Eviation Alice (Electric Regional Airliner)

[alberchico]

https://www.seattletimes.com/busine...ic-airplane-ceo-ousted-ahead-of-first-flight/

The timing is so odd. You would think he would have stayed on board for just a few more days to oversee the first flight and handle all the media appearances that would be required of the company. He had been with Eviation since the very beginning and had been doing an effective job promoting the company.

Edit: based on this article it appears that he was ousted by the board. Mabye they realized that they had been misled regarding the exact capabilities of the aircraft regarding range as well as future battery improvements. The article I mentioned in my last post claims that this project has serious range deficiencies and that Eviation is basically lying while quietly hoping that improving battery tech will catch up and resolve those issues.

I would also like to point out that on Jan 6 another top executive, who had senior leadership roles at both Eviation and Magnix, which are owned by the same conglomerate, also abruptly stepped down. Something is going on.

https://www.geekwire.com/2022/elect...tement, Eviation,a board member for Eviation.

 

[alberchico]

https://twitter.com/x/status/1494371963267010562

View: https://mobile.twitter.com/jonostrower/status/1494371963267010562


Now I wonder if maybe the battery makers have been misleading these electric aircraft companies regarding projected future developments and capabilities. I found an interesting article about an upcoming court case that involves an EV battery maker accused of misleading investors.

https://news.bloomberglaw.com/envir...ace-investor-suit-over-electric-car-batteries
https://investorplace.com/2022/01/qs-stock-alert-why-is-battery-maker-quantumscape-stumbling-today/

BTW if anyone is looking for a high resolution version of the image in the article I found it:

 

[VTOLicious]

Speaking of battery makers...
AMPRIUS TECHNOLOGIES SHIPS FIRST COMMERCIALLY AVAILABLE 450 Wh/kg, 1150 Wh/L BATTERIES

 

[GTX]

I suspect the issues here are more than something related to batteries or even technology. Given both Omer Bar-Yohay and Magnix's CEO, Roei Ganzarksi, have resigned in the last month or so. Both companies have the same primary shareholder in the form of Richard Chandler's Clermont Group, and while Roei has remained quiet, I suspect there might be similar issues behind the scenes as hinted by Omer. Extremely bad timing for them with the first flight days away.

​

 

[Zoo Tycoon]

One observation about “Alice in wonderland” is the mass distribution. All the aeroplanes we see we judge by what’s gone before, which have all been quite different because of the fuel, which is normally wing stored so tends to move mass afterwards.

From Bjorn table in the link above and the pictures of the battery compartments.

Electric Alice tips the scales at 7.5 tons, of which 1 ton is payload and 3.7 tons is battery. The remaining airframe weighs 2.8 tons, let’s say 25% of that’s in the cabin, so that’s 5.4tons in front of the wing leading edge…… and only 2.1 tons behind, and remember some of that’s in the wing which is still forward of the CG so the assumption is conservative. Given the wing flex on the clip they don’t seem to have batteries and being high aspect/finess ratio I doubt it.

Wow, at least 5.4 ton forward of the cg and 2.1 tons aft. ….. I know it’s moment arm dependant but where’s the neutral point?

The horizontal tailplane looks awfully small, probably sized for the smallest tail volume for low cruise drag, glider style keep the restoration moment to minimum, so low parasitic drag. But, but Alice’s substantial pitching down momentum from all that weight up front has to balanced by a hard working horizontal tail, hence massive parasitic drag;- all precious battery energy is needed just to snow plough the horizontal stabiliser through the air just to keep the nose level. .

So another question from the big nose down pitching moment and small tailplane. Can Alice lift its nose to rotate for takeoff?

Maybe, the wan’na be, but clueless genius that brought the nonsense/inherently dangerous Alice mk1 to prototype has struck again. Might explain a lot.

 

[VTOLicious]

I have strong doubts that the engineers made such a fundamental mistake.
With modern CAD systems it is quite easy to evaluate the mass distribution very precisely. And sizing wing and empennage isn't rocket science as well.
The extra wide fuselage is actually the only extraordinary feature (from an aerodynamic perspective).

When I look at that top view I actually see a very long tail fuselage with engine nacelles mounted pretty far aft and a horizontal stabilizer sitting at the very end of it.
However, let's see how they progress and judge them by deeds

Edit: I just noticed that the engine nacelles are actually a lot further back than shown in the drawing! See the photo attached.

 

[TomcatViP]

There is a battery compartment in the tail section also.

 

[Zoo Tycoon]

I have strong doubts that the engineers made such a fundamental mistake.
With modern CAD systems it is quite easy to evaluate the mass distribution very precisely. And sizing wing and empennage isn't rocket science as well.

When I look at that top view I actually see a very long tail fuselage with engine nacelles mounted pretty far aft and a horizontal stabilizer sitting at the very end of it.
However, let's see how they progress and judge them by deeds

I just noticed that the engine nacelles are actually a lot further back than shown in the drawing!

During a high pressure and demanding design/build program mistakes are common, some can even be quite fundamental, particularly if it’s co ordinated by an individual who’s technically a bit lacking. Seen it happen and sorted a few out in my time.

Anyone know if proof wing load testing has been preformed? Not seen anything or even a suggestion of such. Given the extremely low structure mass fraction, missing out such a step is foolish.

 

[Nicknick]

With a battery weight of 3.7 t and an energy denstity of 200 Wh/kg (not some future break trough wonder batteries) this would be 740 kWh. For a three hour flight, this would be an avarage of 246 kW with an estimated engine performance of 226 kW (306 PS). This appears to be a little to low for an aircraft of that weight.

 

[TomcatViP]

Cruise power requirements are less than what other phases of flight might need. The simple ratio doesn't translate automatically into a realistic number.
For example, descent from cruise alt would be at reduced throttle and could last significantly if a rapid climb to cruise alt is done after takeoff (batteries deliver near cte power at all alt).
Given the weight and the small wing surface, it is most probable that Alice's designers have privileged a fast climb speed to gain a high rate of climb with the lowest drag for cruise.

The fact that power is a cte Vs altitude, makes also power settings difficult to comparable with that of a piston aircraft (GA), usually having no turbo or compressor.

I would say intuitively that 10 to 15% of that power usage will be at a high settings for climb, 60 to 80% at 50% throttle and 10 to 15% at a near idle for the descent (10%).

So, to complete the results from @Nicknick above, you'll then have an equation that should approach a convenable result:

0.15M + 0.7M/2 + 0.15M/10= 740
Hence M= 740/(0.15+0.35+0.015)=740/0.515=1436kW
Something like 900hp per engine.

 

[Fluff]

Cruise power requirements are less than what other phases of flight might need. The simple ratio doesn't translate automatically into a realistic number.
For example, descent from cruise alt would be at reduced throttle and could last significantly if a rapid climb to cruise alt is done after takeoff (batteries deliver near cte power at all alt).
Given the weight and the small wing surface, it is most probable that Alice's designers have privileged a fast climb speed to gain a high rate of climb with the lowest drag for cruise.

The fact that power is a cte Vs altitude, makes also power settings difficult to comparable with that of a piston aircraft (GA), usually having no turbo or compressor.

I would say intuitively that 10 to 15% of that power usage will be at a high settings for climb, 60 to 80% at 50% throttle and 10 to 15% at a near idle for the descent (10%).

You'll then have an equation that should approach a convenable result:

0.15M + 0.7M/2 + 0.15M/10= 740
Hence M= 740/(0.15+0.35+0.015)=740/0.515=1436kW
Something like 900hp per engine.

I'd like to think they will get some energy back on the decent? Rather than create drag/gear etc.

 

[Nicknick]

If 7.5 tons was the right maximum weight and we would have a very good glide ratio of 1:24 (without prop) we would need at leat 340 kW Power.

250 mph = 400 km/h = 111 m/s

P = 7500 * 9,81 `* 111 *1/24 = 340 kW in cruise. (with 100 % efficiency from the battery to trust).

With an electric efficiency of 92 % and a prop efficiency of 85 % this will be 434 kW battery power.

The airplane has just a slightly better power to weight ratio than the compeding Tecnam Trevellor, so climp performance will not be very different.

The best way of recuperation is still gliding, best done with feathered props (this could really be done in an electric aircraft).

 

[Nicknick]

I did some more rough calculations about the range.

as said, the plane can cruise 400 km (1 h) with an energy consumption of 434 kWh.

For decent in an ideal world, this plane could switch out its electric engines and feather the propeller, so that it can glide most efficiently. With a glide ratio, of let’s say 22:1 (lower than the 24 mentioned before, because the feathered props still make some drag) and a flight high of 10.000 m, it could glide about 220 km (I know, its usually not possible to glide very flat into an airport). This would need no energy in theory (of course, pressurisation and cabin heat still need some energy).

As said, one hour at cruise (400 km) speed takes about 434 kwh and we still need to cover 180 km distance for the 800 km range and the climp (180 + 400 + 220). The energy needed for the climp is:

W = 7500 kg * 9.81*10000 = 735750 kJ = 204 kWh.

With a prop efficiency of 85% and an electric efficiency of 92 % it takes 261 kWh

For the still missing 180 km distance, I would assume the same energy consumption per kilometer as in cruise flight (I know its to optimistic)this would be 434 * 180/400 = 195 kWh

The total energy consumption for 800 km would be around 890 kWh with very optimistic and simplified assumptions. The battery weight is 3700 kg, so they need an energy density of 240 Wh/kg, this is quite high, but not totally unrealistic (as Lilium).

Note that by my assumptions the plane always flys with the best glide angle and no energy is wasted in the decend. I know, this is hard to archieve in the real world.

The useful range would be much lower, maybe 500 km or so, because using all the battery capacity will reduce their life and the landing approach by gliding is not practical at busy airports.

 

[red admiral]

The energy needed for the climp is:

W = 7500 kg * 9.81*10000 = 735750 kJ = 204 kWh.

There is still drag to overcome rather than just gravity.

 

[yasotay]

Turning off the engines would be a very hard sell to the paying public. That said, boxes don't care.

 

[Nicknick]

@red admiral : sure therefore I added 195 kWh for the 180 km to the 204 kWh, so this is included.

@yasotay : true, but now that the props are positioned in the rear, they might be invidible to the passengers.

 

[GTX]

https://spectrum.ieee.org/eviations-maiden-flight-to-usher-in-era-of-electric-aviation

 

[sienar]

Note that by my assumptions the plane always flys with the best glide angle and no energy is wasted in the decend.

What plane cruises at "best glide angle"?

 

[Nicknick]

The Otto Celara e.g., is intended to do so. As said, I tried to figure out, what would be possible under the best circumstances, not necessarily matches the real world.

 

[TomcatViP]

Don't forget that any commercial descent in a controlled airport will be subject to regulations/procedures. Those are not VFR aircraft, they are then to file a flight plan that allow them to land in any weather, according to their time slots, under controlled flights.
Descent might start 20nm from runway threshold, with speed and rate of descent to adhere to.

 

[VTOLicious]

I did some more rough calculations about the range.

as said, the plane can cruise 400 km (1 h) with an energy consumption of 434 kWh.

For decent in an ideal world, this plane could switch out its electric engines and feather the propeller, so that it can glide most efficiently. With a glide ratio, of let’s say 22:1 (lower than the 24 mentioned before, because the feathered props still make some drag) and a flight high of 10.000 m, it could glide about 220 km (I know, its usually not possible to glide very flat into an airport). This would need no energy in theory (of course, pressurisation and cabin heat still need some energy).

As said, one hour at cruise (400 km) speed takes about 434 kwh and we still need to cover 180 km distance for the 800 km range and the climp (180 + 400 + 220). The energy needed for the climp is:

W = 7500 kg * 9.81*10000 = 735750 kJ = 204 kWh.

With a prop efficiency of 85% and an electric efficiency of 92 % it takes 261 kWh

For the still missing 180 km distance, I would assume the same energy consumption per kilometer as in cruise flight (I know its to optimistic)this would be 434 * 180/400 = 195 kWh

The total energy consumption for 800 km would be around 890 kWh with very optimistic and simplified assumptions. The battery weight is 3700 kg, so they need an energy density of 240 Wh/kg, this is quite high, but not totally unrealistic (as Lilium).

Note that by my assumptions the plane always flys with the best glide angle and no energy is wasted in the decend. I know, this is hard to archieve in the real world.

The useful range would be much lower, maybe 500 km or so, because using all the battery capacity will reduce their life and the landing approach by gliding is not practical at busy airports.

The attached PDF might be of interest (Electric Flight – Potential and Limitations; published in 2012 by Martin Hepperle, German Aerospace Center / Institute of Aerodynamics and Flow Technology).

In particular Chapter 4 and 5...

 

[TomcatViP]

5.3.DESCENT SEGMENT
The descent segment is flown with a given descent angle, which is steeper than the maximum of lift over
drag ratio of the airframe to minimize the energy consumption. During this flight phase only auxiliary
power for the aircraft systems has to be provided by the battery. No recuperation is considered here due to
the high drag and low efficiency of the windmilling propellers, which would allow to recover about 5% of
the total energy (in case of a 500 km flight of a regional aircraft at H = 3000 m the potential energy
mgH ⋅ ⋅ is about 20% of the total energy consumed during the flight).

I am sorry but this, IMOHO, in a a paid paper at NATO level, is unacceptable. The set of equations is also disctutable to describe range when it force us to take the aircraft design into account when Battery efficiency is the object of the discussion. And more straightforward equations are available.

L/D is also the result of an (informed) choice by the designer, not a consequence of the propulsion system, at least when engines units are available and cover the range of targeted performances.

And last but not least, nobody is gonna dive, windmilling the Propellers, during normal flight conditions without having her/his CPL license revoked.

 

[Nicknick]

@VTOLicious :Nice catch, at first glance it looks quite similar but more refined than my estimation. I have no clue what energy density is really realistic, there are so many wonderbatteries anounced that I can’t decide which value is typical scam for investors and which one is true.

@TomcatViP :Yes, I know, the landing approach usually is not done by gliding in a flat angle, but in a rather steep decline with airbrakes.

 

[Nicknick]

5.3.DESCENT SEGMENT
The descent segment is flown with a given descent angle, which is steeper than the maximum of lift over
drag ratio of the airframe to minimize the energy consumption. During this flight phase only auxiliary
power for the aircraft systems has to be provided by the battery. No recuperation is considered here due to
the high drag and low efficiency of the windmilling propellers, which would allow to recover about 5% of
the total energy (in case of a 500 km flight of a regional aircraft at H = 3000 m the potential energy
mgH ⋅ ⋅ is about 20% of the total energy consumed during the flight).

I am sorry but this, IMOHO, in a a paid paper at NATO level, is unacceptable. The set of equations is also disctutable to describe range when it force us to take the aircraft design into account when Battery efficiency is the object of the discussion. And more straightforward equations are available.

L/D is also the result of an (informed) choice by the designer, not a consequence of the propulsion system, at least when engines units are available and cover the range of targeted performances.

And last but not least, nobody is gonna dive, windmilling the Propellers, during normal flight conditions without having her/his CPL license revoked.

II’m not promoting electric airplanes, but to be fair, starting an electric engine or operating it with a speed of zero rpm is no big deal. You really could glide down with standing propellers and let them turn whenever needed. This is really different than with turbines or combustion engines which you would never switch off during flight (except in a Motorglider).

 

[TomcatViP]

The problem is not in the feasibility of such. An approach to a controlled airfield (with an ATC) for a commercial flight is subject to regulation and local procedures to guarantee safety and the flow of traffic. In normal conditions, you can't come and land requesting the trajectory that fit your L/D that day. You have to abide to the procedures relevant for your a/c that might involve descending on a required flight path, turning at a specific rate of turn and maintain level flight for a certain period of time. Not even mentioning holding pattern etc...
If I agree with you that this is perfectly doable on a remote airfield, away from airways and other regulated airspace, this is not a procedure that could be included in the certification process. A commercial aircraft don't fly like a sailplane. It has not the freedom and the privilege to get the priority among other aircraft.

 

[Nicknick]

Tue, but it was my intention to estimate something like an upper limit for the range. Mabe it would be practical to glide from 30.000 ft to 15.000 ft before the steep decline.

 

[sienar]

Their published performance targets are pretty benign. Something like 10k ft cruise at 250kt with 2-2.5hrs cruise.

I ran the numbers a while ago and I strongly suspect the first version of the aircraft is running at quite a low power setting in cruise, probably well under 50%. This is the only way their published target can really make sense. They seem to be planning for a lot of growth potential as batteries improve, which is probably the smart approach to take.

 

[Nicknick]

With a given speed (400 km/h) and weight (7,5 t) the cruise power soley depands on the glide ratio/ angle of attac.

As written before:
250 mph = 400 km/h = 111 m/s
P = 7500 * 9,81 `* 111 *1/24 = 340 kW in cruise. (with 100 % efficiency from the battery to trust).

With an electric efficiency of 92 % and a prop efficiency of 85 % this will be 434 kW battery power

 

[alberchico]

Their published performance targets are pretty benign. Something like 10k ft cruise at 250kt with 2-2.5hrs cruise.

I ran the numbers a while ago and I strongly suspect the first version of the aircraft is running at quite a low power setting in cruise, probably well under 50%. This is the only way their published target can really make sense. They seem to be planning for a lot of growth potential as batteries improve, which is probably the smart approach to take.

That's the big problem with all these electric projects, they're all crossing their fingers hoping that battery improvements will solve their performance shortfalls. And, if it doesn't improve quickly enough, they they are out of luck. According to Leeham, after accounting for reserves, the range of the Alice with today's battery tech will be substantially less that what they are claiming:

https://leehamnews.com/2022/02/11/bjorns-corner-sustainable-air-transport-part-6-energy-consumption/
"The Alice, with its large 3720kg 820kWh battery, can fly a still air 200nm route in Europe and land with a 30 minutes regulatory VFR reserve. For the 45 minutes US reserve, there is not enough energy. If an IFR alternate of 100nm is required with 30 minutes circling (EU rules), the range falls below 100nm"

It's interesting that the Tecnam P-Volt, even taking into account the battery improvements that will be available in 2030, only has a projected range of 145nm, despite it being a much lighter aircraft. Granted, the Tecnam design holds less batteries than the Alice, but it illustrates just how modest the battery gains are expected to be. Not to mention that the design might gain weight as improvements and modifications are made throughout the flight test program. This project reminds me of the infamous Beech Starship, a revolutionary aircraft that tried to take the aviation world by storm but turned out to be a massive flop.

https://airfactsjournal.com/2018/01/why-the-starship-was-such-a-disaster/

 

[Fluff]

My car has a 90kw/h battery, weighing 600KG, so they are 9 times more power, 8 times the weight. I'm not seeing a massive improvement from car to aircraft there.

It can also drive 200 miles, with 5 adults, on one charge. So efficient this is not.

Add in the reserves they need, and this becomes untenable as is.

A 30% improvement power to weight, would get them somewhere close to that 200 mile flight, with reserves. Cars are not showing this level of improvement so far......

 

[TomcatViP]

Let's not forget that Alice is a pressurized aircraft with a 30000ft cruise altitude. Battery power is not affected by altitude. This is why you see a small fraction of available power used during the cruise segment.
Then, the trick was to have a fast climb rate with a low cruise drag. They do that by climbing at high speed, thanks again to the power band available at all altitude (the higher the alt, the less the power setting).

The P-Volf is not a pressurized airplane. It can't fly passenger higher than 10kft and hence spend its cruise segment at a higher density level with more drag.

 

[alberchico]

Let's not forget that Alice is a pressurized aircraft with a 30000ft cruise altitude. Battery power is not affected by altitude. This is why you see a small fraction of available power used during the cruise segment.
Then, the trick was to have a fast climb rate with a low cruise drag. They do that by climbing at high speed, thanks again to the power band available at all altitude (the higher the alt, the less the power setting).

The P-Volf is not a pressurized airplane. It can't fly passenger higher than 10kft and hence spend its cruise segment at a higher density level with more drag.

You raise some excellent points, but considering the short range the Alice has, wouldn't the majority of the short hops that it does be conducted at a low altitude similar to that of unpressurized aircraft ? Also, ATC restrictions, particularly in the busy Northeast corridor where Cape Air conducts their flights, may prohibit the use of an optimal flight plan.

 

[Nicknick]

Seems like my max. optimistic approximation came quite close-

Bjorn’s calculation resulted in:

200 nm (=370 km) + 0,5 h reserve (with 400 km/h) = 570 km (without gliding down).

So, with an additional and hypothetical (but not practical) landing approach by gliding (220 km), this would result in 790 km.

 

[Zoo Tycoon]

The problem with glide to extend range is its highly dependent on what the airs doing around you. If you get into a down draft from say frontal or mountain wave your L/D really doesn’t count for toffee. There’s been cases where sailplanes with 50:1 have been reduced to 5:1. Added to this is the detrimental effect of surface contamination such as bugs and/or ice and/or general surface degradation which can and will knock maybe 30% off L/D which is highly laminar flow dependent and you have a situation that even if the regulator would allow (oh no they won’t) would not be conducive to operating a scheduled service. “Today’s scheduled service to X, well we might get there” would you buy a ticket?

No one’s mentioned the stunning difficulty in achieving these low structural mass fractions. Modern aero structures are highly optimised against historical sizing case’s. Alice’s mass fractions seem to suggest one kilogram in every three used today can be discarded. Something’s got to give, and when far lesser departures from established design criteria has been tried before it shows in an airframe that is so fragile that it’s never on the flight line.

There was a mention of harvesting descent energy. A few years back, when this investigated the energy conversion are amazingly poor;- maybe 5% of the climb energy.

 

[Fluff]

The problem with glide to extend range is its highly dependent on what the airs doing around you. If you get into a down draft from say frontal or mountain wave your L/D really doesn’t count for toffee. There’s been cases where sailplanes with 50:1 have been reduced to 5:1. Added to this is the detrimental effect of surface contamination such as bugs and/or ice and/or general surface degradation which can and will knock maybe 30% off L/D which is highly laminar flow dependent and you have a situation that even if the regulator would allow (oh no they won’t) would not be conducive to operating a scheduled service. “Today’s scheduled to X, well we might get there” would you buy a ticket?

No one’s mentioned the stunning difficulty in achieving these low structural mass fractions. Modern aero structures are highly optimised against historical sizing case’s. Alice’s mass fractions seem to suggest one kilogram in every three used today can be discarded. Something’s got to give, and when far lesser departures from established design criteria has been tried before it shows in an airframe that is so fragile that it’s never on the flight line.

There was a mention of harvesting descent energy. A few years back, when this investigated the energy conversion are amazingly poor;- maybe 5% of the climb energy.

Logically, from the EP producers, they would want to be close to Zero at the start of the descent - as they will get back 'some' power, to make their reserve. Hopefully the authorities are considering the peculiarities of battery power in the rules.

 

[Fluff]

I don't understand why this idea of harvesting energy in the descent keeps coming back all the time.

Has has been pointed before, the most efficient way to convert your potential energy to range is to glide at best L/D.

If you make any attempt to generate power from wind milling the props, the additional drag will steepen the descent slope.

The energy required to cover the lost range due to the steeper slope will always be more than the energy you recovered by wind milling the props with some torque. (unless you're descending faster than best L/D)

It's like taking energy from a pot, transforming it, and miraculously hoping to put back more energy in the said pot.

A car can regen in a descent because its drag does not increase as its speed goes down when regen activates, since a car does not need lift. It will just arrive at the same bottom of descent a little bit later.

Physics.

I think we are contrasting with a ‘traditional’ powered aircraft, which has residual thrust, and approaches with increased drag, I.e doesn’t glide in. Change flaps/gear for prop drag/regen. Of course that’s not as totally efficient as coasting/gliding. Adding that a car, has to brake sometimes, so regen is needed, efficient or not.

 

[sienar]

For what it's worth, the Piaggio Avanti requires 1682 kWh at the propeller shaft to cover a range of 440 nm at 250 KTAS plus 45 min reserves.

Since this is calculated at the propeller shaft (integrated from the AFM torque tables) it is powerplant agnostic and directly comparable to electric propulsion.

The Avanti is a good proxy because it has the same overall dimensions, same aerodynamics (laminar flow, wing shape, etc.), same 850 shp takeoff power and same cabin. The Avanti is much lighter though so the Alice cannot reasonably use less energy.

So you can imagine that 820 kWh will not get you anywhere close to that 440 nm range claim.

The biggest problem is the empty weight fraction which is wildly unrealistic. Unless they drastically increase takeoff weight, they will only be able to carry 5000 lb worth of battery and end up with a range of about 200 nm without any reserves, thus no practical range at all according to my calculations. No doubt they must know something I don't.

Where are you getting weight data from? I see 16500lb gross with a 2500lb payload listed on their website now? This had to be one of the worst empty weight fraction of all time. Unless you are subtracting the battery weight? In which case yes, they do seem to be optimistic there.

I'd like to see the results of whatever structural testing they did. It will also be nice to know what kind of fire suppression approach they are taking.

Let's not forget that Alice is a pressurized aircraft with a 30000ft cruise altitude. Battery power is not affected by altitude. This is why you see a small fraction of available power used during the cruise segment.
Then, the trick was to have a fast climb rate with a low cruise drag. They do that by climbing at high speed, thanks again to the power band available at all altitude (the higher the alt, the less the power setting).

The P-Volf is not a pressurized airplane. It can't fly passenger higher than 10kft and hence spend its cruise segment at a higher density level with more drag.

While they advertise cruise at 30k, their currently advertised 440nm cruise is at an altitude of just 10k. There is no way the aircraft with current batteries could climb up to 30k and reach 440nm unless it was feathering/gliding - which isn't viable for a commercial aircraft. I don't really think 440 is doable either.

I take that 30k cruise alt to be what they are targeting down the line, post 2030 when batteries might have the density to make that possible. And this leads to an interesting question; is it better to design a high alt cruising electric and operate it way off design poitn for ages until batteries mature? Or make a simpler electric aircraft meant for 10k and treat that as a learning/market pen attempt, then come out with a big boy 30k machine when appropriate?

Their published performance targets are pretty benign. Something like 10k ft cruise at 250kt with 2-2.5hrs cruise.

I ran the numbers a while ago and I strongly suspect the first version of the aircraft is running at quite a low power setting in cruise, probably well under 50%. This is the only way their published target can really make sense. They seem to be planning for a lot of growth potential as batteries improve, which is probably the smart approach to take.

That's the big problem with all these electric projects, they're all crossing their fingers hoping that battery improvements will solve their performance shortfalls. And, if it doesn't improve quickly enough, they they are out of luck. According to Leeham, after accounting for reserves, the range of the Alice with today's battery tech will be substantially less that what they are claiming:

https://leehamnews.com/2022/02/11/bjorns-corner-sustainable-air-transport-part-6-energy-consumption/
"The Alice, with its large 3720kg 820kWh battery, can fly a still air 200nm route in Europe and land with a 30 minutes regulatory VFR reserve. For the 45 minutes US reserve, there is not enough energy. If an IFR alternate of 100nm is required with 30 minutes circling (EU rules), the range falls below 100nm"

It's interesting that the Tecnam P-Volt, even taking into account the battery improvements that will be available in 2030, only has a projected range of 145nm, despite it being a much lighter aircraft. Granted, the Tecnam design holds less batteries than the Alice, but it illustrates just how modest the battery gains are expected to be. Not to mention that the design might gain weight as improvements and modifications are made throughout the flight test program. This project reminds me of the infamous Beech Starship, a revolutionary aircraft that tried to take the aviation world by storm but turned out to be a massive flop.

https://airfactsjournal.com/2018/01/why-the-starship-was-such-a-disaster/

Going from memory, hitting that 45min reserve would only be possible if the engines were at some comically low power in cruise, like under 30%.

Tecnam, being an established company, seems to have a pretty good idea as to whats possible. Eviation looks to be taking the perfect day perfect atc perfect everything approach to advertised performance. Or maybe its a startup needs investors kind of thing.

 

[sienar]

I don't understand why this idea of harvesting energy in the descent keeps coming back all the time.

Has has been pointed before, the most efficient way to convert your potential energy to range is to glide at best L/D.

If you make any attempt to generate power from wind milling the props, the additional drag will steepen the descent slope.

The energy required to cover the lost range due to the steeper slope will always be more than the energy you recovered by wind milling the props with some torque. (unless you're descending faster than best L/D)

It's like taking energy from a pot, transforming it, and miraculously hoping to put back more energy in the said pot.

A car can regen in a descent because its drag does not increase as its speed goes down when regen activates, since a car does not need lift. It will just arrive at the same bottom of descent a little bit later.

Physics.

I think we are contrasting with a ‘traditional’ powered aircraft, which has residual thrust, and approaches with increased drag, I.e doesn’t glide in. Change flaps/gear for prop drag/regen. Of course that’s not as totally efficient as coasting/gliding. Adding that a car, has to brake sometimes, so regen is needed, efficient or not.

Its not a matter of "not as totally efficent" - its more like a couple orders of magnitude distance. Windmilling props are giant airbrakes where the drag is equal (actually a bit greater) to the power being generated.

Assuming a rate of descent of 1k ft a minute you've got maybe 10mins of descent from 10k cruising alt. This would work out to be a whopping 213kw assuming everything is perfect. Feathering the props and flying at best L/D would give you much more than that, but that is a fantasy for a commercial aircraft.

 

[sienar]

Going from memory, hitting that 45min reserve would only be possible if the engines were at some comically low power in cruise, like under 30%.

Regulations always require reserves to be flown at "normal cruise speed".

That is what I meant. Normal cruise power being very low is the only way their numbers can make sense.

Going off the data from their website and here; https://www.flightglobal.com/airfra...-system-first-flight-days-away/147456.article

820/900kw of battery
1280kw for both engines
2000fpm climb
250 knot cruise @ 10k ft
440nm range

So it takes about 5mins to climb to cruise alt from SL, presumably climbs would be full power. This would require ~107kw. Add in some for TO and some for taxi, lets call it 150kw consumed to get the aircraft up to cruising alt. This leaves 670-750kw for the rest of the flight.

It'll take 1.76hrs at 250 to hit that 440nm range, add in a reserve and its about 2.5hrs of flying at cruise. This is in line with what the CEO of the company said "Alice will have sufficient battery power to fly for about 2.8h at maximum take-off weight"

This means anywhere from 300kw an hour to ~240kw (750kw/2.5hrs). Which is around 19-25% cruise power. For an aircraft to fly 250 @ 10k on ~300kw it'll need to have a flat plate equivalent of ~3.4ft.

I take back some of the things I said earlier, this aircrafts numbers are more fanciful than I remember. That 250 knot cruise must be for really short range, or they are hoping for a battery miracle before it hits market.

 

[Nicknick]

seems like you are mixing kW with kWh.
It takes 204 kWh to lift 7500 kg from zero to 10,000 m. To do it within 5 min you need 2450 kW (with 100 % efficiency and no air resistance).