Aeronautics and astronautics – Landing gear – Retractable
Reexamination Certificate
1999-12-29
2001-07-24
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Landing gear
Retractable
C244S10000R, C244S121000
Reexamination Certificate
active
06264139
ABSTRACT:
DESCRIPTION
1. Technical Field
This invention relates to an aircraft landing gear equipped with a device for the protection of a fuel tank located behind the landing gear.
The invention also relates to an aircraft, particularly a commercial aircraft, such as an aircraft designed for passenger and/or freight transport, comprising a landing gear of this type.
2. State of the Art
In commercial aircraft, the fuel tanks are normally located in the wing and in the lower part of the fuselage segment supporting the wing, in front of the main landing gear. This central position of the tanks symmetric to the longitudinal plane through the center line of the aircraft facilitates management of the aircraft center of gravity. In other words, the position of the center of gravity of the aircraft changes very little as the mass of fuel reduces as it is burned in the engines.
When it is required to increase the capacity and range of an aircraft, it may be necessary to modify the aircraft and design a new version, but without modifying its essential characteristics. This makes it possible to use the maximum number of parts in common on different versions of the same aircraft.
Consequently, a new version of an existing aircraft characterized by a higher capacity and range than in the basic version, may be defined without modifying the wing or the segment that supports the wing. Under these conditions, fuel tanks contained in the wing and in this segment are not modified either, such that their capacity remains unchanged. An additional fuel tank then has to be added to enable the aircraft to fulfill its new mission, which requires that an additional quantity of fuel is available in order to increase its range. A preferred position for this additional tank is in the lower part of the fuselage behind the main landing gear. This position located on the center line of the aircraft automatically enables good fuel management without changing the center of gravity of the aircraft, in other words without any mechanical, hydraulic or other action.
However, this position of the additional fuel tank can be critical under particular landing conditions. When the aircraft is landing, friction induced by the action of brakes on the wheels can increase the temperature of the braking device to very high values (up to 1200° C.). In the case of a bad landing, the main landing gear can fold backwards, for example due to the presence of an obstacle on the track or due to breakage of some structural parts. In this case there is a severe risk that the landing gear, and particularly the braking system located on the wheels, can strike and penetrate the partition that separates the landing gear from the additional fuel tank. Under these circumstances, contact between braking elements at a very high temperature and the fuel could cause explosion of the fuel and consequently fast and complete destruction of the aircraft.
In practice, it is impossible to completely eliminate the risk of a bad landing. Consequently, explosion of the aircraft following a bad landing would be unacceptable.
A comparable risk exists close to the jet engines on aircraft. There is a turbine behind the combustion chamber for each jet, in which the blades are at a very high temperature. Therefore, in the case of a blade breakage, it is essential that the blade could never come into contact with elements vital to control of the aircraft, such as flight controls, hydraulic circuits, etc., or fuel, during its trajectory. The current solution used for fuel consists of eliminating the presence of any fuel (circuit, pump, tank, etc.) along the probable ejection cone of a blade.
However, this solution cannot be applied to the case of a fuel tank located behind the main landing gear of the aircraft. Due to the reasons mentioned above, this position has essential advantages that make it unavoidable when an additional tank has to be installed on the aircraft.
DESCRIPTION OF THE INVENTION
The main purpose of the invention is a landing gear designed to be located in front of a fuel tank and in which the landing gear is equipped with protection means for eliminating any risk of collision between elements of the landing gear increased to very high temperature and the fuel under abnormal landing conditions, thus protecting the integrity of the aircraft.
This result is achieved according to the invention by means of an aircraft landing gear that can be connected to part of the aircraft structure by local assembly means, characterized in that the said landing gear is equipped with means of protecting a fuel tank possibly located behind the landing gear, to automatically disconnect at least some of the local assembly means when the landing gear accidentally tilts backwards beyond a predetermined maximum angle.
Thus, if a bad landing causes the landing gear to tilt backwards, the landing gear is automatically partially or completely disconnected from the aircraft structure. Consequently, any risk that hot parts of the landing gear, and particularly the braking device located on the wheels, can come into contact with the fuel, is eliminated. Complete destruction of the aircraft due to fuel explosion caused by the fuel coming into contact with hot parts of the landing gear is thus prevented.
According to one preferred embodiment of the invention, the protection means comprise at least one disconnection control part installed on part of the landing gear structure such that it is free to move and can engage on part of the aircraft structure located between the fuel tank and the landing gear, when the landing gear accidentally tilts backward by a predetermined minimum angle less than the predetermined maximum angle at which the landing gear is automatically disconnected from the aircraft structure.
Part of the aircraft structure on which the disconnection control part is supported is advantageously reinforced in order to protect any perforation in the wall of the fuel tank.
Normally, the localized assembly means by which the landing gear is connected to the aircraft structure include at least one pin connected to the structure of the landing gear, that normally fits into a housing connected to the aircraft structure. In this case, the protection means also comprise at least one mechanism capable of displacing the above mentioned pin parallel to itself to gradually release it from its housing, in response to a displacement of the disconnection control part with respect to the structure of the landing gear, after the landing gear has rotated through an angle between the said predetermined minimum angle and the said predetermined maximum angle.
In order to prevent accidental operation of the protection means and to eliminate parasite movements, for example due to poor condition of the landing runway, the mechanism advantageously includes a frangible device that normally fixes the pin with respect to the structure of the landing gear when the force exerted on this frangible device remains below a predetermined threshold.
Normally, the localized assembly means comprise two pins in line connected to the landing gear structure that normally fit into two housings in line with each other connected to the aircraft structure. The protection means may then comprise one or two mechanisms capable of moving one or both of the two pins simultaneously, parallel to itself.
Furthermore, in particular the disconnection control part may be installed to pivot on the structure of the landing gear, for example about an axis parallel to the axis of the pin and along a direction transverse to the aircraft.
In this case, the mechanism advantageously comprises a first lever connecting the disconnection control part to a linkage part installed free to pivot on the structure of the landing gear, and a second lever connecting the linkage part to the pin.
The invention also relates to an aircraft comprising at least one landing gear connected to an aircraft structure by localized assembly means, and at least one fuel tank, characterized in that the fuel tank is located behind the landing gear and in th
Aerospatiale Matra
Best Christian M.
Burns Doane Swecker & Mathis
Jordan Charles T.
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