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Skids and Slips
A slip is a turn that is stopped by use of the rudder. The forward slip has the aircraft moving toward the runway with the nose pointed at an angle to the runway. The side slip is used in crosswinds. It has the aileron holding a wing low while the rudder keeps the nose aligned parallel to the runway center line Any increase or decrease in aileron will cause the aircraft to slide to one side or the other of the center line. Both the skid and the slip are uncoordinated maneuvers. A skid, in which the turn is being 'helped' by the rudder is more dangerous. A skid has too much rudder used in the direction of bank.

A slip does not have enough rudder, or more likely rudder opposite to the direction of the bank. The airspeed indicator will be unreliable in either situation. A slip or skid away from the static port will give a low airspeed reading. The forward slip is used to lose altitude; the side slip is used for runway alignment. Both slips can be varied at will. The forward slip is best performed without power since it is using the fuselage to control the descent rate. Aircraft tend to be stable in the slip and easy to control as to airspeed. Inexperienced slippers tend to allow an increase in airspeed. The slip entry need not be abrupt. Lead with the aileron and use opposite rudder to prevent a turn. Incremental additions of aileron and rudder can increase the descent rate. The slip is very easy to control and can be gradually reduced to give a smooth transition into the flare.

In any uncoordinated stall, the rudder will be turned towards the slower wing. This wing will stall first. It is this factor that makes the slipping stall a safer stall. The rudder is toward the high wing that, when stalled must fall through level before dropping into the spin mode. This gives you additional time to correct the problem. In a skid the low wing stalls first. You don't get the time or attitude opportunity that a slip-stall gives before going inverted.  Neither stall is something you would want to happen turning final.

Your eyes need to be outside the cockpit when you're on final. You should be trimmed for your approach speed on final. You should automatically apply forward pressure on the yoke in s slip. Being trimmed for my approach speed means that releasing the slip pressures will put you at the correct speed. In a slip the rudder may reduce the elevator authority by 'blanking' part of the airflow. A full flap slip may cause pitch oscillations on Cessnas. You should practice your slipping and skidding maneuvers at altitude.

Regardless of all the flight and aircraft variables at the time of stall break, spinning is prevented by rapid correct use of the rudder. This means rudder applied to prevent any yaw from precipitating into a spin as the nose is moved to break the critical angle of attack. A pilot learns the required rudder for spin recovery by doing the falling leaf-type maneuvers and oscillation stalls., and wild Dutch rolls.

In a skidding base to final turn the possibility of getting a stall spin is because the excess rudder application causes the nose to drop while elevator is used to keep it up. G-forces increase, angle of attack becomes greater, stall speed rises and indicated airspeed drops--BANG..Stall and spin occur as one. All the forces and factors for spinning are present in a skidding turn.

A slip is a stabilized maneuver in which the airplane is held with rudder, aileron, and elevator in steady flight with no change in attitude on any flight axis. The slip uses the fuselage as a speed brake and angles the wing to reduce lift and its angle of attack. We are being kept in the air by the fuselage's air resistance. Once the slip is set the yaw and roll forces are, unlike in a skid, in opposite directions. The more intense the slip the farther we fly away from any stall /spin situation. Slips are inherently stall/spin resistant unless controls are misused in such a way as to change a slip into a skid.

In a slip or skid the wings will not stall at the same time since one is wing is slower than the other. The slow wing will always stall first. In a skid the low wing will always will stall first. The stall will cause it to tuck under even more and initiate a 'spin.out the bottom'. Use of ailerons to raise the wing will only aggravate the spin..

In a slip, the high wing will stall first since it is moving more slowly. When the high but slow wing of the slip stalls it must drop through level. This breaks the stall and centering the rudder removes the lateral imbalance. A stall in a slipping turn can become a spin if the wing is allowed to drop through level. The resulting unexpected 'over the top' spin will get your attention.

What Makes a Sideslip?
In a sideslip the relative wind has an influence from the side of the aircraft. This wind presses on all the vertical aircraft surfaces to one side. Because the vertical surfaces are not evenly distributed over the length of the aircraft, this relative wind from the side causes the aircraft to turn or yaw about its vertical axis. If the wings have dihedral this wind initiates a roll as well by giving one wing more lift than the other.
---A relative wind from the right causes the aircraft to swerve left
---The right yaw comes from the aircraft turning into the relative wind.
--- A roll is caused by dihedral
---A right sideslip causes the nose to pitch down due to propeller effect.
---A gust of wind from the side can cause all of these during the flare.

As part of your flight test you may be expected to both explain and demonstrate the slip. The forward slip in a C-150 is a power off, no flap, cross control, and low speed maneuver. (There is no logic to slipping to lose altitude with power on.) (Cross control means that you may be using right aileron to lower the right wing while applying left rudder to move the nose to the left.) The purpose of the slip is to produce a dramatic increase in the rate of descent. The plane is flown sideways to increase the downward slope of the glide path without increasing the airspeed. The slip does this by using the side of the aircraft against the direction of the relative wind as a brake. The performance of the slip requires the pilot to apply carburetor heat and take all the power off. Having power on during a slip for purposes of descent is self-defeating. The aircraft is trimmed for 60 kts with three down turns of the trim wheel. The wing is lowered into the wind and opposite rudder is applied. The yoke is pressed forward to maintain 60 kts. The further the wing is lowered with corresponding more opposite rudder, the more rapid will be the altitude loss. You can practice the skills required in side slipping by doing Dutch-rolls and forward slip skills at altitude with some power and following a ground reference line.

When a turn is initiated with inadequate or even opposite rudder the result is a slip. The amount of bank is commanding a turn greater than the nose is making. The aircraft is leaning and sinking, not turning. A slip is unpleasant in the way it makes passengers feel.

The slip causes errors in airspeed indications. Some of this is due to the angle of the pitot tube but most of it is due to the location of the static air hole. With the static port on the left and a slip to the left the static pressure (now partly dynamic) is increased. This causes a decrease in the indicated air speed. Your indicated air speed is lower than you are really going. A slip to the right reverses the effects and indications. Your indicated airspeed will be higher than you are really going. Be more aware of an adverse situation developing (Cross control stall) while slipping to the right. Always anticipate the decrease in indicated airspeed by applying forward yoke pressure to maintain at least 1.3 Vso. I suggest that this pressure not be trimmed off since you will be returning to coordinated flight shortly. If landing in a crosswind you should always initiate a forward slip into the wind and at approach speed. Equal effects of aileron and rudder cause the plane to move forward while flying sideways. This will make the transition into the crosswind sideslip easier with the correct wing already low and partial removal of rudder used to straighten the nose. The canted lift of the raised wing is used to offset the drifting effect of the crosswind.

At 1.3 Vso a full cross-controlled slip can be maintained without stalling. Do as many slips to the right as you do to the left and note the difference in airspeed indications. Flying indicated airspeeds when the pitot tube is not directly aligned with the direction of flight provides a margin of additional safety. Get used to the sound, feel and yoke pressure requirements of the slip. Maintain your ground track and use a simultaneous relaxation of rudder and aileron to set pitch for approach speed. Examiners like good slips. 

The beauty of the slip is how easily it can be controlled. The angle of slip can be delicately controlled so as to affect the rate of turn and descent. The effect is real time and not delayed as with flaps and power. The aircraft is not flying normally nor as designed in a slip and will come out of the slip once pressures are removed. Yet, the aircraft is both stable and controllable in the slip.

The smoothest way to enter a slip is with an initial application or aileron soon followed by opposite rudder. The ailerons starts a turn, the rudder stops it. It is the side of the airplane that is turned toward the direction of flight. The side is not aerodynamically designed for flight and acts as a brake that both slows and causes a descent. When the rudder is applied so as to direct the nose parallel to a runway while preventing a turn initiated by the aileron we have a sideslip.

Coming out of a slip can be as smooth as is the entry. Such a slip can be carried to a height lower than would be used in a normal flare. By not leveling the wings until the last moment we can exercise greater control for the actual touchdown.

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