Fuel Tank & CG

Of course that mass wasn't all converted to energy -- it mostly went out the exhaust pipe with just a few hundred picograms (if my calculations were correct) actually converted to energy.

For weight control in a long-distance electric you could jettison spent batteries.

Fuel cells keep showing promise -- perhaps one day it'll be a methanol fuel cell and an electric motor?

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Oh, you mean like a spring motor that has been wound up. It now contains energy. Does it weigh more?

Ed Cregger

| Oh, you mean like a spring motor that has been wound up. It now contains | energy. Does it weigh more?

Yes.

(Is that the answer you were expecting? I'm not quite sure.)

Doug, Last I heard earth is part of the universe. Laws of Conservation of mass/matter/energy are universal. BTW, what was the source of that energy you added to the battery?

| Last I heard earth is part of the universe. Laws of Conservation of | mass/matter/energy are universal.

We must be not understanding each other or something. What you're saying isn't wrong, but it's like you're arguing with something I didn't say or something.

When you fill up the tank of your (glow) plane, the total mass of your plane goes up. The mass of the Universe doesn't, but the mass of your plane does. This effect is easily measurable -- well, at least the first part is. (Unless you have a way to measure the mass of the Universe.)

When you charge a battery, the mass of the battery increases (assuming that things like outgassing don't happen.) The effect is miniscule, but I suspect this sort of thing has been experimentally confirmed. The total mass of the Universe has not changed, but I'm only talking about the battery here.

When you compress a spring, it's mass increases. The effect is miniscule, but ... { copy the rest from the previous paragraph. }

When you heat up your (plug-in) soldering iron (so you can solder your ESC to your motor), it's mass increases. The effect is miniscule, but ...

When you heat up your rechargable soldering iron, it's mass stays roughly the same, at least at first. The battery loses energy (and therefore mass), but the tip gains mass due to the energy flow. Of course, heat energy is also lost as the tip gets hot, so the total mass of the soldering iron will start going down as the tip gets hotter and hotter (the hotter it is, the more heat it will lose.) The effect is miniscule, but ...

The increases in mass due to stored chemical, mechanical or heat energy are miniscule and can be ignored in pretty much every case. (And even measuring them will be a difficult or impossible challenge.) The increase in mass due to added glow fuel seen in the first case is much much larger, and it should *not* be ingored when setting up your plane. But for all our purposes (beyond the purpose of arguing on Usenet), the difference in mass of a battery between it's charged and uncharged state can be totally ignored.

| BTW, what was the source of that energy you added to the battery?

My wall-wart charger. Or the 12v power supply that powered it. Or the electrical grid. Or the power plant. Or the coal that powered the power plant. Or the geological or bioligical processes that created that coal. Or the process that created those materials ...

Either way, I was only talking about the battery. Not the entire Universe. The Universe is presumably a closed system, but the battery is not, at least not while you're charging it. When you take mass and add it to a system, and mass isn't lost from that system somewhere else, the total mass *of that system* increases. This really should be common sense, no?

| > Now, how can I bring this around and make it all relevant to this | > newsgroup again? :) | >

| > When Maynard flew his 11 lb plane across the Atlantic a few years ago, | > the total was roughly half plane and half fuel -- 5.5 lbs of each. He | > had fuel crammed in pretty much everywhere he could fit it. Keeping | > the CoG somewhat constant as the fuel was consumed was probably a | > *major* consideration of the design of that plane.

And the only reason I mentioned this is that this thread was previously talking about shifting CoGs due to fuel consumption, and I was at least trying to at least keep the newsgroup topic (R/C model airplanes) even if we're getting pretty far from it.

OK! OK, enough already! I am sorry I mentioned the charged battery thing shifting the CG. After reading all these comments, my brain is hurting. I was only joking...

Ken

But I will still charge the battery if...

E=MC^2 is not a joke, it's the law

I saw in the paper this morning some old timer charged every battery pack he owned all at once and threw the Earth off it's axis by ,00000000000000000000000000000000000000001 inches due to the increase in mass.

hehe

I was joking...the math may or may not have been. Don't get too cocky over the current absolute law of physics. We have had a lot of them.

Ken

Well...now...see there!

Ken

Hi Doug, My brain is going into atrophy mode . I think you may be confusing mass and weight (as most of us do). Essentially Mass is the amount of matter in an object (measured in slugs). Newton realized that all objects have an intrinsic property that doesn't depend on the planet pulling on the object, a property that stays the same whether or not the object is on the Sun, the Moon, or on the Earth. This intrinsic property of any body, independent of where it is in the universe, is called the body's mass. And a body's mass can be obtained by taking its weight -- which depends on how much a particular "planet" is pulling on it to make it "heavy" -- and dividing its weight by the strength of the particular planet's pull on it (result = slugs)..

I think I may be correct in saying that the compressed spring has the same mass compressed or uncompressed because it contains the same amount of matter. Unless, of course, the compressed spring has exchanged some matter for energy --- Oh to hell with it - I'm confusing myself but I think you get my drift . This is almost better than discussing downwind turns at the field! I'm out never to return ;-))