Sliding curve

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As a sliding curve (engl. Skid a is) in the aviation curve flight referred to in which the yaw axis (vertical axis) is not parallel to the slip stands, but the inside of the curve deviates (too little skew ). In most cases, the outer side of the aircraft receives a stronger flow than that facing the curve. The opposite is the lubrication curve (Engl. Slip ), in which the vertical axis is inclined to the outside and the aircraft because of "slips" excessive tilt inwards.

root cause

The reason for a sliding curve is that the longitudinal axis of the aircraft does not form a tangent to the circle to be flown (and thus the nose of the aircraft points into the circle) because the cross slope that is flown is too small. The pilot will also by a (rarely inclinometer) with a ball dragonfly combined turn coordinator or - (English Turn and bank.) - the glider thread informs. In the smear curve, the tail of the aircraft points into the circle, so the cross slope flown is too great.

Disadvantages and dangers

Since an aircraft that flies a sliding curve experiences a higher air resistance than one that flies a "clean" curve (spherical vial in the middle), the fuel consumption increases in order to maintain the same speed relative to the ground (ground speed, GS) to be able to. This is caused by the fact that the longitudinal axis of the aircraft is not parallel to the direction of flow, but rather deviates in the direction of the curve from the streamlines (see sliding angle ). Furthermore, a non-frontal flow onto the pitot tube (also called pitot anemometer) leads to a false display of the speed relative to the surrounding air, which in turn can mislead the pilot. In extreme cases, the speed not to be exceeded (V NE ) will be exceeded if the flight was already in the yellow area of ​​the airspeed indicator and the pilot increased the engine power due to the incorrect display in a shift curve in order to maintain the original speed, but also at the same time comes that the acceleration of the power increase has a higher amount than the negative acceleration of the increased air resistance.

advantages

In gliding, slight smear curves are sometimes intentionally flown (thread slightly outwards, sphere of the dragonfly slightly inwards) in order to enable stable flight in curves in updrafts (e.g. thermals) with a smaller rudder deflection, which slightly reduces the resistance. The retarding moment occurring in the sliding curve can also be used sensibly to z. B. to slow down a glider before landing (see also: side gliding ).

Adequate countermeasures

Since the spherical vial of the turning pointer shows the direction of the plumb bob (vectorial sum of centrifugal force and gravity), a statement can be made about the change in bank angle to be made in order to get back into "clean" turn. In the case of the sliding curve, the pilot must increase the bank angle (in the direction of the curve) until the ball of the inclinometer is in the middle of the two markings and the dummy perpendicular is at a 90 ° angle to the wing (or forms the vertical axis of the aircraft) and the condition of a "clean" turn is restored. In the case of the lubrication curve, the pilot must reduce the bank angle.