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Comment by berti | Hacker News Reader

Electric plant is also stressed by higher loads (thermal mainly, which has a number of downstream effects), and cyclic thermal stress would lead to cycle limits just the same. You also still have a lot of mechanical components just the same as combustion engines.

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> You also still have a lot of mechanical components just the same as combustion engines.

This certainly wasn't true for cars, a fully electric vehicle is simpler, resulting in an immediately noticeable reduction in maintenance overhead - are you sure it will be different for aeroplanes?

Keep in mind that the combustion engine of a propeller aeroplane will have an entire electrical system as part of the combustion engine because it turns out even most private pilots are not inclined to get out and start the propeller by hand ever time.

I think, if I'm conceiving of this properly in my head, that electrically powered props would alleviate the need for variable pitch propellers; a complicated affair involving oil pressure and governors. Since the torque curve of an electric motor is flat I don't think it'd be needed. Although a feathering system may still be required to twin engine electric planes.

You'd still need it for reverse.

Very view piston powered planes have reverse as it stands. But wouldn't running the prop backwards work?

There would still be benefits to variable pitch propellers with an electric motor (motor efficiency, correct propeller pitch for the airspeed to name two).

I work in the UAV industry and would adopt variable pitch in an instant if it didn't come with complexity and weight penalties!

Interesting. I've always thought of variable pitch propellers as being more efficient by allowing the engine to stay at it's peak horse power. For a piston engine this is obviously at the peak of the nice curve you'll see on any dyno run. A fixed pitch propeller sized for climb would allow the engine to run above this speed in cruise and vise-versa if it were pitched for cruise.

Now an electric motor has maximum torque at 0rpm (stalled) and practically no torque at it's no load speed. The relationship in-between is practically linear. So long as the motor was matched and / or geared so that during all stages of flight the RPM stayed within a reasonable band I don't see what the advantage is. Maybe some second order effects of efficiency at lower speeds perhaps.

Edit: Actually, thinking again, it's the exact same reason that cruising at the lowest possible RPM for the required power output in a piston engine is typically the most efficient. Just less friction. Still think it'd be a smaller effect given we're talking roller bearings rather than plain bearings and piston rings.

Even if you disregard motor efficiency (which I don't, as with a battery powered vehicle you treasure every Wh more than you treasure every gram of fuel!), propeller efficiency is also important. Ideally you want to match your motors power handling and efficiency with your propeller. A given propeller/motor combination will have a design point in terms of torque/airspeed/rpm, and operating significantly outside of that (e.g. having a power system designed for cruise but operating at zero airspeed) has penalties.

Unfortunately I'm traveling at the moment, but I spend a large amount of my time at work balancing propellers and motors and could provide some plots that might help explain this. One of the few things years of working in academia proved to me, is that I'm terrible at explaining things like this!

Tesla maintenance is more expensive than regular combustion engined cars.

EDIT: Yes, I was surprised as well. IIRC the service plan for a new car was more than a thousand euros per year. Considering they don't do oil changes or many other things, that is a lot.

Anyway, maybe not much for someone who spends 70 000 euros on a new car, but it's something that does not further the argument of economics.

Thermal stress on a coil of copper wire must have less of an effect than on a piston engine where wear occurs dramatically faster when cold. Obviously the rest of the airframe would be more-or-less the same but electric motors (especially when running off VSDs) don't really suffer per start the way ICUs do.

It's not so much the copper itself, but the surrounding components, especially insulation.

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