[Ref. Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 5-14]

Stability – the inherent quality to return to the original flight path.

There are 2 sub-types of stability

1. Static Stability
   – aircraft’s initial response (tendency) when disturbed from a given pitch, yaw, or bank
2. Dynamic Stability
   – the aircraft response over time

 

Notes:

Positive static stability – initial tendency to return to the original state

Neutral static stability – initial tendency to remain in a new condition

Negative static stability – initial tendency to continue away from the original state

 

Positive dynamic stability – over time, tendency to return toward previous state

Neutral dynamic stability – over time, tendency to remain in new condition -neither increases nor decreases

Negative dynamic stability – over time, tendency to continue away from the original state and become more divergent

 

Stability affects maneuverability AND controllability.

Stability affects two areas significantly:

1. Maneuverability ≈ Is it easy be changed and is it within limit?
   • the quality of an aircraft that permits it to be maneuvered easily and to withstand the stresses imposed by maneuvers
   • governed by weight, inertia, size and location of flight controls, structural strength, and powerplant.
   • There is a trade-off between stability and maneuverability – e.g, a passenger airplane would require more stability, whereas a fighter requires greater maneuverability.
2. Controllability ≈ Can it be changed/managed
   • capability of an aircraft to respond to the pilot’s control, especially with regard to flight path and attitude,
     BUT regardless of its stability characteristics.

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Read More –

[Ref AircraftSystems: Mechanical,electrical,andavionicssubsystemsintegration,Third Edition ISBN: 978-0-470-05996-8]

# CG-CP, manoeuverability

The distance between the CG and the centre of pressure (CP) is a measure of how stable and also how manoeuvrable the aircraft is in pitch. The closer the CG and centre of pressure (CP), the less stable and more manoeuvrable the aircraft.