Yaw String (Slip String)
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The yaw string, or slip string, is a simple, highly sensitive device that indicates a slip or skid in flight. Mounted in the pilot’s field of view—typically on the canopy or nose—it provides real-time feedback on sideslip angle, unlike traditional panel-mounted slip-skid indicators.
Function
The yaw string shows whether the aircraft is in coordinated flight. If the string is displaced, rudder input is required toward the direction of the string’s head (or “step on the head”). It is especially useful in:
- Gliders, where minimal slip maximizes performance,
- Jet aircraft like the F-14 Tomcat and U-2, which also use yaw strings during precision maneuvers,
- Twin-engine aircraft during engine-out scenarios, where the ball is unreliable.
Construction
Made from yarn or string, it may be enhanced with a paper cone and is often attached with tape or mounted on a mast. It operates best in clean airflow areas, and is typically ineffective on nose-mounted tractor propeller aircraft due to propeller wash.
History
Wilbur Wright reportedly invented the yaw string in 1902, mounting it on their glider’s elevator. It was aviation’s first “flight instrument” and remains in use across a wide range of aircraft types.
Operation
The yaw string aligns with airflow. If off-center, it indicates sideslip. Pilots “step on the head” of the string to correct. It is the most reliable visual indicator during spins and other dynamic flight conditions.
Side String
A variant called the “side string” indicates angle of attack in gliders, helping optimize glide and thermalling speeds, independent of airspeed or other instruments.
References
- Reichmann, Helmut. Cross Country Soaring. Soaring Society of America, 1988.
- FAA. Glider Flying Handbook.
- FAA Library
- Flying Magazine: Yaw String Discussion
