The patent's assignee for patent number 8755164 is
News editors obtained the following quote from the background information supplied by the inventors: "An aircraft includes a very large number of pieces of electrical equipment or apparatus of various kinds. They may be motors or indeed electronic devices such as computers.
"Among such pieces of equipment, many are electrically powered with a single phase. For this purpose, the equipment is connected to the positive terminal of the generator by means of a cable. As for the connection to the negative terminal generator, this takes place by connecting the other terminal of the equipment to the metal ground of the airplane which also has a negative terminal of the generator connected thereto. That constitutes the circuit for operating currents.
"It is also necessary to make provision for carrying possible fault currents relating to the equipment. By way of example, this type of current may be a leakage current or a short circuit current and it may appear in the event of an anomaly. When the airplane is made mostly out of metal, fault currents can be carried in the same way as operating currents, with the equipment being connected to metal parts of the airplane.
"However things are different when it is desired to make a portion of the airplane out of composite material comprising a plastics material matrix reinforced by non-metallic fibers. Such a material is a less good conductor of electricity than is metal.
"In order to connect the metal ground of the aircraft to the pieces of equipment present in an aircraft of this type so as to carry operating currents, each piece of equipment is connected to said ground by means of a specific cable. It is thus known to envisage a specific metal network that, in the fuselage, is sometimes referred to as being the electrical structure network or 'ESN'.
"Furthermore, provision must be made for a possible fault current from the equipment to return to metal ground. For this purpose, a specific fault network is used that is referred to as the metallic bonding network or 'MBN'. This network coincides in part with structural metal parts of the airplane such as seat rails in order to provide the airplane with a mesh or lattice capable of carrying fault currents from equipment. In this context, it is known to provide specific components such as metal tapes on each frame and each crossmember of the airplane so as to provide electrical continuity between the metal parts of the airplane in spite of the presence of the composite material, which continuity serves to carry fault currents to the ground of the airplane.
"However, together these metal elements can form a mesh that is complex and that gives rise to numerous problems. Thus, adding specific components increases the weight of the airplane. It increases the length of time needed for accomplishing all assembly operations. The associated cost is not negligible. These elements also make the current return network more complex. Such elements require special studies to be made relating to dimensioning, to maintenance, to corrosion, and to interconnecting different portions of the ESN."
As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "An object of the invention is to provide a simpler solution for carrying fault currents on board an airplane that includes parts made of composite material.
"To this end, the invention provides an aircraft including at least one piece of electrical equipment and a composite material part to which the equipment is connected, the aircraft being arranged in such a manner that a fault current circuit for the equipment passes via the part.
"Thus, any fault currents from the equipment can be carried by means of a non-uniform network made up both of composite material and of metal. The metal portion of the network corresponds to the metal ground of the aircraft. This is the main network. The part(s) made of composite material then form(s) a delivery network enabling fault currents to be directed to this main network. It is thus the composite material parts themselves that are used for carrying fault currents from the equipment. The invention takes advantage of the fact that the electrical properties of composite materials on board aircraft do not enable them to carry to ground the operating currents of the aircraft, but in contrast do enable them to carry fault currents. Implementing the invention does not require a large number of specific components to be added. It does not give rise to extra weight nor does it significantly increase the length of time required for assembly operations. There is no significant extra cost, and the electric current return network is not made more complicated. Finally, there is no need to provide for the above-mentioned studies for interconnecting the various portions of the ESN.
"Advantageously, the aircraft includes at least one contact member connected to the equipment and assembled to the part by means of a tight fit between the member and the part.
"This ensures good electrical connection between the equipment and the composite material part so as to enable fault currents to be carried appropriately. More precisely, this tight fit serves to make the contact resistance between the member and the part minimal or even negligible, thereby making it easier to carry fault currents via the composite material part.
"Preferably, the contact member extends in an orifice of the part, the diameter v of the member and the diameter e of the part satisfying the following equation: (v-e)/v.gtoreq.0.0025
"This relationship between the diameters ensures that the contact resistance is negligible.
"Advantageously, the composite material comprises a plastics material reinforced by carbon fibers.
"Preferable, a majority of the length of the fault current circuit comprises parts of the aircraft that are made of metal.
"Thus, the network is made up for the most part out of metal elements, in particular structural elements of the airplane, thereby obtaining the lowest possible mesh electrical resistance.
"Advantageously, the number of pieces of electrical equipment and the number of composite material parts are at least two, the aircraft including a metal structure connected to the composite material part such that the fault current circuit of each piece of equipment passes via the associated part and the metal structure without passing via the part associated with each other piece of equipment.
"Preferably, the aircraft includes a monitoring device suitable for detecting a fault current relating to the equipment.
"This device serves to protect the equipment from the possible consequences of a fault current appearing.
"Preferably, the device is suitable for interrupting an electrical power supply to the equipment on detecting a fault current relating to the equipment.
"Advantageously, the monitoring device forms part of the equipment.
"The device is thus dedicated to the equipment. In the event of fault current, it is capable of isolating the equipment without interrupting the operation of other pieces of equipment. It does not require a specific assembly operation to be performed on the aircraft assembly line.
"The invention also provides a method of making an aircraft, in which a piece of electrical equipment of the aircraft is connected to a composite material part, and the aircraft is arranged in such a manner that a fault current circuit for the equipment passes via the part.
"Preferably, at least one contact member is connected to the equipment and the contact member is assembled with the part by means of a tight fit between the member and the part."
For additional information on this patent, see: Pons, Francois; Larrose, Nicolas. Aircraft Including Pieces of Electrical Equipment and Parts Made of Composite Material. U.S. Patent Number 8755164, filed
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