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low. This state is pictured below.
In order to bank the aircraft, the pilot must turn the control wheel (or
move the control stick) to the left. The Right Aileron lowers This
increases the angle of attack of that part of the right wing, causing the
right wing to rise. At the same time, the Left Aileron raises. The
angle of attack of that part of the left wing decreases, causing the left
wing to lower. This increased lift of the Right and decreased lift of
the Left Wing causes the aircraft to roll to the Left.
NOTE: During the time the Right aileron is down, the right wing has MORE DRAG than does the left
wing. The effects of this unequal drag is discussed later under Adverse Yaw.
When the aircraft reaches the bank angle the pilot wishes, the ailerons must be neutralized. This causes
equal lift by left and right wing, and the aircraft roll stops. Basically, the aircraft will remain in this
banked attitude until the pilot rolls the aircraft back to level attitude by operating the control wheel ( or
stick) in the opposite direction.
Note in the diagram that some of theTotal Lift ( force T) goes into a Horizontal Force ( H ). This is the
force which pulls the aircraft in a circular motion (turn). Note also that the Vertical Lift ( force V)
becomes less. If the bank angle becomes large, say 45 degrees, the vertical lift is appreciably less. The
pilot may have to hold some up elevator and/or add power to prevent loosing altitude.
Adverse Yaw
During the time that the ailerons are activated, an unwanted effect occurs. In the left turn shown above
the pilot turns the control wheel to the left, raising the left aileron, and lowering the right aileron. The
intent is to turn left.
Unfortunately while the ailerons are activated, the left wing has less drag; the right wing has more drag.
This causes the airplane to want to turn to the Right, and not to the left. This tendency to turn in a
direction opposite to the intended turn direction is called ADVERSE YAW. So how does the pilot
overcome this tendency to initially turn in the wrong direction? He uses the Rudder. By applying just the
right amount of rudder in the direction of the turn, the pilot can offset the adverse yaw. When the pilot
does this correctly, applying just the right amount of rudder, a Coordinated turn results. If the pilot
applies too little or too much rudder, anUn-Coordinated turn results. How the quality of the turn is
measured will be covered in the Instruments section.
If the pilot uses too little rudder, the nose of the aircraft wants to stay yawed opposite the turn. The rest
of the aircraft wants to "slip" toward the inside of the turn.
Aerodynamics
http://www.uncletom2000.com/gs/aerodyn.htm (4 of 12) [1/23/2003 11:18:49 AM]
If the pilot applies too much rudder, the tail wants to remain outside the radius of the turn, and a "skid"
results. Its similar to the rear end of an automobile wanting to skid outside the turning radius of a car.
Therefore, a principle use of the rudder is to control the adverse yaw while rolling into a bank.
Slips
A slip is created by applying rudder in the opposite direction to the turn. This is called Cross
Controlling. There are 2 forms of the slip.
l   Side Slip
l   Forward Slip
Side Slip
This manuever is primarially used to compensate for a cross wind while landing. If the wind is from the
right of the aircraft, the aircraft will drift to the left side of the runway unless some force is applied in the
opposite direction keep the aircraft straight with and on the centerline of the runway. The pilot uses a
Right Side Slip to compensate for the leftward drift caused by the wind. The pilot turns the control wheel
to the right to initiate a right turn, but simultaneously applies opposite Left rudder just enough to keep the
aircraft from turning. Thus the pilot induces just enough right side slip to offset the leftward wind drift.
This way, the pilot can keep the aircraft both over the centerline of the runway, and aligned with the
runway. This prevents a "side load" on the landing gear on touchdown.
Forward Slip
The forward slip is used primarially on aircraft with no flaps. This configuration is used to loose altitude
quickly without increasing airspeed.
In this manuever, the pilot simultaneously turns the aircraft left or right, and applies a lot of opposite
rudder so the side of the aircraft is presented to the relative wind. It is almost like slipping a sled down a
hill somewhat sideways. The pilot maintains this configuration until the desired altitude is lost,
whereupon he neutralizes controls to continue straight flight.
Since most modern aircraft have effective flaps to slow the aircraft on landing, and to allow a steeper
　
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