The aerodynamic forces and moments are defined below –
Lift is a component of force acting upwards perpendicularly to the direction of flight or the undisrupted system.
Drag is a component of force acting opposite to the direction of the line of flight or in the same direction as the motion of undisrupted stream. It is the force that resists the motion of the aircraft.
Crosswind Force (Y)
Crosswind force is the component of force which is mutually perpendicular to the lift and drag i.e. in the spanwise direction. This force is positive when acting towards the starboard wing.
Pitching Moment (M)
This is the moment action in the plane containing lift and drag force i.e. in the vertical plane when the aircraft is flying horizontally. It is positive when it tends to increase the incidence.
Rolling Moment (L)
This is the moment tending to move the aircraft float about the flight direction i.e. tending to depress on wind and rise on the other. It is positive when it tends to depress the starboard wingtip.
Yawing Moment (N)
This is the moment that tends to rotate the aircraft about the left or right direction i.e. swing the nose to the one or the other side about the flight direction. It is positive when it swings the nose to the right.
So these are the aerodynamic forces and moments.