Leeham News and Analysis
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Leeham News and Analysis
- How Trump tariffs affected, and could affect, Airbus, Boeing and Embraer December 6, 2024
- Start-up hybrid plane OEM MAEVE teams with MHIRJ for sales, more December 5, 2024
- Production increase delays hurt Airbus costs December 2, 2024
- Books to consider for Christmas November 29, 2024
- Slow, methodical process to restore Boeing’s trust, efficiencies November 28, 2024
Bjorn’s Corner: Air Transport’s route to 2050. Part 3
By Bjorn Fehrm
November 1, 2024, ©. Leeham News: We do a Corner series about the state of developments to replace or improve hydrocarbon propulsion concepts for Air Transport. We will find that development has been very slow.
Last week, we listed the different projects that have come as far as flying a functional model or prototype, as we need this filter to reduce the hundreds of projects that have declared they want to develop such an aircraft type. We can see that we have only a certified two-seat trainer, and one project has a prototype that has started certification, the CX300 six-seater in Figure 1.
Why is the progress so slow?
Figure 1. The Alia CX300 six-seater started certification in 2023. Source: Beta Technologies.
The background to slow progress
The first reason progress has been slow is that too many projects have been initiated by people with little or no knowledge of aircraft design.
Investors saw what happened in the car industry: The established players underestimated Tesla’s chances of making an alternative to the normal roadgoing car.
When types similar to Elon Musk, claimed they could reinvent the aeronautical world and produce battery electric passenger aircraft that could replace Boeing and Airbus within 10 years, investors jumped on without any checks.
But the art of making passenger aircraft is a bit more complicated than cars, something that aircraft designers have perfected for the last 120 years. Startups that promised the world have started to fold. Investors are getting disappointed and moving to AI.
Here is the picture and a quote from the easyJet and Wright Electric press release of 27 September 2017: “ Wright Electric has set itself the challenge of building an all-electric commercial passenger jet capable of flying passengers across easyJet’s UK and European network within a decade.”
Figure 2. The Wright Electric vision of a battery electric airliner taking over from A320 by 2027. Source: easyJet press release.
To date, Wright Electric has not finished certifying a 2MW electric motor for such an aircraft, let alone the batteries needed or any part of the aircraft itself.
The electric motor and its inverters are probably the easiest part of aircraft development, yet to my knowledge, we have no motor certified for aircraft use beyond the Pipistrel motor.
The batteries are the big challenge
If the electric motor and its support electronics (motor inverter, power, and safety switches, etc.) are the easy part, the batteries have been much more challenging than envisioned.
Battery capacity has not developed as planned or hoped. Thoughts were (including mine) that we were at 400Wh/kg for a battery system around 2017, and this would progress upwards by, say, 5% per year. The reality is we are today at 200Wh/kg at a system level for certification in 2025 or 2026.
End of the decade, we could perhaps see 250kWh/kg system level for reasonably priced aeronautical batteries.
Why this halving of the battery capacity seven years after 2017?
There are several reasons:
- Enthusiasts mixed Cell, Pack, and System capacities. With systems designed today, you lose 20% of capacity in each step (it was worse in 2017). This means you are, in the best case, at 70% of the cell kWh/kg at the system level in the aircraft. So, a 300kWh/kg cell gives you a 210kWh/kg system.
- The safety problem of battery systems for aircraft use was underestimated. In the air, a thermal runaway, like the odd battery electric car runaway, is a fatal disaster. Consequently, the rules for how to design and certify propulsion power level batteries for aeronautical use have gone from missing or inadequate to comprehensive and stringent. The writing was on the wall after one fatal air accident, and several aircraft/VTOL prototypes burned to ashes on the ground, so the authorities reacted.
- Batteries are not fuel. This is the headline of this very good article series written by Rob McDonald, ex-Uber Elevate.
The article series is a lot to take in. Here in short:
Batteries wear, more the more you stress them. The faster they then reach 80% capacity at which time you need new battery packs. I used to calculate a new pack at $400 per kWh. Today, after several talks with experienced aeronautical battery suppliers, I use $700 per kWh, where a second-use scenario can reduce this by 20%.
Batteries are designed to their C-rate charge and discharge level. A 1C 100% charge or discharge means it has taken 1 hour. Reduce this to 30 minutes, a typical charge time for aircraft ground stops, and we are at 2C. Increase the C-rate and the battery wears faster, reduce it and it lasts longer. Aircraft use is found in the 2C spectrum, VTOLs in the 3-5C spectrum. A typical 2C use spectrum will allow a battery to stay in the aircraft for 2,000 to 3,000 cycles, but only if the charge times are left at the design C rates.
Batteries don’t like to be emptied. To have the battery last the cycles mentioned, you need to leave around 25% of the capacity untouched, or you increase the wear.
Aeronautical cell production is and will be nothing compared to car and power tool applications. That’s why companies that have undertaken to develop special cells for aeronautics have folded or been absorbed one after the other over the last years. New chemistries will hit the car and power tool markets first. This will make the cells economically viable for the microsized aeronautical market. Right now, the total aeronautical market is a handful of battery packs for the Pipistrel Velis per year.
The battery is the culprit in hybrids as well.
Car hybrids work very well, as they employ energy recovery each time the car brakes for a stop light or for any other reason. However, there is no recovery segment in an air transport mission (no, the descent will not allow energy recovery), so the airborne hybrid loses its biggest advantage.
People who haven’t worked through the aeronautical hybrid problem boast about the gains the hybrid aircraft will achieve. To date, NO-ONE has demonstrated any verifiable gain from hybrid system flight tests. The reason is simple: The needed battery for a propulsion power hybrid, active during a mission, is too heavy and destroys any theoretical gain, both from a performance and cost point.
The only hybrids that will be produced seem to be mild hybrids, meaning they are designed with small batteries to assist today’s propulsion system, either for the internal processes of a gas turbine or during ground taxi and takeoff and landing. Thus, they reduce noise and pollution around the airport. This will then gradually expand to other parts of the mission as battery performance improves.
Next Corner
I apologize for the next Corner of this series to appear in mid-December. Our other activity has gotten a bit too busy.
Thank you Bjorn for summarizing recent developments. And adressing the key challenge of unavailability of suitable batteries.
In recent years, prototypes, commitments from big brands, confidence expressed by powerfull people made many doubt if there was an opportunity after all. (E.g. flying athletes around at the Olympics, people were made to believe in it, until half 2024!) https://www.electrive.com/2024/07/15/volcopter-might-not-fly-during-the-olympic-games-after-all/
Now it seems like a feet back on the ground period has started. I hope the billions invested in new technology will at least have some spin-off into automotive and aerospace..
The desig in fig.1 at least looks to have some decent forward flying capability. But power/ energy storage will probably br the bottle neck..
What about time needed to fully load almost empty batteries
Can a single go bak home after a 2000 miles one way trip the same day ??
As said, 2C is OK, and it will fill the battery to capacity in 30 minutes. As you typically only consume 75% of capacity (you shall leave 25% to save the battery), you will need 0.75*30 minutes. Alternatively, you can go down to 1.5C if you have 30 minutes of turnaround time. I think the airlines will do the latter. Getting the batteries to last the longest possible will be important for the economy.
thanks for explanation … how many Kwh is needed to get full capacity
is 75% of capacity able to cover 2000 miles for a 200 seat single aisle.
What is your estimated weight for batteries and how much it will take out of the cargo capabilities.
I understand nothing can be estimated now … some guess estimates are welcome anyway
Thanks for sharing your experiences on leehmanwews
We can estimate this as our Airliner Performance and Cost model does it. For the typical 800nm domestic mission flying 194 passengers in an A321neo, you need 26,000 kWh. This includes reserves. With today’s battery system at 210 Wh/kg at system level, you need a 123,800kg battery system. Your small problem is that the empty weight of today’s A321neo is 52,000kg, and you take off for the 800nm trip, including reserves, with a gross weight of 76,500kg.
Mille mercis
this explain the multiple obstacle to overcome to an old engineer
:=))
Mille mercis
this clearly explain to an old mechanical engineer that many, many obstacles are here to overcome the idea … another writer is suggesting a nuclear power plant on board !! :=))
Sounds like battery swap after landing is the best option for now. Hydrogen fuel cells or LH2 combustion looks more mass effective. Starting with replacing the APU with a fuel cell and a small battery pack for taxi and power on all systems derived from electrical truck batteries. The LH2 burning jets/turboprops could be designed to give minimal NOX and mostly pure water emissions, still the whole hydrogen system need certification rules with acceptable means of compliance and airports to produce and sell LH2 for reasonable prices. Airbus hydrogen passport jet engine A380 test flights will set the pace.
Adds weight and complexity to do battery swap. The economics arent great already and having even more expensive battery’s sitting at multiple routes . I dont think so.
Seconded
seconded too !!!
Minimal mass increase, but to save time and battery life you add cost.
Thanks for this column highlighting the difficulties of electric
power for commercial aircraft.
The question that I have is whether aeronautical applications become viable with commercialization of solid state batteries, which are less prone to degradation and have potential for higher energy densities.
https://www.flashbattery.tech/en/how-solid-state-batteries-work/
Maybe in 10 years but even more expensive than current car lithiums
I think that electric battery-powered aircraft will prove to be, um, unworkable; but not before a bunch, bunch more VC/QE munny is conveniently laundered in the process.
#energydensity
#notgonnahappen
And Speaking of swindles: what’s the latest from that Boom! outfit?
Just put nuclear fusion reactors + elec motors where the engine pylons currently are. Easy-peasy!
/s
@Jefferyt Berner:
Interesting you should mention that. I did a deep dive into solid state batteries for my backup generators as the battery is one of if not the most common failure to start problems. And a backup generator is worthless is it does not do its job and start and support its intended system.
Code would not allow it. I could add a apparel set of Solid State batteries but then a battery failure could still absorb the Solid State and you wind up with no gain or a very expensive one.
A Standby or Backup Gen set is both heated and the batteries are required to be charged all the time (charge as low as you can so you do not cook the battery).
Many batteries would not tolerate it and dead in 1.5 years. Some were outstanding (Interstate at one time) but over time the quality fell and lucky to get 3 years out of a set of batteries (which meant you needed to replace at 2 years)
I regret not pursing a NICAD solution early on, very costly but it would have paid for itself in savings not to mention they are extremly reliable.
Auto use for the SSB is not a candidate right now, they need to be charged at all times to maintain the max CCA. I hope that changes.
From my viewpoint a SSB is really a variation on Capacitors.
> From my viewpoint a SSB is really a variation on Capacitors.
This seems like a decent analogy to my untrained mind.
Its at least in the general category even if the stuff to do it is a bit different.
both are “stored charge”.
Capacitor is plain stored charge between plates.
Battery is charge stored in a chemistry process.
Bjorn”
I thought that the RTC made the specs for Li Ion batteries post the 787 battery debacle?
It covers batteries up to the size of the 787 standby batteries or similar applications. Propulsion-level batteries are in another league, and there are special certification requirements for these, both for aircraft and eVTOLs.
Bjorn:
Thank you. Silly me for thinking they covered all the bases on the 787 size.
How on earth have these scammers been able to get away with it for so long? They must have quickly realised it was unviable
Meanwhile,this knowledge hasn’t gone completely to waste as I am going to stop running my mums Dyson vacuum cleaner completely down from now on.
You can carry on with your battery tools as per normal.
I am not sure what Bjorn is quite getting at.
Basically stuff run by DC has a low voltage limit it quits working at. A relay coil will not pickup unless it has 8 volts (ballpark) or so on a 12 Volt DC system. You need high enough energy levels to make things go.
A 12 volt car battery needs to drop down to no less than 9 volts on start. The famous clicking sound means the relay will not pull in but you need the 9 volts to spin the starter motor, they don’t work on less.
If you are using the DC via a Converter (DC to AC) then you need a minimum voltage to have that work. My best example was a DC to AC system that put out 480 volts. The DC link only worked down to 360 volts but it also shut down at that point.
And therein is the aspect of things. There will be an auto shutoff because you no longer have the output below that. So, the stuff on the end no longer makes 480 VAC and the batteries are protected. The only system that will drain a battery is a flashlight. Anything with any sophistication just shuts off.
Most of the aircraft stuff I believe is AC motors. With the right inverter (converter, they go by a lot of different names depending on the area using it) you can vary the speed on those motors. An AC motor is a lot simpler than a DC motor, so they are preferred. The obstacle back in the day was getting DC into AC, with modern electronics that is a piece of cake. I saw it used commercially in running building fans and pumps back in the early 80s.
Your equipment self protects as a DC voltage getting down too far will burn it out.
A car won’t even try to start on 2.5 volts. It can’t. Coils won’t pickup and there is no ooomph to turn the starter even if it did (and that assumes a geared starter)
Your cordless drill self protects (probably 15 volts on a 20 volt system). Ditto the electric lawnmower etc. They just turn themselves off it they hit the limit or they won’t start in the first place.
NICAD, WetPB cells are reasonably misuse resistant.
all the modern chemistries show catastrophic faults from parametric excursions ( i.e. overvoltage, undervoltage, temperature, current .. )
The reason why they all get wrapped and thus “save for use”
in a protective battery management system.
IMU Boeing killed their 787 batteries with naive overcharging.
( full charge required for a savety relevant “no engines emergency braking” while engine start on battery also consumed large parts of available capacity. i.e. need for quick high power charge. )