An aircraft turns mainly by banking, not by simply pointing the nose with the rudder. When the wings tilt, the lift force tilts with them, so part of lift pulls sideways toward the center of the turn. That sideways part of lift provides the centripetal force that curves the airplane’s path.
Understanding this helps explain why smooth turns require both correct bank angle and coordination.
Key Facts
- In a banked turn, lift tilts with the wings and has vertical and horizontal components.
- Horizontal lift component = L sin(theta), where theta is the bank angle.
- Vertical lift component = L cos(theta), so total lift must increase in level turns.
- Centripetal force for a turn is F_c = mv^2/r.
- For a coordinated level turn, tan(theta) = v^2/(rg).
- The rudder coordinates the turn by reducing adverse yaw and keeping the airplane from slipping or skidding.
Vocabulary
- Bank angle
- The angle between the airplane’s wings and the horizontal horizon during a turn.
- Lift vector
- The direction and size of the aerodynamic force produced mainly by the wings.
- Centripetal force
- The inward force needed to make an object move along a curved path.
- Adverse yaw
- The tendency of an airplane’s nose to yaw opposite the intended turn when the ailerons are used.
- Coordinated turn
- A turn in which aileron, elevator, and rudder inputs are balanced so the airplane turns without slipping or skidding.
Common Mistakes to Avoid
- Thinking the rudder is the main control for turning, which is wrong because the banked lift vector supplies most of the inward turning force.
- Forgetting that lift must increase in a level banked turn, which is wrong because only L cos(theta) supports the airplane’s weight.
- Using ailerons without rudder coordination, which is wrong because adverse yaw can make the nose initially yaw away from the turn.
- Assuming a steeper bank always makes a safer turn, which is wrong because steeper banks increase load factor and require more lift to maintain altitude.
Practice Questions
- 1 An airplane flies a coordinated level turn at 60 m/s with a turn radius of 500 m. Use tan(theta) = v^2/(rg) with g = 9.8 m/s^2 to find the bank angle theta.
- 2 A 12,000 N airplane is in a 30 degree level bank. Use L cos(30 degrees) = W to find the total lift L required to maintain altitude.
- 3 A pilot rolls into a left turn using left aileron, but the nose first yaws slightly right. Explain what effect is happening and how rudder input helps coordinate the turn.