Yaw string

The yaw string, also known as a slip string, is a simple device for indicating a slip or skid in an aircraft 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. [cite book
last = Reichmann
first = Helmut
editor = Lert, Peter
title = Cross Country Soaring (Streckensegelflug)
year = 1988
origyear = 1975
edition = English ed.
publisher = Soaring Society of America
id = LCCCN 77-86598
pages = p. 77 ] Technically, it measures sideslip angle, not yaw angle, [cite web
url = http://www.av8n.com/how/htm/multi.html#@default1498
title = See How It Flies
accessdate = 2007-01-21
author = Denker, John S.
year = 2002
quote = The slip string is commonly referred to as a “yaw string”, even though it measures the slip angle, not the yaw angle (i.e. heading)....] 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. [cite book
title = Glider Flying Handbook
year = 2003
publisher = U.S. Federal Aviation Administration
location = U.S. Government Printing Office, Washington D.C.
id = FAA-8083-13_GFH
pages = p. 4-14
url=http://www.faa.gov/library/manuals/aircraft/glider_handbook/ ] In closed cockpit aircraft, it is usually taped to the aircraft canopy. 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. [cite book
last = Selvidge
first = Harner, S.D.
editor = Licher, Rose Marie
others =
title = American Soaring Handbook
origyear = 1963
edition = 2nd ed.
year = 1976
publisher = Soaring Society of America
id = LCCCN 59-15668
pages = pp. 30-31
chapter = Ch. 7 : Equipment I ] They are commonly used on gliders, but may also be found on jet aircraft (especially fighters), ultralight aircraft, light-sport aircraft, autogyros [cite book
title = Rotorcraft Flying Handbook
year = 2000
publisher = U.S. Federal Aviation Administration
location = U.S. Government Printing Office, Washington D.C.
id = FAA-8083-21
pages = p. 18-4
url=http://www.faa.gov/library/manuals/aircraft/media/faa-h-8083-21.pdf ] , airplanes and helicopters. Its usefulness on airplanes with a tractor configuration (single propeller at the nose) is limited because the propeller creates turbulence and the spiral slipstream displaces the string to one side. [cite web
url = http://www.challengers101.com/YawString.html
title = The Yaw String
accessdate = 2007-01-21
author = Hurt, George]

The yaw string dates from the earliest days of aviation, and actually was the first flight instrument. The Wright Brothers used a yaw string on their 1902 glider tied on their front mounted elevator. [cite web
url = http://www.first-to-fly.com/Adventure/Hangar/gliderrep.htm
title = 1902 Glider Replica
accessdate = 2007-01-21
author = Wright Brothers Aeroplane Company and Museum of Pioneer Aviation
quote = For all the progress that has been made in a century of aviation, the Ventur 2 still has a "yaw string" attached where the pilot can see it. As does the Wright glider. This was the first flight instrument....] Wilbur Wright is credited with its invention, having applied it concurrently with the movable rudder invented by his brother Orville in October 1902, [cite journal
quote= [Wilbur Wright] responded, “Yes...we will install a short piece of string out front where we can see it. This string will tell us all we need to know!” (paraphrased) Wilbur had just invented the yaw string — the first aircraft instrument.
last=Knauff
first=Tom
year=1995
month=Feb/Mar
title=Inventing the Rudder
journal=free flight
volume=1995
issue=1
pages=p. 26
id=ISSN 0827 – 2557
url=http://www.wgc.mb.ca/sac/freeflight/95_01.pdf
accessdate=2006-01-21|format=PDF] although others may have used it before. Glenn Curtiss also used it on his early airplanes.

The yaw string is considered a primary flight reference instrument on gliders, which must be flown with near zero sideslip angle to reduce drag as much as possible. It is valued for its high sensitivity, and the fact that it is presented in a head-up display. Even the most sophisticated modern racing sailplanes are fitted with yaw strings by their pilots, who reference them constantly throughout the flight.

Yaw strings are also fitted to the Lockheed U-2 high-altitude surveillance aircraft. [cite web
url = http://www.barryschiff.com/high_flight.htm
title = High Flight
accessdate = 2007-01-21
author = Schiff, Barry
year = 2006
quote = A yaw string (like those used on sailplanes) above each canopy silently admonishes those who allow the aircraft to slip or skid when maneuvering.] 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. [cite book
author = Paul A. Craig
title = Multiengine flying
publisher = McGraw-Hill
location = New York
year = 2004
isbn = 0-07-142139-4
quote = You will see that with the wings level the yaw string does not lay along the centerline, yet the ball is in the center...] In a multiengine airplane with an inoperative engine,the centered ball is no longer the indicator of zerosideslip due to asymmetrical thrust. The yaw string is the onlyflight instrument that will directly tell the pilot theflight conditions for zero sideslip. [cite book
title = Airplane Flying Handbook
year = 2004
publisher = U.S. Federal Aviation Administration
location = U.S. Government Printing Office, Washington D.C.
id = FAA-8083-3A
pages = pp. 12-23
url=http://www.faa.gov/library/manuals/aircraft/airplane_handbook/ ]

See also

*Glider
*Gliding
*Sideslip angle
*Slip (aerodynamic)
*Tuft
*Critical engine

References