Slip (aerodynamic)
A slip is an aerodynamic state where an 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...

 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
Relative wind
In aeronautics, the relative wind is the direction of movement of the atmosphere relative to an aircraft or an airfoil. It is opposite to the direction of movement of the aircraft or airfoil relative to the atmosphere...

 (in the side-to-side sense).

A slip is also a piloting maneuver where the pilot deliberately puts the aircraft into a slip.


Flying in a slip is aerodynamically inefficient. Inexperienced pilots will often enter slips unintentionally during turns by failing to coordinate the aircraft using the rudder
A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...

; however there are common situations where a pilot
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...

 may enter a slip deliberately by using opposite rudder and aileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...

 inputs, most commonly in a landing approach at low power. Without a slip it is difficult to increase the steepness of the glide without adding significant speed. This excess speed can cause the aircraft to fly in ground effect for an extended period, perhaps running out of runway. In a slip much more drag is created, allowing the pilot to dissipate altitude without increasing airspeed, increasing the angle of descent (glide slope). Additional airspeed will further increase the steepness of descent.

Slips are especially useful when operating aircraft that have neither high-drag flap
Flap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...

s nor spoilers (typically pre-1950s training aircraft, or in aerobatic aircraft such as the Pitts Special
Pitts Special
The Pitts Special is a series of light aerobatic biplane designed by Curtis Pitts. It has accumulated many competition wins since its first flight in 1944...

), or in any aircraft in which the flaps cannot be extended due to a system failure, or when finer control is needed.

As with any low altitude maneuver it is important to maintain correct airspeed in order to prevent a stall. However, if an airplane in a slip is made to stall, it displays very little of yawing tendency that causes a skidding stall to develop into a spin. The airplane in a slip may do little more than tend to roll into a wings level attitude. In fact, in some airplanes stall characteristics may even be improved.

Forward-slip vs. Sideslip

Two forms are employed, the forward-slip and the sideslip. Aerodynamically these are identical once established, but they are entered in different manners and will create different ground tracks and headings relative to those prior to entry. Slips are particularly useful in performing a short field landing over an obstacle (such as trees, or power lines), or to avoid an obstacle (such as a single tree on the extended centerline of the runway), and may be practiced as part of emergency landing procedures. These methods are also commonly employed in flying into farmstead or rough country airstrips where approach hazards are present.


The forward slip will change the heading of the aircraft away from the down wing, while retaining the original track (flight path over the ground) of the aircraft.

A forward-slip is useful when a pilot has set up for a landing approach with excessive height or must descend steeply beyond a tree line to touchdown near the start of a short runway. Assuming that the runway is properly lined up, the forward slip will allow the aircraft track to be maintained while steepening the descent without adding excessive airspeed. Since the heading is not aligned with the runway, the slip must be removed before touchdown to avoid excessive side loading on the landing gear, and if a cross wind is present an appropriate side slip may be necessary at touchdown as described below.

In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, student pilots are required to know how to do forward slips before embarking on their first solo flight. The logic is that in the event of an engine failure, the pilot will have to land on the first attempt and will not have a chance to go around if the aircraft is too high and/or too fast.


The sideslip also uses opposite aileron and rudder. In this case it is entered by lowering a wing and exactly enough opposite rudder so the airplane does not turn (maintaining the same heading), while adding airspeed as required.

In the sideslip condition, the airplane's longitudinal axis remains parallel to the original flightpath, but the airplane no longer flies straight along its original track. Now, the horizontal component of lift forces the airplane to move sideways toward the low wing.

A sideslip is also one of the methods used by pilots to execute a crosswind landing
Crosswind landing
A crosswind landing is a landing maneuver in which a significant component of the prevailing wind is perpendicular to the runway center line.-Significance:Aircraft in flight are subject to the direction of the winds in which the aircraft is operating...

. In order to land crosswind using the sideslip method, the pilot puts the airplane into a sideslip toward the wind to maintain runway centerline position while maintaining heading on the centerline with the rudder, touching one main landing gear, followed by the second main gear, and finally the nose gear (or tail gear if employed). This allows the wheels to be constantly aligned with the track, thus avoiding any side load at touchdown.

The slideslip method for cross-wind landings is not suitable for long winged and low sitting aircraft such as sailplanes, where instead a crab angle (heading into the wind) is maintained until a moment before touchdown.

Other uses

There are other, specialized circumstances where slips can be useful in aviation. For example, during aerial photography, a slip can lower one side of the aircraft to allow ground photos to be taken through a side window. Pilots will also use a slip to land in icing conditions if the front windshield has been entirely iced over — by landing slightly sideways, the pilot is able to see the runway through the aircraft's side window. Slips also play a role in aerobatics
Aerobatics is the practice of flying maneuvers involving aircraft attitudes that are not used in normal flight. Aerobatics are performed in airplanes and gliders for training, recreation, entertainment and sport...

 and aerial combat
Aerial warfare
Aerial warfare is the use of military aircraft and other flying machines in warfare, including military airlift of cargo to further the national interests as was demonstrated in the Berlin Airlift...


Notable employment of the slip

  • Gimli Glider
    Gimli Glider
    The Gimli Glider is the nickname of the Air Canada aircraft that was involved in a notable aviation incident. On 23 July 1983, Air Canada Flight 143, a Boeing 767-200 jet, ran out of fuel at an altitude of ASL, about halfway through its flight from Montreal to Edmonton via Ottawa...

     - a 767 captain made a successful engine-out landing despite excessive approach altitude by employing a slip

How a Slip affects flight

When an aircraft is put into a side slip with no other changes to the throttle or elevator, the pilot will notice an increased rate of descent (or reduced rate of ascent). This is usually mostly due to increased drag on the fuselage. The airflow over the fuselage is at a sideways angle, increasing the relative frontal area, which increases drag.

See also

  • Coordinated flight
    Coordinated flight
    In aviation, coordinated flight of an aircraft is flight without sideslip.When an aircraft is flying with zero sideslip a turn and bank indicator installed on the aircraft’s instrument panel usually shows the ball in the center of the spirit level...

  • Crab landing
  • 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...

  • Skid (aerodynamic)
    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...

  • Slip landing
  • Slip-turn
    A slip-turn is a maneuver in which an aircraft turns using only the rudder. In most aircraft, the presence of a fixed vertical stabilizer complicates the maneuver...

External links

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