Siemens electric air plane engine, how does it stack up to Tesla engines? | Hacker News Reader

Siemens electric air plane engine, how does it stack up to Tesla engines?

andreas.heiberg.io

17 pointsAndHeiberg18 comments

Why is this article posted? None of the numbers make sense. Tesla weight 32kg, Tesla Roster [sic] 1235 kg.

Well then...

Yeah my bad, had that thought at 6 in the morning. I've updated it. My central question still stands though. Tesla seems to outperform the Siemens engine by quite a lot, why are did they make such a big splash?

The "BMW 7 Series" motor weights 2.3t? Or if it's not the motor weight but the car weight, a Tesla weights 32kg?

Yes, seems like a very misleading or even outright wrong comparison to me as well. Combustion engines are not much heavier than electric engines if you only count the motor block. And if you look at motorbikes (which have probably the most compact engines) their power/weight ratio should be even higher than that of an electric engine.

That said, the limiting factors in terms of power per unit of weight are probably the conductivity of the wires (as the generated heat must be dealt with) and the magnetic force that acts on the motor during its operation (actio=reaction). In a combustion engine it's probably the ability of the cylinder walls to withstand the explosion pressure.

Concerning high power densities, I'd look at electricity generator turbines as well, as they are basically reverse motors and should have a very efficient power to weight ratio (e.g. several MW for a few tons).

Would be great to see a detailed comparison of these factors, which the article does not provide unfortunately.

And, like other people have already pointed out, what really matters in most circumstances is the combined weight of the motor and the energy source. Here, gasoline unfortunately still beats battery-based energy storage by a large factor.

I think the table mixed motors and cars (first motors then cars), so you have a comparison car power/weight and motor power/weight

Do the 32kg include the inverter and reduction gear? I highly doubt they do. My guess is that with those included it weighs AT LEAST 100kg, probably closer to 200kg. I can't find any details on what Siemens includes in their weight figure. Even if all the numbers are comparable (I'm pretty sure they are not), the Siemens motor (apart from being flight rated) is able to continuously output 260kw, the Tesla motor isn't even close to that. I've personally tried it a few times on the Autobahn and the Tesla limits the output to about 100kw (displayed) after less than a minute of full throttle.

+9001 this!

> My guess is that with those included it weighs AT LEAST 100kg, probably closer to 200kg.

Interesting, that would put the power to weight ratio down to combustion engine levels.

I found this http://www.teslarati.com/tesla-model-s-weight/ that supports your thought by putting it at 150 kg.

> I can't find any details on what Siemens includes in their weight figure

Well they don't have a transmission so that shouldn't be a concern.

> is able to continuously output 260kw, the Tesla motor isn't even close to that. I've personally tried it a few times on the Autobahn and the Tesla limits the output to about 100kw (displayed) after less than a minute of full throttle.

In did try to correct for this sort of thing by picking one of the lower kW ratings for the Tesla. I was not aware it was that drastic. If we account for this the Tesla is almost in Honda accord territory. That's rather disconcerting given Musk citing figures like the ones I outlined. https://youtu.be/PULkWGHeIQQ?t=41m30s

Why are we comparing motors to whole vehicles?

Plus the tesla motor isn't flight rated

See other comments I had it mixed up for sec there.

What's the difference between a flight rated motor and a no flight rated one mechanically? Why is the comparison between Tesla and Siemens engines unfair?

> What's the difference between a flight rated motor and a no flight rated one mechanically?

- A crapton of certification

- Increased reliability

- Some materials may be different for weight purposes

- They also have different power/torque characteristics, also depend on the type of propeller used (is it a constant speed propeller?)

[This](https://forums.teslamotors.com/forum/forums/motor-rpm-155-mp...) does suggest that the RPM of 18.000 is quie different than the 2.500 mentioned for the Siemens.

I do think the figure of 32 kg for the Tesla motor includes the fixed gear though. So I don't so why that would be of any concern.

idk I still don't understand where the unique ability of the Siemens engine is. Obviously not the power to weight ratio. Not certification as it's still in development.

As for materials and power/torque I have no clue.

Surely the problem is not the engine weight but the battery weight.

You could do with mimnimum battery ans send energy to the plane with laser maybe ?

Good joke!

Saving weight anywhere on an airplane is a win. The new engine claims to have more power output than other engines of the same weight.

Yeah exactly, but given the numbers, it doesn't seem to outperform Tesla's engines? Perhaps they're also taking in to account the power usage as battery weight is more significant in planes... idk would love if it someone could help me understand it better though.

don't forget that the power available to the Tesla motors decreases as the battery is used up. Seems odd, but as usable stored power decreases you are not able to pull as much from the battery anymore.

then there is that whole bugaboo of battery weight.

Is this different in the Siemens engine though? Is that why they say "delivers a continuous output of about 260 kilowatts" emphasis added. I guess all that means is that they're really able to deliver more power than advertised on a full charge?

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