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Old 12-14-2020, 06:46 AM
BillL's Avatar
BillL BillL is offline
Join Date: Sep 2007
Location: Central IL
Posts: 6,906

The electric motors in a Tesla are constant torque up to rated speed. It will make 200 HP at about 3500 RPM for the rear S motor. Google Tesla motor torque curve. Just announced the new battery - check the stock price increase. They have a nice video on the technology. Claims full charge in 15 min , 50% increase in energy density.

240 lbs of fuel takes an RV7 700nm, but even the solid state battery won't do that.

If at altitude and the battery goes flat point the nose down and recharge, some anyway. Or set a neutral torque speed and glide with no prop drag.

By then it will auto land anyway. No worries.

Maybe, since the motor speeds are up to 15-18k then it would be best for a nice ducted fan, like the Sonex jet. That could be real fun to blast up to 25,000ft and coast for a while. 350HP zoooooom.

If I was wishing for something more attainable it would be a liquid cooled reciprocating engine, gasoline direct injection (500 bar), turbocharged/compounded (with electric spool), 11-13 Cr, and operate on mogas with half the fuel burn of todays engines (50% OTE), and twice the life. Oh - same or better power/weight ratio. Likely a steel piston. Electric compound allows electric air-conditioning. Maybe the FAA would underwrite funding for a common core development just to get rid of lead. But this is off topic. :-(

Last edited by BillL : 12-14-2020 at 07:17 AM.
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Old 12-14-2020, 09:40 AM
andrewtac andrewtac is offline
Join Date: May 2014
Location: Friendswood TX
Posts: 318

When you scale up RC planes to something we fit in, all things do not scale up. Otherwise we'd have an IC engine that would allow me climb straight up and hover with the prop size I have now. I don't think RC airplanes are indicators as much as we might like.
Mark Andrew Tacquard

RV8 N189DK
RV10 in progress
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Old 12-14-2020, 09:43 AM
bkervaski's Avatar
bkervaski bkervaski is offline
Join Date: Mar 2017
Location: Birmingham, Alabama
Posts: 1,984

Really, the problem comes down to just charging. All the other stuff is mostly figured out. The only reason Tesla's make sense is that they are super easy and really fast to charge while on trips due to Tesla's "Supercharger" network. The charging at home (or in the hangar) is easy, it's the trips that are the problem.
N196 RV-14A #140376 (Selling) 2019 Bronze Lindy
N169 Carbon Cub EX-3 (Finishing)
N15Z RV-15 (Waiting ... impatiently)
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Old 12-14-2020, 09:53 AM
andrewtac andrewtac is offline
Join Date: May 2014
Location: Friendswood TX
Posts: 318

The solid state stuff looks promising, but still needs to be scaled up. I think the energy density problem still exist, as far as keeping range close. But again the solid state stuff might work for that as well.
Mark Andrew Tacquard

RV8 N189DK
RV10 in progress
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Old 12-14-2020, 10:16 AM
rockwoodrv9 rockwoodrv9 is offline
Join Date: Dec 2011
Location: Meridian ID, Aspen CO, Okemos MI
Posts: 3,266

The charging availability could be worked out pretty easy in many of the mid size airports. We put them in at all of our apartments and most of our developments. They are not that expensive and we use a credit card and app to bill for the charge. Just because they are not expensive to install, they will not pay for themselves from charge revenue. We consider it an amenity for our residents or tenants so the cost is absorbed into rent.

If you could set them up close to car parking they could be used for both. Maybe it could become a draw for restaurant. They could get listed on the charging station app and maybe get people traveling to stop by, charge, and get a hamburger.

But, until there are elect planes flying around, not much upside to having charging stations.
Williamston MI
O-320 D2A
Flying N376E
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Old 12-14-2020, 10:18 AM
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RV7Guy RV7Guy is offline
Join Date: Jan 2005
Location: Chandler, AZ
Posts: 3,098
Default Interesting

I have a Tesla Model 3. (FYI, that's as Green as I get. I'm a Ford guy. I got it for my 106 mi RT drive for work). The car absolutely hauls A$$. But it is just loping along at highway speeds. Battery consumption is spot on. Absolutely the finest car I've ever owned. I'm old so I've had a bunch!!!

Now for planes, the batteries are very heavy. The CG would be a major problem and, as has been mentioned, where ya going to charge it!! My 220 home charger charges at a rate of 40 mph. I have seen Super Chargers hit 500 mph charge rate. My home charger costs about $10 a month to operate.

Electric is coming for sure. The entire practicality comes from addressing the above listed issues. When it happens it will be great. Think about it, you'll likely be able to get a power package for $20K or so with unlimited fuel!!
Darwin N. Barrie
Chandler AZ
RV-7 N717AZ Painted and Complete
2021 Outstanding Workmanship Sun N' Fun
2021 Gold Lindy Grand Champion Kit Plane
2022 Copperstate Fly in Grand Champion/Best Metal
2022 Reserve Grand Champion Sun N' Fun
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Old 12-14-2020, 10:41 AM
sailvi767 sailvi767 is offline
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,527

Originally Posted by bkervaski View Post
Really, the problem comes down to just charging. All the other stuff is mostly figured out. The only reason Tesla's make sense is that they are super easy and really fast to charge while on trips due to Tesla's "Supercharger" network. The charging at home (or in the hangar) is easy, it's the trips that are the problem.
I wish I could find a copy of the one article on electric aircraft power. It was really good. The current Tesla batteries would have to weigh somewhere in the 4000 lb range to provide 3 hour flight time at 150 HP and 70F temps assuming you donít heat the aircraft. In 10 to 15 years they might get that down to 1500 lbs. it could take a lot longer. The batteries also have to be conditioned meaning you need a cooling and heating system for the battery pack to get optimum output and input and that adds significant additional weight. They hate cold and range is dramatically reduced with cold temps. The current Teslaís see a 30% loss of range at 20F temps with a heated pack. Tesla recommends that you keep the batteries between 10 and 90% charge or battery life will be impacted further reducing range. Supercharging again reduces the life of the battery. Tesla almost always makes supercharging claims for adding a specific amount of miles not to full charge. This is because the last 20% of charge takes far longer than the middle 50%. I am 62 and donít expect to live long enough for meaningful cross country light aircraft to become battery powered. One last point is cost. Tesla is very closed mouth on battery costs but the current 75KW battery in the 3 and Y models is about 150.00 per kilowatt. The needed 300 KW pack will be 45,000 at todayís rates plus the cost of the conditioning and BMS system plus profit margin for sales. I am guessing 60-70,000 per pack to the consumer. Tesla has stated they think the can produce batteries at 100.00 per kilowatt in 3 years. That is however the actual cost to produce not market price.
RV-6 sold
F-1 Rocket
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Old 12-14-2020, 11:00 AM
molson309 molson309 is offline
Join Date: Jul 2009
Location: Longmont, CO
Posts: 255

Flying around with that much energy able to release in a short period of time (think either thermal runaway or catastrophic failure in a crash) gives me pause. Gasoline is energy dense, but it requires oxygen to release energy. Batteries do not...
Mark Olson
RV-7A First flight 2005 Sold 2019
F1-EVO Rocket First flight 2010
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Old 12-14-2020, 11:05 AM
AlpineYoda AlpineYoda is offline
Join Date: Nov 2019
Location: Boulder, CO
Posts: 418

Everyone has about 15 years to work this out. I received word last week that Lycoming has started building my engine.

2,000 hours down the road, I see myself at overhaul time replacing the engine and the gas tanks with a motor and batteries.

So, figure first flight late 2021. 100-200 hours a year.... By 2035 I trust that someone will have worked all of this out and I can make a simple swap.

8%-10% improvement in energy density per year means about a 300%-400% aggregate increase by then. Which is plenty for my needs, thanks!
RV-10 build blog --
Started 12/19/2019
Engine hung 1/9/2021
Hoping to fly in August 2022

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Donated Jan 4 for 2022
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Old 12-14-2020, 11:29 AM
Cumulo Cumulo is offline
Join Date: Apr 2015
Location: KHMT
Posts: 112
Default won't happen

Bad, bad old arithmetic. It takes the fun out of everything, even my longing for an imagined quiet, comfortable electric airplane.

IC engine ~36% efficient (Carnot, another bad hombre in the world of reality)
electric motor ~90% efficient

Efficiency advantage of electric motor conversion of energy verses internal combustion engine = 2.5 times more output per energy input. Looks good so far.


gasoline energy =12.06 KwH/Kg
battery energy = 0.20 KwH/Kg (best lithium tech readily available today)

That's a weight to energy ratio ~60 to 1 in favor of gasoline!

Then, even with the efficient electric motor, the weight of the "electric fuel" will be 60/2.5 or 24 times heavier than gasoline. That would mean about 1500 lbs of "fuel" for a 200 mile RV hop. Not going to happen, likely ever.

That's the arithmetic and the way I see it. Maybe some short range, sailplane-like specialty aircraft are or will be within engineering reach, but batteries as a source of stored energy as a general replacement for liquid fuel in aircraft is a pipe-dream.


Last edited by Cumulo : 12-14-2020 at 11:33 AM.
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