Side glide
The side glide or slip (English slip , French glissade , also in German-speaking Switzerland Glissade ) is a special stable and fully controllable flight position . It is mostly used for the controlled, rapid decrease in altitude. Side gliding is possible with all aircraft that are aerodynamically controlled on three axes (i.e. with rudders). In doing so, the otherwise undesirable sliding flight is brought about in a targeted manner: the aircraft no longer moves along its longitudinal axis, but is clearly “tilted” by the surrounding air and is then strongly braked by the significantly higher air resistance.
Rapid sinking, e.g. B. for a steep approach , can be achieved with a steeper flight angle by appropriate elevator control, but the airspeed also increases. The side glide enables a steep descent without increasing speed, as the greatly increased air resistance in this flight position has a braking effect. Before there were spoilers , slipping was the only way to reduce altitude in a short time on approach without exceeding the optimal approach speed. Another use of the slip enables crosswind landings without a lead angle .
Flying in side glide is called slipping in the aviation language , also in German-speaking countries .
Initiation of a brief
The introduction of a slip usually takes place in the landing configuration with the aileron at a speed that is just above the approach speed (without flaps ) customary for the respective aircraft type . When the desired bank angle is reached, the rudder is used to counteract this, whereupon the stable slip adjusts itself. In many gliders, a pronounced negative turning moment supports the initiation: A turn around the longitudinal axis by the aileron automatically leads to an opposite turn around the vertical axis, which is then maintained by the corresponding rudder deflection.
A sideslip at too high a ride (for fear of a stall ) causes significantly higher rudder pressures, or may cause the slip can not be flown stable.
The direction control in the slip is done with the aileron. Increasing the inclination causes a rotation in the direction of the hanging surface. Reducing the lean angle causes rotation in the opposite direction. In the slip, the aileron is therefore slightly deflected in the slip direction and the rudder is usually deflected as far as it will go against the lean angle. This combination of rudders results in a stable flight condition that the aircraft returns to even after being disturbed by gusts.
In summary, this means for the right slip, for example:
- Aileron held slightly to the right
- Rudder pedal fully left
- Elevator pulled slightly
The aircraft glides at an angle to the runway in the landing configuration, pushing with the wing hanging in front and quickly losing altitude. A stall is not to be feared in this configuration, since the flow against the wing profile changes only slightly.
Rejection of a panty
A slip is first removed by restoring the normal horizon position with the elevator. Then the slip is ended by simultaneous side and aileron movements and the normal flight attitude is established. When exiting, it should be ensured that it is not too aggressive and that there is sufficient speed, as the aircraft moves close to the breakaway speed (stall speed ) in the slip . Otherwise it can happen that the hanging surface that is left behind when exiting becomes too slow, the flow breaks off there and the aircraft tips over into a tailspin over this surface.
In the case of a glider, the removal of a slip should always begin with the release of the elevator, as this is often pulled quite strongly during the side-gliding flight. An exit with transverse or rudder alone can a glider into a beginning of the stall with subsequent stall bring from which there is no chance of interception are more due to the possibly only low altitude above ground.
Technical explanation
The elevator is only about 60% effective due to the side flow of the rudder and the large rudder deflection. This effect consists of the shadowing of the elevator by the rudder and the pressure distribution disturbance due to the rudder deflection. This reduced elevator efficiency results in the aircraft becoming top heavy after initiating the side-glide flight. In order to keep the nose up, the elevator must therefore be pulled after introducing the slip.
With the fuselage now positioned transversely, the air resistance increases considerably, as the aircraft fuselage is no longer approached from the front, but rather from the side. In addition, the wing profile (see also: Wing ) is flown slightly from the side, which in terms of flow technology leads to a slight reduction in the span (also because part of the wing is located in the lee of the fuselage) and to a change (deterioration) in the profile and thus a decrease of buoyancy .
The loss of lift is compensated for by increasing the angle of attack (maintaining the pitch), the drag increases and the rate of descent increases. Both effects lead to a significantly steeper glide angle (loss of altitude per flight route).
Events
- A Boeing 767 was emergency landed on Air Canada Flight 143 on July 23, 1983 using the side-glide flight after the fuel ran out prematurely due to a miscalculation.
- A Bombardier CRJ100 had an accident on Bombardier Aerospace Flight 388 after a side glide flight to the Deep Stall and a loss of control.
particularities
With some aircraft types, care must be taken to ensure that the airbrakes are retracted when slipping , others only slip stable when the flaps are extended. The maximum speed in the slip is significantly below that for normal flight, as considerable forces act on the fuselage and control surfaces in the slip. If the slip speed is too high, there is also the risk of "falling" out of the stable slip.
In most aircraft is not in too much tail-heavy center of gravity , to the extent restricted the elevator effect that even with full back stick a coating in the slip is not possible. Therefore, the flight manual must be inspected for peculiarities of the respective aircraft before slipping.
It should always be slipped against the wind, because effective changes of direction are only possible in the direction of the hanging wing. Depending on the bank position, slipping is superimposed on the sliding flight. As a result, the aircraft describes a curve slip around the lower wing and can turn even more into the wind if necessary. In addition, the nose of the aircraft moves back into the wind when exiting to hold up.
A particularly long and steep side glide is jokingly referred to as California giant slip. Airplanes that do not allow a stable slip can benefit from the sliding flight properties with the so-called changeable slip.
In aircraft with a static port (sensor for the static air pressure) on the side of the fuselage, the airspeed is incorrectly displayed during a slip if the static port is blown by the airstream as a result of the inclination of the fuselage and thus the static pressure is too high (see Aircraft speed measurement ). For example, Cessna C150 aircraft with a static port on the left side of the fuselage display a speed that is 15 knots too low during a left side glide.
With some gliders, a steep slip can result in a speed reading of almost 0 or negative values. The main reason for this is less the inclined blowing of the static pressure decrease, as in gliders this often consists of four bores distributed around the rear fuselage tube. Rather, a “sucking out” of the pitot tube (e.g. Schleicher ASK 21) or a detachment at the inlet of the Venturi tube (e.g. Schleicher Ka 2) can be observed. The pilot then has to rely completely on his experience and the horizon picture. In this flight condition, in particular, flight students can be tempted by little experience to pull the elevator too little in side-gliding flight. After the exit, the aircraft is then significantly faster than usual for a landing, which means that the planned touchdown point can be missed.
Web links
- Piper L-4 forward slip, landing and high tail taxi Landing of a Piper L-4 with a steep approach in extreme side slip ; Video on YouTube
