In a turn, the wings are angled toward the ground. The lift is considered to be broken into two components, the vertical and the horizontal. The vertical component of lift counters the airplane's weight, while the horizontal component of lift acts to turn the airplane. The horizontal component of lift turns the airplane by accelerating the airplane toward the center of the turn.
Since a portion of the lift is used to turn the airplane, total lift must be increased by adding back pressure to the yoke during the turn. This will maintain the vertical component of lift sufficient to support the weight of the aircraft, preventing the airplane from descending as it turns.
Load Factor
The steeper the bank angle, the more total lift must be increased in order to maintain level flight. As a result, a greater and greater acceleration into the turn results from steeper and steeper bank angles in level flight. This acceleration is felt as load factor.
Under normal circumstances, the load factor is 1.0. An airplane in a level turn at a 45 degree bank angle experiences a 1.5x load factor. In a 60 degree bank level turn the load factor is 2.0x. This means if the airplane weighs 2,300 lbs, the wings must support a load of 4,600 lbs with a 2x load factor.
Stall speed increases with load factor. The amount of excess load that can be imposed on the wing of an airplane depends on the airplane's speed.
Overbanking Tendency
In a turn, the outside wing travels a further distance than the inside wing. As a result, it sees a slightly higher airspeed, compared to the inside wing. Since lift is affected by airspeed, the outside wing produces slightly more lift than the inside wing, resulting in an overbanking tendency, in which the airplane tends to roll into the turn.
Most general aviation airplanes are designed so that as they fly, they naturally seek straight and level flight. This is called positive stability.
At low bank angles of about 15 or 20 degrees, the turn is gradual. The overbanking tendency is weak, and overcome by the airplane's positive stability. As a result, the airplane will tend to roll back to wings level, requiring the pilot to hold slight aileron pressure into the turn to maintain the bank angle.
At medium bank angles of about 30 degrees, overbanking tendency counteracts airplane stability. The airplane will tend to remain at the same bank angle with very little pilot correction required.
At higher bank angles in excess of 30 degrees, overbanking tendency tends to overcome the airplane's stability. The pilot must maintain a slight aileron pressure opposite the turn in order to prevent the airplane from rolling more into the turn.
At steep bank angles of 45 degrees and more, the pilot must maintain a significant amount of aileron against the turn in order to prevent the bank angle from increasing due to overbanking tendency.
Adverse Yaw
As the outside wing produces slightly more lift, it also produces slightly more induced drag. This causes adverse yaw, which is the tendency of a turning airplane to yaw toward the outside wing. The pilot must counter adverse yaw by using the rudder to keep the tail in line with the nose.
To turn, a pilot must use aileron and rudder together to initiate the turn. During the turn, an appropriate amount of back elevator pressure must be maintained to prevent altitude loss, and an appropriate amount of rudder must be used to keep the tail in line with the nose. Additionally, the bank angle must be maintained, not allowed to decrease or increase on its own.