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Old 07-16-2014, 09:06 PM   #1
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Cool At what point does electric powered flight become impractical?

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. You would likely be flying 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 big battery pack for your big 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, 09:07 PM   #2
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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 on that size pack.

I would want to have 3 packs, figure about $150 each. You can charge those 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.

How about you?

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Old 07-16-2014, 09:18 PM   #3
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For me it's the cost of batteries. I only fly electric, just don't want the hassle of glow or gas right now. I want to fly bigger though, so it's a trade off. I got the Carbon Z cub when it came out. Overall I thought a pretty good deal. I also got in last week on the great deal for the last of the Splendors too. Both take 6 cells. The price goes up bigtime on 6 cells, even from the lower cost providers. I was happy to find a couple for $70.00 a piece, but you need at least 3 (for me at least). Sure, I could double up some 3 cells, but i'd rather go 6. I also have the 96" Telemaster than I can use them on, or go with 5 cell. Then you need a good charger too. I've never done a study to see which is more cost effective in the long run. I have about 25 4/5/6 cells now, and about 40 2/3 cells. I cycle through about 10 a year, but I also get some good deals on used ones too.

Another factor for me at least is the hassle of building at the field. I'm inpatient in general when I get there, I don't want to spend 30 minutes putting something together. I want to attach the wings and go. The Carbon Z is pretty easy, but the Telemaster is a pain with the poor design for the wings and struts. At some point I'll figure out a way to cut the struts down so the piece that goes into the fuze stays put, and I pin the rest of it to the wing. Someday.
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Old 07-16-2014, 09:43 PM   #4
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If you are going big I think there is a good argument to switch from LiPo to A123 cells. Less delicate than LiPos and you can charge in the plane. Many threads here by kyleservicetech on these.
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Old 07-16-2014, 10:03 PM   #5
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The line is constantly moving. As of right now, I would say the break even-point is at about 50cc. In the 30cc class (meaning 2000-3000w), the electric power systems are still significantly lighter than their gas counterparts and comparable in cost. For 50cc, the weight seems to be about the same, but the cost starts to rise dramatically once you get into big 12s systems.

Last weekend I saw a beautiful electric 108" Extra with insane power. It had a 12s system running 15000mAh of batteries! That was a demo plane from 3DHobbyShop and probably not something any regular flyer would ever get.

Personally, I have three 30cc planes. One of them is gas and the other two are electric. Although I love the one on gas (has a 36cc engine in it), I'm definitely going electric if (OK, "when", who am I kidding?) I get another one. If I get another 50cc, it's a different story. Right now, I would probably get a gasser, but the trend is definitely that more and more 3D flyers go electric in the 50cc segment.

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Old 07-16-2014, 10:04 PM   #6
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Electric becomes impractical about the time you can't figure out how to get the model to the airfield.

Just like gas power or glow power.
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Old 07-16-2014, 10:06 PM   #7
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As for charging, I'm using simple Turnigy 2x 200W charger as my field charger. It charges two 4s 4000mAh in about 20 minutes if I run 2s charge current. Since we have a solar powered charging station at the field, I typically only have to bring two sets to keep me flying more or less constantly.

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Old 07-16-2014, 10:10 PM   #8
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Originally Posted by fhhuber View Post
Electric becomes impractical about the time you can't figure out how to get the model to the airfield.

Just like gas power or glow power.
I used to use that excuse. Then I bought a trailer...


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Old 07-16-2014, 10:11 PM   #9
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Originally Posted by NJSwede View Post
As for charging, I'm using simple Turnigy 2x 200W charger as my field charger. It charges two 4s 4000mAh in about 20 minutes if I run 2s charge current. Since we have a solar powered charging station at the field, I typically only have to bring two sets to keep me flying more or less constantly.
Solar charging station? What is that? Inquiring minds want to know.

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Old 07-16-2014, 10:13 PM   #10
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Originally Posted by AEAJR View Post
Solar charging station? What is that? Inquiring minds want to know.
It's a bunch of car batteries (5-6 or something like that) connected to a solar panel sitting on top of our shed. If the weather is reasonably sunny, it keeps us going for an entire weekend and spends the following week recharging. Works like a charm!

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Old 07-16-2014, 10:14 PM   #11
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I have a friend who has gotten into building big bombers. So far he's done a B-17, B-29, B-36 (6 motors only, no EDFs just dummy pods), and now he's working on a B-24. They are made primarily of foam and ply, and the smallest wingspan is 9 feet. The largest is 12 feet.

He is running all of these on cheap Suppo motors, ESCs and 3S 5000 packs (typically two motors per pack). These models are now getting upwards of 15+ pounds AUW. He uses the same packs for all his birds, so the cost of lipos is spread out over several planes.

His typical spend for one of these? Usually $300 or less. This includes building materials (his dad owns a picture framing shop, so he gets materials for cheap), electronics, and what he pays me to install all the electronics (he detests soldering ).

If you want to see some of his stuff, look up "greenseaships" on RCGroups. Here's his B-36 thread:

http://www.rcgroups.com/forums/showthread.php?t=2089566

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Old 07-16-2014, 10:20 PM   #12
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I have 105 watts of solar panels and 4 X 120 AH 14V batteries in my model trailer... I can continuously charge 2X 3S 2200 mah packs just from the solar cells as long as there is daylight.

Not Lead Acid batteries in the solar system they can deliver 100 amps for 4.5 hr continuous.

12 ft (+ V nose) custom "Road Force" (Well Cargo) trailer set up just for the models...

I could run the refrigerator and some lights in my house from the trailer if the power grid goes down.
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Old 07-16-2014, 11:28 PM   #13
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Originally Posted by crxmanpat View Post
I have a friend who has gotten into building big bombers. So far he's done a B-17, B-29, B-36 (6 motors only, no EDFs just dummy pods), and now he's working on a B-24. They are made primarily of foam and ply, and the smallest wingspan is 9 feet. The largest is 12 feet.

He is running all of these on cheap Suppo motors, ESCs and 3S 5000 packs (typically two motors per pack). These models are now getting upwards of 15+ pounds AUW. He uses the same packs for all his birds, so the cost of lipos is spread out over several planes.

His typical spend for one of these? Usually $300 or less. This includes building materials (his dad owns a picture framing shop, so he gets materials for cheap), electronics, and what he pays me to install all the electronics (he detests soldering ).

If you want to see some of his stuff, look up "greenseaships" on RCGroups. Here's his B-36 thread:

http://www.rcgroups.com/forums/showthread.php?t=2089566

an amazing build, and even better video of the flight. Great to hear 6 motors going at once. Love Dag's stuff too, just fantastic.
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Old 07-17-2014, 02:03 AM   #14
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Originally Posted by AEAJR View Post
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. You would likely be flying 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 big battery pack for your big 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?

Ah yes

You are going to get a whole pile of different comments on this subject. As for me, IMHO, the practical limit for electric power would be around 1200 - 1500 watts or so. With this power level, you've got a model that would normally be powered by a glow 4 stroke 70 or similar size. That model would be about 60 - 65 inch wingspan, and around 8 pounds ready to fly with electric power.

As for batteries, again, a lot of trade offs. Going LiPo batteries, that just about calls for a bunch of 5S or 6S LiPo packs, around 4000 Mah.

Going with those A123's allows leaving those packs IN the model during charging. Since A123 allows charging at up to 10 Amps, they can be recharged in 15 minutes or so. A good charger, such as the Cellpro Powerlab 6 or 8 series will handle that charging rate just fine. Plus, you can get about a half dozen flights out of a quality 120 Ampere Hour deep cycle battery.

Going past that 1200 watts to 2500 or 3000 watts is a whole different situation. Buying a big box of 10S or 12S LiPo batteries is going to get expensive. They will also have a limited number of flights, which has to be added to the cost per flight of your model.

Using a 12S2P A123 pack does resolve a lot of the issues with a big LiPo pack. I've got several A123 packs that are 5 years old or so, and have several hundred flights on them. Those packs turn the same propeller on the same motor at the same RPM as when the battery pack was brand new.

Charging them in 15 minutes can be done, but you won't be using a single 120 Ampere Hour pack to run it. I've been there, you will kill that big lead acid battery in less than 50 flights. It would take perhaps three or four 120 Ampere Hour deep cycle batteries to run the charger. (I'm charging my 12S2P A123 packs as a 6S4P pack, with a charge rate of 30 Amperes.)

One very important item with electric power though, is absolute reliability of the power system, compared to gas, and the near total lack of vibration on your model and its servos. Just last Sunday, a club member lost all control of a $500 model, plus the cost of the engine, radio and servos. We're pretty certain vibration got to something important.

Here is a whole pile of info on this subject:

Model airplane Power Systems
http://www.wattflyer.com/forums/showthread.php?t=73275

Giant Scale Power System:
Battery Backup System
http://www.wattflyer.com/forums/showthread.php?t=63794

Carl Goldburg Extra 330 Electric Conversion
http://www.wattflyer.com/forums/showthread.php?t=59273

Giant Scale electric motors vs Gasoline Engines
http://www.wattflyer.com/forums/showthread.php?t=58035

Harbor Freight Gasoline/Alternator Setup
http://www.wattflyer.com/forums/showthread.php?t=66066,

Great Planes Giant Big Stick Electric Conversion
http://www.wattflyer.com/forums/showthread.php?t=65052

Giant Scale Cessna Model
http://www.wattflyer.com/forums/showthread.php?t=66414

Redwing MXSR Model
http://www.wattflyer.com/forums/showthread.php?t=72225

That Redwing MXSR model now has near 100 flights on it, and it's becoming my favorite model to fly.

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Old 07-17-2014, 02:21 AM   #15
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LiPos when properly cared for tend to last more than 3 years. My packs generally die from age, giving more than 300 cycles per pack.

Around 3 to 3 1/2 years they are losing ability to deliver rated current even though they might still have more than 80% of rated capacity.

Sometimes that loss of ability to deliver curent is very sudden and I had a set in the big EDF that worked fine one flight, recharged and I had them fail to get the plane off the ground.

But compare the appx $120 in LiPos giving 300 flights of the 14 lb model with the cost of that many 12 to 16 oz tanks of fuel... You can take your pick glow or gasoline.
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Old 07-17-2014, 04:41 AM   #16
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Originally Posted by fhhuber View Post
LiPos when properly cared for tend to last more than 3 years. My packs generally die from age, giving more than 300 cycles per pack.

Around 3 to 3 1/2 years they are losing ability to deliver rated current even though they might still have more than 80% of rated capacity.

Sometimes that loss of ability to deliver curent is very sudden and I had a set in the big EDF that worked fine one flight, recharged and I had them fail to get the plane off the ground.

But compare the appx $120 in LiPos giving 300 flights of the 14 lb model with the cost of that many 12 to 16 oz tanks of fuel... You can take your pick glow or gasoline.
Yeah
It's pretty hard to beat the capabilities of a gasoline powered model, versus an electric model, especially with the higher powered units.

Seems that has all ready been shown with the electric versus gasoline powered automobiles.

On the other hand, our club has had more than a few models go in for unexplained reasons over the past few years. And, none of them have been electric. So far. Nice thing about higher powered electric models, or any sized electric for that matter. Just plug them in, and go fly. Last Sunday, we had one member spend a half hour trying to start his glow powered model. Finally got it running, only to have it quit in the air, resulting in an off field landing, tearing off the landing gear. Another spend a whole afternoon trying to start his gasser. Finally found the ignition module was kaput. That gasser was brand new.

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Old 07-17-2014, 06:08 PM   #17
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I fly gliders a lot and electric gliders are in explosive growth. You never see a glow launched glider anymore, unless someone had one from years ago.

The motors are so small and light and the batteries have gotten small, light and powerful.

You can now put an e-glider into the air at or near the same weight as a pure glider so there is little if any penalty for having an on-board launch system. And, unlike a pure glider, if you get into trouble or misjudge your energy you can power up rather than dropping into the woods or worse.

Electric launch puts a lot less stress on the wings than a winch launch so a lot of old woodies are coming out of the racks, getting motors installed and are being found to be competitive in the ALES electric launch format. A device in the plane lets the motor run for 30 seconds or until you get to 200 meters altitude, whichever comes first, then shuts the motor off, prop folds and you are flying a glider. No need for expensive winches or retrievers. And you can work from smaller fields.

Electric launch also extend soaring to those who might not be able to handle hi-start or haul around winches and such. Pop in the battery, power up and up you go to hunt for thermals.

In ALES competition I fly a 134" wing span molded e-Supra that weighs 68 ounces all up with a 1300 mah 3 cell and 500 watt motor. I have a pure glider supra that weighs 64 ounces all up.

That 1300 mah pack will get me to 200 meters in 24 seconds. If I hit good lift I could be up there for an hour or more without ever restarting the motor.

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Old 07-17-2014, 07:15 PM   #18
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Speaking of glow powered gliders. Never knew they were around prior to getting this one:

http://www.rcuniverse.com/market/item.cfm?itemID=985390

Needed some TLC, but no doubt will be up and flying soon. Took me a while of digging online before I could really i.d. it. The motor pod attached to a bracket above the wing joiner and had a tiny little fuel tank. I'm guessing it ran for a very limited amount of time.

The field I fly at used to do winch launches, stopped doing it at least 10 years ago. I hope to get a group of glider guys from a club in Salem CT to come up and spend a day doing demos etc. We're in a flat area overall but some tall trees surround part of the field and there is plenty of lift, just follow the birds!
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Old 07-17-2014, 08:32 PM   #19
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I'm old school = anything over 5 kilos (11.somethin pounds) is no longer a model airplane. That would translate to 1100 watts or maybe 1600 watts for a hot 3D rig.

Old school pattern planes went around 7 1/2 pounds give or take a handful of ounces, maybe a pound porkier with retracts.

Although I think Humungous scale aircraft are very pretty I believe a 50+ pound model should be licensed & insured, not "secondary" insured as with AMA but primary coverage like your vehicle.
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Old 07-17-2014, 09:43 PM   #20
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Originally Posted by carpetbagger View Post
I'm old school = anything over 5 kilos (11.somethin pounds) is no longer a model airplane. That would translate to 1100 watts or maybe 1600 watts for a hot 3D rig.

Old school pattern planes went around 7 1/2 pounds give or take a handful of ounces, maybe a pound porkier with retracts.

Although I think Humungous scale aircraft are very pretty I believe a 50+ pound model should be licensed & insured, not "secondary" insured as with AMA but primary coverage like your vehicle.
I was disappointed in AMA when they raised the limit from 28 lbs... You have to have a VERY large model to get even that heavy.
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Old 07-17-2014, 09:46 PM   #21
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Originally Posted by Porcia83 View Post
Speaking of glow powered gliders. Never knew they were around prior to getting this one:

http://www.rcuniverse.com/market/item.cfm?itemID=985390

Needed some TLC, but no doubt will be up and flying soon. Took me a while of digging online before I could really i.d. it. The motor pod attached to a bracket above the wing joiner and had a tiny little fuel tank. I'm guessing it ran for a very limited amount of time.

The field I fly at used to do winch launches, stopped doing it at least 10 years ago. I hope to get a group of glider guys from a club in Salem CT to come up and spend a day doing demos etc. We're in a flat area overall but some tall trees surround part of the field and there is plenty of lift, just follow the birds!
I would lose the bracket, cut the nose and put in an electric motor. One of the Turnigy GliderDrives would probably work well.
http://www.hobbyking.com/hobbyking/s...3_5_960kv.html

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Old 07-17-2014, 09:57 PM   #22
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That might be what is going to happen to it. Sold it to a fellow in your state, he's on RCG and RCU as Dr E. One of the nicest guys I've met in the hobby so far.
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Old 07-17-2014, 11:56 PM   #23
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It seems to me that whats practical is entirely a matter of budget and desire.

If you can afford it and want to do it badly enough, you will suddenly find that its practical. Sometimes even if you cant really afford it

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Old 07-18-2014, 04:13 AM   #24
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great question.
I don't go more than 7 cells and that's only in the extra 64"ws 300s kit build from great planes.it is the only plane in the hanger that requires the wing to be removed to fit in the car other than the gliders.

one area electric doesn't cut it is in large scale war birds. I was at NJS's field during a funfly and a guy had a large corsair similar to topflights giant kit.it ran on 12 cells and had a sound system to mimic a motor idling.
it flew great but such a beautiful bird needs a 4 stroke engine for real scale sound.

narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 07-18-2014, 04:35 AM   #25
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Originally Posted by tobydogs View Post
snip...

one area electric doesn't cut it is in large scale war birds. I was at NJS's field during a funfly and a guy had a large corsair similar to topflights giant kit.it ran on 12 cells and had a sound system to mimic a motor idling.
it flew great but such a beautiful bird needs a 4 stroke engine for real scale sound.
Now that is interesting. Putting a sound system in an electric plane to make it sound like a gas plane.

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