Center of lift
The center of lift (abbreviated COL) is one of three measurable forces in the Vehicle Assembly Building and Space Plane Hangar. Used mainly when creating planes, it shows the axis and direction of lift provided by wings, control surfaces and winglets. Inside the editor it is showed as a cyan-coloured sphere (axis) along with an arrow (direction of the lift).
Uses in plane bulding
The location of the center of lift in relation to a plane's center of mass defines the plane's behavior in flight. Depending on where the center of lift is placed, the consumption of fuel may affect the center of mass in such a way that the plane becomes back-heavy and very unstable over time. To counteract this, it's recommended to place the center of lift slightly behind the center of mass, as this will keep the plane stable throughout the flight despite the shifting weight of the fuel.
The center of lift can tell how a plane will move in flight. If the lift is to far behind the center of mass then the plane will pitch slightly forward, if it is to far forward then it will pitch backwards. Similarly, if it is too far to the right it rolls left and if it is to the left it rolls right. It is good to have it close to the center of mass to prevent tipping in any direction.