Take-off
Take-off
Introduction to aircraft
Introduction to aircraft
Introduction to aircraft
Introduction to aircraft
Introduction to aircraft
On-board systems
An on-board system is a mixture of a computer system and an electronic system. It is specialised in a specific task and must meet certain constraints.
In Aircraft, the on-board systems are very diversified. It concerned the fly command, the auto-pilot, the communication system air/ground and also the recording system called the black box.
All those systems must meet certain constraints like the space, the cost and the environment. Those systems have to obey the DO-178C certification in order to guarantee the security of the passengers. Imagine if a pressure sensor doesn't work and the system doesn’t apply the right pressure in the plane. That’s why there are five levels of failure depending on the severity of the dysfunction.
Most of the time, on-board systems are composed of sensors which take information from the environment. In planes like the Airbus A380, there are around 10 000 sensors which are disposed everywhere. They can be on the wings, in the engines, in cargo compartments, in every place where information is needed. We can quote the temperature sensor, pressure sensor, speed sensor, the GPS (Global positioning system), … All those sensors allowed the pilot to better direct the aircraft.
Ice sensor: It detects the formation of ice on the aircraft. The principle is simple, the detection probe resonates at a certain frequency. When ice forms on it, the resonance frequency changes. When the limit frequency is reached, an emergency signal is sent to initiate several de-icing methods. It can be by heating surfaces by hot hair, by electrical equipment or by chemical application. Ice formation is very dangerous, indeed it makes the aircraft heavier, decreases lift and makes it difficult to maintain its speed.
Angle of attack sensor : It measures the angle between a reference line and the relative wind speed vector. The greater the angle, the greater the lift, but if the angle is too important, the pilot is warned that there is a risk of stalling.
Radar altimeter : It measures the altitude under the aircraft. It emits a signal towards the ground and measures the time between the emission and the reception of the signal. Then it calculates the altitude by the relation : h = c * t / 2
h : altitude c : velocity t : time
Information received from sensors creates big data. All this information can be treated and analyzed to predict routes and improve safety. For example, information about the position and the fuel level can be used to determine the best trajectory for refuelling the aircraft. Data analytics can also be useful to reallocate ground sources in order to economise the carburant.
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Data analysis is an important issue. It has helped to reduce the cost of travel by reducing fuel consumption and travel time.
Another use of the on-board system in aircraft is the autopilot. This is a system that is used to maintain the correct trajectory without human intervention. In fact, it does not replace the pilot, but it helps him to better control the aircraft. Autopilots are constantly evolving, and today they are even capable of landing and taking off without human supervision. There are three levels of autopilot corresponding to the control of three axes.
1. Control of the roll axis corresponding to the rotation around the longitudinal axis.
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2. Control of the roll axis plus the pitch axis corresponding to the rotation around the transverse axis.
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3. Control of the two previous axis plus the yaw axis corresponding to the rotation around the vertical axis.
Automatic piloting is divided into several phases corresponding to the different parts of the flight (take-off, climb, cruise, descent, approach and landing)
The autopilot system has two modes: manual mode and automatic mode. In manual mode the pilot selects all the maneuvers that the aircraft will do, then the autopilot executes them. In automatic mode, the pilot selects only the direction and the attitude of the aircraft, then the autopilot chooses the maneuvers to be performed. In most cases, the autopilot incorporates navigation aids, flight directors and automatic throttle systems.
In short, there are many systems and flight indications that allow pilots to better steer the aircraft. You can see the most important of them just below.
EHSI (Electronic Horizontal Situation Indicator) : This screen replaces a lot of instruments that are found on a more conventional airplane. It gives information about the heading, the track, the lateral deviation from a selected track, distance and time to go, weather information, and other information depending on the model.
EICAS (Engine Indicating and Crew Alerting Sytem) : It provides information on engine parameters and alerts pilots to malfunctions. It also informs on cabin pressure, fuel stock and landing gear.
FMC (Flight Management Computers) : It allows the pilots to give the instructions to the autopilot system.
Flight director: It gives information on the attitude of the aircraft. It allows pilots to know how to keep the right trajectory thanks to the flight director control bar.
We notice that there are many technologies used to assist pilots in safety, but there is one that we have not yet mentioned. This is air/ground communication. In the early days of aviation, communication was very primitive and consisted of hand signals or colour paddles. During the First World War, communication became more serious. Pilots used telegraph systems to send messages in Morse code. Wireless communication then began to be experimented with and in 1915 Captain J.M. Furnival was the first person to hear a voice from the ground by radio.. In the 1930s, radar began to develop. It represented a great advance in air/ground communication. It is used to track aircraft by determining their distance, direction and speed. During the Second World War, it was used to determine if the aircraft was an enemy or not by detecting the type of aircraft.
How does the radar work?
A transmitter is placed on the ground and sends a signal to the aircraft. The aircraft acts as a reflector that reflects the radar beam. Then a radar antenna receives the signal. This mechanism is very fast because the signal is an electromagnetic wave that travels at the speed of light (3*10^8 m/s). To find out the speed of an aircraft, we use the Doppler effect. It is based on the frequency variation between the transmitted and received signals.
Despite all these navigation aids, a crash can occur. In this case, if the aircraft is found, the black box allows investigators to know what happened before the crash. To do this, black boxes are divided into two boxes. One records cockpit voice and one records flight data but both must resist the crash. Despite their name, black boxes are painted bright orange to be found easily on an accident site. They are located in the tail of the aircraft where they have the best chance of survival due to the large structure. Furthermore,the black boxes withstand a deceleration of 3400G over 6.5 seconds which is equivalent to going from 70mph to 0 in the space of 1.5cm. They can also take 1100 degrees for an hour. Besides, black boxes record around 25h of flight data. The other box records pilots' conversation and ambient sounds for around two hours before the crash. Black boxes are very useful for investigations and allow engineers to understand what the problems are. In the end, they help to increase flight safety.