# Pound for pound.. electric vs gas

Discussion in 'The light stuff area' started by ryanjames170, Oct 2, 2018.

1. Oct 3, 2018

### Aesquire

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All you need is the most advanced technology, lifetime dedication to aviation, really good soaring skills, and, yeah,. money & time. Practical? not so much.
https://www.solar-flight.com/

2. Oct 3, 2018

### blane.c

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3. Oct 3, 2018

### Toobuilder

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200 KTAS, 1000NM range, 500 pounds of people and their stuff, recharge in 15 minutes.

When that gets here, I'm interested. Until then I'll stick with my 540 Lyc.

4. Oct 3, 2018

### Tiger Tim

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Pound for pound? I’ve wondered that myself so let’s try a little math. Since this is the UL section I’ll take a look at the Sky Pup as an example: https://en.m.wikipedia.org/wiki/Wood_Sky_Pup

Wikipedia lists the Cuyuna 215 as the smallest common engine for the Sky Pup. It was a two stroke that produced 20hp and a wild guess would be that a five gallon ultralight tank probably gives around 2.5 hours’ total endurance. The engine weighs 42lbs and a full tank of fuel would be about 32lbs for a total of 74. I’ll assume that since both power plants will have mounts and props that those would weigh about the same, and the same goes for fuel lines versus wire and fuel tank versus battery box. I’m rounding pretty heavily here.

20hp works out to 15kW, and here’s a brushless outrunner which claims that much power: https://alienpowersystem.com/shop/brushless-motors/12090-outrunner-brushless-motor-130kv-15000w/
It seems too physically small to do the trick but hopefully is close enough for the numbers’ sake. The website lists its weight at just under 6.5lbs and a reduction gear and ESC would bring it up to what, fifteen pounds at most? That leaves 59lbs for batteries. Wikipedia claims LiPo batteries can store up to 265 Watt hours per kilogram so for our 59 pounds of batteries that shakes out to 7,100 Watt hours, or 28 minutes with the motor specified above. I’m not sure how exactly that battery capacity is measured but if it’s to total depletion of the battery that will ruin your LiPo cells so the right answer might be closer to ten minutes endurance. Yikes.

Is that about right? I really don’t know for sure if power ratings and the like can be compared like that but the units match at least.

In other news, I’m much less interested in building an electric Sky Pup now.

5. Oct 3, 2018

### lr27

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If I recall correctly, the FAA doesn't let you count batteries as fuel. But I think the Sky Pup tank is supposed to be much smaller. I'm pretty sure you can run lipos well below 40 percent without trashing them, though of course the less discharge the better. They're supposed to be stored at 40 percent or so. You can probably find a motor that has a lower kv so that it can use either higher voltage or spin a bigger prop.

As I recall, the SP is meant for up to 60 lbs for the motor, redrive, and prop.

Unless you're climbing the whole time, you're not going to need 20 hp all the time. The SP is supposed to get 12:1 L/D, but let's say that's optimistic and call it 10 at 35 mph. At 400 lbs gross, that's 40 lbs of drag and 51.5 feet per second, or about 2,060 ft-lbs per second. Unit conversion gives us 2800 watts. Let's assume the prop is 75 percent efficient, and the motor is 85 percent efficient. Now we need 3,230 watts, except when climging. So, if your other calculations are correct, I think you can fly for much longer than 28 minutes with all those batteries.

6. Oct 3, 2018

### BBerson

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That likely isn't continueous power. Might last 10 seconds at that power. It doesn't list continueous power.
200 X 70= 14000watt not the 15000 listed.

7. Oct 3, 2018

### Tiger Tim

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That 40% figure is based on a range between max charge at 4.2V and minimum at 3.0V. Discharging a LiPo below three volts causes permanent damage to the cell.

8. Oct 3, 2018

### Armilite

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Originally Posted by pictsidhe View Post
No, you'd only need about 18ish kW. But higher capacity cells than 3Ah are only good for 1/2 the current, so you'd have less than 18kW with a your lighter pack with less cells. Inadequate. Running cells at their max ratings isn't great for life. Considering what you'd spend on a pack, you probably want to consider life.

If you have specs of better cells, list them?

A123 are 3.3V, 1.1Ah and 39g. Your 19.4MJ pack is now 57kg of bare cells, though the power will be awesome. The A123s are about the best specific power, though. I would shy away from used ones, myself.
A123's were my suggestion for a hybrid system.

===========================================================================

There is No such thing as a Free Lunch in POWER, there is only about 4-5 different Size Lithium Cells to use and different Voltage of Lithiums, 3.3v, 3.7v, 4.2v and different Ah Ratings. For 99% of the USA Part 103 Ultralight Airframes ever Built, your probably going to want a Minimum 20kw = 26.82044hp. So knowing that HP Number needed, then Build a Battery Pack out of the 4-5 different Spec Lithium Cells in a Spread Sheet for a Minimum 1hr 15min of Flight, with at least a 15min Reserve, showing Quanity of Cells needed, Total Weight of that Spec Battery Pack, Cost, Vendor Parts Name used, etc!

A Rotax 277UL is Rated 26hp and gets 1.8gph at Crusie using 20hp, so with 5 Gallons = 5/1.8 = 2.7hrs, let's call it 2hrs Max with a .7 Reserve! $3 x (4) gallons =$12 for 2hrs, or $6 for an 1hr. Just because a Lithium Cell is Small and maybe Cheap (A123 3.3v 1.1Ah and 39gr, doesn't make it the Best Cell for a Part 103 Ultralights. You might have to use many of them to equal those Larger Cells which takes up more Space. Most of these Electric Motors are 120v! So You have to Compare them all. Make up a list in a Spread Sheet. Prices do vary. A123 ? 3.3v 1.1Ah$ 39gr 0.09oz
Headway 38120S 3.7v 10.0Ah $16 350gr 11.3oz Headway 40152S 3.7v 15Ah$24 550gr 17.7oz
Headway 40160S 3.7v 16Ah $20 550gr 17.7oz Panasonic 18650 3.7v 10Ah$3 40gr 1.3oz Telsa Car Batteries use these. My Local Battery Store wants $6ea. Interesting Read on 18650 Batties. http://www.batteries18650.com/ Quick Fact: The Ford Focus Electric, Volvo V60 & Chevrolet Volt are powered by LG batteries. Telsa 85kw/114hp Car Battery made out of 18650's. https://electrek.co/2016/02/03/tesla-battery-tear-down-85-kwh/ Telsa https://www.topspeed.com/cars/car-n...y-and-profitability-projections-ar177281.html A123 Batteries. https://www.buya123products.com/CellsList.php 9. Oct 3, 2018 ### lr27 ### lr27 #### Well-Known Member Joined: Nov 3, 2007 Messages: 3,341 Likes Received: 488 Yes, of course. I meant 40 percent of capacity, not 40 percent of the voltage. I think that's supposed to be around 3.8 volts per cell. If you take an aircraft that's designed for light, inexpensive 2 stroke power, with cheap fuel, and try to fly it with something else, it MIGHT not work so well. Which is why I did my figures for an aircraft designed to be more efficient. No way you'd need or want 19.4 MJ in a hybrid system! Not sure why you picked the smallest A123 cells. I'm sure that's the most expensive way to go. If you use the pouch cells, which are 20 Ah apiece, they's supposed to be 131 watt hours/kg. A watt hour is 3,600 joules, so we have 42 kg or so, probably slightly more to make things come out even. But I suspect a fifth of that, maybe less, would be more than enough for a hybrid. Very approximately, at bulk prices you'd be looking at around$3,600 for the overly heavy pack, or $900 for the hybrid pack. Based on this site: http://a123batteries.com/20-ah-nanophosphate-prismatic-pouch-amp20m1hd-a/ Gotta admit I'd be a bit nervous about the regular lithium cells. Once met someone who'd burned his house down with them, and almost his grandmother! If they've been made a lot safer, I'd like to know about it. 10. Oct 4, 2018 ### rdj ### rdj #### Well-Known Member Joined: Sep 10, 2009 Messages: 293 Likes Received: 186 Location: Northern California If the material scientists ever get solid state Lithium-Air batteries working in production quantities and pricing then I could see electric power "taking off", so to speak. Pound for pound that's about where you hit the crossover point. 11. Oct 4, 2018 ### pictsidhe ### pictsidhe #### Well-Known Member Joined: Jul 15, 2014 Messages: 7,227 Likes Received: 2,064 Location: North Carolina I didn't pick the A123s, someone mentioned them so I gave the numbers. Most lithium fires are after cell abuse, mostly people who misunderstand the risks and think they can use them without protection or ignore correct charging procedure. A house is a terrible place to abuse lithiums. It doesn't help that much lithium related stuff you can buy is unsuitable for the task.The meteor factor is why I'd go for the mass produced cells from a major manufacturer. They've already minimised the risks. For a hybrid, the samsung 25r cells appeal to me. Last edited: Oct 4, 2018 12. Oct 4, 2018 ### Armilite ### Armilite #### Well-Known Member Joined: Sep 6, 2011 Messages: 3,111 Likes Received: 251 Location: AMES, IA USA ======================================================= There are literally Many Multi Millions of Lithiums used in everything from Hand Tools, Laptops, Phones, Tablets, RC Stuff, on Bikes, Snowmobiles, ATVs, Ultralights, Cars, etc. Many of these Objects are kept in Homes, Garages, Shops, ShirtPants Pockets, etc. Probably 400+ Million Batteries. You use hear about maybe 10 a year when they first came out, and People are still promoting or spreading that OLD Limited Data about them catching Fire. Many of the early ones that did Fail was from Abuse or Over Charging them. Your talking about maybe .0000001% that may Fail and catch Fire. Lead Acid Batteries Fail also. "With over a million electric vehicles (EVs) expected to be on the road globally by the end of 2015 and an increasing number of jurisdictions around the world focusing seriously on the growth of EV sales, we can expect strong growth in lithium-ion battery demand." Do you have any idea just How many Lithium Cells just (1) Car use's? This (1) Plant in China makes 500,000 Lithium Cells a Day. https://www.youtube.com/watch?v=5X2YYNQWm_k 13. Oct 4, 2018 ### pictsidhe ### pictsidhe #### Well-Known Member Joined: Jul 15, 2014 Messages: 7,227 Likes Received: 2,064 Location: North Carolina A myth? The cells made by the million have had their issues fixed, as have the industrial sized 18650. Smaller manufacturers, such as the hobby cell makers, have significantly lower reliability. Since the 18650s are so good, I don't see a good reason to use the much riskier hobby cells when the meteor factor could result in cremation before you hit the ground. That plane that burned then crashed a few months ago had it's battery built by Siemens. Siemens have huge R&D, yet they haven't eliminated the meteor factor... 14. Oct 5, 2018 ### lr27 ### lr27 #### Well-Known Member Joined: Nov 3, 2007 Messages: 3,341 Likes Received: 488 I think it was me who mentioned the A123's. I was just expressing surprise that you picked the smallest cell they make. (made??) 15. Oct 5, 2018 ### pictsidhe ### pictsidhe #### Well-Known Member Joined: Jul 15, 2014 Messages: 7,227 Likes Received: 2,064 Location: North Carolina I gave the numbers for the 60A peak current ones that were mentioned. 16. Oct 5, 2018 ### lr27 ### lr27 #### Well-Known Member Joined: Nov 3, 2007 Messages: 3,341 Likes Received: 488 When I brought them up, I had the next size up in mind. Here's the eBay listing I mentioned: https://www.ebay.com/itm/40V-18-4AH...OWERWALL-RV-DIY-EV-BATTERY-2250A/183164236384 and the battery spec. https://a123batteries.com/product_images/uploaded_images/26650.pdf 76 grams and 2.4 Ah I was wrong about the 60 A, they're only rated for 50 Amps continuous. The 120 amp rating for 10 seconds is pretty amazing, though. The little ones are "only" rated for 30 amps, although perhaps the "peak", which isn't mentioned in this spec, is higher: https://a123batteries.com/product_images/uploaded_images/APR18650M1B.pdf In any case, the pouch cells would "only" require 41 kilograms of batteries! That leaves 163 lbs for the rest of the aircraft unless the FAA relents. 17. Oct 5, 2018 ### Armilite ### Armilite #### Well-Known Member Joined: Sep 6, 2011 Messages: 3,111 Likes Received: 251 Location: AMES, IA USA =============================================================== It's not that 18650's are any better than the Bigger Cells, it's that they are Smaller and Cheaper so they fit in more things used by People. Manufactures who Build things that use them 18650's get them for about a$1 each since they Buy in Big Volume Lots of 20,000+. My local Battery Store wants $6 each for 18650's, if you shop on line Avg is$3 each.

For Ultralights & Kitplanes with Limited Space to put Battery Packs, and Ultralights with a 254lb Weight Limit, we need to use Bigger Cells that give us our desired TIME for FLIGHT! For me, I wouldn't want less than 1:15min Flight Time with at least a 15min Reserve. So like I said, for that 1:30min, just figure out How many Cells it takes to meet that objective, and figure out the different Weights, and Space needed for them different Size Battery Packs.

There is always New Battery Technology coming out all the Time, usually at High  when introduced, it's a matter of if you can wait for it to arrive, and it's Price to lower. Probably 15+ years ago now, those first New Lithiums Batterys for Snowmobiles/ATV's/etc., came out on the Market and were $350+. Many Years later I finally bought mine at$98. So, do you have them 8-10+ years to wait, or jump in with what's available and go Flying?

FLIGHT TIME in MINUTES
WEIGHT of Battery Pack
COST of Cells/Pack
SIZE of Battery Pack

18. Oct 5, 2018

### Armilite

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=========================================================

Unless you can put approximate Flight Time in Minutes using these different Size Lithium Cells with an Avg Pack Cost to these different Electric Motors at their different HP's, you're just throwing out Numbers. I would think for most People a Minimum Flight Time of 1:15min, with at least a 15min Reserve.

You have to answer these Questions.
HP used for Takeoff and Minutes used. Hp used in Cruise and Minutes used. On Ground Taxi in Minutes used.
FLIGHT TIME Total in MINUTES
WEIGHT of Battery Pack
COST of Battery Pack
SIZE of Battery Pack

19. Oct 6, 2018

### lr27

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The mission I used as a reference, which I may or may not have mentioned earlier, was a 5 minute climb at 20 hp or so, followed by flying around at a much lower hp (6? 7?) for 55 minutes. The aircraft considered would be a long winged ultralight motorglider, since that's probably one of the more favorable uses. Or, at least, long winged enough to get 10:1 L/D

Tiger Tim likes this.
20. Oct 6, 2018

### DonEstenan

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Hmm, I think the point of an electric airplane is not whether pound per pound you can get deal better than the ICE one, but the whole package:

1. you get much simpler and hassle-free operation (& maintenance too)
2. quieter ride
3. (once the technology has matured a bit) greater reliability due to inherent mechanical simplicity

And to achieve these comforts, you are willing to have a bit heavier/costlier (but cheaper to operate) aircraft.

You still won't get purely electric cross-country cruiser (the physics simply does not allow that), but hopefully soon the technology will be good enough to get a practical pleasure flying aircraft.

Ultimately, you will want to have a clean sheet design that takes advantage of everything electrics has to offer.

Btw, does it make sense to have an electric motor around the tailboom?
- allowing large propeller without messing the thrust angle and overall aerodynamics
- no need for twin tail booms or long power shafts

Does it make sense to have lightweight fixed pitch foldable takeoff/climb propellers on the wings and a simple fixed pitch pusher/tractor cruise propeller?