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Fractals, Chaos, and Control Systems on Rails


Control Systems 102: GNC and Human Pilot

Posted by Harry Seldon on May 19, 2009

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: man in an Unmanned Aerial Vehicle is for “soon”)
  • About GNC wordings
  • About the various control loops

About the human pilot

At the beginning of aeronautics, the human pilot was actually a pilot. That is the person had to stabilize the airplane. He was permanently using the flight stick. This was a full time job and a navigator was required to keep track of the aircraft position. Then thanks to a better Navigation System and thanks to the autopilot, the human pilot became more a navigator and a flight manager giving high level orders (altitude, etc.) to the plane in accordance with the flight plan and the Air Traffic Control (ATC).
The next steps are:

  • Fully automatized flight. The commercial airplane flies autonomously, it receives its orders from the ATC through a radio data link. The captain is responsible for the flight safety and can fly the aircraft in case of emergency. This can be forecast for within 20 years. A passenger will be aboard a small UAV (unmanned air vehicle) in probably less than 10 years.
  • Fully automatized ATC. This can be forecast for within 30 years. Unless videoconference kills aviation before that!

To prove that what I am speaking about is not utopia. Here is a news I learned a few days after writing this article. Boeing has filed a patent for an aircraft that could fly autonomously, with one pilot or two pilots. It seems to be for a helicopter. For the moment, the autonomous mode is meant to work when there is nobody inside the aircraft but the step to an autonomous flight with people on-board is then very small (even if it would be a giant step for mankind). So I tell you it is for sooner than you may expect.

By the way, the world will need more and more Control Systems Engineer. Even today, at this time of crisis, the world (France, UK and US at least) is lacking of such engineers so you can study it safely, you won’t be unemployed.

About GNC written GN&C or GCN written GC&N

The acronym GNC can appear in several variations according to what you want to emphasize. GN&C means you separate the low level stabilization (C) from the higher level orders (G&N). GC&N means you associate G and C which are technically similar and you separate them from the Navigation which uses more advanced tools such as the Kalman filter. Both wordings are then completely justified.

About the control loops

Notice we have a lot of Control Systems working on top of each other in an airplane:

This is something to keep in mind that in order to control a system you need several loops from the low level to the high level. The most important system being the pilot (the Stability and Control System). Once you can safely achieve your basic moves (once you have a stable system), then you can think about making long trips and accomplishing a complete plan.

I am anticipating on the conclusion but never forget that the low level control loops are the most important even in “company control”, else you are going straight to a crash. Our (financial but not only) world has completely forgotten that.

Next part will be the conclusion.

Stability and Control
About GNC written GN&C or GCN written GC&N
About the human pilot
About control loops

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  1. 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...


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