![[A4NA sideslip.png]] Engineers define "sideslip" as a misalignment of the relative wind with the longitudinal axis of the aircraft. Pilots may use this in a variety of circumstances, so we have a few more specific definitions for the slips we use. ![[GFH slips.png]] ### Sideslip - The purpose of a sideslip (as used in pilot terminology) is to keep the aircraft's longitudinal axis aligned with the runway centerline, and compensate for wind drift during a crosswind landing - The pilot uses rudder to keep the longitudinal axis aligned with the runway centerline; "use rudder to point the nose down the runway" - The pilot uses aileron to maintain a small bank and horizontal component of lift to eliminate side drift; "use aileron to keep the aircraft over the centerline" - In practice, this will involve continuous adjustment of the flight controls during the approach and landing; wind speed/direction variations, changes in wind profile during approach, and changes in control effectiveness as the aircraft decelerates are all in a constant state of variation ### Forward slip - The purpose of a forward slip is to increase descent rate without increasing airspeed; this may be used if the aircraft is still high on approach with full spoilers/dive brakes, or in the event of a spoiler/dive brake failure - The pilot intentionally uses the aircraft's longitudinal misalignment with the relative wind to increase drag and increase descent rate - If a crosswind exists, the rudder and aileron should be deflected in the same direction as a sideslip, to ease the transition from forward slip to sideslip - The pilot should use full rudder (or less, if less than maximum descent rate is desired), and enough aileron to prevent a turn or drift from runway centerline - When the aircraft has returned to the desired approach angle, the pilot can return to wings level flight, or transition to a sideslip for landing ### Turning slips - The purpose of an intentional turning slip is the same as a forward slip; to increase descent rate without increasing airspeed, in a turn - The pilot uses "outside" or "top" rudder during a [[Slip]]; "inside" or "bottom" rudder results in a [[Skid]], and greatly increases the risk of a low altitude stall/spin accident - After applying rudder, the pilot adjusts ailerons to maintain the desired rate of turn ### "Crab and kick" method - Another possible method for landing in a crosswind is the "crab and kick" method - The "crab" refers to the use of a wind correction angle in wings level flight to compensate for wind drift and remain over runway centerline - The pilot maintains the "crab" until just before touchdown, then "kicks" rudder to align the longitudinal axis of the aircraft with runway centerline before touching down ### Additional considerations - The pilot may choose between the sideslip and "crab and kick" method of landing in a crosswind. They both achieve the same goal: keeping the longitudinal axis of the aircraft aligned with the aircraft's direction of travel during landing, to avoid potentially damaging sideloads on the landing gear and loss of directional control. - The "crab and kick" method is more challenging, as it requires precise timing and control inputs to perform correctly. The sideslip method is often preferred by instructors and student pilots, however, it can carry additional risk of a wingtip striking the ground during landing with low-wing, long span aircraft designs in higher crosswinds. - Any time the aircraft's longitudinal axis is misaligned with the relative wind, instrument indications (particularly airspeed) can become erroneous. The pitot tube is no longer aligned with the relative wind, and the static port may be subject to abnormal pressure distributions about the aircraft. The pilot should note the pitch attitude used prior to the slip, and maintain this pitch attitude once established in the slip. [<iframe width="560" height="315" src="https://www.youtube.com/embed/03LJjg5eBak?si=XvgL5ZshwkBr6vL2" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>] ### Common Errors - Improper use of slips - Improper crosswind correction - Improper airspeed control - Rough or hesitant use of flight controls ### Completion Standards - Initial attempts: performs the task with instructor assistance - Solo: recognizes the situation where a slip should be used, uses the slip appropriately, and transitions to a normal/crosswind landing - Sport/Private/Commercial Pilot: recognizes the situation where a slip should be used, establishes a slip without the use of drag devices, maintains desired ground track and approach attitude, and touches down in the designated landing area