Yaw String - Use On Powered Aircraft

Use On Powered Aircraft

Yaw strings are also fitted to the Lockheed U-2 high-altitude surveillance aircraft. Some light twin-engine airplane pilots place yaw strings on their aircraft to help maintain control in the event of an engine failure, because the slip-skid indicator ball is not accurate in this case. In a multiengine airplane with an inoperative engine, the centered ball is no longer the indicator of zero sideslip due to asymmetrical thrust. The yaw string is the only flight instrument that will directly tell the pilot the flight conditions for zero sideslip.

Yaw strings are also used on some (especially smaller) helicopters.