i'm setting the cg on a plane an i just dont get it ? i don't understand why get the cg right an then add oz's of fuel that's not on the cg line? you do check cg with a empty tank don't you david

You always check the CG with the fuel tank empty. In most planes the fuel tank is forward or on the CG. A full tank will make the plane a little nose heavy, but easy to fly. When the tank is low, or empty, the balance will be where it should be. If you balance when the tank is full, when it's empty your plane will be tail heavy. Then the following saying comes into play

"A nose heavy plane flys poorly, a tail heavy plane flys once."

Ken ir right on. You balance the plane for the worst case scenario which means empty fuel tank. The fuel tank is usually in the nose. With fuel in the tank, the extra weight adds to the nose weight which doesn't hurt anything. When the fuel is gone or almost gone you still want the balance to be slightly nose heavy. You never want to be tail heavy, makes for a short and scary flight![X(]

If one would ask, "why does a tail heavy plane hard to fly??" Could a newb like me answer, "it's because you would be much much more susceptible to stalls???"

It causes the elevator to become VERY sensitive

DUH!!! Oh well, I tried.

Yeah, You have it right as do fast sky and RC ken. Think about it this way, No matter what, You won't have a full tank for long. And when you get up 500 feet and go deadstick, your in a neutral position.

I know that really makes no sense, but honestly, you won't have a tank full long. Rather be nose than tail heavy for SURE!

What are you doing at 500 ft? Can barely see the plane, let alone control it well.

You can always add tail weight to a nose heavy airplane. You may, or may not, be able to repair a tail heavy airplane.

Jim

Think of an Arrow. An arrow has a small heavy weight at the front, and and big, light feathers at the back.

As the arrow travels through the air, the feathers catch the air and keep the back of the arrow, well... in the back.

Now imagine replacing the arrow point with one made of balsa, and replace the feathers with lead fins - when you shoot the arrow, even though the fins are as broad as they were, they are still heavier than the tip, so the arrow will flip soon after it leaves the bow.

It's the same thing with an airplane - if there's too much weight in the back, it will try to fly tail-first.

I think you can see why this would be bad.