Yaw string
Encyclopedia
The yaw string, also known as a slip string, is a simple device for indicating a slip
Slip (aerodynamic)
A slip is an aerodynamic state where an aircraft is moving somewhat sideways as well as forward relative to the oncoming airflow. In other words, for a conventional aircraft, the nose will not be pointing directly into the relative wind .A slip is also a piloting maneuver where the pilot...
or skid
Skid (aerodynamic)
In flying, a skid is a specific type of slip.It often means a turn where the sideways movement of the aircraft is outwards from the centre of the turn...
in an aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
in flight. It performs the same function as the slip-skid indicator ball, but is more sensitive, and does not require the pilot to look down at the instrument panel. Technically, it measures sideslip angle
Sideslip angle
Sideslip angle, also called angle of sideslip , is a term used in fluid dynamics and aerodynamics and aviation. It relates to the rotation of the aircraft centerline from the relative wind...
, not yaw angle, but this indicates how the aircraft must be yawed to return the sideslip angle to zero.
It is typically constructed from a short piece or tuft of yarn placed in the free air stream where it is visible to the pilot. In closed cockpit aircraft, it is usually taped to the aircraft canopy
Canopy (aircraft)
An aircraft canopy is the transparent enclosure over the cockpit of some types of aircraft. The function of the canopy is to provide a weatherproof and reasonably quiet environment for the aircraft's occupants. The canopy will be as aerodynamically shaped as possible to minimize drag.-History:Very...
. It may also be mounted on the aircraft's nose, either directly on the skin, or elevated on a mast, in which case it may also be fitted with a small paper cone at the trailing end. They are commonly used on gliders, but may also be found on jet aircraft
Jet aircraft
A jet aircraft is an aircraft propelled by jet engines. Jet aircraft generally fly much faster than propeller-powered aircraft and at higher altitudes – as high as . At these altitudes, jet engines achieve maximum efficiency over long distances. The engines in propeller-powered aircraft...
(especially fighters
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...
), ultralight aircraft, light-sport aircraft
Light-sport Aircraft
A Light-sport aircraft, also known as light sport aircraft or LSA, is a small aircraft that is simple to fly and which meets certain regulations set by a National aviation authority restricting weight and performance...
, autogyro
Autogyro
An autogyro , also known as gyroplane, gyrocopter, or rotaplane, is a type of rotorcraft which uses an unpowered rotor in autorotation to develop lift, and an engine-powered propeller, similar to that of a fixed-wing aircraft, to provide thrust...
s, airplanes and helicopters. Its usefulness on airplanes with a tractor configuration
Tractor configuration
thumb|right|[[Evektor-Aerotechnik|Aerotechnik EV97A Eurostar]], a tractor configuration aircraft, being pulled into position by its pilot for refuelling....
(single propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...
at the nose) is limited because the propeller creates turbulence and the spiral slipstream displaces the string to one side.
The yaw string is considered a primary flight reference instrument on gliders
Glider (sailplane)
A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...
, which must be flown with near zero sideslip angle to reduce drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
as much as possible. It is valued for its high sensitivity, and the fact that it is presented in a head-up display
Head-Up Display
A head-up display or heads-up display is any transparent display that presents data without requiring users to look away from their usual viewpoints...
. Even the most sophisticated modern racing sailplanes are fitted with yaw strings by their pilots, who reference them constantly throughout the flight.
History
The yaw string dates from the earliest days of aviation, and actually was the first flight instrumentFlight instruments
Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with information about the flight situation of that aircraft, such as height, speed and altitude...
. The Wright Brothers
Wright brothers
The Wright brothers, Orville and Wilbur , were two Americans credited with inventing and building the world's first successful airplane and making the first controlled, powered and sustained heavier-than-air human flight, on December 17, 1903...
used a yaw string on their 1902 glider
Wright Glider
The Wright brothers designed, built and flew a series of three manned gliders in 1900-1902 as they worked towards achieving powered flight. They also made preliminary tests with a kite in 1899. In 1911 Orville conducted tests with a much more sophisticated glider...
tied on their front mounted elevator. Wilbur Wright is credited with its invention, having applied it concurrently with the movable rudder invented by his brother Orville in October 1902, although others may have used it before. Glenn Curtiss
Glenn Curtiss
Glenn Hammond Curtiss was an American aviation pioneer and a founder of the U.S. aircraft industry. He began his career as a bicycle then motorcycle builder and racer, later also manufacturing engines for airships as early as 1906...
also used it on his early airplanes.
Use on powered aircraft
Yaw strings are also fitted to the Lockheed U-2Lockheed U-2
The Lockheed U-2, nicknamed "Dragon Lady", is a single-engine, very high-altitude reconnaissance aircraft operated by the United States Air Force and previously flown by the Central Intelligence Agency . It provides day and night, very high-altitude , all-weather intelligence gathering...
high-altitude surveillance aircraft
Surveillance aircraft
A surveillance aircraft is an aircraft used for surveillance — collecting information over time. They are operated by military forces and other government agencies in roles such as intelligence gathering, battlefield surveillance, airspace surveillance, observation , border patrol and fishery...
. 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.
See also
- Glider (sailplane)Glider (sailplane)A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...
- GlidingGlidingGliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.Gliding as a sport began in the 1920s...
- Sideslip angleSideslip angleSideslip angle, also called angle of sideslip , is a term used in fluid dynamics and aerodynamics and aviation. It relates to the rotation of the aircraft centerline from the relative wind...
- Slip (aerodynamic)Slip (aerodynamic)A slip is an aerodynamic state where an aircraft is moving somewhat sideways as well as forward relative to the oncoming airflow. In other words, for a conventional aircraft, the nose will not be pointing directly into the relative wind .A slip is also a piloting maneuver where the pilot...
- TuftTuftIn the aviation field, the term tuft refers to a strip of yarn or string of varying length attached to an aircraft surface in a grid pattern and imaged during flight. The motion of these tufts during flight can be observed and recorded in order to locate flow features such as boundary layer...
- Critical engineCritical engineThe critical engine of a multi-engine, fixed-wing aircraft is the one whose failure would result in the most adverse effects on the aircraft's handling and performance.- Description :...