The sideslip is a flight maneuver. It is used when a pilot wishes to alter his track to the left or right of directly forward, while maintaining a nose-forward attitude. The most common reason to use a side-slip is when performing an approach on a runway in a crosswind. By entering and maintaining a sideslip, the pilot can continue to 'fly the plane at the runway' while introducing a side vector to compensate for the wind.

To enter a side-slip, the pilot uses aileron input to lower the wing on the side that he wishes to slip towards. Due to aerodynamics, the airplane will begin to translate towards the low wing. However, in order to prevent the airplane from actually turning, the pilot will introduce just enough opposite rudder input to prevent the start of an actual turn. The net effect will be for the airplane to fly in the direction of its nose while drifting towards the low wing side. If the low wing is upwind, the pilot can easily match the side-slip to the wind speed by watching his ground track, and hence fly an apparently straight approach to the runway.

The slip is usually removed at the last minute in order to avoid placing undue stress on the 'down' landing gear at touchdown.

While it is of course also possible to compensate for a crosswind drift by simply adjusting the airplane's heading, it is more complex (and slower) to correct the heading at the last moment to match the runway in a coordinated turn - especially because entering a turn will raise the airplane's stalling speed (making a stall more likely if the pilot misjudges) whereas removing a slip will lower the airplane's stall speed, making a safe landing easier. During cruise, it is much easier and more efficient to compensate for winds by flying 'clean' with the heading offset to compensate for the wind.

Unlike a forward slip, the sideslip is used to compensate for wind, not to prevent increased airspeed during descent.

NOTE: Do not use this writeup to fly your airplane. Find your instructor and ask them to train you on slips - they are part of any light aircraft training program.

Lousy ASCII Art attempt:

                                     runway
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Wind Direction---------- >            | |
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                                      ---
                                      
                                       ^
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                                  Ground Track   
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          <-- side-slip left                             
                                                 right wing high
                              V    ====T====   ^
                 left wing low        -|-
                                       \   rudder right

Side"-slip`, v. i.

See Skid, below.

 

© Webster 1913

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