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Electric CityAirbus NextGen makes its debut

Airbus recently presented its full electric CityAirbus NextGen prototype to the public, ahead of its maiden flight later this year. The two-tonne class CityAirbus, with a wing span of approximately 12 meters, is being developed to fly with a 80 km range and to reach a cruise speed of 120 km/h, making it suited for operations in major cities for a variety of missions.


The unveiling coincided with the opening of the new CityAirbus test center in Donauwörth, which will be dedicated to testing systems for electric vertical takeoff and landing vehicles (eVTOLs).

The center, which is part of Airbus’ ongoing and long-term investment in Advanced Air Mobility (AAM), began its operations with the CityAirbus NextGen’s power-on in December 2023 and it will be now used for the remaining tests required before the prototype’s maiden flight later in the year.

These tests cover the electric motors with their eight rotors as well as the aircraft’s other systems such as flight controls and avionics.

Airbus is expanding its global network and partnerships to create an ecosystem that will foster a successful and viable AAM market. Airbus recently signed a partnership agreement with LCI, a leading aviation company, to focus on the development of partnership scenarios and business models in three core AAM areas: strategy, commercialization and financing.



Airbus is trying to improve, it is just a shame that the wheels have come off its sole competitor, which hardly incentivises it.

Just in is news that they have now put a timeline on the choice between fuel cells and turbines for their medium sized hydrogen aircraft which they hope to produce in the 30's:

' The airframer will essentially choose between burning hydrogen in a turbine engine—which is the lighter-weight option—and using it in a fuel cell to produce electricity—which favors efficiency. Then, the technology readiness level (TRL) will have to grow to the usual TRL 6—or validation in a relevant environment—before program launch in 2028-29, Andriamisaina added, speaking at the Clean Aviation Annual Forum in Brussels on March 6. Airbus is targeting 2035 for the entry into service of a hydrogen aircraft.

Until 2026-27, Airbus is maturing technologies, studying aircraft configuration, conducting flight demonstrations, and endeavoring to be a catalyst for a hydrogen ecosystem to emerge, Andriamisaina said.

In two-to-three years, a broader decision than just propulsion will be made; Airbus refers to it as product selection. The company is targeting a capacity of 200 seats and a range of 2,000 nm, with minima of 100 seats and 1,000 nm, Andriamisaina said. The exact numbers will depend on where engineers stand with the technology, he said.

Airbus is studying two options for turbine engines. A turboprop would support the smaller capacity and range, while a turbofan would correspond to the higher capacity and range. In both cases, a degree of hybridization would be introduced.

To reach TRL 3 or 4, Airbus is conducting large-scale demonstrations. That has been the case with the so-called iron pod, a 1.2 MW fuel cell and associated electric motor, since late 2023. As for hydrogen combustion, demonstrations are needed especially with pumps, Andriamisaina added.'


For Airbus's hydrogen efforts:

' During this test, the subscale dewar-tank experienced only 2.8 watts of heat load. Based on this, GTL expects that the flight tanks will see only 1% LH2 boiloff per day.

Results showed the composite dewar-tank’s ability for rapid chill-down, paving the way for aircraft to be refueled in minutes, versus waiting hours for a metal tank and transfer lines to cool. The inner composite tank went from ambient room temperature to 20K (degrees Kelvin) and holding liquid hydrogen in less than 20 seconds and the GTL composite tubes achieved full LH2 flow in less than 1 second. The tests also show that no-vent fills of the composite dewar-tanks are achievable, which greatly improves refueling safety.


' This gives the GTL composite dewar-tank a hydrogen fraction (gravimetric index) of more than 55%, which is about 10x better than current hydrogen tanks. When stretched to carry 50 kg of LH2, the hydrogen fraction increases to over 62% with a mass of 30 kg, with larger versions able to achieve over 70% hydrogen fraction.

The GTL dewar-tank performance significantly exceeds the 35% hydrogen fraction goal needed for hydrogen to achieve parity with kerosene fuel (e.g., equal flight range). With GTL technology, hydrogen powered aircraft can exceed the performance of kerosene fueled aircraft, while eliminating carbon emissions and reducing cost per passenger mile by more than 25%. '

Loads of caveats of course, including that this is a small tank, and upscaling is not always trivial, how many refills it can handle and lifetime, and as always, cost.

But together with analysis just in that contrail mitigation via altering flight paths is less costly than had been thought, it gives more grounds than previously for thinking that very low emission flight may become possible, albeit far from imminently:


Fuel cells weigh more than turbines, but are more efficient.

So it would appear that the range of a hydrogen powered aircraft using fuel cells would be even more superior to a kerosene one than the hydrogen fraction giving more energy than kerosene would indicate.

Since the big problem in aircraft is GHG for long range, that would appear to be very good news.

Just a 'tad' more upscaling needed though! ;-0
And perhaps a FEW more engineering issues to be sorted out!


Fuel cells weigh more than turbines...
Maybe by a bit but not much. I was looking at a 1000 horsepower Pratt & Whitney
turbo shaft, it weighs over a thousand pounds. Now add even more weight for the alternator and you have a pretty heavy range extender.
Let's assume the turbo shaft runs on hydrogen, in this case liquid hydrogen, so we've removed the cost of the tanks and so on. A turbine alternator weight compared to the equivalent output of fuel cells is about the same.


Thanks, SJC

I was being a bit sloppy and unreferenced, as my remark was arguing against, not for, my thesis that fuel cells are looking good, so any error was on the conservative side, and in any case, for a proper evaluation it needs engineers, not me, as I am of course wholly reliant on what I can find of their analyses.

I also find it interesting that (ibid)

' “With these successful validation tests, we have achieved a critical milestone in aircraft decarbonization. GTL is now proceeding with the fabrication of flight prototypes of the small composite LH2 dewar-tank,” said GTL President Paul Gloyer. “Our 28-inch diameter by 53-inch long flight-type tank weighs only 15 kg, including inner tank, outer vacuum shell, multi-layer vacuum insulation, internal tubing, and sensors, but can hold 19 kg of LH2.”

19kg of hydrogen at 33KWh/kg is 600KWh or so, which would be one heck of a battery pack weighing 2000kg or so, to be generous.
A fuel cell is less efficient that a battery of course, and they don't much like high power draws, but even so just this small demo version sounds like a pretty handy bit of kit.

That is right now, and the somewhat larger 30kg tank holding 50Kg of hydrogen gives you 1650KWh


Dunno how relevant this is.
I have just tracked down some specs for a home fuel cell:

So 78kg for 110Kw, which comes out to 7kg/Kw
So 700kg for 1000Kw

Dunno what factors come into the scaling, what is in or out to make it run, or what weight can be saved for aerospace use though.

But anyway, FWIW.


You weren't that far off as far on the weight, the other factors are pollution and noise. Turbines really spew out the pollution and they're very noisy. It wouldn't help Joby to have such a nice quiet eVTOL then install a turbine alternator that makes a lot of noise.
However, they can take 2,000 lb of batteries out make it 500 lb of batteries and a thousand pounds for fuel cells, 500 lb for tanks and hydrogen, then go 400 mi instead of 100 miles, their choice.


Being me, I was like a dog with a bone last night when I was supposed to be sleeping, checking in my head.

The figures I have given for the low temperature fuel stack are about right, pretty good actually, for weight.

So you are talking about substantial extra weight compared to a turbine, I assume, although since my ignorance of how they work and what extra heavy bits they need to make them go is profound, I rely on you engineering folk to correct me.

However with an HT fuel stack you are up from around 1.4Kw/kg to 2.5Kw/kg with what Zero Avia have demonstrated at the cell level, and they hope 3Kw/kg for their production version.
You have still got to add the electric motor of course.

I am even further out of my depth trying to figure out engine weight against power, but I turned up this reference which is perhaps relevant:

They are giving 450kg for 1775kw

So at 3kw/kg an HT fuel stack would weight 591kg for 1775Kw, with the electric motor on top of that.

They would look a better deal the further you are going, as the lower weight of fuel assuming Dewar tanks would really kick in on take off weights,

I am going to give up there, as my feet have not touched the bottom for some time, and I am not waving, but drowning! :-0


This bit raises questions for me(ibid):

' The GTL dewar-tank performance significantly exceeds the 35% hydrogen fraction goal needed for hydrogen to achieve parity with kerosene fuel (e.g., equal flight range). With GTL technology, hydrogen powered aircraft can exceed the performance of kerosene fueled aircraft, while eliminating carbon emissions and reducing cost per passenger mile by more than 25%. '

It is the cost claims, as to eliminate carbon emissions you either need to use still expensive green hydrogen, or have sequestration.
If you just stick in cheaper grey hydrogen, then GHG emissions are around 3 times as much as kerosene!


On eVTOL batteries, it turns out they have only just started measuring the performance against actual flight profiles for take off, cruising and landing, including importantly degradation rates!

' Systematic investigation linking actual flight profiles to real-time physical battery operation is rare. However, it is key groundwork for developing new battery chemistries to achieve safe flight performance.

The study incorporates testing of a new ORNL-developed electrolyte — a material through which electrodes exchange ions — against the current state-of-the art version used in lithium-ion batteries. Using the eVTOL mission profiles, the ORNL electrolyte performed better, retaining more capacity during the most power-demanding flight phases.

These results demonstrate the need for diversifying how battery performance is measured, Dixit said. “Your battery is not just capacity at the end of 1,000 cycles. It’s what’s happening within a cycle that tells you whether your system is going to work or crash. And the stakes are much higher here because you’re asking how safe it is to go up in the air. This is a question we don’t know the answer to — yet.” '

So far it looks as though they have just more or less stuffed an EV battery into an e-VTOL

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