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Old 07-16-2014, 01:38 PM
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When do planes get too big for electric powered flight?

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 two to four 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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Old 07-16-2014, 02:46 PM
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Quote:
Originally Posted by AEAJR View Post

I used to say that 6 pound electrics were practical for almost anyone and 10 pound electric airplanes were reasonable for most committed modelers.
I'd say this is still spot-on for the average Joe.
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Old 07-16-2014, 02:51 PM
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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 7-9 minutes mixed flying.

Figure 3 6S 5000 mah packs at $150 each. But you can also buy lower cost 3S packs and connect them serial to get to 6S.

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 at the field I would probably call that my practical limit. I am nowhere near that today. My heaviest electric is about 4.5 pounds using a 3S pack. So I have plenty of room to grow.
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Old 07-16-2014, 04:47 PM
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About a year ago I ran through a bunch of numbers on this and came up with roughly the same answers you do. At the 1kW power level the setup costs for electric are a little lower than gas, and the operating costs are a bit higher. I used 2.5 kW for the high power evaluation, and there setup costs were significantly higher for electric and operating costs were al lot higher. That didn't even count the chargers and generators you mention, just the cost of replacing the batteries every once in a while. They don't last forever, and can't be rebuilt when they go bad.
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Old 07-16-2014, 05:37 PM
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I'm playing with a 30cc size SU26 with 2600watts on 8s. Getting 7-8 minute flights. Using 2x 4s 5000mah in series.
We have power at our field so I can plug up to recharge. And only takes about 20 minutes to recharge both packs with my new icharger
It adds a new challenge learning the proper setups for the given application. But I probably would not go any bigger. Maybe?
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Old 07-16-2014, 06:43 PM
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I am working on a 88" / 50cc size Raven. Rimfire 50cc motor, Castle 120HV on 12s.
Still far from complete, but after flying my 62" Diabolic on a 6S / 5000 pack, with an 80a ESC & EMP 4250 - 650 motor, the power is ridiculous, and after 12 minutes of flying time I still have 46% battery remaining.... it's a hard act to follow!

No slime, no tuning, unlimited power.

If the 50cc project ends up successful, I will be doing a 100c version.
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Old 07-16-2014, 07:18 PM
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Batteries die to quicly for me to invest in anything bigger than 3s 2200 lipo ~ 400-500W. After that, give me an IC engine!
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Old 07-16-2014, 07:18 PM
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As a person who learned, with glow, I'll say that as many flightstudents as you can squeeze in , in x amount of time is critical, for training as lono as your receiver battery is good, glow is a go, in electric format I'd look for a 1500 mah battery , at 7.4 volts, in a light trainer. Easy on the pocket book, easy to find a decent power source, and an easy to ship size.
As for how big is too big , well, there's rome, a ferris wheel not in London, and Shelby GT1 that will do 200 mph, so it's all in b your audience.
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Old 07-16-2014, 08:00 PM
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My friend converted his 50cc gas Yak to electric. He did lighten the airframe, and he has as much power and performance with electric as he did with his gas engine.

If you want to see how fast batteries can be emptied, try an 8s pack, 5000mah, in an EDF. Answer is 3-4 minutes depending on throttle managment,,, but going faster is so much more funner!

I have seen too many people have problems tuning a gas engine, thats why I think electric is taking over small and mid size planes. I have a 64" MXS, electric, and this thing is alot of fun to fly.

Jeff
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Old 07-16-2014, 08:11 PM
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Quote:
Originally Posted by 401HITMAN View Post
My friend converted his 50cc gas Yak to electric. He did lighten the airframe, and he has as much power and performance with electric as he did with his gas engine.

If you want to see how fast batteries can be emptied, try an 8s pack, 5000mah, in an EDF. Answer is 3-4 minutes depending on throttle managment,,, but going faster is so much more funner!

I have seen too many people have problems tuning a gas engine, thats why I think electric is taking over small and mid size planes. I have a 64" MXS, electric, and this thing is alot of fun to fly.

Jeff
Cost wise anything over 7 lbs makes no sense. Batteries are expensive since to really fly you need 150 W per lb. Safety wise give me IC engines, bump the throttle with IC when it isn't spinning the prop, nothing happens. Prop strike with IC engine stops, electric keeps chopping, ask me how I know.
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Old 07-16-2014, 09:47 PM
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Cost wise anything over 7 lbs makes no sense.
I am not sure that is quite fair.

On my 50cc Raven project. Motor ($249), ESC (199) & 4 Batteries ($160) cost me a total of $610.

The DLE55 is $400, ignition batt $30, Opto Kill $13, tank, filter, filter clunk, tygon line & fuel dot is another $30 easy for a total of $475 or so. So the difference is $135.00. Not really that big of a difference either way when you think about it.

The PLUS side is no more $6.00 a gallon 100LL from the airport. No more expensive oil. No more carb tuning or carb cleaning if it sits a while. No more plugs. No more mess to clean up. No more big expensive starter with a $150 miller belt reduction & Li-Po battery.

I think the cost of electric is very affordable and makes perfect sense. Especially if you hunt & peck for used stuff or off-brand parts. I could have easily purchased all the stuff I needed from HK and spent LESS than a DLE 55.

I do agree 100% about the safety aspect of it. But honestly, it's no different than going shooting. I have been around guns since I was 7 years old. Dad owned a gun club when I was a kid. I was taught at a very young age to ALWAYS assume its loaded. 40 some odd years later... never had an incident, a misfire or accidental discharge.

Treat the electric the same way and it can be as safe at a gasser in that respect. And yes, you have to treat it and the guys around you a little differently when at the field. But as long as your boys adhere to your rules when around your electric, you can eliminate alot of the nonsense injuries. For example, batteries should only be installed or plugged in on the same safety stand you start your glow or gasser on. An Armsafe switch should be just about mandatory and not allowed to be installed until your ship is on the ground and ready to taxi.

I am warming up to the electrics. Almost looking for to just plugging in and going up.
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Old 07-16-2014, 11:57 PM
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^ +1
I love my gassers, but recently the power of batteries and motors for electrics has re-thinking my thoughts,, there are some advantages of electric.


Still not giving up my DA 120
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Old 07-17-2014, 05:25 AM
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Electric keeps getting better, but the big batteries run the costs up. Also the higher power electric systems weigh significantly more than their gas equivelants. Some of that can be recovered in the reduced airframe strength requirements, but not all. Up front costs go up a lot for those who want to fly a lot. Multiple sets of batteries and/or high rate charging systems.

The advantages of electric are real. Quiet, clean and reliable.
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Old 07-17-2014, 06:12 AM
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In my case my largest electric is a Carden Extra at 89" and my heaviest is a H9 30cc 81" Spitifre at 22 1/2lbs. The biggest reason that I got into the larger electric is I already had an inventory of 6S-5000 oaks for 550 and 700 heli's that I fly so for my example there is no entrance fee on the cost of the 6S-5000 paks. If I did not fly electric heli's at my farm almost daily I doubt I would be flying big electric. I love plug and play with no vibration problems but the flight times are short compared to the equivalent gas times.
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Old 07-17-2014, 06:25 AM
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Check it bleed,bro was on.
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once a plane requires anything larger than a 6S Im out.Id say planes like the EF exp series,edge,extra & mxs are as big as I would go.My 85 MXS build will be a gasser,probably VVRC
40cc twin.I love my smaller electrics but I cant spend a lifetime charging batteries for 7 minutes of flight.103 Extra DA120,thats 15 minutes of ballistic power with a little gas left over.
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