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Battery in my RC airplane

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audioguru

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My cheap RC airplane came with an 8.4V Ni-MH battery made with 7 AAA cells.
The power was barely enough for the plane to fly level then slowly get lower and land. Each flight lasted only a minute or two if it didn't stall then crash. Wind caused spectacular crashes.:(
I tried another similar battery and it performed the same.

Then I tried two Lithium-Ion cells from a lap-top pc that are heavier and have a typical total voltage of only 7.4V. The plane quickly goes up high like a rocket and the charge lasts for a long time (15 minutes).:D

The motor's speed controller circuit shuts off the motor when the battery voltage gets too low so the radio controls still work. After a short rest the "discharged" battery powers the plane again for a long time. After the second time and after a second rest the battery measures 7.7V which is far more than the 6V minimum allowed.

Now I have a bunch of lithium-ion batteries. I can swap them quickly.
I charge them with an LM317 regulator fed "9V" from a 500mA wall-wart and the regulator is set to 8.4V. Each battery is fully charged in less than 4 hours.

Lots of fun.
 

BrownOut

Banned
So are you saying the plane's motor is powered by the batteries? Usually, there is a small 2-stroke fuel engine on RC planes. 'Course, I'm no RC hobbiest. I've only observed.
 

dknguyen

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So are you saying the plane's motor is powered by the batteries? Usually, there is a small 2-stroke fuel engine on RC planes. 'Course, I'm no RC hobbiest. I've only observed.
Not nowadays they're not, especially for smaller planes. It's difficult and counterproductive to fit an engine onto a plane that weighs less than 500g (sometimes even 1kg). Plus you can't fly indoors lol. There are some ridiculously small nitro engines though.
http://www.youtube.com/watch?v=e61CAdTjNrQ
 
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audioguru

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I used to fly 2-stroke engine powered model airplanes 48 years ago.
My electric plane weights 1.3 lbs. It is kind of heavy so it flies pretty fast. Flying into a stiff breeze it looks like it is hovering.

New electric RC airplanes are big and little. I saw a big one smoke its very expensive Li-Po battery. The smallest ones are tiny.

These ones are small and fly is a school gym or outside when there is no wind. They weigh 20 grams and 34 grams complete with battery, receiver and servos.
 

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dknguyen

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There are still lots of fuelies around. THey are mainly in the larger ones though. Batteries aren't that good yet!
 
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audioguru

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Last week I saw a smoking RC helicopter flying upside-down.
I also smelled it and heard it so it must have been a fuelie.

You cannot hear my electric RC airplane. I had another one with a huge propeller that was driven through noisy gears.
 

dknguyen

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Electric helicopters sound more like turbines since you can only hear the rotor beating against the air.

The plane I'm working on looks very non threatening (because it doesn't look heavy or like a scale plane) but I just finished the main wing and I didn't realize how big it is. It's big enough that it might look threatening to people when I go fly it in a park.

The main thing left is to attach control horns to the tail surfaces and tie everything to the fuselage.
 
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microtexan

New Member
RC PLane

Electric helicopters sound more like turbines since you can only hear the rotor beating against the air.

The plane I'm working on looks very non threatening (because it doesn't look heavy or like a scale plane) but I just finished the main wing and I didn't realize how big it is. It's big enough that it might look threatening to people when I go fly it in a park.

The main thing left is to attach control horns to the tail surfaces and tie everything to the fuselage.
We'd love to see it when you're finished.:)
 

arunb

Member
what would be the normal range of a battery powered airplane and a fuel powered one. Also what's the maximum altitude ??
 

microtexan

New Member
electric rc planes

Electric planes are still a minority, they will never approach the performance of a glow-plug engine.
Never is a powerful word. 10 years ago, who would have believed we would have the battery capacities we do today.
 

Nigel Goodwin

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Never is a powerful word. 10 years ago, who would have believed we would have the battery capacities we do today.
It's a VERY powerful word, but battery development is nowhere near the energy density of fossil fuels - and unless something completely new and incredibly better than existing technology comes along, it's never going to get there.

Todays capacities are evolution, not revolution - and fossil fuel engine efficiencies are increasing as well.

If you prefer it, I'll rephrase to "not in anyone here's lifetime" :D
 

microtexan

New Member
batteries

It's a VERY powerful word, but battery development is nowhere near the energy density of fossil fuels - and unless something completely new and incredibly better than existing technology comes along, it's never going to get there.

Todays capacities are evolution, not revolution - and fossil fuel engine efficiencies are increasing as well.

If you prefer it, I'll rephrase to "not in anyone here's lifetime" :D
Sorry, Nigel I forgot the :D and I'll go with "not in anyone here's lifetime".
 

dknguyen

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Actually electric helicopters can and do outperform glow engines in terms of performance. If you're talking about flight times, however, that's a different story.
 
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MikeMl

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... battery development is nowhere near the energy density of fossil fuels - and unless something completely new and incredibly better than existing technology comes along, it's never going to get there...
Most folks don't understand the concept that with fossil fuels, due to the stoichiometric nature of a combustion engine, you only have to haul around 1/15th of the fuel you actually burn because the remaining 14/15th comes from the air the engine breathes, while in an electric system, you have to haul 15/15th on your back :mad: Not good for airplanes or cars.
 
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