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Electric Airplanes for Dummies

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Electric Airplanes for Dummies

Old 11-30-2009, 02:14 PM
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TIA
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Default Electric Airplanes for Dummies

Is there a single page somewhere that just gives all the simple rules of thumb for putting an electronic power system into an airplane?

ei., If I have an "ABC" plane you would need a "123" motor and an "XYZ" battery. (not brand equipment but ratings or size)

I get confused about voltages, amps, watts, "C" rating formulas, Io ratings etc.

How does it all come together?

Is there something I can print and stick on my wall in the garage so if I buy an electric plane down the road I can look at it and just by the weight of the plane I'll know what size battery and motor to buy for it?

I think I get the ESC thing, you just want something that will exceed the amps of the system right? So it's mainly the battery to motor corrolation I don't get.


Thanks for anyones help.
Old 11-30-2009, 02:45 PM
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Default RE: Electric Airplanes for Dummies

Is there a single page somewhere that just gives all the simple rules of thumb for putting an electronic power system into an airplane?
Most manufacturers are starting to recommend power systems for their airplanes. But, no, there is no one page that will cover everything.

I get confused about voltages, amps, watts, "C" rating formulas, Io ratings etc.
When using Lipo's, each cell is 3.7 volts. When they are wired in series (S), the total voltage is equal to the sum of the cells. A 3 cell battery will be 11.1 volts and would be called a (3S) or a (3S1P) battery. The (P) stands for a parallel pack. If you take the same battery and parallel it with an identical battery, it is now a (3S2P). It is a still an 11.1 volt pack, but the capacity (mAh) has doubled.

When using two 3S packs wired in series (6S), you now have a 22.2 volt pack. But, the capacity will remain the same as the individual 3S packs.

The amp rating is the total capacity of the pack, as in how much energy is contained in the pack.

Watts = Volts x Amps. Total watts will determine what kind of performance you will get from a system. For 3D flight, you want 150 watts per Lb for the aircraft. Scale Aerobatics, you can get by with 100 watts per Lb.

C rating is is how much energy you can safely pull from a battery pack. For example, a 1300 Mah battery rated at 10C, can safely be discharged at 13 amps (10x1.3=13).

How does it all come together?
Are you with me so far?
Doug
Old 11-30-2009, 03:24 PM
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dignlivn
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Default RE: Electric Airplanes for Dummies




There is tons of info on the Electric flight forum
here on RCU. Have you been there ?

Bob
Old 11-30-2009, 03:26 PM
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Default RE: Electric Airplanes for Dummies


ORIGINAL: TIA

Is there a single page somewhere that just gives all the simple rules of thumb for putting an electronic power system into an airplane?

ei., If I have an ''ABC'' plane you would need a ''123'' motor and an ''XYZ'' battery. (not brand equipment but ratings or size)

I get confused about voltages, amps, watts, ''C'' rating formulas, Io ratings etc.

How does it all come together?

Is there something I can print and stick on my wall in the garage so if I buy an electric plane down the road I can look at it and just by the weight of the plane I'll know what size battery and motor to buy for it?

I think I get the ESC thing, you just want something that will exceed the amps of the system right? So it's mainly the battery to motor corrolation I don't get.


Thanks for anyones help.
Electrics tend to be a fair amount of guesswork and then "fine tuning" (prop, gearbox, etc) to get what you want. Motocalc has been an invaluable aid to me, and I have found that Motocalc is USUALLY pretty close to this General Rule of Thumb.


This is a "GENERAL RULE OF THUMB" that will USUALLY get you close to what you want/need. You will need to get a "READY TO FLY WEIGHT" (or close approximation) for each plane.

For trainers/general sport flying you will need 100 - 125 watts per pound of RTF weight.

Aerobatics will need 125 - 175+ watts per pound of RTF weight.

Warbirds and MOST SCALE aircraft will need 150 - 200 watts per pound of RTF weight. (Planes similar to scale Piper Cubs are an exception. They can use the trainer ratings)

3D you will need 200 - 300 watts per pound of RTF weight.

At 300+ watts per pound of RTF weight wings are frequently optional {:-)

These wattages will vary by style of plane, and wing area, however they will usually get you close.

Once you know how many watts you need, Hobby K*ng lists many motors with their wattage and cell rating (the power rating is typically based on max cells). Now you can select the size battery and esc you will need.

FWIW - MOST 40 size SPORT aircraft will require a motor with 550 - 700 watts of power.

Beware of one thing though - not all motors with the same numerical designation will generate the same power.

Hope this is of help.
Old 11-30-2009, 03:40 PM
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Default RE: Electric Airplanes for Dummies

3D you will need 200 - 300 watts per pound of RTF weight.
[X(] Now you're getting serious!

Beware of one thing though - not all motors with the same numerical designation will generate the same power.
And, that is the most difficult part of learning about electric power systems. Trial and error, disappointments and sometimes exceeded expectations. For me, it's easiest to stick with brands I am familiar with.

Wattmeter! Wattmeter!Wattmeter!
Old 11-30-2009, 06:03 PM
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Default RE: Electric Airplanes for Dummies

I'm going through this right now. I went into the electric forum and joined Watt Flyer and there is gobs of information there that you can read and down load. Perfect for those of us just getting into the learning curve.
Old 11-30-2009, 06:43 PM
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Default RE: Electric Airplanes for Dummies


ORIGINAL: firstplaceaviator

Is there a single page somewhere that just gives all the simple rules of thumb for putting an electronic power system into an airplane?
Most manufacturers are starting to recommend power systems for their airplanes. But, no, there is no one page that will cover everything.

I get confused about voltages, amps, watts, ''C'' rating formulas, Io ratings etc.
When using Lipo's, each cell is 3.7 volts. When they are wired in series (S), the total voltage is equal to the sum of the cells. A 3 cell battery will be 11.1 volts and would be called a (3S) or a (3S1P) battery. The (P) stands for a parallel pack. If you take the same battery and parallel it with an identical battery, it is now a (3S2P). That would mean that it it is a 22.2 volt pack.

The amp rating is the total capacity of the pack, as in how much energy is contained in the pack.

Watts = Volts x Amps. Total watts will determine what kind of performance you will get from a system. For 3D flight, you want 150 watts per Lb for the aircraft. Scale Aerobatics, you can get by with 100 watts per Lb.

C rating is is how much energy you can safely pull from a battery pack. For example, a 1300 Mah battery rated at 10C, can safely be discharged at 13 amps (10x1.3=13).

How does it all come together?
Are you with me so far?
Doug
Nice intro breakdown!!!
Old 11-30-2009, 06:58 PM
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Default RE: Electric Airplanes for Dummies

Thanks Ro! [8D]

TIA, are you getting this?
Old 11-30-2009, 07:10 PM
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Default RE: Electric Airplanes for Dummies

This link may help: http://uterc.org/node/214
Old 12-01-2009, 12:38 AM
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Default RE: Electric Airplanes for Dummies

ORIGINAL: firstplaceaviator

TIA, are you getting this?
I think so. I think all this info helps but in the end these discussion boards seem to be the best bet to talk about what would be most efficient.

So I was looking at this Extra. http://www.nitroplanes.com/extra330l-3d-plane.html

Would my batteries work for this plane? They are Zippy 20C 3S 2,000mAh lipo's.

Would the best motor be a Hacker C50-7XL? With a 16x8 APC-E prop?

Thoughts anyone?

TLH that link helped as well as the others.

Looks like this is a craft all of its own that I'll be forever learning...



Another alternative was this Yak. http://www.nitroplanes.com/yak523d5056v.html

Can I run my Zippy's in this if I put them in series? what prop and motor would I want for the task?

Thanks again for everyones help!
Old 12-01-2009, 01:28 AM
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Default RE: Electric Airplanes for Dummies

[link=http://www.rcuniverse.com/forum/m_7100376/tm.htm]Everything you need to know about electric flight[/link] is right here. I learned a bunch from the page (you can read about it!) - enough to choose and install an appropriate power system for whatever plane I feel like. I don't know everything, but enough to get started, and that's pretty cool[8D]
Old 12-01-2009, 09:10 AM
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Default RE: Electric Airplanes for Dummies

So I was looking at this Extra. http://www.nitroplanes.com/extra330l-3d-plane.html
Okay, cool plane [8D] It weighs about 5.5 Lbs. For sport aerobatics and mild 3D you will want about 825 Watts. For unlimited 3D, 1100 watts.

Would my batteries work for this plane? They are Zippy 20C 3S 2,000mAh lipo's.
With those packs wired in series (6S) You will have a 22.2V 2000mAh pack. 20C is equal to 40 amps. 40Ax22.2V= 888 Watts MAX

Wired in parallel, (3S2P) You will have an 11.1 4000mAh pack. 20C is equal to 80 amps. 80Ax11.1V= 888 Watts MAX

Would the best motor be a Hacker C50-7XL? With a 16x8 APC-E prop?
If you can find a suitable gearbox, that motor may work. It's awfully heavy even without a gearbox. It would take some experimenting to get it to work. I personally wouldn't recommend it.

I prefer the simplicity of an outrunner. An Axi 4120/14 with a 15x8 would work perfectly with an 80 amp ESC.

Hope that took some mystery out of it... And I hope I got it right. Someone double check it for me?
Old 12-01-2009, 12:47 PM
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Default RE: Electric Airplanes for Dummies

The 3S2P example in post #2 would have 11.1 volts with double the capacity, not double the volts.
Old 12-01-2009, 12:58 PM
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Default RE: Electric Airplanes for Dummies

Caught it and corrected it, at the exact same moment you posted. Thanks Huck!
Old 12-01-2009, 01:10 PM
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Default RE: Electric Airplanes for Dummies

Ok question, if it the same watts, what is the difference in pack configurations for flying?
Old 12-01-2009, 01:18 PM
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Default RE: Electric Airplanes for Dummies

Ok question, if it the same watts, what is the difference in pack configurations for flying?
Amperage is the amount of electrons flowing out of the battery. Voltage is the amount of push behind those electrons. With the 6S set up, you are likely to have a cooler running system and quicker throttle response. Not all motors or speed controls can handle 22.2 volts.

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