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  #11  
Old 01-25-2021, 09:08 AM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
Posts: 1,362
Default My thought process

So by going electric, the battery just stores the energy. The electrons stored in the plane need to be generated somewhere. With batteries, the generation of the energy (electrons) is just moved to a bigger plant that is on the ground somewhere.

But Avgas creates the energy through a chemical process that also uses another chemical readily available, namely oxygen. So only half the constituents needed to create the energy for flight are carried aloft. Since rockets are in the same boat as electric airplanes, they are actually closer cousins in terms of efficiency than gas fueled airplanes.

So the green-ness of electric vehicles come from having the option of generating the electrons off site at various types of powerplants.

I find it interesting that an electric RV will always have the same landing weight as the takeoff weight. This eats into the range since the aircraft doesn't get lighter as it flies along.
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WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

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RV9A- Status:
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  #12  
Old 01-25-2021, 09:39 AM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 181
Default Back to the thread ?

I've thought about this too. The motor isn't a problem, plenty of suitable motors. Also note that you get the same power regardless of altitude. So a lower power motor may be fine. You give up some in take off performance, but have unchanged performance at 10,000 and up.

Batteries - LiIon (ala Tesla) or LiFEPO4? LiIon has better energy per pound but more prone to run-away. One thought I had ... if the battery was at the CG point, could there be a quick release mechanism? If all safety items fail we can just drop the battery pack?

Due to the expense of batteries (currently I'm putting together some off grid packs) of just under $200 per kwh, the packs get really pricey fast. (that is about 1.3 HP for 1 hour) And as others mentioned, not light. That's why things like all-electric motor gliders are practical now. Little power needed due to low speed and hence low drag. The RV9 is likely a better candidate than the RV6. And a Kitfox probably better by far.

There are flexible solar panels... maybe put those on the wings and fuselage? Every bit helps.

I keep leaning back toward a series hybrid. On board engine & generator. But the problem we run into is while this works well for cars, it doesn't fit the model for aircraft. In a car the demand is very peaky with stops and starts. At times of low demand the engine/generator fills up the batteries. Then when you floor it at a green light you for a short time use max power.

An airplane profile (for most of us) is long duration of max cont. power. So then the genset needs to be sized as big as the original Lycoming... or it is just there to delay the exhausting of the battery.

In our use case, nothing prevents us from putting up a few cheap solar panels and using those to charge our hypothetical electric RV directly.
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  #13  
Old 01-25-2021, 10:05 AM
ssokol ssokol is offline
 
Join Date: Jan 2016
Location: Cupertino, California
Posts: 118
Default Fuel Cells?

Apparently we're at about 260 Watt-hours / kilogram (Wh/kg) for current lithium ion technology. Next-generation batteries may take that up to 400 Wh/kg. Things still in the lab (lithium-sulphur, lithium-air) can apparently get into the low 1000s range.

Hydrogen is 33,600 Wh/kg. Even with relatively inefficient fuel cells you get a whole lot more electrons out of a lot less mass.

There are a few production cars running on hydrogen fuel cells. (I actually saw a few when I was in California.) Anyone have any idea how much the fuel cells and storage tanks weigh? Are those capable of producing enough power to run a 120 kW motor?

(Yes, I also picture the Hindenburg - oh the humanity!)
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  #14  
Old 01-25-2021, 10:18 AM
Mike S's Avatar
Mike S Mike S is offline
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,773
Default

Quote:
Originally Posted by ssokol View Post
Anyone have any idea how much the fuel cells and storage tanks weigh? Are those capable of producing enough power to run a 120 kW motor?

(Yes, I also picture the Hindenburg - oh the humanity!)
Sure you can produce enough power to run the motor, question is whether there is an airframe that can carry that weight.

Methinks the RV platform is not going to be the correct one for that use.

As was previously mentioned, battery pack on C/G for safety dump of the flaming mass----this would also allow for swapping a flat battery pack for a charged one. Now you need to create a network of battery exchange facilities at airports around the country. And, only one or two standard battery packs----think avgas or Jet A.


The lift distribution of a canard platform might be something to look at here.
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  #15  
Old 01-25-2021, 10:45 AM
gap gap is offline
 
Join Date: Oct 2019
Location: Alpharetta
Posts: 19
Default

I'm sure there's someone looking for investors for a all-electric self-piloting flying car project.

Get out your checkbook.
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  #16  
Old 01-25-2021, 10:45 AM
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Bill Boyd Bill Boyd is offline
 
Join Date: Sep 2006
Location: Landing field "12VA"
Posts: 1,634
Default

It's all fun and games until somebody on a school playground catches a flaming battery pack.
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  #17  
Old 01-25-2021, 10:52 AM
rocketman1988 rocketman1988 is offline
 
Join Date: Jun 2010
Location: Sunman, IN
Posts: 2,397
Default Or

...or a traditional IC aircraft crashes into a house...oh, wait, that has happened...
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  #18  
Old 01-25-2021, 11:19 AM
Northernliving Northernliving is offline
 
Join Date: May 2005
Location: Boston, MA
Posts: 507
Default

Battery technology will have to radically change/improve for this to be any thing more than an interesting science fair project. 100LL has over 100 times the power density of current lithium-ion batteries. When we get a step function change in battery tech, we will all be flying electric.
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  #19  
Old 01-25-2021, 11:42 AM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 1,248
Default

The year is 2029, Oshkosh Airventure has drawn 1000 EV aircraft. Imagine the lineups for the 50 recharge stations?

Reminds me of only a few years ago when there were a hand full of electrical outlets in all the camping areas and all those iphones to charge.
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Last edited by Ralph Inkster : 01-25-2021 at 11:45 AM.
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  #20  
Old 01-25-2021, 11:48 AM
terrye terrye is offline
 
Join Date: Feb 2010
Location: Vancouver, BC, Canada
Posts: 929
Default EV-6A: A Thought Experiment

Does anyone remember the CAFE/NASA Green Flight Challenge of 2011? It was won by the Pipestral Taurus G4. All electric, 4 passenger. As a comparison, the fuel weight of my RV is 32 gal x 6 lb/gal = 192 lb. This is 9% of the gross weight of 1750 lb. In contrast the battery weight of the Pipestral Taurus G4 was equal to the airframe weight and 30% of the gross weight (batteries ~500 kg, airframe less batteries ~500 kg, gross weight 1500 kg). Has battery technology developed substantially since 2011?

Nearly in my back yard, the electroBeaver flew over a year ago to great fanfare and media coverage. Only flown a few times since. I had heard the payload was one person (the pilot).

Excellent paper by the design team of the Pipestral Taurus G4
https://www.sv-jme.eu/article/pipist...hallenge-2011/

Click on the black PDF button to download a copy.
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Last edited by terrye : 01-25-2021 at 05:37 PM.
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