Hello, my first post here. I'm an avid flight sim enthusiast. I wanted to ask what is the formula for calculation of sink rate for aircrafts? I know 4 forces act on the airframe: lift drag gravity thrust sink rate is the amount of distance/time the aircraft sinks from final position to reach touchdown on the runway threshold. usually measured in feet/second. Another thing I wanted, is how drag is represented. I mean what is drag? how to calculate drag on an aircraft grossing 31,000 lbs. what factors must be taken into account? thanks in advance.