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Electric Aircraft Propulsion 1

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Sparweb

Sparweb

Aerospace
May 21, 2003
5,173
I'm seeing more and more of this. The hourly operating costs are appearing to be extremely low. There are plenty of other practical matters, but the hourly fuel cost to operate an aircraft remains one of the major parts of the total operating cost. Reducing it by an order of magnitude opens up margin for "other things" to cost a bit more, if the total is still lower.

My favourite quote:
Roei Ganzarski said:
“This 30-minute flight would have cost us $6 in electricity compared to $300 to $400 in fuel, and the Cessna 182 chase plane was louder than the Caravan".
Click to expand...

Another Cessna, this one a hybrid based on the push-pull Skymaster

And Harbour Air is still making progress:

The Pipistrel has its LSA certificate:

Airbus may have given up (too ambitious?) but many others haven't.

 
yes but in a plane, where is that $6 worth of electricity coming from ? A petrol fed turbine engine ? Sure very small (ie very small payload) planes can be made to work with solar cells.

And I think the propulser (propeller/fan) is responsible for most of the noise. The electric motor driving the propulser may be quieter, but I'd've thought that was a small component for the airplane noise.

another day in paradise, or is paradise one day closer ?
 
Seems to be a bit of hyperbole; 30 minutes of cruise in a Cessna 182 supposedly consumes about 8 gal of fuel, and at 5$/gal that's about $40 worth of fuel.

Conversely, 8 gal of fuel works out to 317 kWh, and assuming 2x better efficiency and 13 cents/kWh, that works out to about $20 of electricity

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
The measure we actually care about is payload per $ of operating cost. Feels abit like the VLJ hype all over again.

“Over the next 12 to 24 months, everyone recognizes that there will be a substantial improvement in the energy density for flight-worthy battery systems,” added Human.
That seems rather optimistic given long term trends.

Lots of interesting design issues relating to battery's (heating, cooling, fire control). Given the inertia relief and anti-flutter mass possibilities of battery's, I can't see a successful retro-fit using stock wings, when you can get a span increase with a reduction in structural weight.
 
hype ? hype, do you say ? … imagine that !

another day in paradise, or is paradise one day closer ?
 
Be careful when estimating electric aircraft performance using regular aircraft as a comparison. For electric your take-off weight is the same as your landing weight. Many large aircraft, especially a 'heavy' may have a max take-off weight that is far greater than the max landing weight. I've seen people quote quick estimates of battery size with maximum takeoff weight numbers used for the comparison.

Also when making comparisons for range. Regular aircraft become more efficient as they burn-off fuel. An electric aircraft is always dealing with the same load.
 
Jeez, 6$ only buys you about 60 kWhr of electricity. That will only get your Tesla to the grocery store and home again.
Gotta check the math myself, now.

The test aircraft in this article ( was a Cessna 208B Caravan whose PT-6A engine rated at 675 HP (504kW) was replaced by a Magni500 rated at 751 hp (560 kW).

Average fuel consumption of a PT-6A engine is about 50US gallons per hour of Jet A, with peak at takeoff probably like 70.
The electric consumption of the MagniX test engine is about 620 kWe at rated power, and they could have run it at 75% power during cruise, like you would do with a fuel engine.

At 6$USD/gallon (purchased BEFORE the economy hiccup) the regular Cessna 208B Caravan would burn about 200-300$ in fuel for a 1-hour flight (agreed some exaggeration there).
At 10 cents/kWhr the modified electric engine would consume (620 * 0.10/hr * 15 minutes) + (465 * 0.10/hr * 45 minutes) = 50 dollars for a 1-hour flight (dammit more exaggeration).

I'm starting to regret starting this thread.

 
GregLocock said:
Plus battery wear and tear.
Click to expand...
Aircraft engines need overhaul just about as regularly as battery packs need changing. The two burdens are comparable.

Comcokid said:
Many large aircraft, especially a 'heavy' may have a max take-off weight that is far greater than the max landing weight. I've seen people quote quick estimates of battery size with maximum takeoff weight numbers used for the comparison.
Click to expand...

Not fair. The large aircraft that have a big difference between MTOW and MLW are much much bigger than a Caravan. In the case of the Cessna 208B, the figures are 8750 lb. takeoff and flight VS. 8500 lb. landing.

What hasn't been publicly discussed in detail, and having a more significant effect on the usefulness of the electric aircraft, will be the proportion of weight dedicated to the batteries VS. the fuel weight eliminated, and the reduction in engine weight replaced with a lighter electric motor. This is still very unclear. The actual engine weight in a certificated aircraft is known to the pound, and it represents a complete engine that ACTUALLY can power the aircraft. Unlike the numbers flung around for electric motors, which ignore the substantial control units, rechargers, voltage converters and cables that constitute a complete system that can actually power the aircraft.


 
Sparweb said:
Average fuel consumption of a PT-6A engine is about 50US gallons per hour of Jet A, with peak at takeoff probably like 70.
The electric consumption of the MagniX test engine is about 620 kWe at rated power, and they could have run it at 75% power during cruise, like you would do with a fuel engine.
Click to expand...

Are you sure that figure is right, for a simple cruise power setting with a SfC =.65 & 75% power I get ~100 US gallons hours an hour.
 
Found a general description...
5.1 hours endurance at Max Cruise power and 7.5 hours at maximum endurance power. 332 Gallon usable fuel tank. 65 GPH and 44 GPH respectively. I was close. Takeoff power would use more.

 
“Over the next 12 to 24 months, everyone recognizes that there will be a substantial improvement in the energy density for flight-worthy battery systems,”
Click to expand...
That seems rather optimistic given long term trends.
Click to expand...

It may depend on that adjective that was used: "flight-worthy". There are a number of Lithium chemistry batteries that are being used as starting and back-up electrical power supply on a number of aircraft, and the list is growing. What they are referring to above is the type that would be suitable for use as a prime-mover supply instead. The solution to that is the solution that Tesla pioneered: PACKAGING.

There are a lot of mass-produced cheap Lithium cells that are easy to wrap in plastic boxes and sell, and they are C-R-A-P for heat loss. And the cylinders waste 20% of the space in a rectangular container. And trying to cool a cylinder inside a square means uneven cooling so it's still not quite a win. The packaging suitable to an aircraft prime-mover battery pack will probably be very different from the "big cube" package of your everyday starter battery.


 
geez, are people seriously thinking of batteries for electric power ?

Consider the electric vehicles we see. They struggle to go 400km on a charge, think of the extra work a plane has to do.

Nah, I'm passing on this koolade.

another day in paradise, or is paradise one day closer ?
 
RB,
Just thinking it through, one step at a time.

The battery pack from Tesla has an energy density of about 100 Whr/Lb in the pack itself. That's without the cooling fluid.
To carry 500kWhr (the flight above) with no reserve you would need:
(500,000 Whr) / (100 Whr / Lb) = 5000 Lb of battery.

The original Caravan could carry 2,200 Lb of fuel (in the wings) and has capacity for only about 1,200 Lb cargo once the fuel tanks are full. Total usable weight would be about 3,400 Lb. Meaning you can only use 340 kWhr for a flight if all fuel and cargo capacity is dedicated entirely to batteries. That would limit a 600HP motor to about 1/2 hour flight. You wouldn't want to operate an aircraft as large as a Caravan, and over 8,000 pounds all-up weight, with less than 500HP.

So that doesn't sound great, for now. How much does it have to improve before the balance turns in favour?

 
The contrast is pretty stark; 5000 lb of fuel has 30 MWhr of energy. Even giving 30% efficiency, that's still 20 times the energy density of batteries. The only downside, of course, is the carbon/pollution footprint and the non-renewable fuel.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
the woefully low energy density of batteries is their problem.

Let's take SW's "Canavan" example. You have to significantly increase the gross weight of the plane to make it battery powered, but you could probably do it for a limited flight duration (a 0.5MWhr energy consumption). Swapping 2200 lbs of fuel (13 MWhr) for 13000 lbs (!!) of batteries to carry 1200 lbs for cargo in an (originally) 8000 lbs plane ?? For 1/2 the range the battery weight reduces to 6500 lbs, which may be tolerable. Perhaps we need energy density of 1000 Whr/lb to start to become an option ? An advantage you'll have is (I suspect) the volume of the batteries is less than the fuel (maybe not) but at least putting more weight in the wings is "good" for structure weight.

For any "reale world" flight you need a gas engine to make the electricity … something I still question but I can see the small opportunity for improved effcicency.

As for the environmental side of the discussion, you have to remember the environmental impact of making the batteries.

another day in paradise, or is paradise one day closer ?
 
Electric is obviously the end goal. So the question is how.
I'm working my day job with a few projects that swing propellers.

But have you all seen the microwave plasma turbine!? THAT. I've been talking about that since before undergrad but nobody even wanted to talk about it.
I mean if you're using plasma, just magnetize the turbine nozzle and maybe the blades. Heat never even touches the blades. Microwave-Air plasma temperatures of 10,000 °F is real. Imagine if I had a TIT of 10k°F

SSTO anyone?






 
And I thought I was going overboard with hyperbole...

The physical density of a Lithium chem battery is about 1500kg/cu.meter (1.5 kg/L) (94 Lb/ft^3)
The physical density of Jet A is 6.75 Lb/USGallon (50.5 Lb/ft^3)

This makes the batteries 2x as dense as liquid fuel, which is good in a vehicle that is limited for space. The original fuel tanks held 332 US Gallons, and a very well packaged Lithium battery might fit 4000 pounds in that space and carry 400 kWhr. That gets you a 1/2 hour flight but still blows your weight budget. Can't carry no cargo or passengers. Placing that much more load into the wings has consequences - in flight it's beneficial but at landing it's a problem. The wings of a Caravan are strut-braced and I wonder if reinforcing those would be enough.

Another thing I wonder about is battery replacement. Here I'm talking about inserting batteries into wings but that's not going to be easy. And as every component of an aircraft needs to be removable for maintenance, that limits the choices for fitting them between ribs and spars and other things.

 
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