Sideslip Angle - Background

Background

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; however there are common situations where a pilot may enter a slip deliberately by using opposite rudder and aileron 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 flaps nor spoilers (typically pre-1950s training aircraft, or in aerobatic aircraft such as the Pitts Special), 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 the 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.