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Bod

I/C versus Electrical propulsion

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Hello.

On some R/C Forums, this debate is highly controversial.

Do you think the energy density of a Electrical powered propulsion system is higher than a internal combustion powered one, such as a Li-Po powered motor versus a gasoline, or even a methanol-driven combustion engine ?

The benefits of electrical motors, having no exhaust goop, having low vibration level and such, are omitted in this comparison.

I use both myself, I use Electrical propulsion for small machines and I/C for larger ones and I like both very much.

I think electrical motors are best if you fly smaller machines and/or you do not need to fly for extended time periods such as more than 10 minutes.

It is also generally less messy to start a Electrical motor, but perfecting the start procedure of a combustion engine could be regarded as fine art by itself.

One major drawback with electrical motors is that they tend to severely degrade radio-link quality, reducing practical range, however this problem can be mastered by selecting good quality components. This is also true for spark-ignition combustion engines.

I lost the focus partially, the original question was about the energy density :)

I have seen people stating that electrical driven model-airplanes are physically more efficient than internal combustion driven ones, isn't that funny ? I wonder why electrical model air-planes tend to be on structural diet in terms of strength and rigidness, mostly not explained by abcence of damaging vibrations.

I mean, why isn't every car driven by Li-Po batterys and three phase engines, what about the space shuttle ? Why have no electrical airplanes crossed the atlantic, except cheating special solar-panel driven ones, almost with no payload whatsoever?

My car can go 750 km on 50 liters of gasoline and it weigts in at approx 1350 kg at full tank with driver. It is a safe car that can protect the passengers from deadly injury in a violent chrash such as a moose or frontal car collision at 70 km/h or more. (It is not a Volvo or Saab, it is good anyway, however it is not a Renault either) That is totally out of reach with current electrical propulsion systems, so what gives ?

Is it a P.C. thing, thinking that battery driven vehicles are more efficient than internal combustion driven ones ?

Bo

Edited by Bod

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Do you think the energy density of a Electrical powered propulsion system is higher than a internal combustion powered one, such as a Li-Po powered motor versus a gasoline, or even a methanol-driven combustion engine ?

To be short, I'd say no.

I can fly my ~2.5kg multi with a .46 engine for ~30 mins with ~200gr of fuel, while a battery of the same weight will keep my 1kg electric in the air for 15mins.

On a more scientific approach, http://en.wikipedia.org/wiki/Energy_density

The energy density of a li-ion battery is in the range of 0.54–0.72 MJ/kg, methanol is 19.7MJ/kg.

Petroleum products are between ~43-47 MJ/kg.

There's no miracle, if they were comparable it would be a long time we'd have battery-powered cars/planes/... but go imagine an electric transport plane when you can store more than 50 times less energy in the same weight...

The same is valid for cars, but now it's more the energy by volume which is interesting. The ratio here is a bit lower, but still about 20-30...

However, it's true an electrical powerplant will have a much better efficiency. The typical efficiency of an IC engine is 25-40%. A "good" electrical one can have a 70% efficiency. So depending on the combination you would have to store 2-3 times less energy to get the same output on an electrical powertrain. Still out of range for transportation though...

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As with most things it is a trade off. There is no right answer for all situations. Only you can decide whats right for your project.

Terry

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As usual, your replies are sound and intelligent, Terry.

I meant mass And enegery efficency (as I know you know), if a combustion engine wastes 80 percent into heat is unlucky, but still it punches a lot of power for the weight.

I made this post because I got owned by some club members who do not count in kilowatts, kilograms and stuff :P

Bo

Edited by Bod

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Absolute effincency could often be of minor interest compared to mass/power output efficiency, I like to fly for 30 minutes with x grammes of fuel. If My motor wastes 99% of those grammes into heat, I do not care whatsoever and I do not think most others do either.

:D Bo

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Both systems are needed, I use electrical for my T-rex helicopter and I would not replace that with an unreliable .12 glow. I would also never replace my trusty balanced .70 4C engine with an electrical motor.

:lol:

Edited by Bod

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"Horses for courses!" Apart from the duration question, what about cost? Conversion from I.C. to electric power means a hefty outlay for decent motor, Li-Pos, charger, etc etc. For serious duration, serious battery cost,etc.

OK once youve got it all, running costs are peanuts,just plug into mains,(or car battery). Plus, another consideration, ambient and operating temperatures, where I.C. engines are a lot less fussy.

One good thing about electric, the engine doesnt run out of puff at altitude.

Recently had the experience of flying at very high(ground) altitude with a small .32 powered vid plane.At sea-level, toss in the air and up like rocket. At altitude, run like heck and throw like a javelin, whilst not slipping in the snow! 50% nitro, (good for the engine life!) and a very modest climb rate. Landing, fly up the slope and stall it on for a bit of uphill sking!

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