Think when you change a tire on your car. You have some type of wrench that gives you leverage on the nut. The distance from the nut, where you push on the wrench is the arm. Sometimes people extend the wrench with a hollow pipe....this extends the arm. How hard you push on the wrench is the force. How hard you push times the arm is the moment. Therefore, your strength is magnified when you lengthen the wrench (maybe with a pipe) because moment = force x arm
everything makes great sense however in the plane demo you assigned the empty weight of aircraft an arm of 28, my question is how and why? that marks a point behind pilot but IN front of all other weights, would it not be the center of aircraft in relation to the datum? couldn't you simply choose any nominal distance in this exercise and still be correct if not my suggestion?
@Chris Fillmore Keep in mind that there is significant weight in front of the datum for the aircraft in the example. The engine, nose gear and tire, propeller, etc. That factors into the empty weight and the total moment of all the arms and weights in front of and behind the datum.
Explaining some terminology here: 1. weight is the force exercised by any mass due to gravity - I think this is clear for anybody; 2. moment is the torque that appears when a force is applied at the end of a lever - consider this a "rotating effort" 3. arm is the distance from the fulcrum to the force application point, perpendicular per force direction, as all the forces here are due to gravity, the distance is horizontal
