The blades of a fixed blade broadhead want to steer the arrow. Field points don't have these air dragging attachments. Like fletch, be it vanes or feathers steer the arrow, the blades fight to steer the arrow as well. That is why adequate fletch is necessary to counter the blades. If your arrow is not exiting the bow pefectly straight be it vertically or horizontally, the broadhead will want to emphasize that error in flight until the fletch straightens out the arrow, if at all. That's what is refered to as planeing.

We preach either offset or helical fletch because the faster and sooner you get an arrow spinning out of the bow, the quicker it will stabilize in flight because of the blades of the broadhead. A straight fletch arrow will want to be steered by the broadhead.

Several things can cause that errant arrow flight. A poorly tuned bow, unmatched arrows or arrows who's inserts are not aligned with the shaft properly causing wobble in the head, the wobble is caused by the insert not pointing the broadhead in a straight line with the arrow.

I'm not sure if I worded that right but I know what I wanted to say. [&:]