their capabilities. A number of rotations around these short hops without recharging should reveal actual endurance and operability.

https://www.jobyaviation.com/news/jo...i-service-uae/
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