Really interesting new electric plane

[deonb]

Yes, today's batteries are not up to the task. We need a better battery, or whatever electrical energy storage device that may be. On this point I agree. However there are no physics that dictate we can't achieve this, or that what we have now is as good as it gets. That's ridiculous naysayer talk.

There are no physics that said we can't make a better battery. The physics discussion was about if you round-trip energy to and from a battery it will always be less efficient than just directly using it. This will not change.

1. We don't need to match gasoline's energy density 1:1. We only need to match end performance. The best piston engines today are still only about 30% efficient, so 70% of that fantastic energy density of gasoline is ****ed away in hot air.

Turbines are 60% efficient in flight.

1. Because electric motors are more like 98% efficient...

Charging and discharging a battery also has losses that bring this down quite a bit.

You have an EV right? Have you ever compared how much kWh you used from the wall when you charge it, compared to how much goes into the battery? The difference is quite a bit - I get only about 78% usable on my Tesla charging from 240V. If I charge from 110V I get about 55%.

...battery energy density only has to be maybe 35% that of a gallon of gasoline pound for pound.

35% of a gallon of gasoline pound for pound still means 4295 Wh/kg. Current state of the art is 254 Wh/kg. 25 years ago it was 118 Wh/kg.

Now let's say we can stop doing stupid stuff like burn 50% of the fuel on the ground, then we can cut down the 4295 by 50% to 2147 Wh/kg. Still not going to happen anytime soon.

 

[tspear]

Wow, I'm amazed that taxiing accounts for that high a proportion of fuel use for a turbine!

The problem is turbines idle at a very high percentage of full power. In fact a few posts I read suggest taxi burns more fuel than cruise at higher altitudes. And since multiple pilots posted the same stuff in a few forums, I assume there is a modicum of truth to the statement.
So when you look at the target market for the initial plane the OP referenced, a range of 100 miles, fuel burn is on the taxi, take off and landing is a rather large portion of the total fuel burn.
This is why i said it makes sense for these types of feeder routes.

Tim

 

[fasteddie]

One of the commentors on a recent Aviation Week article had a decent analysis (copied in below).

Also, this article from July was informative: http://aviationweek.com/aircraft-de...style-approach-developing-electric-propulsion

It really makes it sound like Zunum recognizes that the battery technology isn't here yet, but they're designing their airplane with the hope that, by the time it's ready for flight tests, the battery technology will have improved enough to make it work.






Commentor "Tuna" from http://aviationweek.com/new-civil-aircraft/boeing-backed-zunum-s-first-aircraft-be-12-seat-commuter


I have read through various articles and press statements to try to make sense of Zunum's technology, and it isn't making sense.

Here are some of their points:

-12,500 lbs MTOW to be certified as a small aircraft
-"Maximum of 20% of MTOW as battery" e.g. battery weight 2,500 lbs
-"Economics work at the current energy density being produced at the Tesla Gigafactory" e.g. ~120 WH/lb = 300,000 WH = 300 kWH battery capacity
-"1 Megawatt power class" = e.g. consumes 1,000 kW at full power
-"range extender turbine in the 500 kW class" which is about 680 horsepower. As in, they are looking for a ~680hp turbine to serve as a power generator, which could supply about half the max power.
-"340 mph at max power" e.g. if ran at 1 megawatt, it could fly at 340. My rough guesstimate of what it would therefore fly at if only using half power: 270 mph.

What I seem to be reading is that this plane can consume up to 1 mW of energy, but will likely use much less (maybe about half that) since it only has 500 kW of generator capacity and 300 kWH of total battery capacity. It probably has 1 mW capacity for redundancy reasons. Each of the 2 engines will be able to use 500 kW, maybe dual battery converters each able to deliver 250kW to 500kW, so that there is redundancy in case of failure, but in actual use probably not consuming more than 500 kW.

At full 1 mW power, it would drain the batteries from a full charge in 18 minutes.

At full 1 mW power, with the range extender producing 500 kW, it would drain the batteries from a full charge in 36 minutes, still nowhere near the range.

The most likely operating scenario I can imagine is that the generator will actually be running the whole time, or as soon as the plane climbs above FL15 or something like that, with battery power contributed during takeoff, and maybe stored aboard as backup power in case the generator fails.

I don't see the big benefit. Seems like relatively little power will come from the batteries. Their generator is going to supply 500 kW/hr and their whole battery system has maybe 300 kWH of capacity, and has to keep much of that in reserve as backup power.

 

[Tantalum]

• Yes, today's batteries are not up to the task. We need a better battery, or whatever electrical energy storage device that may be. On this point I agree. However there are no physics that dictate we can't achieve this, or that what we have now is as good as it gets. That's ridiculous naysayer talk.

• We don't need to match gasoline's energy density 1:1. We only need to match end performance. The best piston engines today are still only about 30% efficient, so 70% of that fantastic energy density of gasoline is ****ed away in hot air. Because electric motors are more like 98% efficient, battery energy density only has to be maybe 35% that

Hopefully you are right. On a quasi related note, wish we could capture more energy from the sun.. the wings would make great real estate for panels...

 

[Tantalum]

The most likely operating scenario I can imagine is that the generator will actually be running the whole time, or as soon as the plane climbs above FL15 or something like that, with battery power contributed during takeoff, and maybe stored aboard as backup power in case the generator fails.

Right, the whole exercise is like buying a Prius and then wondering why your miles per gallon are no better than that old Toyota Echo you just traded in when all your driving is on the highway. There's no free lunch

PS, @Dav8or I do wonder if there's a theoretical limit as to how much energy can be stored in a battery. Fossil fuels, in other words hydrocarbons, store a tremendous amount of energy because the numerous chemical bonds within them that can easily be broken and then reform as they react with oxygen. Battery relies on the flow of electrons between an anode and cathode.. as it is now it is not entirely uncommon for lithium batteries to encounter thermal runaway and like others have posted we have had batteries for over 100 years and yet their improvements have only been incremental. You mentioned that the internal combustion engine is very inefficient because a ton of it goes to heat. That is totally right, but a gas turbine engine approaches 60% efficiency. Maybe instead of racing to put batteries on airplanes and waiting for a technology that doesn't exist, and may never, we continue to perfect known tech. The TWIN-engine diamond diesel da62 burn something crazy like 14 gph combined.. that is better than many single engine GA airplanes

Hopefully I'm wrong, I think a new breakthrough in clean and efficient power plant technology in aviation would be amazing, but at this point we still have a very long way to go, it's not like we are just around the corner

 

[Mistake Not...]

Jumping in late, but...

Is that even the right shape for a plane that has to efficiently as possible fly a load from point to point? Shouldn't it be more glider shaped, and if it flies slow enough, have props instead of jet looking things? Or did I not read the article correctly?

(I'm not trying to restart the whole electric / battery / physics discussion. You guys hammered that one. )

 

[Tantalum]

Is that even the right shape for a plane

Definitely did not pass the Boeing "looks about right" rule. IMHO

All right, I'm signing out of this one LOL. Cheers

 

[deonb]

Hopefully you are right. On a quasi related note, wish we could capture more energy from the sun.. the wings would make great real estate for panels...

The maximum solar coverage at 90 degree angle is 1kW/square meter - about 100w/square foot. What's a C172 wing size - maybe 150 square foot?

So that's 15kW. Now that's max theoretical - in practice we'd be at about 3.75 kW right now (25% efficiency).

That's the equivalent of providing an extra 0.25 gallon of gasoline per hour... And in order to even get that you'd have to orient the wings 90 degrees towards the sun all the time, which would probably cause all the other pilots to make fun of you.

You will NOT believe how many people ask why Tesla doesn't put a solar panel on the car roof... It doesn't do anything in practice. The amount of energy required is in a different order of magnitude. Like when I bought my Nissan Leaf the salesman told me: "If you need to preserve battery, turn off your radio since it uses the battery". Dude, that battery can drive a car radio for 50 years - turning it off isn't going to make even a 1 yard difference in range.

 

[3393RP]

"Zunum plans to make a larger plane seating up to 50 passengers at the end of the next decade, and the range of both would increase to about 1,000 miles as battery technology improves, Knapp said."

This is the ultimate in optimism. Trending out the most optimistic trend on battery improvements, we're at 8% improvement per year. (And this has started to slow down).

To get a 10-fold improvement from 100 miles to 1000 miles will require 30 years to get there.

Of course miracle discoveries can happen and advance this, but you can't build a business on betting someone makes a miracle discovery. It's just as likely someone discover teleportation in that time.

The public are being fed this hooey about the miracle energy density discovery for cars, home solar power with storage batteries, and now this aircraft.

That's a real pretty rendering of the vaporware aircraft, but they seem to have forgotten to show the batteries. It's not worth my time to figure out the kW power necessary to drive the aircraft at 340 MPH.

The aircraft shown and discussed in the article will never meet the goals they claim. Of course someone will counter my viewpoint with visions of supercapacitors and a tenfold increase in battery energy density, but those things aren't going to happen.

 

[tspear]

That's a real pretty rendering of the vaporware aircraft, but they seem to have forgotten to show the batteries. It's not worth my time to figure out the kW power necessary to drive the aircraft at 340 MPH.

The aircraft shown and discussed in the article will never meet the goals they claim. Of course someone will counter my viewpoint with visions of supercapacitors and a tenfold increase in battery energy density, but those things aren't going to happen.

Actually, they do show the batteries. If you want the power requirements, read the thread.
And the back of the napkin numbers posted in the thread match what the PR says. Most of the debate is on if it makes sense, or basically if it is stupid.

Tim

 

[blueskyMD]

After going through this post it seems like an impossible idea from physics and technology point. But here is one benefit I see for us , little guys. I liked when they mentioned small underused GA airports. The mention of our GA airports will soften attitude of public to our airports and they will have more interest in supporting GA airports thinking they ( small airports ) might be useful someday even though this will remain a pipe dream.

 

[StevieTimes]

The take off roll is minimal. The taxi is the real fuel killer. But I think robo taxi which pulls the plane and is controlled by the pilot is more likely.

Who will be the first to take off with the robot still attached to the nose wheel? I will be embarrassed when I land, taxi to the fbo, and they point out the robot still attached to the front.

 

[tspear]

Who will be the first to take off with the robot still attached to the nose wheel? I will be embarrassed when I land, taxi to the fbo, and they point out the robot still attached to the front.

I would expect it to attach in such a way it would break off or unhook. Easy enough to make the hook come from underneath and as soon as the nose wheel lifts the hook disengages.
Or add other safety measures, such as using GPS or other Navaids, have the taxi auto disconnect when 500ft from runway and return back to the dispatch point.

Tim