6.2 Stall Phenomena and Recovery Techniques
3 min read•august 12, 2024
Stalling is a critical flight phenomenon where wings lose lift due to excessive . Understanding stall characteristics, warning signs, and recovery techniques is crucial for pilots to maintain control and safety during various flight phases.
Stalls can occur in different configurations and scenarios, from power-on takeoffs to steep turns. Recognizing pre-stall indicators and executing proper recovery procedures helps pilots avoid dangerous situations and regain stable flight conditions.
Stall Characteristics
Angle of Attack and Critical Angle
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- Angle of attack measures the angle between the wing's chord line and the relative wind
- Increases as the aircraft's nose pitches up or airspeed decreases
- represents the maximum angle before stall occurs
- Typically ranges from 15 to 20 degrees for most aircraft
- Exceeding the critical angle leads to a rapid decrease in lift
Flow Separation and Aerodynamic Effects
- Flow separation occurs when airflow detaches from the wing's upper surface
- Begins at the trailing edge and progresses forward as angle of attack increases
- Results in a significant reduction of lift and increase in drag
- Causes the center of pressure to move aft on the wing
- Pitch-down moment generated due to the aft movement of the center of pressure
- Helps the aircraft naturally lower its nose and reduce angle of attack
Stall Indications
Pre-Stall Warning Signs
- Stall warning systems provide audible or visual alerts (horn or light)
- Activate at about 5-10 knots above
- Reduced control effectiveness as airflow over control surfaces diminishes
- Mushy or sloppy control feel indicates approaching stall conditions
Physical Stall Indicators
- Stall buffet manifests as airframe vibrations or shaking
- Caused by turbulent airflow over the wings and control surfaces
- Wing drop involves one wing stalling before the other
- Results in sudden roll or bank in the direction of the stalled wing
- Can lead to spin entry if not corrected promptly
Types of Stalls
Power Configuration Stalls
- occurs with engine at full power (takeoff or go-around)
- Characterized by a nose-high attitude and rapid loss of altitude
- simulates landing approach or engine failure scenarios
- Features a more gradual nose drop and less severe pitch change
- Both types require proper recovery techniques to regain controlled flight
Advanced Stall Scenarios
- Accelerated stall happens at higher speeds due to increased load factor
- Can occur during steep turns or abrupt pull-ups
- Requires less angle of attack to induce compared to unaccelerated stalls
- Spin develops when one wing experiences more stall than the other
- Characterized by simultaneous stall and yaw, causing autorotation
- Requires specific recovery procedures distinct from normal stall recovery
Stall Recovery
Stall Recovery Procedure Steps
- Recognize and confirm the stall condition
- Reduce angle of attack by lowering the nose below the horizon
- Apply full power to increase airspeed and energy state
- Level the wings using coordinated aileron and rudder inputs
- Climb gently to regain lost altitude once flying speed is reestablished
- Maintain and avoid secondary stalls during recovery
Recovery Technique Considerations
- Minimize altitude loss during recovery, especially at low altitudes
- Avoid abrupt control movements that could induce a secondary stall
- Use proper rudder coordination to prevent spin entry
- Practice stall recovery procedures regularly to maintain proficiency
- Adapt recovery techniques based on aircraft type and specific situation
Key Terms to Review (19)
AC 120-109: AC 120-109 is an advisory circular issued by the Federal Aviation Administration (FAA) that provides guidance on stall prevention and recovery training for pilots. It outlines best practices for understanding stall phenomena, including aerodynamic principles and specific recovery techniques to ensure pilots are equipped to handle stalls safely during flight operations.
Angle of Attack: The angle of attack is the angle between the chord line of an airfoil and the oncoming airflow. This angle is crucial because it directly influences lift generation, stall behavior, and the overall performance of an aircraft during various flight maneuvers.
Configuration: Configuration refers to the arrangement and setup of an aircraft's control surfaces, landing gear, and other critical components that influence its aerodynamic performance and flight characteristics. The configuration can significantly affect how an aircraft behaves during various phases of flight, especially during critical situations like stalls, where understanding the current setup becomes essential for recovery techniques.
Controlled Flight Into Terrain: Controlled flight into terrain (CFIT) occurs when an aircraft is flown unintentionally into the ground, water, or obstacles despite the pilot having control of the aircraft. This dangerous situation often arises from pilot error, loss of situational awareness, or misinterpretation of altitude and position, leading to tragic accidents. Understanding CFIT is crucial as it emphasizes the importance of maintaining awareness and proper altitude management during flight.
Critical Angle of Attack: The critical angle of attack is the maximum angle at which an airfoil can be tilted relative to the oncoming airflow before it begins to stall, meaning it can no longer produce sufficient lift. This angle is crucial because it determines the limit for safe maneuvering and performance of an aircraft. Understanding this angle helps in analyzing how changes in angle of attack affect lift production, stall behavior, and the overall aerodynamic performance of an aircraft.
FAA Recommendations: FAA recommendations refer to guidelines and best practices issued by the Federal Aviation Administration to enhance safety and operational efficiency in aviation. These recommendations provide critical insights into handling specific flight situations, including stall phenomena and recovery techniques, which are vital for pilots to understand and implement to ensure safe flying.
High angle of attack: A high angle of attack occurs when the angle between the wing's chord line and the oncoming airflow exceeds a critical threshold, leading to a decrease in lift and an increased risk of stalling. This situation is crucial to understand because it plays a significant role in stall phenomena, affecting aircraft performance and safety during various flight maneuvers.
Incipient Stall: An incipient stall is the initial stage of a stall condition where an aircraft begins to lose lift due to the angle of attack becoming too steep. During this phase, the airflow over the wings starts to separate, leading to a reduction in aerodynamic efficiency and an impending loss of control. Recognizing an incipient stall is crucial for pilots, as it enables timely corrective actions to restore lift and maintain control of the aircraft.
Level wings: Level wings refer to the condition when an aircraft's wings are parallel to the horizon during flight, allowing for straight and level flight without any banking or turning. Maintaining level wings is crucial for ensuring stability and control, especially during critical maneuvers like recovery from a stall, where the aircraft needs to regain controlled flight efficiently and safely.
Low airspeed: Lows airspeed refers to the condition when an aircraft is flying at a speed that is close to or below its minimum control speed, which can lead to a stall. Understanding low airspeed is crucial as it directly impacts an aircraft's ability to maintain controlled flight and affects the risk of entering a stall condition, highlighting the importance of recognizing and managing airspeed during various flight maneuvers.
Pitch down: Pitch down refers to the aircraft's nose moving downward relative to the horizon, which can happen when the elevator control surfaces are deflected to decrease the angle of attack. This action is crucial in various flight scenarios, especially during stall recovery, as it helps regain control and stabilize the aircraft's flight path. Understanding pitch down is vital for pilots to manage their aircraft effectively during critical situations.
Power-off stall: A power-off stall occurs when an aircraft experiences a loss of lift due to insufficient airspeed during a descent with the power reduced to idle. This situation usually arises when the pilot attempts to maintain altitude or execute a landing approach, leading to a critical angle of attack that exceeds the aircraft's stall threshold. Understanding this stall is crucial for recognizing how altitude changes can affect performance and recovery techniques during flight.
Power-on stall: A power-on stall occurs when an aircraft exceeds its critical angle of attack while maintaining engine power, typically during takeoff or climb. This type of stall can happen when the pilot attempts to climb too steeply or applies too much back pressure on the control stick without reducing power. Understanding power-on stalls is crucial for pilots as they navigate the risk factors associated with stalls, especially in critical phases of flight like takeoff and approach.
Situational Awareness: Situational awareness refers to the perception of environmental elements and events, understanding their meaning, and projecting their status in the near future. This skill is crucial for pilots as it helps them interpret flight instruments, anticipate changes in aircraft performance, and make informed decisions, especially in complex environments like busy airspaces or during emergencies.
Stall horn: A stall horn is a warning device typically installed in an aircraft to alert pilots when the aircraft is approaching a stall condition, which occurs when the angle of attack increases beyond a critical point. This audible alert is crucial for preventing loss of control during flight, as it provides timely information to the pilot about the imminent risk of stalling. Understanding how and when the stall horn activates helps pilots recognize and respond to stall phenomena effectively.
Stall recognition: Stall recognition refers to the ability of a pilot to identify when an aircraft is approaching or entering a stall condition, which occurs when the airflow over the wings is insufficient to maintain lift. Recognizing the signs of an impending stall is crucial for pilots as it enables them to take corrective actions before the aircraft fully stalls, ensuring safety and control during flight maneuvers.
Stall speed: Stall speed is the minimum speed at which an aircraft can maintain controlled flight before the onset of a stall, which occurs when the wing can no longer generate sufficient lift. Understanding stall speed is crucial as it relates to drag reduction, aerodynamic efficiency, wing loading, lift distribution, turning performance, load factor, compressibility effects, and recovery techniques, as these factors all play a role in how an aircraft performs in various flight conditions.
Stick shaker: A stick shaker is a safety device used in aircraft that provides tactile feedback to the pilot when the aircraft approaches a stall condition. It works by vibrating the control yoke or stick, alerting the pilot to take corrective action to prevent an aerodynamic stall. This device is crucial for enhancing situational awareness during critical flight phases and is designed to operate before an actual stall occurs.
Weight and balance: Weight and balance refers to the distribution of weight in an aircraft and how it affects its performance, stability, and safety during flight. Properly calculating weight and balance ensures that an aircraft is loaded within its limits for safe operation, preventing issues like stall or loss of control, particularly during takeoff, landing, and maneuvers.