Comment by krasin | Hacker News Reader

Comment by krasin | Hacker News Reader

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Let's consider Cessna-172S ([4]). Its characteristics:

- 130 kW engine, Lycoming_O-360 that weighs 117 kg. For comparison, an electric motor of this range would weigh 11-13 kg (at 10-12 kW/kg, [2]). That saves 100+ kg weight immediately and we can put 50+ kWh batteries instead.

- It carries up to 200 liters of kerosene ([3]), which weighs 164 kg. We can place 82 kWh of batteries instead.

- The engine consumes around 30 liters/hour ([1]), which gives us ~6.7 hours of flight time or the equivalent of 6.7*130=871 kWh for an electric-power plane.

- The fuel tank weighs about ~14 kg (source: an LLM, sorry) and gives us another 7 kWh.

So, we can put 50+82+7=139 kWh. By using modern materials, we can probably increase it to ~180 kWh, which will give us about 1.5 hours of flight time / 300 km range. This is much less than 6.7 hours, but quite practical for recreation and short flights. And it would be much cheaper to run too.

That said, still not practical for medium and long flights.

1. https://en.wikipedia.org/wiki/Lycoming_O-360

2. https://cleantechnica.com/2021/03/25/groundbreaking-h3x-moto...

3. https://www.globalair.com/aircraft-for-sale/specifications?s...

4. https://en.wikipedia.org/wiki/Cessna_172

The airplane would be a bit heavier at landing, though. I expect that will require a somewhat heavier landing gear.

I also think taking out the weight of the tank is unfair if you don’t add weight for the structures for holding the batteries.

But yes, for many smaller planes, we’re close to flying electric on shorter flights being economically feasible.

Fair points.

But the point that CATL makes with this announce is that before this capacity boost, electric planes were a complete joke. Now, they are only somewhat funny.

What I am more excited about is that electrically pumped rockets are now a lot more practical. As an example, Electron is such a rocket ([1]). It can now reduce the weight of the battery pack and increase payload.

1. https://en.wikipedia.org/wiki/Rutherford_(rocket_engine)

> before this capacity boost, electric planes were a complete joke. Now, they are only somewhat funny.

Ha! Well put.

Maybe dropping battery just before landing could be a thing - on a small parachute or some catch ground in front of landing strip.

Silly as it sounds just thinking :)

Sounds about as realistic as shooting nuclear waste into space.

Nuclear waste can be stored on the Moon. Just be careful that it doesn't overheat and turn into a giant rocket, propelling the Moon out of the solar system.

I have an imagined invention where battery packs drop off an electric jet as it cruises and they glide to a landing somewhere when they are out of power.

The maximum take off and landing weights for a Cessna 172 are the same, so I don't think a heavier landing gear would be required.

Harbour Air successfully tested electric plane based on De Havilland Beaver. This is still a super short distance but I think the longest route Harbour air has is Vancouver <-> Seattle and it's a 55 minute flight.

Whistler Victoria is about that long too

The point not considered is the Cessna 172 is an extraordinarily draggy airframe - it didn't need to be clean and laminar because fuel was (relatively) cheap.

Electric aircraft of the future will have half the drag or less. High aspect ratios, flush fairings, streamlined cockpits etc.

> quite practical for recreation and short flights

Perfectly agree with everything, but 1.5hr may be very short if you need to have 30 minutes of reserve at landing. On the saving side, you don’t have to have an alternator to transform ICE energy into energy for the dashboard instruments. On the downside, you now need to heat the cabin manually, rather than reusing the ICE heat.

> you now need to heat the cabin manually, rather than reusing the ICE heat.

Interestingly, the Boeing 787 has already dispensed with bleed air. It uses compressors for heat and electric pumps for hydraulics.

That's probably less of an efficiency concern, but more likely to avoid future legal cost for supplying contaminated air to the cabin.

https://en.m.wikipedia.org/wiki/Aerotoxic_syndrome

No alternator, but some dc-dc to get the voltage of the main battery down to 14/28 V for the avionics, lights, etc.

> On the downside, you now need to heat the cabin manually, rather than reusing the ICE heat.

Most modern airliners do not use bleed air for climate control in the cabin anymore.

The electric motor is not 100% efficient so some heat must be available for cabin. Large synchronous generators are 97% efficient not sure about 100 kw e vehicle Motors

The power requirement at cruising speed would quite a lot less than max power would it not? If cruse consumed 60% of max you'd be using closer to 80kW which would give you over 2 hours flight time.

For a direct conversion you could just look at the Alpha Electro

https://en.wikipedia.org/wiki/Pipistrel_Alpha_Trainer#Alpha_...

324 nmi range for the regular variant. Around 65 nmi for the electric version.

This is with older batteries, probably with very bad pack-level energy density. The battery pack can even be swapped. Great to avoid having to wait for charging, but probably terrible for weight.

If you design the aircraft for electric flight from the ground up (see Maxwell X-57 for how you could do that), with a structural battery pack, and with 300-500wh/kg batteries, I'm willing to bet a 2-5 times increase in range is viable.

Could you run a big power rail along the runways for delivering takeoff power?

A lot of people won't fully fuel up their 172 so they can bring more weight, either baggage or passengers. I don't think anyone would fly 6.5 hours in one either, but 2+ is normal for non-training flights.

A combustion engine itself has a lot more weight than an electric motor too.

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