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.
Understanding Aviation: How an Aircraft Turns
A turn begins with the ailerons. Moving the control wheel deflects the ailerons in opposite directions. One wing produces a little more lift while the other produces less, so the aircraft rolls into a bank.
This roll creates a problem called adverse yaw. The wing with more lift usually has more drag, which pulls that wing backward.
The nose initially yaws away from the intended turn. Pilots use rudder in the same direction as the turn to cancel this unwanted yaw while the bank is being established.
Once the desired bank is reached, the pilot mostly relaxes the aileron input. The aircraft needs enough back pressure on the elevator to maintain altitude. Banking reduces the upward part of lift, so an unchanged wing angle of attack would allow the aircraft to descend.
Pulling back slightly increases angle of attack and total lift. This makes turning flight feel different from straight flight. The wings are carrying the airplane upward while providing the inward force needed to follow the curved path.
Greater bank angle makes a tighter turn possible at the same speed, but it raises the load on the wings. Load factor describes how many times the aircraft weight the wings are supporting. In a level turn at about sixty degrees of bank, the wings must produce about twice the lift needed in straight level flight.
The occupants feel heavier because their seats must support that extra load. Airplanes have structural limits, so pilots must avoid abrupt control movements or steep banks at high speed. A steep turn can become unsafe quickly if the pilot keeps pulling harder.
A higher load factor increases stall speed. A stall happens when the wing exceeds its critical angle of attack, not simply when the airplane is moving slowly. During a steep, slow turn, a pilot may pull back to stop altitude loss, raise the angle of attack too far, and stall the wing.
If one wing stalls before the other, the airplane can roll sharply toward the stalled wing. Student pilots practice gentle turns first because proper bank, speed, and elevator pressure must be balanced. Looking outside at the horizon helps keep the bank and pitch attitude under control.
Coordination is checked with the small ball in the turn coordinator or slip skid indicator. In a correctly coordinated turn, the ball stays centered. If the ball moves toward the inside of the turn, the aircraft is slipping.
It is not turning enough for its bank angle and has too little rudder in the direction of the turn. If the ball moves outward, the aircraft is skidding. It is turning too much for its bank angle and has too much rudder.
Slips and skids increase drag, reduce comfort, and can be dangerous near a stall. A useful training rule is to press the rudder pedal on the same side as the ball to bring it back to the center.
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.