by: Russ O’Brien
In airplanes, toe-in aids in keeping an airplane going straight during takeoff roll and landing roll-out, particularly with tail-draggers. Airplanes with tricycle gear have the center of gravity (CG) forward of the main gear. This helps straighten out an airplane that has developed a yaw angle between where it is pointed and where it is actually going. A tail-dragger has the CG behind the main gear and a slight yaw angle is not automatically corrected but is made worse and can result in ground loop.
Here is where toe-in of the wheels helps both types. An airplane rolling straight ahead has equal drag from each of the wheels. When it takes an unwanted turn to the left, the drag from the left wheel goes to zero while the drag at the right wheel increases. The net effect is the unbalanced drag exerts a retarding force and turns the airplane back to the desired direction. This wouldn’t happen without toe-in.