Stability and Controllability
Objective
To understand the effects of design choices on the stability of an aircraft along its three axes.
Motivation
Helps a student develop an intuitive understanding of stability and controllability that they can use to make sense of the control inputs as they fly in different conditions.
Timing
45 minutes
Format
Elements
Stability
- Airplane axes: Longitudinal, lateral, vertical
- Static stability (positive, negative, neutral)
- Will the system course-correct back to a neutral position when disturbed
- Example: Ball in a halfpipe/flat surface, on a hill
- Dynamic stability (positive, negative, neutral)
- After the system course-corrects, does it overshoot and continue to oscillate
- Or, do the osculations dampen naturally
- Longitudinal / pitch stability: Tail downforce, thrust line
- Elevator downforce in slow, level, and high speeds
- Lateral / roll stability
- High wing: Pendulous effect / keel effect
- Low wing: Dihedral, uncoordinated turn will make bigger AoA on down wing
- Aerobatic planes: neutrally stable
- Vertical / yaw stability: Wind striking fuselage aft of CG
- Rudder has it's own angle of attack
- Spiral instability vs Dutch roll
Maneuverability
- Controllability is dependent Cp vs Cg
- Elevator authority range shifts up/down with a fore/aft CG
- Maneuverability: How fast an aircraft can change its direction of flight or attitude
- Maneuverability vs stability