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Generally to turn left you bank left using ailerons. This angles the lift vector to the left and the airplane will turn that way without using the rudder, but it's not fully coordinated - the plane won't be pointing properly into the turn - it will "skid" a little, creating more drag than necesssary. To coordinate the turn, a small amount of left rudder is used to yaw the plane left just enough. In a forward slip the goal is to descend more quickly than you otherwise could. If you just point the nose down, the airplane will gain airspeed. If you're trying to descend quickly you'll overshoot where you're aiming. What you want is a lot more drag, which allows you to point the nose down (reducing lift) without gaining airspeed. Normally flaps, spoilers or airbrakes allow you to do this (depending on the aircraft). If you don't have these, as the Gimli glider didn't, what can you do to increase drag? Well, you can use the whole fuselage as an airbrake. To do this, you can use the rudder to yaw the plane, so it's flying a little bit sideways. Say we yaw it to the left. If the wings have dihedral (they point slightly upwards) then the right wing now has a greater angle of attack than the left wing - the right wing produces more lift and so the plane will bank left by itself without touching the ailerons. If the wings are swept back, as on large jets, yawing left will mean the right wing is longer with respect to the airflow than the left wing, and it will bank left even more. To fly pointing left, but not turn left, you cross the controls: you use the rudder to yaw left, and the ailerons to bank right. The airplane is now flying partly sideways, pointing to the left of the flight path, with the right wing lower than the left wing, but if you balance rudder against ailerons correctly, you fly in a straight line. The fuselage is partly sideways to the wind, creating a lot of drag. The airplane is skidding downwards to its right, and you need to pitch the nose down to maintain airspeed and avoid stalling. And then you've got to be fairly well coordinated as you come out of the slip so you keep flying in the direction of the runway. Source: I used to fly gliders. Presumably swept wings increase the amount of aileron needed, but the principle is mostly the same. |