How to simulate gravity acceleration animation (free fall) in After Effects.

Hello,

   I want to make men falling from the sky. That meens that they don't have to fall with the same speed but they have to be accelerating in order to simulate gravity drop. They have to accelerate by "G" (9,81m/s)2.

How can I achieve this accelerated animation by just manipulating the keyframes?

Or, what is a very simple expression which includes G acceleration (9,81)?

I don't like expressions, so it has to be an extremely short, simple and very effective one.

Thanks