Aeronautics and astronautics – Aircraft – heavier-than-air – Helicopter or auto-rotating wing sustained – i.e. – gyroplanes
Reexamination Certificate
2002-08-28
2004-08-17
Carone, Michael J. (Department: 3641)
Aeronautics and astronautics
Aircraft, heavier-than-air
Helicopter or auto-rotating wing sustained, i.e., gyroplanes
C244S158700, C188S377000
Reexamination Certificate
active
06776370
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an energy-absorbing connecting strut designed to link two components and capable of undergoing axial stresses in tension/compression between these components, so as to absorb energy in case of shock or impact on at least one of the components linked by the strut and which would be such as to develop in the latter a compressive load greater than a specified threshold, so that the shock or impact energy is not wholly transmitted by the connecting strut from one to the other of the two components which it links, and preferably so as to limit the amplitude of the force transmitted.
As an application for which the connecting strut according to the invention is of great relevance for the applicant, the invention also relates to the use of this connecting strut as a suspension strut for a main gearbox on the structure of a rotary wing aircraft, and preferably a helicopter, so that hereafter the invention is described and explained more particularly in this application.
More precisely, the energy-absorbing connecting strut according to the invention is described in its application as a so-called crash-resistant suspension strut, as it is designed to fulfil its functions of absorbing energy and limiting transmitted loads in case of a rotary wing aircraft crash, it being understood that the field of application of such an energy-absorbing connecting strut is not limited to the protection of rotary wing aircraft or at least a part of the latter, in the case of a crash.
BACKGROUND OF THE INVENTION
In general and schematic terms, when a body strikes the ground, it is subjected to inertia forces which are a function of the kinetic energy accumulated by this body prior to the impact and of its deformation caused by the impact, according to the following formula:
1
/
2
m
(
V
2
-
Vo
2
)
=
∫
o
D
F
(
x
)
ⅆ
x
where ½ mVo
2
is the kinetic energy of the body prior to the impact, ½ mV
2
is the kinetic energy of the body after the impact, this energy being zero after an aircraft has crashed, F(x) represents the inertia forces applied to the body, and D is the deformation of the body caused by the impact.
From this general formula, it can be deduced that the inertia forces F(x) are greater the smaller the deformation D of the body.
If we consider the crash of a rotary wing aircraft, particularly a helicopter, in order to ensure the survival of the crew and passengers in the rotary wing aircraft, it is necessary to preserve the volume of the cabin of the rotary wing aircraft to prevent the persons occupying it from being crushed, to limit the deceleration undergone by the crew and passengers to a tolerable level and to preserve the integrity of the fuel tanks in order to prevent a fire or explosion.
In case of impact of a rotary wing aircraft with the ground, the cabin of the rotary wing aircraft is subjected to forces introduced in particular by the landing gear, the contact of the structure of the rotary wing aircraft with the ground, and all the mechanical items attached to the top of the rotary wing aircraft structure such as, in the case of a helicopter for example, the elements of the power unit, the main rotor or rotors and the main gearbox or gearboxes.
In fact, it is known that on state-of-the-art rotary wing aircrafts, and in particular helicopters, the so-called upper mechanical assemblies, namely the engines, rotors and main gearboxes are linked to the structure of the rotary wing aircraft by being bolted directly onto this structure or by a connecting device comprising a set of at least three rigid, non-deforming, straight and inclined suspension struts distributed around the gearbox and tilted so as to converge towards each other at their upper ends by which each strut is connected in a hinged manner to the gearbox, while at its lower end each strut is connected in a hinged manner to the structure of the rotary wing aircraft.
Generally, each suspension strut is hinged at its upper end directly to the main gearbox or, as a variant, to a lever supporting a flapping mass resonator and itself mounted pivotably on the main gearbox, as described for example in U.S. Pat. No. 5,190,244 and U.S. Pat. No. 6,145,785 and, at its lower end, either directly to the structure of the rotary wing aircraft, as described in FR 2 232 481, EP 718 187 and U.S. Pat. No. 5,782,430, or to a lever supporting a flapping mass resonator and itself mounted pivotably on the structure of the rotary wing aircraft, as described in U.S. Pat. No. 4,431,148, U.S. Pat. No. 4,458,862, U.S. Pat. No. 4,720,060, FR 2 777 861, FR 2 787 762 and FR 2 795 386, to which reference should be made for further details.
Currently, protective crash-resistant measures adopted on helicopters are intended to allow the absorption of energy by the landing gear, to limit the forces introduced into the helicopter structure, absorption of energy by the part of the structure under the cabin, known as the subfloor structure, to limit the forces introduced into the cabin structure, and dimensioning of the cabin structure to withstand being crushed by the upper mechanical assemblies mentioned above, linked to this structure by non-deforming means, particularly the suspension struts mentioned above.
In fact, when a crash occurs, the inertia forces originating from said upper mechanical items are very great, because of the weight of these items and the rigidity of their connection to the cabin structure.
If it is wished to preserve the volume of the cabin to prevent its occupants being crushed, the initial dimensioning of the structure, to withstand normal flying loads, is not sufficient. It is necessary to over-dimension the structure in order for it to withstand the loads during the crash, which in practice means that this structure is made very appreciably heavier.
A purpose of the invention is to propose an energy-absorbing connecting strut, the use of which as a suspension strut for a main gearbox on a rotary wing aircraft structure, as part of a crash-resistant connecting device, allows the volume of the rotary wing aircraft cabin to be preserved in the event of a crash, due to the fact that the upper mechanical assemblies can be linked to the cabin of the rotary wing aircraft by means of such connecting struts absorbing the kinetic energy of these upper mechanical assemblies, and preferably also limiting the amplitude of the forces transmitted to the cabin.
Moreover, another purpose of the invention is to propose an energy-absorbing connecting strut which, when it is used to constitute a crash-resistant device, protecting the cabin of a rotary wing aircraft from crushing by the upper mechanical items mentioned above, simultaneously provides a remedy for a number of disadvantages of known crash-resistant devices, such as presented below.
The function of all these known crash-resistant devices is to absorb energy, represented by the product of the load by the deformation.
To limit the load transmitted to a structure and which constitutes a danger of damage to the structure, it is necessary to allow a certain deformation, and known crash-resistant devices introducing deformation are of two types:
one type with elastic deformation of at least one connecting component, and
one type with plastic deformation of at least one connecting component.
The main disadvantages of known elastic deformation devices, comprising any spring system, are that they do not dissipate a substantial proportion of the energy which they receive, since they store this energy and then return the greater part of it, which results in practice in a rebound after the initial impact, which is thus followed by a succession of secondary impacts on components already weakened by the initial impact. Moreover, compared with a device absorbing energy by plastic deformation, the amount of travel required to absorb the same quantity of energy in an elastic deformation device is about twice as great because of the difference in the areas below the
Salvy Jacqueline
Salvy Michel
Scala Vincent
Struzik Alain
Carone Michael J.
Eurocopter
Salvy Jacqueline
Semunegus Lulit
Sturm & Fix LLP
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