Josh,

When you are flying upright, the air movement is downward, keeping the heli in the air...the reason there is downward airflow is because the blades are in a positive pitch position, pushing air down towards the ground...

Then, when you want to fly inverted, you set the helicopter up to have negative pitch, which if applied in the upright position, will push the helicopter downwards...pushing the air upwards in the process...

So, when the heli is upside down, the negative pitch acts just like positive pitch when the heli is upright...just the opposite effect...

The blade 400 comes out of the box 3D ready, so it would have negative pitch if you switched the idle up switch, or F. mode, or stunt, as Eflite calls it...but for normal, upright flight, you would want very little, if any negative pitch, but a little is good for flying in the wind...

Hope this helps...

Glenn