Stability and Control
Control answers the question ”How can the vehicle be stable?”. For an aircraft, it means “how can the aircraft accomplish basic moves such as flying straight, climbing, descending?”. A more technical definition of stability would be “the tendency of the vehicle to maintain or deviate from an established flight condition”. Control is the ability of the vehicle to be manoeuvred or steered from one flight condition to another.
It is very important to notice that questions regarding the stability (as opposed to a crash) are mainly addressed by the control and not the guidance nor the navigation. That is why one often speaks about Stability and Control System (SCS) and not only Control System.
The SCS is made of two parts: Stability Augmentation System (SAS) that stabilizes the aircraft (if it is naturally unstable) and improves its handling qualities. Then, the Control Augmentation System (CAS) typically allows the vehicle to maintain its altitude or heading. These functions are called altitude hold and heading hold modes in the AutoPilot (AP). The SCS creates the low level orders directly sent to the actuators (ailerons, rudder, elevator, engines, etc.). It is also sometimes called the Piloting System, meaning piloting is associated to low level, stabilization work.
Thus, how to fly is known by the control. Once it is done, higher level objectives can be achieved such as following a trajectory, that is going from a point A to a point B. High level orders will be sent by the guidance system.
Next chapter will be about Guidance.
Use the following link to trackback from your own site:
This post is part of a series about Guidance, Navigation and Control. See the table of contents here. Guidance Guidance refers to the questions ”where am I going to?”, “How can the vehicle follow a trajectory?**”. The traje...
This post is part of a series about Guidance, Navigation and Control. See the table of contents here. 3 parts are in this post because they are shorter: About the human pilot (with fresh news) About GNC wordings About the various control loops Abo...
If economy was an airplane, that airplane would go across a severe zone of turbulences. Then, a passenger would ask the air hostess “can I talk to the pilot, please? Because this pilot does not seem very good”. The hostess would answer...