Yaw String

Yaw string used in front of the cockpit of an F-14D Tomcat

Diagram showing yaw string deflection on a multi-engine airplane flown incorrectly with wings level after an engine failure.

Side string

Overview

The yaw string, also known as a slip string, is a piece of yarn attached to an aircraft's canopy, primarily used as a visual indicator of side slip during flight. Invented by Wilbur Wright in 1902, it's considered the earliest flight instrument and is still used on some gliders and some military aircraft today.

History and Development

• 1902: Wilbur Wright incorporated a yaw string into the 1902 Wright Glider.
• Early Aviation: The yaw string served as a basic but effective method for pilots to understand and correct for aircraft yaw, especially in turns.
• Modern Uses: While modern aircraft have more sophisticated instrumentation, yaw strings remain a useful tool for visual confirmation of aircraft coordination, particularly in gliders and some military aircraft.

How it Works

• The string is attached to the aircraft's canopy, allowing it to move freely in the airstream.
• When the aircraft is flying straight and coordinated, the string hangs straight ahead.
• If the aircraft starts to slip or skid (e.g., during a turn), the string will deviate to one side, indicating that the pilot needs to adjust the rudder to regain coordination.
• By keeping the string centered, the pilot can maintain a stable and coordinated flight path.

Advantages of the Yaw String

Direct Visibility

The yaw string provides immediate visual feedback in the pilot's field of view.

Sensitivity

It's highly sensitive to changes in airflow, allowing the pilot to react quickly to any deviations in flight coordination.

Simplicity

It's a simple and reliable instrument that requires no electricity or complex maintenance.

Cost-Effectiveness

Yaw strings are inexpensive to manufacture and maintain.

Modern Relevance

• While not universally used, yaw strings continue to be valuable tools in some aircraft types.
• They serve as a backup to more sophisticated instrumentation and provide a visual confirmation of aircraft coordination, especially during turns or in situations where other instruments may be unavailable.