At what point do electrics become impractical or too costly?

AEAJR

Looking for Lift
You are talking to a new pilot at the field. He says he wants to fly electric airplanes. More and more new pilots are coming into the hobby flying electric. Some say electric has taken over the hobby.

As electric motors and lithium batteries have advance in power and come down in cost the size airplane you can fly electric has been steadily moved up. But, at what point does it become too costly or impractical to go electric? What do you tell that new pilot?

Now, I realize there are people flying 1/4 scale, 1/3 scale and maybe even 1/2 scale with electric motors. There are now full size electric airplanes and gliders, so e-power is here to stay. If you have enough money there is no limit.

But for us mere mortals who do not drive Bentleys and have our own yachts, what is a reasonable size before you really should be changing over to glow or gas? What would you consider practical?

I used to say that 6 pound electrics were practical for almost anyone and 10 pound electric airplanes were reasonable for most committed modelers. But has that gone up? Is it 15 pounds today? 20 pounds? More?

If you figure 100 watts/pound as a good target for a typical sport flyer, a 20 pound airplane needs a 2000 watt/2 KW motor and a BIG battery pack. Likely a 10 or 12 cell Lipo pushing 50 to 60 amps.

And you need to charge that battery pack. Perhaps you need to have 2 or 3 battery packs so you can fly one, have one ready while you charge the third.

And what do you use to run the charger? You aren't going to charge a 10 or 12S 10,000 mah Lipo pack off your car battery unless you keep the car running all the time. And even then you would probably need to break that into 2 5 or 6 cell packs and have multiple chargers to make it practical charging off a 12V car system.

Do you now go and buy a gas generator so you can run a 110 V charger to charge your electric plane? Or does this only work if you have access to 110V power?


So, what is your opinion? When do they get too big for electric power to be practical?
 
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BRUTUS

Plank Junky
Lifetime Supporter
When I need more then a 3 cell 2200 lipo. That's my line. After that its gas and an electronic ignition!
 

AEAJR

Looking for Lift
For me, I would peg it at about 11 pounds or 1100 watts.

You can power that with a 6S 5000 mah lipo pack. Figure 3 packs at 150 each. Figure 7-9 minutes mixed flying.

You can charge that with a single charger from a car battery at 2-3C. A charger that can do that would be about $150

If I didn't have access to 110V power I would probably call that my practical limit. I am nowhere near that today. My heaviest electric is about 4.5 pounds using 3S pack.
 
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Tired Old Man

Staff member
The moment two or three flight packs cost more than a 120cc engine. Unfortunately that means there's no economical justification for large multirotors. One set of flight batteries can run upwards of $1,200.00
 

BRUTUS

Plank Junky
Lifetime Supporter
It's cost of ownership that kills me. When people start talking about comparable price between a gas engine and a set of battery's, esc, and motor to me the argument doesn't hold water. Those batteries are going to be crap in 2 years, and will need to be replaced. I can let an IC engine sit for a decade and still have 100% performance out of it. Plus, try selling used batteries. Not going to happen!

But hey, some people love technology and quiet airplanes. Me, I love cheapness, and durability. Hence, 3 cell 2200's! Cheap enough to be semi-disposable, and I can afford to get a new set every couple years for the price of one nice dinner out. When battery costs are 50% of an IC engine, it's time to put the genny IN the airplane!
 

AEAJR

Looking for Lift
It's cost of ownership that kills me. When people start talking about comparable price between a gas engine and a set of battery's, esc, and motor to me the argument doesn't hold water. Those batteries are going to be crap in 2 years, and will need to be replaced. I can let an IC engine sit for a decade and still have 100% performance out of it. Plus, try selling used batteries. Not going to happen!

But hey, some people love technology and quiet airplanes. Me, I love cheapness, and durability. Hence, 3 cell 2200's! Cheap enough to be semi-disposable, and I can afford to get a new set every couple years for the price of one nice dinner out. When battery costs are 50% of an IC engine, it's time to put the genny IN the airplane!
I think you have your components crossed up.

You can let a gas motor sit for 10 years and you can let a brushless electric motor sit for 10 years and both will likely perform well after the 10 years but the electric won't need to be cleaned, lubricated, tuned or otherwise prepared for use. Just blow the dust off.

Sell use batteries? Tell me, do you sell used fuel? I don't think so. And remember, when you get new batteries you essentially get a new fuel pump too.

Let those lipos sit for two years and they will likely work fine. I have lipos that are older than that and they work great! Would you want to use 2 year old fuel that has just been sitting there?


This is not a fuel vs. electric comment. I am just trying to get the components lined up in the comparison you made.
 

Bunky f. knuckle

Cover shot, MA 10/09!!!
It becomes not worth it at anything over 30cc airframes. To keep great performance, you gotta cut weight somewhere. And then cutting weight, you are going to be cutting propulsion system performance.

Unless you have a Cub and want to make it something else.
 

BRUTUS

Plank Junky
Lifetime Supporter
Big electrics are just too expensive and heavy. Even buying good batteries is like playing roulette. Get a 12S pack and your probability of a single cell going bad in the first 20 cycles goes way up. A buddy had a 72" Great Planes Skylane set up for electric. Flew like a heavy warbird. He bought a set of three 6s batteries for it, flew them a few times one season, put them away for the winter, and the next spring the packs all had dead cells. $450 down the tube, no returns, no warranty, just a hole in his wallet. Then he dumped all his electric gear, and put a DLE 20cc in that airframe instead. That engine cost less then the 3 sets of batteries alone, the plane lost a full pound of weight, and now it flies like an over-powered trainer.

I'm not saying that happens to everyone, but it's just too expensive when you look at cost of ownership over time. If you have money to burn, and don't mind replacing big, expensive batteries every so often, more power to you. Me, I don't have money to throw away on perishable goods. When batteries come with an iron clad 5 year warranty, maybe my tune will change, but for now, no way. Give me an electronic ignition any day.
 

AEAJR

Looking for Lift
So 10 -12 pounds, something in that area? Thanks.


So, if I do an unscientific averaging of the posts in this thread it looks like reasonable average would be in the 10-15 pound range for people's high end size for electrics. Some go higher and some are much smaller but the feeling I get right now is that 10-15 pound range would cover most people's high end point.

Some people express it more in terms of the engine size that the electric would replace. Seems 30CC is a typical break point from what I am reading. And I think that is in that weight range.

Let's keep the discussion going.
 
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Yeti

New Member
Yes, the biggest difference IMO is the longer flight times you get with gas.

Electric-quieter, cleaner, shorter flight times, smaller planes (12-78"), must charge batteries (30-60min to first flight), risk of prop injury from being live but not making any noise

Gas-noisier, dirtier, longer flight times, larger planes (60-150"), 15-20min to first flight, risk of prop injury from starting
 

BRUTUS

Plank Junky
Lifetime Supporter
AEAJR,

One thing you should be aware of is that you are asking the 3D crowd for their preferences. Thrust to weight is an extremely important factor for us. We are not flying hotliners or sailplanes or park flyers that only need a fraction (in most cases) of the thrust we do. I recognize that sailplanes can use quick bursts for a few seconds to get to altitude, then power is pulled back. We are typically operating between 50-100% of max power the entire flight, in most cases 70-100% when flying hard.

I'd bet if you asked RCgroups people they might have some different answers.

I do think it's funny, electric guys are saying you don;t need to tune an electric setup, but I beg to differ. In order to optimize electrics you need watt meters and a selection of props to test and see what is best for your system. All I need is a tachometer and a screwdriver.
 

AEAJR

Looking for Lift
AEAJR,

One thing you should be aware of is that you are asking the 3D crowd for their preferences. Thrust to weight is an extremely important factor for us. We are not flying hotliners or sailplanes or park flyers that only need a fraction (in most cases) of the thrust we do. I recognize that sailplanes can use quick bursts for a few seconds to get to altitude, then power is pulled back. We are typically operating between 50-100% of max power the entire flight, in most cases 70-100% when flying hard.

I'd bet if you asked RCgroups people they might have some different answers.

I do think it's funny, electric guys are saying you don;t need to tune an electric setup, but I beg to differ. In order to optimize electrics you need watt meters and a selection of props to test and see what is best for your system. All I need is a tachometer and a screwdriver.
Very good point about 3D and power to weight ratios. And while that may influence what plane you might choose to fly electric or fuel, it doesn't change the nature of the question.

What I wanted to hear and what I wanted people to discuss is what are the factors that influence their decisions. You can certainly put enough watts into a 40 pound plane to fly 3D with electric, but would you want to? If not, why not, and by that I mean each of you personally.

This is not an electric vs. glow vs. gas. This is a discussion about how people make decisions. I have found it very interesting and very enlightening.

The fact that I personally fly gliders and e-gliders is just to put my current state in context. But it is the context from which I make my statements. It has no bearing on the discussion.

If you go back to my second post you see I based my top size of 11 pounds based on 100 watts/pound and an 1100 watt top limit. It had nothing to do with how I fly or what I fly. It was based on how I would charge the batteries at the field. If I wanted to fly at 150 watts/pound it will still be around 1100 to maybe 1400 watts top limit, the weight of the plane would just go down but the watt limit would not change.


I have this same discussion going on several forms. Oddly enough 30CC seems to be a common break point regardless of what people are flying. Now, what you put that 30 CC in probably varies from group to group, but that seems to be a common point were people are saying that e-power is too costly or charging is too inconvenient or ...


Remember we are talking about the engine choice, not how you fly or what planes you fly so it makes sense that you would draw the line by engine size rather than weight. For this group, 30 CC might be 9 pounds. For another group 30 CC might be 14 pounds. But 30 CC seems to be a common break point.

Another major factor seems to be the availability of 110 power at the field. If you have 110 power at the field then there seems to be a tendency to up in engine size because you have better charging resources. If there is no 110 at the field then the tendency is go lower in engine size.

Some people feel generators are fine and others would not even consider it. Rather than bring a generator, just put a gas motor on the plane. I can understand that.


It is also interesting that most of the discussions have been measured in watts or CC for gas. Not a lot of discussion based on glow engine sizes. I would guess a 30 CC motor might be comparable to a 120 glow motor or something like that, but that is not coming up. People seem to be saying, "I fly electric up to something, often 30 CC size planes, then above that I fly gas."

THAT has been the biggest surprise to me. It is electric below X then gas above X and not a lot of people talking about electric below X and glow above X.

Seems people feel electric stacks up very well against glow but that it is not a good replacement for gas above about 30 CC.

Naturally there are those who crave the scream of the engine and the smoke and the smell and all. In that case electric doesn't even get a consideration. They might fly some electric micros or even something in the .15 size in electric and then it is glow above that, but I am not getting a lot of comments about glow overall.

And there are those who will only fly electric because it is clean or quiet or reliable or that is all that is allowed at their field, or .... whatever the reason. And whatever their top motor size is, that dictates the largest plane they will fly.

In the end it is all very individual. The factors vary but the themes are quite similar across all the discussions I have running. Even the discussion on Wattflyer, an all electric forum, follows the same pattern.
 
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Tired Old Man

Staff member
So 10 -12 pounds, something in that area? Thanks.


So, if I do an unscientific averaging of the posts in this thread it looks like reasonable average would be in the 10-15 pound range for people's high end size for electrics. Some go higher and some are much smaller but the feeling I get right now is that 10-15 pound range would cover most people's high end point.

Let's keep the discussion going.
No, it would be rare for a 30cc plane to tag 15lbs. I said half, or less. Most flying a 15 pound plane are using a 50cc engine.
 

Tired Old Man

Staff member
AEAJR,

I do think it's funny, electric guys are saying you don;t need to tune an electric setup, but I beg to differ. In order to optimize electrics you need watt meters and a selection of props to test and see what is best for your system. All I need is a tachometer and a screwdriver.
100% correct, but most electric people have yet to figure that out. You forgot to toss in ESC sizing ans selection.
 

Tired Old Man

Staff member
Now, if I'm flying an airplane that was in real life size equipped with an engine, it was not silent. It made engine noise and I think it's pretty stupid when electric flyers put noise makers on their planes to make engine sounds.

Using that 300cc break point you seem to like, if I put a 16 ounce gas tank in the plane, and for sake of argument we'll call it a 3d plane that works the engine fairly hard, I'll get pretty close to 25-30 minutes of flight time before I hit a dry tank. Perhaps more if I know how to tune an engine. When all is said and done my engine and fuel tank will end up close to the same weight as the battery powered plane, and I'll have maximum thrust from engine start until the moment the gas tank runs dry.

That same plane with an electric motor might, on a good day, get 10-12 minutes of flight time. Sure, I could increase battery capacity or quantity but the weight starts stacking up while the flight time really doesn't gain much for the added weight and expense. If I treat my batteries really, really good, break them in nicely, and never discharge below 3.8v/cell they will last longer but my flight times will be quite a bit less than 10-12 minutes. I'll have to carry a box full of batteries to the field if I want to fly 6 or 8 times, or hope the field has an electrical outlet I can plug my charger and all the associated cords into. Of course I can leave the hood of my car up and use the car battery, or buy some trick item that lets me charge from the trunk of the car. Don't forget to unplug the open door light. When I get home I can string all the cords and cables across the kitchen counter to charge the batteries, which I'll have to move before I make supper.

Truthfully, electric power is far less efficient that gasoline, and much, much dirtier for the environment. Those are heavy metals being used that have to be refined, using a considerable amount of power, then charged, suing a considerable amount of power, then disposed of, hopefully in an ecological manner but that's unlikely because they have to be broken down, using a considerable amount of power, before they can be disposed. Dead dinosaurs are much cleaner, and more abundant than the materials making up your batteries. Also requires less support equipment, which reduces the foot print even further.

Oh, almost forgot, flying glow is like flying electric, only more mess. Expensive as hell with short flight times for the amount of fuel consumed. Who wants to spend $16.00-$20.00 for a gallon of fuel to use 24 ounces of the stuff for 10 minutes of flight time?
 
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