1. Introduction
It's been days since the 321 crash, and as the search and rescue progresses, more and more details are being dug up. On March 23, the cockpit voice recorder (CVR) was found. On March 26, a second black box, the Flight Data Recorder (FDR), was also found. Both black boxes have been sent to Beijing for data analysis, and preliminary analysis is expected to be completed within 30 days. When the two black boxes were found, they could not be regarded as a complete one, and what was found was a cylindrical structure, and the voice data and flight data existed inside the cylinder. The black box is an important instrument for aircraft to save data, falling from a height of more than 8800 meters, how does it protect the internal data security?
The cylindrical column of the black box
2. Know the black box
The black box is not black, and in order to facilitate the discovery during the search and rescue process, it is sprayed with a conspicuous orange color. The black box we see now is generally the third generation, unlike the previous black box, the third generation of black box is obviously smaller in size, which is actually related to the upgrade of the storage medium. I checked and the 2 black boxes of the Boeing 737-800 were located at the rear, the FDG on top of the back kitchen, and the CVR on the electronics rack in the rear cargo compartment. It's not the media saying one is in the cockpit, one is in the tail. Obviously, the position of the tail of the aircraft can avoid direct collisions as much as possible and maximize data security. CVR is used to record the voice data of the pilot in the cockpit to analyze the pilot's actions. FDR records all the states of the aircraft during flight, including speed, altitude, heading, deflection, rolling and other data, which is an important basis for in-depth restoration of the cause of the accident.
FDR location
CVR location
3. The structure of the black box
In order to maximize the protection of data security in the black box, the black box itself will be made strong enough. It can withstand tons of shocks, temperatures of nearly a thousand degrees, and corrosion from seawater, and it looks really flawless. I saw that some students on the Internet had such a question: Since we can make the black box so strong, why not make the whole machine as strong as it is? The starting point of the students is very good, but such an aircraft does not exist, and the cost performance is too low. In addition, the knot is not strong, it is also relative. The dao is one foot high, and the devil is one foot high. No matter how strong the black box is, there is also a limit to withstand. If you fall from a higher place, or fall on a rock, or burn continuously for more than a certain period of time, these conditions can destroy the black box and cause data loss.
Early black boxes
Early black boxes were made into a large square block, with data storage, circuit boards, etc. wrapped in metal leather. In the data storage section, there is also a thick shell layer of protection. Now the third generation of black boxes, data storage and other circuit parts separated. Like this black box, the right square contains the power supply, circuit board and other components, the bottom rectangle also contains a circuit board, the most important component is this cylindrical structure, called CSMU, contains a storage unit. This design can make this cylindrical structure more easy to fall off after impact, smaller in size, and less likely to be hit and squeezed by other objects, which is safer. Students all know that geckos break their tails to survive, and they work the same way here.
Black box contrast
Although the other parts of the black box also have metal shells, this boxy metal shell is not thick, and may not even be a steel shell, and in terms of body shape, it is completely possible to smash the shell into the shell with a stick. But it doesn't matter, because the data is in the CSMU. This cylindrical CSMU shell is made of steel, which has a layer of insulating high-temperature-resistant vibration damping buffer layer, and then there is a small steel shell of about this large size, and the inside of the small steel shell is the storage medium, and the vibration damping buffer layer of insulation and high temperature resistance is filled again. It is this layer of protection that protects the internal storage media.
Black box structure
Obviously, the steel shell is the first line of defense to protect data, and the thicker its thickness, the stronger the protection ability. But for the aircraft, the size of the mass is very critical. Therefore, the thickness of this layer of steel shell is calculated under the specified impact load, and if the impact acceleration is too large, the steel shell cannot be protected. In addition, the cylindrical design also tries to disperse and slide the impact force as much as possible to avoid the shell from collapsing. The second line of defense is the internal vibration damping buffer layer, the thermal conductivity of steel is very high, and the heat transfer is very fast. This buffer layer can not only reduce the vibration under the action of the shock load, but also isolate the external heat and avoid burning the internal storage medium for a long time. The third line of defense is the small steel shell on the inside, which can provide a certain degree of structural protection and is also an installation bracket for storage media. The fourth line of defense is the buffer layer in the small steel shell, which prevents the impact load from being too large, the storage medium falling off, and also playing a role in heat insulation.
A CSMU structure
4. Summary
Therefore, if the black box falls from a height of 10,000 meters, the CSMU will fall off first, and it will be smaller and easier to survive. Its two-layer cylindrical steel shell inside and outside is the main bearing structure. The internal flexible cushioning layer insulates and dampens vibration as much as possible. Rigidity and flexibility protect internal data security. However, CSMU also has a limit to withstand, the external load is too large, and internal data security cannot be guaranteed. It is hoped that the black box this time can protect the internal data and restore the truth of the accident as soon as possible.