How to calculate a arrows angle while in air

So my Problem is, im lounching an arrow with a certain angle and velocity applied to it. so just like in RL the arrow starts to fall after some time but the the whole prefab will stay at the same angle it was lounched. I want to calculate the angle but i cant find any formula or anything helpfull.

You can use Quaternion.LookRotation and use the arrows current velocity to make it always be rotated ‘forwards’