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DJL

Electric Aircraft - The Thread

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On 10/1/2019 at 8:22 AM, DJL said:

Share it.  This post is for learning about these developing methods.  For us that birdy needs to turn so that's what I'm most interested in.  For basic airline usage they may be able to afford a 30 minute to hour long sit on the ramp but we can't.

Tesla batteries are lasting about 200,000 miles with frequent fast charging.  That's about 3500 hours of operation.  (For comparison, Lycoming recommends engine rebuilds after 2000 hours.)  So it will be a tradeoff between recharge speed and lifetime.

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8 minutes ago, billvon said:

Tesla batteries are lasting about 200,000 miles with frequent fast charging.  That's about 3500 hours of operation.  (For comparison, Lycoming recommends engine rebuilds after 2000 hours.)  So it will be a tradeoff between recharge speed and lifetime.

I guess it'll matter what's required to maintain flight plus 30min?  80% charge time is about 40 min from zero so that seems better than I thought.

 

And in latest news.  NASA and GE work to make an inverter better suited to commercial flight.

https://www.zdnet.com/article/ge-nasa-partner-to-advance-the-future-of-electric-flight/

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12 minutes ago, DJL said:

I guess it'll matter what's required to maintain flight plus 30min?

Well a typical 206 engine is rated (sea level max) at about 220kW, so 130kW at 12,500.  So average 175kW to match the performance of a C206, which means about 90kwhr for the climb.  Add 10kwhr for a 30min reserve (that's OK to rate at best-economy speed) and you're at 100kwhr per load.  That's one Tesla battery, so you'd probably be looking at an actual design of two of them (for redundancy and reduction in charge time.)

Fastest current chargers charge at about 3C, so to get 100kwhr into a 200kwhr battery at 3C will take just under 10 minutes.

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1 hour ago, billvon said:

Well a typical 206 engine is rated (sea level max) at about 220kW, so 130kW at 12,500.  So average 175kW to match the performance of a C206, which means about 90kwhr for the climb.  Add 10kwhr for a 30min reserve (that's OK to rate at best-economy speed) and you're at 100kwhr per load.  That's one Tesla battery, so you'd probably be looking at an actual design of two of them (for redundancy and reduction in charge time.)

Fastest current chargers charge at about 3C, so to get 100kwhr into a 200kwhr battery at 3C will take just under 10 minutes.

Then it's just a question of whether it's better for the batteries to "top off" while boarding or charge the full cycle.

OK, someone go buy one of these C206's and all the necessary electrical infrastructure and let's see how it goes!

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44 minutes ago, DJL said:

Then it's just a question of whether it's better for the batteries to "top off" while boarding or charge the full cycle.

OK, someone go buy one of these C206's and all the necessary electrical infrastructure and let's see how it goes!

"Topping off" takes longer so they will likely avoid that.

I don't know of any civilian skydiving operation that buys new airplanes for jumpers.  (Ray Ferrell's PAC may be an exception here.)  Given that, it's going to be a while before such aircraft are available to skydivers.

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(edited)
1 hour ago, DJL said:

OK, someone go buy one of these C206's and all the necessary electrical infrastructure and let's see how it goes!

There is no C206 electric conversion program. There is work ongoing on a DHC-2 de Havilland Beaver conversion. Both C-208s and C-206s are regularly fitted with a cargo pod under the fuselage. I could easily image a swapable battery being fitted into that space.

Edited by gowlerk

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15 hours ago, gowlerk said:

There is no C206 electric conversion program. There is work ongoing on a DHC-2 de Havilland Beaver conversion. Both C-208s and C-206s are regularly fitted with a cargo pod under the fuselage. I could easily image a swapable battery being fitted into that space.

That's right.  They were testing an engine on a 208 test frame.

https://www.flyer.co.uk/magnix-tests-new-electric-motor-on-cessna-ironbird/

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Looks like it took off from the Flying Beaver Restaurant at dawn on Tuesday, 2019 December 10.

The Flying Beaver Restaurant is on the South Fork of the Fraser River where it passes Sea Island and Vancouver International Airport. That dock is where you can board floatplane flights to Victoria, Seattle, Nanaimo and Vancouver's Inner Harbour.

Great hamburgers too!

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It is still useless for skydiving and it is going to remain such for a long time. As previously mentioned, you would need a 100kWh battery pack to get a load with a 206 up. The most advanced battery pack on the market currently (the one found in Tesla M3) weighs 168 Wh/kg. So a 100kWh battery pack weighs about 600kg. The one that would be made specifically for a plane wouldn't have such density, but lets ignore that.

A C206 has a max payload of around 650kg.

You will get some weight saving with the engine which is only 72kg as opposed to the 220kg of the IO520.

So with the engine weight saving you would get around 200kg of usable payload. So a pilot and 2 very light skydivers.

The Caravan would get you slightly better results, but still unusable for a real operation. The are mentioning 105 miles of range - yeah, but at a very low power setting, in cruise.

 

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7 hours ago, coticj said:

It is still useless for skydiving and it is going to remain such for a long time. As previously mentioned, you would need a 100kWh battery pack to get a load with a 206 up. The most advanced battery pack on the market currently (the one found in Tesla M3) weighs 168 Wh/kg. So a 100kWh battery pack weighs about 600kg. The one that would be made specifically for a plane wouldn't have such density, but lets ignore that.

From the article, doesn't seem like they're using standard production batteries for their test flights.  Perhaps this will help to push the "NASA Batteries" into production use.  Even if the ROI is similar to turbines you have to imagine the short haul market would see the value and help develop it.

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8 hours ago, coticj said:

It is still useless for skydiving and it is going to remain such for a long time. As previously mentioned, you would need a 100kWh battery pack to get a load with a 206 up. The most advanced battery pack on the market currently (the one found in Tesla M3) weighs 168 Wh/kg. So a 100kWh battery pack weighs about 600kg. The one that would be made specifically for a plane wouldn't have such density, but lets ignore that.

A C206 has a max payload of around 650kg.

You will get some weight saving with the engine which is only 72kg as opposed to the 220kg of the IO520.

So with the engine weight saving you would get around 200kg of usable payload. So a pilot and 2 very light skydivers.

The Caravan would get you slightly better results, but still unusable for a real operation. The are mentioning 105 miles of range - yeah, but at a very low power setting, in cruise.

 

I would very much like to know where you get fuel that weighs 0kg...now that would be a bigger game-changer than electric :P

In any case, here are the official weights from the Cessna website for the Turbo Stationair HD Cargo:

Maximum Ramp Weight     3,806 lb (1,726 kg)
Maximum Takeoff Weight     3,789 lb (1,719 kg)
Maximum Landing Weight     3,600 lb (1,633 kg)
Usable Fuel Weight     522 lb (237 kg)
Usable Fuel Volume     87 gal (329 l)
Basic Empty Weight     2,212 lb (1,003 kg)
Useful Load     1,594 lb (723 kg)
Maximum Payload     1,388 lb (630 kg)
Full Fuel Payload     1,072 lb (486 kg)

You won't really lose that much payload with electric, and they're just getting started :)

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3 minutes ago, aonsquared said:

I would very much like to know where you get fuel that weighs 0kg...now that would be a bigger game-changer than electric :P

You must not be aware of the Helium Blend now available in limited markets.

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7 hours ago, aonsquared said:

I would very much like to know where you get fuel that weighs 0kg...now that would be a bigger game-changer than electric :P

In any case, here are the official weights from the Cessna website for the Turbo Stationair HD Cargo:

Maximum Ramp Weight     3,806 lb (1,726 kg)
Maximum Takeoff Weight     3,789 lb (1,719 kg)
Maximum Landing Weight     3,600 lb (1,633 kg)
Usable Fuel Weight     522 lb (237 kg)
Usable Fuel Volume     87 gal (329 l)
Basic Empty Weight     2,212 lb (1,003 kg)
Useful Load     1,594 lb (723 kg)
Maximum Payload     1,388 lb (630 kg)
Full Fuel Payload     1,072 lb (486 kg)

You won't really lose that much payload with electric, and they're just getting started :)

Why does the fuel weight really matter? Based on the data you gave the numbers aren't that much different.

Empty plane 1003kg, max landing weight 1633. You then have 630kg available. When you calculate the engine weight saving you have extra 148kg available. This means total 778kg.

Batteries weigh 600kg, so that gives you 178kg available for passengers and pilot.

"NASA batteries" isn't really a thing yet and it is not going to be for a few decades, and when it comes it is going to be super expensive.

Even if they are not using standard production batteries they are not getting much better energy density the Tesla packs have.

 

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2 hours ago, coticj said:

Why does the fuel weight really matter? Based on the data you gave the numbers aren't that much different.

Empty plane 1003kg, max landing weight 1633. You then have 630kg available. When you calculate the engine weight saving you have extra 148kg available. This means total 778kg.

Batteries weigh 600kg, so that gives you 178kg available for passengers and pilot.

"NASA batteries" isn't really a thing yet and it is not going to be for a few decades, and when it comes it is going to be super expensive.

Even if they are not using standard production batteries they are not getting much better energy density the Tesla packs have.

 

Something must be getting mixed up I think in the comparison, if those beavers on floats are going to be doing commercial service, they gotta be taking up the same or near the same number of passengers, don’t you think? 

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Well the longest flight they did was 3min. And for passenger service you don't need constant full power, like you do for skydiving.

You can check the data avaliable for Pipistrel Alpha Electro: https://www.pipistrel-usa.com/alpha-electro/#technical_data

And then get a sense of what they are getting - but basically they have a 22 kWh battery pack + a 60kW motor and mentioning up to 1h endurance. Then when you read into it, they say up to 45min minutes with cruise at 18kW power.

And the same is with the Beaver.

Edited by coticj

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On 12/10/2019 at 10:48 PM, coticj said:

It is still useless for skydiving and it is going to remain such for a long time. As previously mentioned, you would need a 100kWh battery pack to get a load with a 206 up. The most advanced battery pack on the market currently (the one found in Tesla M3) weighs 168 Wh/kg. So a 100kWh battery pack weighs about 600kg. The one that would be made specifically for a plane wouldn't have such density, but lets ignore that.

A C206 has a max payload of around 650kg.

You will get some weight saving with the engine which is only 72kg as opposed to the 220kg of the IO520.

So with the engine weight saving you would get around 200kg of usable payload. So a pilot and 2 very light skydivers.

The Caravan would get you slightly better results, but still unusable for a real operation. The are mentioning 105 miles of range - yeah, but at a very low power setting, in cruise.

 

Let's see - 

A single battery module from a Model S gives you 5300 watt-hours and weighs 55 lbs.  That's an energy density of 212 wh/kg.  So using them, your battery now weighs 471kg, and your useful load is now ~400kg.  (I also subtracted fuel.)  That's a pilot and 3 jumpers; with standard skydiver weight and balance math it's 4 jumpers.

And that's using a car battery.  An aviation battery is going to be a lot lighter.

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(edited)

(This is my first post since the new forum software.)

I watched Tesla battery day on video.   Even the battery critic gave the new battery design an A+

I wonder if the brand new Tesla 4680 batteries change the ballgame.   Reportedly, they started an assembly line that continuously moves and can manufacture these 20 gigawatt hours of batteries per year in one-seventh the size of factory space.  Just ONE serial assembly line, nothing parallell to it.  Looked like soda bottle manufacturing in a high-speed assembly line!   They could easily scale up to terawatts-hours per year in a decade with what I've seen.

They are planning lithium battery prices planned to fall to $62 per kilowatt-hour by 2030, and about $30 per kilowatts-hours by ~2040.  Even with the extra cost of battery packaging and integration, I would not be surprised that it will become sufficiently affordable enough, that at least one or two skydiving dropzones converts an old Caravan to battery during an ordinary engine overhaul.  Using, say, a FAA-approved Magnix-like overhaul and go through the right regulatory hoops, and it becomes cheaper than a turbine overhaul in about 10 years.  No new airframe needed!

The copper-ends of a 4680 apparently simplifies cooling, since 70% of the heat occurs at the end, allowing a simpler heatsink cooling plate approach (airframe can act as heatsink).  They were able to fit 130-kWh of batteries in the same space & weight as 74 kWh, despite only being 5/6ths smaller, because of the way battery cooling was massively simplified, and that the batteries themselves became structural elements of the new Tesla battery pack.

The batteries recharge faster.  According to my horsepower math (wattage, weight, etc) and the charging speed of the new Tesla 4680 batteries -- there is apparently enough charge speed for 15-minute full power 1 extra skydiving flight after a 15-minute fast recharge (megawatts-scale recharging).  So you could just tolerate and pad the schedule for slower boardings, in order to reap the cost savings.   Even aviation fuel powered often loiter that long waiting for stragglers anyway and tandems to get ready on a semi-slow day anyway.  You'd cycle less often, but you'd cycle much more cheaply, with a fraction of the maintenance cost and fuel cost.    And this is just a shallow cycling (30% to 80% recharge), which is now more than needed for a 13500 feet skydive, given a sufficiently sized battery (at projected circa-2030 capacity).

It might not be till approximately 2030-2040 before this happens, and regulatory makes it easier to do electric-conversions, but it's now within realm of possibility. 

The electric Caravans jump planes of the 2030s may carry 2 or 3 or 4 less skydivers, but at much cheaper than petroleum and much cheaper maintenance -- the DZO economics of a profitable $10-to-$15 funjumper jump ticket is quite tempting even if the Caravan capacity is slightly less (10 passengers or 5 tandems).   Get an extra jump plane instead to make up the capacity shortfall; the savings actually more than pays the salaries of extra pilots.    

The battery of the prototype electric caravans outputs more horsepower, than the turbine motor it replaced; so that compensates quite a bit for reduced capacity -- it can then thus safely haul more weight (its battery) off the runway, reducing the scale of loss of passengers to just a few percent of the plane's passenger capacity. 

And still be able to zoom up to jump altitude like a turbine at full throttle while still only eating under 50% battery charge (which can now be recharged in 12 to 15 minutes) -- whee!   Shallow cycling can be done 10,000 times, since it's the below-30% and above-80% charges that is the most damaging to a lithium battery (1000 full-charges instead of 10,000 half-charges or maybe 50,000 quarter-charges -- it scales somewhat geometrically to an extent, depending on the specific lithium chemistry).   So replacements are rare if you size for shallow cycling, that's how gridscale lithium batteries are designed to last for a couple decades.

Who cares if you gobble 25%-to-50% of battery per skydive, if you can recharge for the next flight in just 12 to 15 minutes (to add back 25%-to-50% capacity) with electricity much cheaper than aviation fuel?  More than enough cost savings and profit to tolerate the longer pauses between flights.

Mind you, the huge price drops of lithium batteries has been rather jawdropping.

I now view electric jump plane conversions economically price-realistic by ~2030-2035 since cost projections suggest potential increases DZO profits / reduces jump ticket prices sufficiently enough to have far quicker ROI than a turbine conversion.   

Give it a decade.  It'll happen to at least a few dropzones after year 2030.

Edited by mdrejhon

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(edited)
25 minutes ago, mdrejhon said:

the batteries themselves became structural elements of the new Tesla battery pack.

If the batteries themselves really could take shear stress, my first question is, "how much?" and this holds the potential to reduce the weight of the wing structure, since you'll be able to reduce or even remove the wing ribs completely. If you reduce the weight, you increase payload/range. This will have to be a new-design electric for certification though.

Wings usually need stiffening against shear stress (caused by bending) because they contain materials with zero shear stiffness.

Edited by olofscience

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