Class 16: Principles of Flight - Stability

Introduction

• Importance of stability and maneuverability in aircraft
• Stability helps counter turbulence and wind changes

Types of Stability

1. Static Stability

   • Initial response of an object after displacement
   • Positive Static Stability: Tendency to return to equilibrium (e.g., ball in a bowl)
   • Neutral Static Stability: No tendency to return or diverge (e.g., ball on a flat surface)
   • Negative Static Stability: Tendency to move further away from equilibrium (e.g., ball on a hill)

2. Dynamic Stability

   • Response over time after displacement
   • Positive Dynamic Stability: Gradual return to equilibrium (e.g., oscillating ball)
   • Periodic vs Aperiodic:
     • Periodic: Oscillates before settling at equilibrium
     • Aperiodic: Non-oscillating return to equilibrium
   • Negative Dynamic Stability: Continues to diverge over time

Graphical Representation of Stability

• Graphs depicting oscillating and non-oscillating behaviors
• The effect of friction on stability

Strength of Stability

• Stability strength is illustrated by the steepness of the curve in a bowl
• More stable objects require more force to move away from equilibrium
• Example: A stable tricycle is harder to maneuver than a bicycle

Aircraft Stability in Three Dimensions

• Normal Axis: Yaw (directional stability)
• Lateral Axis: Roll (lateral stability)
• Longitudinal Axis: Pitch (longitudinal stability)

Definitions of Stability Types

• Yaw Stability: Ability to maintain heading
• Lateral Stability: Resistance to roll
• Longitudinal Stability: Resistance to pitch changes

Key Takeaways

• Stability can be classified as positive, neutral, or negative
• Dynamic stability relies on initial static stability
• The more stable an aircraft, the more force is needed to maneuver it
• Steepness of stability curves influences control and behavior

Next Steps

• Upcoming class will delve into how aircraft implement these stability concepts.