Thanks, I stayed at a Holiday Inn Express last night.
Actually, when I read your post talking about being unable to ground and stuff--I thought to myself "whattheheckishetalkinbout"
You can't really mix AC and DC together, because the AC waveform would be constantly messing with that supposed-to-be constant DC voltage. So that is why we rectify AC, so that we can have DC (because DC is a less efficeint, but much simpler form of electrical power)...
Think about that basic, basic circuit in any electronics textbook, a battery, a resister, and two wires to connect them. In DC, the current always flows that single direction. But in AC, the current direction is CONSTANTLY changing, one moment it goes one way, the next it reverses. But the circuit will work equally effectively in either case, with the same exact components.
A ground is really just a shortcut. When something is grounded, it means that somebody decided to be lazy for whatever reason and use a conductive structure to serve as a wire. In that basic circuit I talked about above, add a bunch of resistors in paralell. Now, even though there are many different loads, ALL of the current must still flow through the same place in two places in the circuit. Into, and out of the battery. But let's say that one resistor is in the nose of an airplane, and oen is in the tail, one is in a wing... Raise your hand if you want to run a wire both to and from each of those resistors to the battery. I am lazy at heart, so I would say to myself: "hey, aluminum can conduct electricity, why not pretend that the body of the airplane is just one big, huge wire?" So, I just connect that end of the battery to the airframe, and I connect one of the leads from every resistor to the frame as well. Basically, we've still got to have one of the wires running to everything (and this wire is what we will use to turn it on and off), but with careful design, we can make it so that EVERY component in the airplane will use the same return path to the battery. This is what the term grounded refers to on an airplane. It means it is connected to the airframe.
Look at your starter, you will see a big cable coming from a realy to it (and that relay will be connected to the battery), and probably another cable that runs directly to the frame of the airplane. That is the cable that grounds it out. Look at a nav light, it will have one wire going into it (the power supply), but we all know that without some sort of return path, nothing will work, so we use the airframe as a return path.
As to that thing about the ground in your house--that is connected to that odd pin on your standard Edison socket. That is there to protect you by always providing a path for electricity to go to the earth (which, in the grand scheme of things is where it would always rather go). This way, if you were to have, say, a drill that was shorted out internally (a wire coming from one of the hot connections, that touches the case), and you touch that case, without that third prong ground, the electricity sees your body as the easiest way to get back to the earth (as opposed to running through the drill motor and travelling all the way back along the power lines to the power company). So, instead of allowing it to travel through your body, they provide a very low resistance path to the ground from the case. Hooray, I don't get shocked!!!
Yes, your car works the same way as an airplane (unless you've got some of those freaky british cars that have positive grounds--wierd). The power in your house is not, in any way, connected to that pole stuck in the ground. That pole has a wire running to all of those third prongs, to the case of every outlet, to the case of every circuit breaker panel, etc... If you've got current running through it, you've got a problem.
As to that DC power travelling one way, using or it being lost... There always has to be a return path. If you've got that circuit with the resistor I talked about above, and you unhooked a terminal from the in side of the battery, you would still have an electrical potential at all points in the system, it just wouldn't be doing anything because it couldn't flow.
Hope that makes sense. I've covered about a weeks worth of class in a few hundred words...
Dan