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ZaphodHarkonnen
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Joined: Sun Jan 04, 2015 10:20 am

A couple of battery electric aircraft questions. 1 noise, and 1 cost.

Fri Sep 24, 2021 3:16 am

Had a bit of a search on these and couldn't really find anything.

Q1: So for the sake of a scenario. Given a B737/A320 size aircraft. If it were powered by electric motors, would we expect the noise levels to be more or less than the equivalent power jet engine?

This question has rattled around in my head as we get closer to having battery electric short haul aircraft. If the noise is extremely low, it makes me wonder if we'd see an increase in demand for inner city airports.

Q2: What sort of hourly cost differential do you think we'll see for battery electric aircraft compared to their fossil fueled brethren? If you want a scenario let's go with a 172 size/capability comparison.

The idle musing here is if the costs are an order of magnitude less or so. Could we see a massive growth in GA flying as it becomes feasible for more people to have it as a hobby.
 
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TWA772LR
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Re: A couple of battery electric aircraft questions. 1 noise, and 1 cost.

Fri Sep 24, 2021 4:09 am

I'm not an aerospace engineer, but I'd imagine the noise would be solely from air displacement caused by the propellers, assuming this hypothetical aircraft is a prop job. If you hear an ATR or Q400 fly over you'd hear the low rumble of the props and when it is directly in front of you you'll start to hear the whine of the turbine, which at least to me, seems quieter than a normal turbofan.

As for costs, itll be substantially cheaper to operate than fuel-powered planes, but an interesting aspect is that batteries don't get lighter as the flight goes on so there's also the question of how MX costs will be affected by a differences in structural stress on the airframe and landing gear.

If/when we're able to make a full sized commercial airliner with electric propellers economical, these questions will be answered. Come to think of it, NASA should try to get their hands on a TU-95 (large, fast, propeller aircraft around the size of a 737) and see if they are able to modify it to operate on batteries. I guess there's plenty of ATRs and Q's lying around they can try that in first.
 
gloom
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Re: A couple of battery electric aircraft questions. 1 noise, and 1 cost.

Fri Sep 24, 2021 6:19 am

TWA772LR wrote:
As for costs, itll be substantially cheaper to operate than fuel-powered planes,


Not quite sure about it.

Yes, the energy cost per flight would probably be cheaper. I fully expect MX to be cheaper, as both electric engines and batteries are less complicated and easier to replace/upgrade.
However, the cost could come from investment cost. There was a calculation done many times here, how much fuel and MX is spent on plane. Will it offset higher purchase price? Over the time, probably. Will it be substantially cheaper? On operating costs, I tend to agree. On TCO, not so much.

After all, if you look at past 20 years, the average car (or TV set, or any product sufficiently advanced) is not cheaper, even with all those advancements. It would kill companies, that are expected to grow. Instead, you get more and more extras (bigger, better, faster). They will not be much cheaper over TCO. Just only to show they are, you know "10% less" marketing stuff. But development costs, aircraft companies growth etc. will likely reduce that to being "much less than substantial".

My two cents.

Cheers,
Adam
 
tommy1808
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Re: A couple of battery electric aircraft questions. 1 noise, and 1 cost.

Fri Sep 24, 2021 9:02 am

gloom wrote:
TWA772LR wrote:
As for costs, itll be substantially cheaper to operate than fuel-powered planes,


Not quite sure about it.

Yes, the energy cost per flight would probably be cheaper. I fully expect MX to be cheaper, as both electric engines and batteries are less complicated and easier to replace/upgrade.
However, the cost could come from investment cost. There was a calculation done many times here, how much fuel and MX is spent on plane. Will it offset higher purchase price? Over the time, probably. Will it be substantially cheaper? On operating costs, I tend to agree. On TCO, not so much.


:checkmark: :checkmark: :checkmark:
Unless talking about something really short ranged, even for a commuter a battery electric aircraft will be very, very significantly heavier than a conventional one. There is no equivalent to recuperation on aircraft and much of their operation is at or close to their engines optimum operating point so the Efficiency advantage on aircraft is a pale shaddow of what you have on a car.
And in a car the battery weights more than 10 times the fuel needed for the same range. On an aircraft the battery will weight just as on landing as on take of.

So you´d be looking at something 747 sized to match the A320.passenger capacity and range. No way that is going to be cheaper to operate.

best regards
Thomas
 
DFW17L
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Re: A couple of battery electric aircraft questions. 1 noise, and 1 cost.

Sun Sep 26, 2021 5:27 pm

When someone cracks the energy storage issues (weight, recharge, pollution from manufacturing,…), they’ll be the richest person in the world.
 
hitower3
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Re: A couple of battery electric aircraft questions. 1 noise, and 1 cost.

Mon Sep 27, 2021 11:42 am

Let's look at the cost:

Jet A1 fuel currently costs approx 0,64€/kg and contains about 12kWh/kg. The cost per kWh is therefore about 5,34ct/kWh
Electricity for industrial scale users currently sells around 6-7ct/kWh.

Now assuming an overall efficiency of a modern turbofan engine of 40% and the one of an electric propulsion fan engine of 80%, the balance gets in favour of the electric plane.
With these figures, a modern A320-sized aircraft with NEO engines will use about 2'000kg of fuel or 24'000kWh per h, which is worth 1280€.
An equivalent electric aircraft will need only 12'000 kWh, which is worth only 840€ at most.
CAVEAT: this consumption figure assumes the propulsive efficiency (2x better than Jet A1 powered) is correct AND there are no side effects like additional weight from the batteries.

All in all, the question about cost competitvity between Jet A1-powered and electric aircraft is impossible to answer at this stage, as there are just too many unknowns for the electric plane:
- Acquisition cost (likely more expensive)
- Weight of batteries (likely heavier. At present, the batteries are too heavy to make a plane with capabilities like A320 even remotely practicable)
- Taxes on fuel in the future (likely)
- Effective propulsive efficiency
- Maintenance (likely less)

Perhaps, for the time being we should consider PTL / E-Fuels?

Hendric
 
tommy1808
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Re: A couple of battery electric aircraft questions. 1 noise, and 1 cost.

Wed Sep 29, 2021 8:36 am

DFW17L wrote:
When someone cracks the energy storage issues (weight, recharge, pollution from manufacturing,…), they’ll be the richest person in the world.


considering it would make TNT look low energy that is only true if it is essentially 100% fail safe.

best regards
Thomas
 
mxaxai
Posts: 2773
Joined: Sat Jun 18, 2016 7:29 am

Re: A couple of battery electric aircraft questions. 1 noise, and 1 cost.

Wed Sep 29, 2021 10:18 am

ZaphodHarkonnen wrote:
Q1: So for the sake of a scenario. Given a B737/A320 size aircraft. If it were powered by electric motors, would we expect the noise levels to be more or less than the equivalent power jet engine?

This question has rattled around in my head as we get closer to having battery electric short haul aircraft. If the noise is extremely low, it makes me wonder if we'd see an increase in demand for inner city airports.

Noise should be less, though not as much as some might hope. The largest advantage of electric aircraft in that regard is that they can use distributed propulsion (i. e. more engines) with little increase in weight and complexity. So more smaller props rather than two super powerful ones, therefore lower tip speed and overall less noise. However, the lack of a duct means that the noise is radiated more uniformly, compared to jet engines where most of the noise is directed to the front and rear.

Same for E-VTOL, most of the noise of a helicopter comes from the spinning blades. A significant noise reduction is only to be expected if the current approach with many smaller rotors is used. The resulting noise is not only less but also higher pitched, which means that it travels less far and doesn't enter people's homes as easily.

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