Google can:In the slow speed flight regime, the airflow over the aircraft can becomeless predictable. For instance, variations in the wind caused by gusts orground obstructions can change the airflow over the aircraft relative tothe aircraft's body and relative to the flight path of the aircraft overthe ground. Also, the aircraft can rotate around its yaw axis due tocontrol inputs so that the body of the aircraft is no longer aligned withthe flight path of the aircraft. Misalignment of airflow over an aircraftrelative to the aircraft's body is known as the angle of sideslip.Excessive angle of sideslip can create serious hazards in the slow speedflight regime. For instance, in the Harrier, if more than a 10°angle of sideslip exists, the aircraft can enter into an uncommanded roll,which can be unrecoverable. To prevent this hazard, the Harrier uses aweathervane-type probe extending into the airflow in front of the cockpitwhich measures angle of sideslip. The weathervane-type probe aligns withthe relative wind, allowing the aircraft to determine angle of sideslip bymeasuring the difference between the rotational position of theweathervane-type probe and the normal alignment of the body of theaircraft with the airflow. In the Harrier, if the angle of sideslipbecomes excessive, a warning is provided to the pilot by a pedal shakerwhich shakes the rudder pedals. The pilot can also visually monitor theangle of sideslip by observing the amount of angular offset of theweathervane probe. However, the Harrier's weathervane probe is fixed inplace even when the Harrier is in normal wing borne flight. This increasesthe drag of the Harrier at higher speeds.