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Electric / hybrid aircraft propulsion (NOT cars)

And for that to work, they are assuming that they can reduce the overall drag by 20%, increase wing span by 50% to further reduce drag, and reduce the weight of the aircraft by 20%.

For the “baseline aircraft”, they would need, using their own figures, 1,080 Wh/kg. See page 21 – they say 2/3 of the baseline range at 720.

Hardly a like for like comparison.

Biggin Hill

Peter wrote:

because – especially within PPL training – currency on type is really crucial and changing the plane part-way will easily cost you 20 hours.

I’m hardly Super Pilot, but I changed planes twice during PPL. The first change was C150 to C172 at about 3 hrs, then I changed from a C172 to a 200hp Musketeer just before my solo cross countries and it cost me one hour flight time (to get checked out in the Musketeer) and some ground time to read the manual, run some W&B calculations etc. 20 hours would be like starting from scratch again – if it takes 20 hrs to transition from one fixed gear trainer to another then there’s a deficiency in instructional technique, somewhere, especially as most people can go from 0 hrs to solo in less time.

Last Edited by alioth at 03 Sep 16:29
Andreas IOM

Airborne_Again wrote:

Maybe, but not in Europe.

And thanks to who? Before EASA we all had SEL (Single Engine Land) class rating. I had SEL until 2002 or something before it was changed with JAR? There were no different class ratings for piston, TP or jet.

The elephant is the circulation
ENVA ENOP ENMO, Norway

Cobalt wrote:

For the “baseline aircraft”, they would need, using their own figures, 1,080 Wh/kg. See page 21 – they say 2/3 of the baseline range at 720.

Well, two-thirds of the range (i.e. 800 km instead of 1200 km) I think offers a future. Governments are banning automobiles based on fossil fuels in the medium future. The same might happen with aircraft once those guys develop their 750Wh/Kg battery. That will really push development.

… and that was at 720 Wh/kg.

Even that does not stack up – it seems off by a factor of 5.

A simple back of the envelope calculation, based on 12,000 Wh/kg for JET-A and 13,000 for AVGAS

720Wh/kg at 95% efficiency —> 684 Wh/kg output
13,000Wh/kg at 30% efficiency —> 3,900 Wh/kg output (piston)
12,000Wh/kg at 25% efficiency —> 3,000 Wh/kg output (turboprop at 30,000 ft)

Biggin Hill
Administrator
Shoreham EGKA, United Kingdom

At least they are honest about the range, and the likelihood of them being hybrids.

But still – why does nobody use a calculator to check the most basic stuff?

They say they need 5MW to keep one of their 100-seaters flying. That is 6,700 hp, so entirely plausible, an ATR-72, for example, has 5,000 for around 70 passengers,

They also mention a target range of 1,500 miles. So let’s take that at face value. Iooking at the straight wing design, it’s not likely to be at jet speeds, but let’s assume 400kt cruise speed for the moment. So including reserves, that thing needs to have 4 hours endurance, and that is without getting to an alternate.

That is around 20 million Wh. Taking the not-yet-existing 720Wh/kg battery, the battery alone would weigh in at 28 tons, and that is entirely without the structure needed to carry the 28 tons.

For comparison – said ATR72 has an MTOW of 23 tons. Fuel capacity is 5 tons, for a similar range.

Were can I short these BS merchants?

Last Edited by Cobalt at 06 Sep 19:55
Biggin Hill

Peter wrote:

Norway to have electric airliners by 2022.

You should hear what Bjørn Kjos, the CEO of Norwegian Air Shuttle said about those “plans” I think they still got a point though. Just for a moment, disregard those insane claims of range and speed and time frame, it’s pretty much irrelevant in any case. It’s all about the economics of bringing persons from A to B. Airlines benefits larger planes, faster planes, going longer distances. The larger, faster and farther, at least up to some point, the more efficient transportation from A to B gets with today’s technology. Electric planes (whenever they should arrive) will be almost opposite. Short hops with small planes travelling relatively slow. Can this be done cheaper with electric planes? Who knows, but I think to make it efficient and cheap, this will rely on other things much more than the planes (more practical airports, airport closer to towns, more efficient check in and so on).

The elephant is the circulation
ENVA ENOP ENMO, Norway

Cobalt wrote:

That is around 5MW*4hr=20 million Wh

I think that assumes Max. Rated Power throughout the whole flight, ignoring a cruise power setting. The 5MW would only be needed for 5 minutes, after which power is reduced to climb power, after which power is reduced to cruise power, after which power is reduced to descent power, after which power is reduced to idle upon touchdown.

I think too the thinking is flawed because it assumes a current model designed for fossil fuels is a valid approach to electric.

Tesla proved that real success is achieved by building Electric from the start. That’s where the future will lie.

Of course once you change to electric propulsion, an entirely new set of aerodynamics come into play, which will make the aircraft more efficient. And the current generation of aircraft deliberately is burning five times as much fuel as necessary because nobody cares about this sort of stuff. [sarcasm emoji here]

I am just using their own figures. And if they meant take off power and will cruise at 4MW, the twice-as-efficient-as-current-technology-hypothetical-battery will still weigh 22 tons.

There is one fundamental difference in cars: they use a lot less fuel per kg-mile, and hence do not need much fuel for their weight.

For a petrol a car, the fuel load is maybe 2-3% of empty mass (an 80l tank in a 2 ton car is quite usual). For a simple piston tourer, it is around 15% of mass. A TBM, 20%. And for an airliner, it is 20-25% for a mid-range turboprop and 40% for a long range jet.

Last Edited by Cobalt at 07 Sep 10:50
Biggin Hill
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