Smooth out animation?

I’ve started messing around with animations. I’ve made a pretty simple one. A fan rotating in the ceiling. It’s pretty easy but when I see the animation it suddenly becomes faster until the half of the timeline and after that it decreases then stops suddenly. How can I smooth out the animation so the model will rotate like a fan rotates in real life?

Go into the dopesheet editor and select the keyframes for the fan rotation, then (T key) to set inTerpolation, and choose “Linear”.

Thanks! (longgggg)