Really interesting new electric plane

[Salty]

I don't doubt that it doesn't make sense to you, but I've been driving the Honda hybrid for 14 years, so the chances of my not knowing its characteristics by now are pretty much nil.

I think that what you're missing is that one of the benefits of a hybrid is that the gas engine can be a lot smaller. When you're driving at a constant speed on a level road, the power requirements are low enough so that no help from the electric motor is needed, and the small gas engine is sufficient to maintain speed. This is confirmed by watching the ammeter, which under those conditions shows the current going into and out of the battery to be zero.

The above explanation does not apply to a Prius, which as I understand it uses the electric motor full time.

I've owned hybrid cars for more than 5 years. One was a Prius, and your understanding of it is wrong.

 

[Palmpilot]

I've owned hybrid cars for more than 5 years. One was a Prius, and your understanding of it is wrong.

Well, it's been 14 years since I did comparison shopping between the Prius and the Civic, so that's my excuse!

 

[deonb]

Second, in coast mode while the engine is shutdown, the spinning of the electric motor charges the battery.

This is still regenerative braking. If it didn't charge the battery, it would be able to coast for longer. It doesn't matter that it doesn't substitute for a direct brake-pedal action, the motor drains kinetic energy to put back into potential energy. Draining kinetic energy = braking.

The most efficient way you can Hypermile a BEV or Hybrid is by minimizing regenerative braking and maximizing coasting (until such a point where you NEED to slow down in order to not go over the speed limit - and if you get to that point, you could have saved even more by just starting the downhill peak at a lower speed. This is of course annoying to everybody else on the road...).

Finally, while the engine is running, it is charging the battery through the alternator. Once the battery gets to a certain charge (highway), the battery kicks in and will power the motor (max 85mph). When the battery gets below a certain level, the auto EV kicks the motor off and the engine engages. Once the battery is charged again, the cycle repeats.

If you were on a flat plain, it would provide better efficiency if the engine/generator was just powering the electric motor directly. It has to - going to and from the battery gives you around 15% losses. If you do the same thing without losses, it will by nature be better.

The reason this works at all is because cars often found themselves in a state of having surplus energy - not because it round-trips energy via the battery.

 

[Velocity173]

You don't gain efficiency converting back and forth to electric. You lose it.

Then why do they get better MPG than a comparable all gas version?

If you were to create a Cmax with just a 141 hp gas engine vs the present Atkins 141 hp (gas)/47 hp (electric), the Atkins cycle engine will beat out the all gas engine. The amount of gas saved by the engine shutting down in coast and electric modes more than makes up for the switch over.

 

[Palmpilot]

...If you were on a flat plain, it would get the same range or better if the engine was just driving the electric motor directly. It has to - going to and from the battery gives you around 15% losses. If you do the same thing without losses, it will by nature be better.

The reason this works at all is because cars often found themselves in a state of having surplus energy - not because it round-trips energy via the battery.

Years ago, I was amused by a Prius ad that showed a driver repetitively speeding up and slowing down and marveling at the energy going into and out of the battery. While it was a cute ad, it of course did not mention the losses!

 

[Salty]

Then why do they get better MPG than a comparable all gas version?

If you were to create a Cmax with just a 141 hp gas engine vs the present Atkins 141 hp (gas)/47 hp (electric), the Atkins cycle engine will beat out the all gas engine. The amount of gas saved by the engine shutting down in coast and electric modes more than makes up for the switch over.

Because In a hybrid, you can reclaim some energy when braking or coasting down hill - even with the loss of efficiency, some reclamation is better than none. Hybrids get their best milage improvement in stop and go traffic. My point was exactly what your question asks. They DON'T get better milage if you are going 70mph on a flat road and not stopping.

An aircraft does not coast or brake very much. Few 12 seat aircraft have any need at all to deploy a brake, and those that do, only do it for a fraction of a percent of a percent of a flight, not long enough to overcome the loss of efficiency, let alone result in a benefit.

 

[deonb]

Then why do they get better MPG than a comparable all gas version?

Because cars don't decelerate with maximum energy efficiency in mind.

Remove the brake pedals from both cars - you'll get better MPG in the gas-only version.

 

[Salty]

Because cars don't decelerate with maximum energy efficiency in mind.

Remove the brake pedals from both cars - you'll get better MPG in the gas-only version.

Or you could just ignore speed limits, stop signs, stop lights, old ladies crossing the road, or traffic in front of you. Then the hybrid car would also be useless. You don't have these things in an aircraft.

 

[Salty]

before we had a hybrid, I used to tell my wife to think of it this way. It's not the accelerator that wastes gas, it's the brake pedal. If you're having to slam on the brakes, then you're wasting energy. You should either let up the gas sooner, or not push it so hard.

 

[Velocity173]

Because In a hybrid, you can reclaim some energy when braking or coasting down hill - even with the loss of efficiency, some reclamation is better than none. Hybrids get their best milage improvement in stop and go traffic. My point was exactly what your question asks. They DON'T get better milage if you are going 70mph on a flat road and not stopping.

An aircraft does not coast or brake very much. Few 12 seat aircraft have any need at all to deploy a brake, and those that do, only do it for a fraction of a percent of a percent of a flight, not long enough to overcome the loss of efficiency, let alone result in a benefit.

Ok, even without a coast, I will get better mileage because the engine IS recharging the battery to a level where it CAN take over. Don't need coast or braking for that.

I never got best MPG in stop and go traffic either. The car listed 47/47. I got probably 36 city and 47 highway. The accel in traffic killed MPG.

 

[Palmpilot]

before we had a hybrid, I used to tell my wife to think of it this way. It's not the accelerator that wastes gas, it's the brake pedal. If you're having to slam on the brakes, then you're wasting energy. You should either let up the gas sooner, or not push it so hard.

This is why I wish more cities would implement coordination of traffic signals. Failing to do so not only wastes gas, it increases air pollution due to the additional gas being combusted.

In some streets in some older cities, one can go a long way without stopping, by using the speed that the signals are set for. It's a beautiful thing!

 

[deonb]

Because In a hybrid, you can reclaim some energy when [...] coasting down hill

Not even. If you have a long downhill followed by a long uphill in a vacuum, and you either:

a) Regen on the way down and then re-use the stored battery energy on the way back up
-vs-
b) Coast in neutral on the way down and then use the momentum on the way back up

You'll get further with (b).

It's obvious why in a vacuum. It's less obvious without the vacuum since drag increases exponentially to speed, but it's still true in practice at low-end highway speeds. Easily provable - if I change the regen to low in my car, I get better mpg on the highway (well kWh/mile for me since it's a BEV, but same principle holds).

 

[deonb]

Ok, even without a coast, I will get better mileage because the engine IS recharging the battery to a level where it CAN take over. Don't need coast or braking for that.

If instead of charging the battery, it just uses that exact same amount of energy to just drive the electric motor directly, it would get even better mileage.

But it needs the battery to be charged for other reasons. And so it does.

If you drive on a straight and level road at constant speed, you'll see that after the initial charge, the car neither adds nor extracts energy from the battery again. (And if it does, the engineers were idiots.)

 

[Marky_24]

Yes, but you have to burn more fuel in the gas engine to make the electricity, and you have losses in the making and transmission of the electricty. There is no free lunch here.

 

[Velocity173]

If instead of charging the battery, it just uses that exact same amount of energy to just drive the electric motor directly, it would get even better mileage.

But it needs the battery to be charged for other reasons. And so it does.

That's a Volt setup and I'd agree, they do better MPG that way. Ford went a different route and ended up with lower MPG. Got $1,000 back from their over inflated MPG claims.

 

[Salty]

Ok, even without a coast, I will get better mileage because the engine IS recharging the battery to a level where it CAN take over. Don't need coast or braking for that.

I never got best MPG in stop and go traffic either. The car listed 47/47. I got probably 36 city and 47 highway. The accel in traffic killed MPG.

I said the best improvement in mpg is in stop and go traffic. These nuances are important.

 

[deonb]

That's a Volt setup and I'd agree, they do better MPG that way. Ford went a different route and ended up with higher MPG. Got $1,000 back from their over inflated MPG claims.

Just comparing battery vs. direct electric here. If either the Volt or Ford uses the exact same engine to just drive the wheels directly, it would get even better MPG than either electrical conversion.

Of course it would make for a very boring and maybe even impractically slow car. But on a straight and level road, for the same speed, the direct drive gasoline engine will outperform both ways of doing electric conversions using the same engine.

There IS a way of getting a better round-trip via the battery. You use a bigger engine. Much bigger. Like power-plant level big. Then the efficiency of the large engine will outweigh the inefficiency of the conversion steps. But on the same engine it can't. Losses are losses.

In practice of course Hybrid IS better. Because cars don't just drive on straight and level roads. But airplanes do.

 

[tspear]

I've owned hybrid cars for more than 5 years. One was a Prius, and your understanding of it is wrong.

In what way? I never have owned a hybrid (I need four wheel drive, and the selection of hybrids was way overpriced). I have however followed and read up a lot on them.
Every model of hybrid I have looked at where there is a gas model and a hybrid model uses smaller engines in the hybrid. Often engines that are tuned for a smaller RPM range and are more efficient.

Tim

 

[Salty]

A Prius does not use its electric motor full time.

In what way? I never have owned a hybrid (I need four wheel drive, and the selection of hybrids was way overpriced). I have however followed and read up a lot on them.
Every model of hybrid I have looked at where there is a gas model and a hybrid model uses smaller engines in the hybrid. Often engines that are tuned for a smaller RPM range and are more efficient.

Tim

 

[deonb]

In what way?

A Prius is not an electric drive car. It's a combo-drive using a planetary gearbox to mix in power from both drive-trains.

Every model of hybrid I have looked at where there is a gas model and a hybrid model uses smaller engines in the hybrid. Often engines that are tuned for a smaller RPM range and are more efficient.

A smaller engine is less efficient, not more. If you double the dimensions of a cylinder, you have 8 times more volume but only 4 times more surface area, and thus you gain power faster than you gain friction.

Small gasoline engines (1.5l) has about 20% thermal efficiency. Larger engines (5.0L) are about 35% efficient. Cruise ships get around 50%. Power plants get around 60%.

However, a smaller engine is also less powerful - so as a result it will use less gas when running at the peak efficient point of that particular engine's curve. It will proportionally give you even less power than the gas savings at the point though (so e.g. you can reduce your gas usage by 50% if you're willing to give up 60% of your power). BUT a hybrid doesn't need a powerful engine to get performance - it has electrical motors to assist it. Hence it can indeed make good use of a much smaller, less powerful engine.

But that's not because the engine is more efficient by itself - it's a nature of cars having variable power demands and can thus store power during surplus times to use during demand times. If your battery runs out your performance would be terrible - if it would even work. Last I looked (a decade ago), you couldn't move a Prius/Highlander/Camry hybrid without the hybrid battery from a stand-still. If you're on the highway they will keep going even with a battery fault, but once you stop, it will refuse to drive again.

 

[tspear]

A Prius does not use its electric motor full time.

Unless I missed something, the poster never said it does. He just said it does not use the battery in cruise. The primary point I believe was hybrid solutions allow for smaller gas engines.

Tim

 

[deonb]

Unless I missed something, the poster never said it does.

...

The above explanation does not apply to a Prius, which as I understand it uses the electric motor full time.

But he also came out after Salty’s comment and said:

Well, it's been 14 years since I did comparison shopping between the Prius and the Civic, so that's my excuse!

So we don’t really need to rehash it.

 

[tspear]

@deonb
I am by no means an engine expert. But multiple engineers, and articles I have read is engines tuned for a specific power range and speed range are significantly more efficient than engines which support a wide band. One possible solution to reduce some efficiency loss is a solution such as the FreeValve concept. However, these solutions are not widely used.
From what I have read, Toyota, Ford, Honda, GM... all have been optimizing/tuning the gas engines for a smaller power band and RPM range for hybrids to increase the MPG. They have all come to rely upon the electric motor to provide power outside of the specific range.
For example, here is a review of the Chevy Volt 2016 power train. You will notice they discuss using a lower band/range of RPMs.
https://www.caranddriver.com/featur...dissected-everything-you-need-to-know-feature

Tim

 

[bflynn]

Comparing instead to an internal combustion engine burning 100LL the ratio isn't quite as bad (about 25lbs/lbs equivalent).

While I agree the comparison doesn't come out nicely for batteries, I'm not sure about this number.

https://spectrum.ieee.org/aerospace...eter-the-electrification-of-flight-is-at-hand

This article has a lot of numbers in it, but the one that strikes me is (the claim of) 5 kW/lb of battery. He says they have a 725 lb battery pack at 83 kwh which is enough for the climb at 80 kwh and then cruise at 18-25 kwh and land 2 hours later. According to your 25:1 ratio, that should take 2500 lbs of batteries.

Bye Aviation has flow a battery powered 172 - no idea of the endurance, but they were able to get 700 ft/min climb out of it out of Centennial. Maybe someone with full FlightAware access can see how long N2474E flies for?

 

[deonb]

@deonb
I am by no means an engine expert. But multiple engineers, and articles I have read is engines tuned for a specific power range and speed range are significantly more efficient than engines which support a wide band. One possible solution to reduce some efficiency loss is a solution such as the FreeValve concept. However, these solutions are not widely used.
From what I have read, Toyota, Ford, Honda, GM... all have been optimizing/tuning the gas engines for a smaller power band and RPM range for hybrids to increase the MPG. They have all come to rely upon the electric motor to provide power outside of the specific range.
For example, here is a review of the Chevy Volt 2016 power train. You will notice they discuss using a lower band/range of RPMs.
https://www.caranddriver.com/featur...dissected-everything-you-need-to-know-feature

Tim

I agree a tuned engine with a smaller band is more efficient than a wide power band engine. I was more commenting that smaller engines by themselves isn't more efficient. But either way, it doesn't matter. Hybrid doesn't make the smaller power band engine more efficient than it already is - it just makes it practical to use so that you don't have 0-60 times in the minutes ranges.

But once you're at speed and on a straight and level road, the smaller power band engine would still get better mileage if it were directly connected to the wheels than if it were connected via a hybrid system.

 

[tspear]

But once you're at speed and on a straight and level road, the smaller power band engine would still get better mileage if it were directly connected to the wheels than if it were connected via a hybrid system.

By hybrid system, you are referencing a serial hybrid. Such as on the first generation Chevy Volt.
I am unaware of any currently produced hybrids which are serial in nature. All the hybrid cars/trucks excluding the Gen1 Chevy Volt I ever considered (GM, Ford, Honda, Toyota) had optional direct connect the gas engine to wheels for cruise.

Tim

 

[deonb]

While I agree the comparison doesn't come out nicely for batteries, I'm not sure about this number.

https://spectrum.ieee.org/aerospace...eter-the-electrification-of-flight-is-at-hand

This article has a lot of numbers in it, but the one that strikes me is (the claim of) 5 kW/lb of battery.

5kW/lbs would be quite a feat... that would make my Tesla get 0-60 in under 1 second . The number they are quoting is 5kW/kg.

He says they have a 725 lb battery pack at 83 kwh which is enough for the climb at 80 kwh and then cruise at 18-25 kwh and land 2 hours later.

a) kW, not kWh
b) 725lbs is for air cooling instead of liquid cooling. (See lifespan limitations above with air cooling). Liquid cooling would have resulted in a 1100 lbs battery. On air you'll get 500 cycles instead of 1500 cycles on your $12000 battery. The economics isn't favorable on this one (yet).
c) They are quoted using 260wh/kg cells. That means 83kWh gives 320kg / 702 lbs. Which means two things to me:

i) They are using only 23 lbs of materials (full pack weighs 725lbs) to hold together and individually connect (solder) around 7000 individual 18650 cells (slightly bigger than AA batteries) that weigh 702 lbs together. It's almost unbelievable...
ii) It also tells me that the 83kWh definitely doesn't include the necessary upper and lower buffers you need from a Lithium battery to prevent it from bricking. So they'll get around 75kWh usable out of that, max.​

According to your 25:1 ratio, that should take 2500 lbs of batteries.

Two things:
a) My ratio is for liquid cooling, not air cooling. Since we have their exact wh/kg ratio for their air-cooled battery, let's use exactly that in the numbers and redo this.
b) I used a large engine that is around 30% efficient for my original numbers. Something like a IO-550. Since this thing needs only about 100 HP, a gasoline engine in that range is much less efficient - maybe 20%.

With that in mind:

100LL published efficiency is 33.5kWh/gallon
100LL in a 100 HP gasoline combustion engine is about 20% efficient, so that's 33.5kWh * 20% / 90% = 7.4 kWh/gallon equivalent in kinetic conversion
7.4 kWh/gallon = 1.25 kWh per lbs of Jet-A (6 lbs per gallon for Jet-A)
Their batteries weigh 8.4 lbs/kWh, so 1.25 kWh weigh about 10 lbs

Thus in the case of their exact air-cooled battery equivalent to a small 100LL engine the ratio is around 10:1. Thus 25kW/33 HP at cruise = 2.5gph.

Now let's compare this with a Rotex 912 iS at 100 HP. It burns 2.65 gph at cruise. Obviously lots of caveats - different airframes, and I have no idea how many HP/kW a Rotex 912iS actually puts out at cruise. But I don't think it's unreasonable for a 100 HP engine to only be burning 2.5gph at a 33 HP power setting.

 

[deonb]

By hybrid system, you are referencing a serial hybrid. Such as on the first generation Chevy Volt.
I am unaware of any currently produced hybrids which are serial in nature. All the hybrid cars/trucks excluding the Gen1 Chevy Volt I ever considered (GM, Ford, Honda, Toyota) had optional direct connect the gas engine to wheels for cruise.

I meant electrical round-tripping (with or without the battery). If you use a gearbox to bypass the electrical system and drive the wheels directly for cruise, it's efficient, but that has nothing to do with hybrid. You can just do that anyway.

 

[tspear]

I meant electrical round-tripping (with or without the battery). If you use a gearbox to bypass the electrical system and drive the wheels directly for cruise, it's efficient, but that has nothing to do with hybrid. You can just do that anyway.

But the point of the hybrid is to give you flexibility of power when you need it (e.g. both gas and electric engines putting power to the wheels), start/stop where electric can regen energy, cruise where the gas can maintain speed and recharge the battery.



Sent from my LG-TP260 using Tapatalk

 

[Palmpilot]

Unless I missed something, the poster never said it does.

Actually I did, and I was apparently mistaken. This was in reference to 2003 sales literature, however, so I don't know whether I simply misunderstood what I read, or if Toyota has changed their design since then.

He just said it does not use the battery in cruise.

That comment was about my Civic hybrid, not the Prius. It applies to a level road when there is no acceleration or deceleration. I don't know enough about how the Prius operates to say one way or the other what it does in those circumstances.

The primary point I believe was hybrid solutions allow for smaller gas engines.

My primary point was to counter the notion that driving 70 mph necessarily runs the battery down.

 

[bflynn]

That comment was about my Civic hybrid, not the Prius. It applies to a level road when there is no acceleration or deceleration. I don't know enough about how the Prius operates to say one way or the other what it does in those circumstances.

On a level road in cruise a prius would typically not use the battery. It would run down and then have to be recharged, the battery is really not very big. If you run it in EV mode, you get like 1-2 miles max. The battery in a prius is for starting out or extra power for acceleration.

 

[deonb]

But the point of the hybrid is to give you flexibility of power when you need it (e.g. both gas and electric engines putting power to the wheels), start/stop where electric can regen energy, cruise where the gas can maintain speed and recharge the battery.

Absolutely - that’s why a hybrid works great for cars where you by nature need flexibility of power and you constantly oscillate between energy demand and surplus.

But, full circle - the same concept doesn’t translate to something that has a constant power profile for the far majority of the time. Like the refrigerator engine on a reefer truck, or a cement mixer, or an airplane.

 

[tspear]

Absolutely - that’s why a hybrid works great for cars where you by nature need flexibility of power and you constantly oscillate between energy demand and surplus.
But, full circle - the same concept doesn’t translate to something that has a constant power profile for the far majority of the time. Like the refrigerator engine on a reefer truck, or a cement mixer, or an airplane.

Your assumption of constant power is for what duration?
The plane in the OP article is designed to cruise about 350 MPH, has a range of 2 hours. Likely flights will be one hour or less; I would speculate that most flights will be to small feeder airports in which case, the flight time will be 30 minutes or less.
That is a climb, short cruise and descend pattern. How is that constant power?
Going back to my original example of LAX to Oxnard CA. Taxi time is longer then flight time in the turboprop. They also only climb to the mid teens because the flight is so short.

Tim

 

[Salty]

Your assumption of constant power is for what duration?
The plane in the OP article is designed to cruise about 350 MPH, has a range of 2 hours. Likely flights will be one hour or less; I would speculate that most flights will be to small feeder airports in which case, the flight time will be 30 minutes or less.
That is a climb, short cruise and descend pattern. How is that constant power?
Going back to my original example of LAX to Oxnard CA. Taxi time is longer then flight time in the turboprop. They also only climb to the mid teens because the flight is so short.

Tim

You aren't reclaiming energy in the decent you describe. There is no benefit to carrying all the extra equipment needed for a hybrid, when it can never reclaim any energy. Making the cruise portion of the flight shorter doesn't solve the problem of a hybrid. Make it short enough, and maybe you solve issues for a full electric solution, but it doesn't help a hybrid solution.

 

[deonb]

Your assumption of constant power is for what duration?
The plane in the OP article is designed to cruise about 350 MPH, has a range of 2 hours. Likely flights will be one hour or less; I would speculate that most flights will be to small feeder airports in which case, the flight time will be 30 minutes or less.
That is a climb, short cruise and descend pattern. How is that constant power?
Going back to my original example of LAX to Oxnard CA. Taxi time is longer then flight time in the turboprop. They also only climb to the mid teens because the flight is so short.

I'll rephrase constant power to constant demand. There is no (useful) opportunity for surplus followed by demand again.

You have your:
a) Climb phase - you can't generate/store electricity in this phase since you need all the power to climb.
b) Cruise phase - you could generate during this phase, but why? Where are you going to use it again? Later in cruise? See above discussions on this thread of how a directly connected drivetrain is more efficient than roundtripping power via a battery.
c) Descent phase - you can generate power here, but you don't need to use it again for the flight so why bother? [EDITED]

The only thing you can possible use it it for is to generate power for the NEXT flight's climb phase. But that's a very inefficient way to do it - if you want to have battery-assist during your climb, just charge on the ground before you take off with electricity that's generated from a much bigger engine for cheaper.

 

[Salty]

I'll rephrase constant power to constant demand. There is no (useful) opportunity for surplus followed by demand again.

You have your:
a) Climb phase - you can't generate/store electricity in this phase since you need all the power to climb.
b) Cruise phase - you could generate during this phase, but why? Where are you going to use it again? Later in cruise? See above discussions on this thread of how a directly connected drivetrain is more efficient than roundtripping power via a battery.
c) Descent phase - there is actually a surplus here, but you don't need to use it again for the flight so why bother?

The only thing you can possible use it it for is to generate power for the NEXT flight's climb phase. But that's a very inefficient way to do it - if you want to have battery-assist during your climb, just charge on the ground before you take off with electricity that's generated from a much bigger engine for cheaper.

I disagree with your c. There is no surplus, unless you are going to fly slower to charge the battery. Aircraft of the type we are discussing don't generally need air brakes, so if you try to reclaim energy, you are just going slower than you need to and arriving later. Looking at it another way, if you increase your speed in cruise so that you arrive at the same time if you descend slower, you're right back to your "roundtripping" energy loss again.

 

[deonb]

I disagree with your c. There is no surplus, unless you are going to fly slower to charge the battery. Aircraft of the type we are discussing don't generally need air brakes, so if you try to reclaim energy, you are just going slower than you need to and arriving later. Looking at it another way, if you increase your speed in cruise so that you arrive at the same time by descending slower, you just used more energy than you generated by reclaiming it.

Agreed. Fixed. The only surplus opportunity is times where you need air brakes.

 

[tspear]

@deonb , @Salty
You guys are making this way to complicated.
When you are sitting on the ground and/or taxing with a traditional turboprop you are burning significant fuel. Especially when you think about the average 15 minutes taxi at a class B airport. That does not include any hold times....
In addition, to meet FAR Part 25 requirements, the engines need to be massively oversized. Which means that either are very inefficient in cruise, on the ground, descent, or in the climb. Current engines are only optimized for a single condition. When moving around the airport, and in descent you need minimal power, but turboprops and turbofans generally require above 60% fuel flow to just stay lit (this is based on what others have posted on the PT6, Garrett turboprops, and Airbus and Boeing airliners).

I would think the extensive bean counters at both JetBlue and Boeing have crunched the numbers. When you read the article, they state they have the estimates for the battery pack using current tech, airframe, engines, fuel... and yet it will save a lot of operational cash for the select and limited mission.

Further, airliners do not use speed brakes as a general rule because it is inefficient. You are just throwing away energy. In this case, using windmilling props you can recharge the battery, so there is no reason to not use regen in descent and stay higher longer (if ATC allows).

And so far you have yet to prove that the stated assumptions, math and other information in the article does not save the airlines money. You just have your assumptions.
I do not know the answer; I think it is an interesting concept, and in the specific mission it may make sense.

Stop thinking inside the current box and assumptions about the kind of flying in GA applies to short hop airliner missions that is the target market.

Tim

 

[Salty]

The "box" is physics, and the limits are real.

 

[deonb]

In addition, to meet FAR Part 25 requirements

They are explicitly going after Part 23 here, not 25.

I would think the extensive bean counters at both JetBlue and Boeing have crunched the numbers.

Their "numbers" are based on extreme hopetimism. They're designing this with the hope of being able to be fully electric. From their website:
"Our series hybrid powertrain was designed for an eventual transition to fully electric, without requiring any mechanical retrofitting..
...
The standardized wing-integrated battery bays are chemistry-agnostic and the fuselage is pre-wired for the eventual transition to fully-electric."

I think it's fair to say that a project that is designed from the start to accommodate technology that does not now nor may never exist, may not have all their ducks in a row with regard to their numbers.

Even if such battery tech does get discovered it may not fit into the chemistry-agnostic wing model anyway. Maybe what we get is a metal that you need to make your hull out of. Other car manufacturers struggled to get a long range electric car and waited for chemistry to catch up, until Tesla showed what you do is you build your chassis out of the battery pack (using 1970's chemistry).

Further, airliners do not use speed brakes as a general rule because it is inefficient. You are just throwing away energy. In this case, using windmilling props you can recharge the battery, so there is no reason to not use regen in descent and stay higher longer (if ATC allows).

How much steeper can you really descent and not have your passengers complain? But even if you do a steep windmilling descend, what purpose does charging in this phase do? You're not going to be using that power until the next flight, but once you're on the ground you can just plug into shore power. The only purpose I can see is to allow you to start your descend with less than 30 minutes of cruise reserve, and instead generate that reserve during your windmilling descend. I'm sure the FAA is very excited about approving a "I don't have 30 minutes reserve right now, but I promise to have it before I get to the ground" rule.

And so far you have yet to prove that the stated assumptions, math and other information in the article does not save the airlines money. You just have your assumptions.

Here's one for you - "designing with batteries at 12 to 20% of total weight." vs. "Current battery technology can only power the plane for about 100 miles so a gas-powered engine would be used to generate electricity to power the motors for additional range."

Let's take a look at the 12-seater equivalent. The PC-12 MTOW is 10'450 lbs. 20% of that is 2090 lbs. Let's also air-cool instead of liquid-cool as well, saving 40%. So 2090 lbs battery is the equivalent of 68 lbs of Jet-A - which is 10 gallons. This is with all losses account on both sides. Let's also completely ignore the descend and reserved parts for the moment.

So now we have a PC-12 that can take off and fly for 100 miles burning only 10 gallons of fuel. Mmm... But maybe they have some sort of fancy carbon fiber fuselage and they get their weight down by 20%. (Which then if you keep your battery at 20% of total still, becomes the equivalent of 8 gallons of fuel. Still not going to happen).

I think whoever came up with these numbers can have a great second job coming up with numbers at 'Raptor Aircraft'.