by Scott Page
Article from club newsletter: Leading Edge – Tri-City R/C Modelers
Introduction
Landing a model airplane can be one of the most challenging aspects of flying, requiring precise control and smooth handling. One crucial element in achieving a successful landing is the method used for direction changes during the final approach. While ailerons are commonly used for rolling the aircraft and making banked turns, the rudder plays a more critical role during the final approach. Understanding why rudder use is preferred over ailerons during this phase can improve landing performance and overall flight safety.
The Dynamics of Final Approach
1. Reducing Speed:
Stall Risk: As the airplane descends for landing, it is typically flying at a lower speed compared to other phases of flight. Using ailerons to change direction while at low speeds can increase the risk of stalling. A stall occurs when the wing exceeds its critical angle of attack and loses lift, potentially leading to a loss of control. If only one wing stalls the plane will roll into the ground, this is called a tip stall.
Maintaining Control:
Aileron Effectiveness: At reduced speeds, the effective-ness of ailerons decreases. Ailerons work by changing the wing’s lift differential, which is less effective when the plane is flying slowly and close to its stall speed. Increasing the de-flection of the aileron to effect a turn will increase the likeli-hood of a tip stall.
Coordinated Turns:
Rudder Use: The rudder is essential for coordinating turns and maintaining balance during the final approach. It helps align the aircraft with the runway centerline and prevents adverse yaw, which can occur when the plane is banked without appropriate rudder input.
Why Rudder is Preferred Over Ailerons on Final Approach
1. Avoiding Adverse Yaw:
Balancing the Aircraft: When turning with ailerons alone, the aircraft can experience adverse yaw, where the nose of the plane moves in the opposite direction of the roll. This is especially problematic during a final approach where precision and stability are crucial. The rudder helps counteract this yaw, ensuring a smooth-er, more controlled turn.
Maintaining Longitudinal Stability:
Pitch Control: Using ailerons to initiate a turn while approaching the runway can affect the pitch attitude and stability of the plane. This can lead to unwanted changes in descent rate and make it difficult to maintain a consistent glide path. The rudder, on the other hand, works independently of the roll control and helps keep the pitch angle steady.
Minimizing Risk of Roll-Induced Stalls:
Safeguarding Against Stalls: During the final approach, the aircraft is closer to its stall speed. Using ailerons to change direction can increase the risk of one wing stalling due to asymmetric lift. The rudder provides a more con-trolled method of direction change that helps keep both wings in the optimal angle of attack.
Enhanced Control Authority:
Rudder Effectiveness: At low speeds, the rudder maintains its effectiveness where ailerons may not. It provides more precise control over the aircraft’s direction without risking a stall or losing altitude.
Practical Techniques for Using Rudder During Final Approach
1. Coordination with Ailerons:
Balanced Input: While the rudder is the primary control for direction changes, it is often used in conjunction with a small amount of aileron input. This combination ensures that turns are coordinated, and the aircraft remains stable.
Monitoring Speed:
Maintain Adequate Airspeed: Always be aware of your airspeed during the final approach. Keeping a safe margin above stall speed helps ensure that rudder and aileron in-puts remain effective and that the plane remains stable.
Practice Smooth Inputs:
Gradual Adjustments: Make gradual and smooth adjustments to the rudder and ailerons. Sudden or excessive inputs can disturb the plane’s balance and make the approach less stable.
Use of Rudder for Crosswind Corrections:
Crosswind Landings: In crosswind conditions, the rudder is crucial for keeping the plane aligned with the runway centerline. Use the rudder to counteract the drift caused by the wind and maintain a straight approach path.
Conclusion
In the final approach phase of landing a model airplane, using the rudder for direction changes rather than the ailerons is essential for maintaining control and stability. The rudder helps avoid adverse yaw, maintains longitudinal stability, re-duces the risk of stalls, and provides effective control at low speeds. By understanding and applying these principles, pilots can achieve smoother landings and enhance the safety and precision of their model airplane flights.