Slip (aerodynamics)

The sideslip (English slip, double glissade, also in German Switzerland Glissade ) is a stable and fully controllable attitude at all airplanes which are triaxial aerodynamic (ie rowing ) controlled. Here, the otherwise undesirable sideslip is induced consciously: the plane does not move along its longitudinal axis, but clearly " diagonally " through the air and is then stopped by the much higher air resistance.

The sideslip is used to increase the rate of descent without increasing the airspeed, such as the landing approach at higher crosswind component or cross-wind to the rapid degradation of height.

Flying in side slip is referred to in the flier language, even in the German language, as slippen.

Introduction of a panty

The initiation of briefs is usually in the landing configuration with the ailerons at a speed which is slightly above the usual for the particular type of aircraft approach speed (without flaps). Once the desired bank is reached, countered with the rudder, to which the stable slip adjusts by itself. Many gliders a very pronounced negative yaw supports the introduction: Rotation about the longitudinal axis through the aileron lends itself to an opposite rotation around the vertical axis, which is then maintained by appropriate rudder deflection.

A sideslip at too high a trip ( for fear of a stall ) causes much higher pressures or rowing can cause the slip can not be flown stable.

The direction of control in the panty is done with the ailerons. Increasing the angle causes a rotation in the direction of the hanging area. Reducing the angle causes rotation in the opposite direction. In brief, the aileron is so easy usually knocked out in Sliprichtung and the rudder until it stops against the inclined position. This rudder combination yields a stable flight condition in which the aircraft returns after a disturbance by gusts.

In summary, this means, for example, the Rechtsslip:

• Aileron easily kept right
• Rudder pedal depressed fully to the left
• Elevator pulled slightly

The plane slides in the landing configuration at an angle to the path, pushing with hanging, of preceding wing and loses altitude quickly. A stall is not to be feared in this configuration, since the flow of the airfoil profile changes only slightly.

Recovery from a Slips

The diversion of a panty occurs first by restoring the normal horizon location using the elevator. Subsequently, the slip is completed and produced normal flight position by simultaneous side and aileron movements. After the release is to be noted that sufficient present movement as the aircraft moves in the slip near the stall ( stall speed ) and could enter into a tailspin.

Note: Recovery from a briefs should always begin in the case of a glider with the decline of the elevator, as this is often quite strongly drawn during the side gliding. A discharging with transverse or rudder alone can bring about a glider in one of the stall with subsequent stall, from which there is no chance of catching more due to the possibly only low altitude above ground.

Technical Explanation

The elevator is effective through the lateral flow of the rudder and the large rudder deflection is only about 60%. This effect consists of the shading of the elevator together by the rudder and the pressure distribution interference by the rudder deflection. This reduced elevator effectiveness means that the aircraft is top-heavy after the introduction of the side slip. To keep the nose up, so the elevator must be taken after the introduction of the panties.

Through the hull now transversely positioned, the air resistance increases considerably, since the fuselage is clearly flows laterally not more from the front, but. Next also the airfoil (see also: airfoil ) is easily flows laterally, which fluidly to a slight reduction of the span (also because a part of the wing is in the lee of the trunk ) and to a change ( deterioration ) of the profile and thus a decrease of buoyancy leads.

The buoyancy loss is by increasing the angle of attack balanced (keeping the pitch ), the resistance increases and the sink rate increases. Both effects lead to a significantly steeper glide angle (height loss per leg ).

Background

• When there were no spoilers at the beginning of aviation, the slipping was the only way to lose height during the landing approach, without increasing the approach speed.
• Air Canada Flight 143 was an emergency landing on July 23, 1983 using the side slip after the fuel had run out prematurely due to a Fehlberechung.

Special

For some aircraft types, make sure that when slipping the airbrakes are retracted, other slippen only stable when the flaps are extended. The maximum speed in the slip substantially below those for normal flight, as acting on the fuselage and control surfaces in slip considerable forces. At too high Slipgeschwindigkeit is also a risk, "fall" from the stable slip to.

In most airplanes, the elevator effect is limited to the extent is not too strong tail -heavy center of gravity position that even with fully drawn stick a coating in the slip is not possible. Therefore, the Aeroplane Flight Manual must be inspected on peculiarities of each aircraft before slipping.

It should always be geslippt against the wind because effective direction changes are possible only in the direction of the hanging wing. According to the transverse position slipping superimposed on the sideslip. This causes the plane to the lower wing describes a Kurvenslip and can if necessary even more turn into the wind. In addition, the nose of the aircraft also moves during recovery for reserving back into the wind.

A particularly long and steep sideslip is jokingly referred to as California Riesenslip. Planes that do not allow stable slip can benefit with the so-called Wechselslip from the shift flying characteristics.

For airplanes with Static Port (probe for the static air pressure ) on the side of the fuselage occurs during a panty to an erroneous display of airspeed when is blown due to the inclination of the hull of the static port by the wind and thus measures a too high static pressure (see velocity measurement in aircraft ). So the pattern of aircraft Cessna C150 with static port is shown on the left side of the fuselage in a sideslip, the left one to 15 nodes at low speed.

Some gliders can cause an airspeed close to 0 or negative values ​​at a steep slip. The main reason here is less the oblique blowing the static pressure loss, which often consists of four distributed around the rear fuselage holes in gliders. Rather, a " sucking " of the pitot tube is (ASK -21 Schleicher, for example ) to watch or a detachment at the inlet of the venturi tube ( eg Schleicher Ka -2). The pilot must completely rely on his experience and the horizon picture then. In particular, student pilot be tempted by this little experience in this flight condition to pull the elevator in side slip too little. After the exit the aircraft is then significantly faster than with a landing common, whereby the planned touchdown point may be missed. Frequent practice of side gliding under known conditions or with an experienced pilot on board is therefore recommended to avoid surprises at an outside landing on a short field landing.