26-11-2012, 06:10 PM
Embedded Control Systems Design
[attachment=41249]
Air Traffic Control
Of all different system levels, ATC is the top level. This is a special level because it doesn’t exist in other applications like automotive, where there is no global communication between vehicles. The primary goal of ATC is collision prevention which requires communication and radar systems. To provide redundancy most aircrafts are equipped with TCAS ( Traffic alert and Collision Avoidance Systems).
Discussion
Flight Control System
Introduction
There are a lot of embedded control systems in an airplane. One of them is the flight control system which controls the flight trajectory and the stability of the airplane. The actuators of this system are the engines and the movable devices of the main wing and tail. They are actuated by the pilot and by the embedded control system of the airplane.
Different kinds of FCS exist. They are categorized according to the number of axes they control. A one-axis FCS prevents the plane of rolling. A two-axis FCS also gives the possibility to control the direction of flight. The three-axis FCS is even more complex by providing the ability of automatic climbing and descending.
File:FCS.JPG
The figure above is a schematic overview of the flight control system. The flight control system (FCS) controls the flight trajectory and the stability of the airplane. The actuators of this system are the engines and the movable devices of the main wing and tail. They are actuated by the pilot and by the embedded control system of the airplane. This includes stability control, automatic pilot and engine control. The control outputs are calculated from sensor inputs, like navigation systems, weather radar, velocity measuring, altitude measuring, sensors in the engine...
Design
Technical requirements
Airplane systems have specific requirements that are not found or are not as critical in other systems:
• Weight
Airplanes are made using strong but light materials. The aviation industry was the first to use aluminium on a large scale, and modern materials such as carbon fibre are beginning to make their entry. The weight requirement is also one of the reasons for the evolution from a mechanical linkage to a fly-by-wire system.
• Safety
Material quality must be high, less variation on material properties is allowed for aviation. Even though the black box is useless considering the safety of a single flight, it provides a crucial feedback loop in the entire design and maintenance process.
• Dependability (Reliability, Maintainability, Availability)
A lot of systems are made in redundancy in order to increase the reliability. Airplanes are also maintained frequently. Dependability is very important regarding safety, the flight control system must be available at all times, unlike automotive where simply stopping is an option.
• Stability control
Larger planes are always equipped with an auto-pilot of some sort. This control system can work in different ways. In most planes, a control system is optional and is used to simplify the pilot's task. Other planes, usually military, need a control system because they are inherently unstable and no human could control them without a control system. More recently, stability control also exists in automotive, where systems such as ABS and ESP are making their entry.
Other more common requirements are size, response time, cost, energy consumption, noise control, fun factor, ... (see how they are dealt with in automotive)
Legislation requirements
Because of the high safety and dependability requirements, regulation for aircraft systems is very strict. Software(DO-178B), hardware(DO-254) and network(AFDX) design are all standardized. Therefore, the certification of a new aircraft design and the paper trail that comes with it are very complex and time consuming. The whole procedure can be found on the site of the Federal Aviation Administration: http://www.faa.gov/licenses_certificates/ Not only the airplane but also the pilot is subjected to high demands. Pilot training, testing and certification procedures can also be found on the site.
Optimization
As one can imagine, there are a lot of possible system designs. There is also the difficult task of combining their strengths in order to be able to meet the imposed requirements. Due to the extra dependability requirements some back up systems must be preserved, which makes everything even more complex. The design of an airplane and more specific of this control system, is an iterative design. The concept is already invented in the early days of aviation. Each airplane is the product of an iteration step in order to approximate more and more the 'ideal' airplane. In the early days design was mainly based on the experience of the designer but since complexity grows, a more systematic method is needed. An example and discussion of such a computer aided design method can be found in the following paper by Airbus. http://www.mip.ups-tlse.fr/publis/files/06.26.pdf
[edit] Pilot
The pilot interacts with the airplane systems and therefore can be considered as part of the flight control system
Training
The pilot must be well trained and experienced so he can react appropriately in case of unexpected situations or system failures. The plane design is based on this assumption, unlike automotive, where far less training is required.
HMI
To make interaction possible between the pilot and the airplane systems the airplane has a HMI (human machine interface). A good HMI design can greatly reduce the amount of effort needed to control the aircraft.
Redundancy
In larger airplanes with an auto-pilot, the pilot can also be seen as a redundant system to fly the plane if the auto-pilot fails. Even the pilots themselves can replace each other. Even though they are supposed to do different tasks, all pilots can fly the plane in case of an emergency. In the early days, up to four pilots where needed to control an airplane, now only two are required for large airplanes.
[attachment=41249]
Air Traffic Control
Of all different system levels, ATC is the top level. This is a special level because it doesn’t exist in other applications like automotive, where there is no global communication between vehicles. The primary goal of ATC is collision prevention which requires communication and radar systems. To provide redundancy most aircrafts are equipped with TCAS ( Traffic alert and Collision Avoidance Systems).
Discussion
Flight Control System
Introduction
There are a lot of embedded control systems in an airplane. One of them is the flight control system which controls the flight trajectory and the stability of the airplane. The actuators of this system are the engines and the movable devices of the main wing and tail. They are actuated by the pilot and by the embedded control system of the airplane.
Different kinds of FCS exist. They are categorized according to the number of axes they control. A one-axis FCS prevents the plane of rolling. A two-axis FCS also gives the possibility to control the direction of flight. The three-axis FCS is even more complex by providing the ability of automatic climbing and descending.
File:FCS.JPG
The figure above is a schematic overview of the flight control system. The flight control system (FCS) controls the flight trajectory and the stability of the airplane. The actuators of this system are the engines and the movable devices of the main wing and tail. They are actuated by the pilot and by the embedded control system of the airplane. This includes stability control, automatic pilot and engine control. The control outputs are calculated from sensor inputs, like navigation systems, weather radar, velocity measuring, altitude measuring, sensors in the engine...
Design
Technical requirements
Airplane systems have specific requirements that are not found or are not as critical in other systems:
• Weight
Airplanes are made using strong but light materials. The aviation industry was the first to use aluminium on a large scale, and modern materials such as carbon fibre are beginning to make their entry. The weight requirement is also one of the reasons for the evolution from a mechanical linkage to a fly-by-wire system.
• Safety
Material quality must be high, less variation on material properties is allowed for aviation. Even though the black box is useless considering the safety of a single flight, it provides a crucial feedback loop in the entire design and maintenance process.
• Dependability (Reliability, Maintainability, Availability)
A lot of systems are made in redundancy in order to increase the reliability. Airplanes are also maintained frequently. Dependability is very important regarding safety, the flight control system must be available at all times, unlike automotive where simply stopping is an option.
• Stability control
Larger planes are always equipped with an auto-pilot of some sort. This control system can work in different ways. In most planes, a control system is optional and is used to simplify the pilot's task. Other planes, usually military, need a control system because they are inherently unstable and no human could control them without a control system. More recently, stability control also exists in automotive, where systems such as ABS and ESP are making their entry.
Other more common requirements are size, response time, cost, energy consumption, noise control, fun factor, ... (see how they are dealt with in automotive)
Legislation requirements
Because of the high safety and dependability requirements, regulation for aircraft systems is very strict. Software(DO-178B), hardware(DO-254) and network(AFDX) design are all standardized. Therefore, the certification of a new aircraft design and the paper trail that comes with it are very complex and time consuming. The whole procedure can be found on the site of the Federal Aviation Administration: http://www.faa.gov/licenses_certificates/ Not only the airplane but also the pilot is subjected to high demands. Pilot training, testing and certification procedures can also be found on the site.
Optimization
As one can imagine, there are a lot of possible system designs. There is also the difficult task of combining their strengths in order to be able to meet the imposed requirements. Due to the extra dependability requirements some back up systems must be preserved, which makes everything even more complex. The design of an airplane and more specific of this control system, is an iterative design. The concept is already invented in the early days of aviation. Each airplane is the product of an iteration step in order to approximate more and more the 'ideal' airplane. In the early days design was mainly based on the experience of the designer but since complexity grows, a more systematic method is needed. An example and discussion of such a computer aided design method can be found in the following paper by Airbus. http://www.mip.ups-tlse.fr/publis/files/06.26.pdf
[edit] Pilot
The pilot interacts with the airplane systems and therefore can be considered as part of the flight control system
Training
The pilot must be well trained and experienced so he can react appropriately in case of unexpected situations or system failures. The plane design is based on this assumption, unlike automotive, where far less training is required.
HMI
To make interaction possible between the pilot and the airplane systems the airplane has a HMI (human machine interface). A good HMI design can greatly reduce the amount of effort needed to control the aircraft.
Redundancy
In larger airplanes with an auto-pilot, the pilot can also be seen as a redundant system to fly the plane if the auto-pilot fails. Even the pilots themselves can replace each other. Even though they are supposed to do different tasks, all pilots can fly the plane in case of an emergency. In the early days, up to four pilots where needed to control an airplane, now only two are required for large airplanes.