Hybrid or electric theory?

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Vigilant1

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Dan Thomas

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rv7charlie

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A straight diesel would be more energy efficient if you had a mega clutch to get the train moving.


BJC
I wonder why the designers didn't just use one, instead of adding a huge generator and electric motors...
 

BJC

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My guess is that a clutch and transmission system that would allow maneuvering and starting the train in motion would be much more compkex and expensive to maintain than the electric drive. Note that the electric drive can apply maximum torque at zero RPM.


BJC
 

rv7charlie

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My guess is that a clutch and transmission system that would allow maneuvering and starting the train in motion would be much more compkex and expensive to maintain than the electric drive. Note that the electric drive can apply maximum torque at zero RPM.


BJC
Bingo.
 

Vigilant1

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Barges are draggy things compared to seagoing ships.
True, and they'd surely burn less fuel than a same-size barge for that reason, if they went the same speed. But, in practice, oceangoing ships tend to have a faster speed of advance. Like airplanes, drag goes up a lot with speed. But I'll cede that seagoing ships are, or could be, more fuel efficient than barges.

FWIW, in the US, for a number of reasons (labor costs and regs, regs on where ships must be built, etc, etc), barge transportation (including seagoing coastal barges) is much more cost efficient than using ships (coastal freighters, etc) to move cargo. Any fuel savings is swamped by the higher labor and capital costs of using ships.
 
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rv7charlie

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Thanks for the info on barge efficiency. It's kinda buried in the source I was using for numbers, and I missed it. Having said that, given the substantial resistance of water to objects moving through it, I suspect that the only reason they are more efficient than diesel-electric trains is that they move so slowly (as Vigilant1 said), and they don't have to deal with the energy lost in climbing hills as trains.

BJC,
I was trying to make a joke (apparently a bad one) about how the mission drives what works; hybrid is obviously the most efficient method of long distance rail, and it looks like it could be a good path for cross-country aircraft with VTOL/STOL capability. Certainly less expensive (and simpler/safer) than something like a compound helicopter.

Charlie
 

BBerson

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Diesels are heavy. Not so good for aviation but fine for a train where the weight of the engine is insignificant compared with the 150 loaded rail cars behind. Not sure why trains go diesel/electric instead of diesel/transmission but that doesn't make it useful for aviation.
 

rv7charlie

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I hope you didn't think I was suggesting that we put diesel-electric locomotive powertrains in a/c.

The train example was intended to be one example of situations where hybrid powertrains can be effective, in spite of the thermodynamic efficiency penalties.

Boy; the interwebs are a hard place to communicate...
 

BBerson

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Well, Mac at EAA suggested that diesel/electric trains meant it would also work for aviation years ago.
The word hybrid can go many different ways. So hard to discuss without getting off the track.
 
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berridos

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I am working on a design that is extremly nose heavy and has severe visibility problems. I am really curious how much efficiency would get lost by instaling an internal combustion generator engine in the back of the plane that feeds an electric motor in the nose. i mean for the same kw output, how much additional fuel should i spend in such a configuration? Such an arrangement could be valuable for unconventional designs and specially tailless configurations and would definitly solve my cg and visibility problems.
 

gtae07

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That's about 1/3 g acceleration!
I’m getting .0000874 g, roughly. That’s apparently very roughly about what you’d expect on an asteroid about 1.9 miles in diameter...


Back on topic, the viable near-term use I see for hybrid power in aircraft is applications where you need some multiple of cruise power (big multiples, like 2-3x or more) for very short periods. Think electric VTOL that transitions to wingborne flight for cruise.
 

Highplains

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The current batteries available have incredible power density but poor energy density. You can easily drain a pack in under a minute if desired though limitations exist if you want multiple cycles. While I don’t share the enthusiasm for the Jetsons approach to flying, I do believe hybrids, and a parallel hybrid offers some areas of interest to general aviation.

Since we live in a world where the term Carbon Tax keeps bubbling up, liquid fuels may become quite expensive. The economic impact will be very severe with multiple cascading effects intruding into everyday life.

In terms of efficiency Carson’s rule offers the most range for the least dollars. But it is somewhat incompatible with the systems of the accepted performance travel machine like an RV-7 or 10. Old post war aircraft from the era encompassing the transition from tube and fabric were quite efficient if flown at the right altitudes. It boils down to low average power. Designs today have an over abundance of power, thus they are also able climb well, and reach speeds far above what Carson’s rule would suggest.

In this conventional power system you typically find the engine, variable pitch prop and governor. The only real reason for the variable pitch prop is to unload the engine on the takeoff so you can reach the engines rated power at the upper end of it’s rpm range. A parallel hybrid design can do the same with a simple fixed pitch prop. So we trade some weight and complexity but still climb like hell for a couple of minutes. A further savings of weight is downsizing the engine. Numbers indicate an RV-10 would fly on any of the Lycoming 4 cylinder engines generally available today.

The group that wants to fly on industrial twins could get that extra 10 hp to put a bit of distance to the terra at the end of the runway. Anyway, just some thoughts from an old engineer.
 
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