Patent Application
20090322147
The present invention pertains generally to aircraft electrical systems. More particularly, the present invention pertains to electrical systems for aircraft having an airframe made of a carbon fiber composite material. The present invention is particularly, but not exclusively, useful as an aircraft electrical system with an isolated ground that prevents electrical current flow from the electrical system through the carbon fiber airframe.
In aircraft having conventional metallic conductive fuselage skins, the fuselage skins are used to ground the electrical components of the aircraft. Typically, a voltage source is connected to the electrical components through power wires, and the electrical components are grounded to the fuselage skin. Therefore, when shorts occur in power wires of conventional metal surface aircraft, the electricity simply flows back to the voltage source through the electrically conductive fuselage skin. As a result, all power will be passed immediately to the fuselage skin and a circuit breaker positioned on the power wire will be immediately tripped.
Unlike aircraft with metal fuselages, an aircraft made of a composite material will not have the same result. Instead, electricity from the shorted wire may pass from the wire to the airframe without tripping the circuit breaker. This may happen because the carbon fibers of the composite material will resist the flow of electricity and produce a current that is below the threshold required to trip the circuit breaker. At the same time, however, the resistance of the carbon fibers can cause an unwanted heating of the composite material. In this context, the carbon fibers may be compared to the filament of a light bulb. Further, the resistance heating may cause a rise in temperature sufficient to ignite the resin in the composite material and thereby cause extremely dangerous conditions during flight.
In addition to internal electrical considerations, composite material aircraft also must include safeguards for lightning strikes. While lightning striking a conventional aircraft often travels quickly through the fuselage skin, it will behave differently for a composite material aircraft. Specifically, the electricity will be resisted while passing through the less conductive composite material airframe. For composite material aircraft, this leads to a higher voltage differential and an increased risk of the current jumping, potentially through a critical electrical component, fuel cell, or persons onboard the aircraft. While it may be impossible to prevent all structural damage to composite material aircraft from lightning strikes, it is important to avoid the risk of lightning electricity jumping through the aircraft on its own path. If the electricity is not directed somewhere, it will find its own way through the aircraft. Therefore, there are important considerations regarding lightning for composite material aircraft that are not faced by conventional aircraft.
In light of the above, it is an object of the present invention to provide a system and method for providing an isolated ground for composite material aircraft. Another object of the present invention is to provide a system and method for isolating and grounding an antenna mounted on a composite material aircraft. Yet another object of the present invention is to provide an isolated ground electrical system for an aircraft that reduces electromagnetic interference and static electricity build up. Still another object of the present invention is to provide a system and method for isolating a ground in an aircraft that is easy to implement, is simple to use, and is comparatively cost effective.
In accordance with the present invention, a system and method for isolating an electrical ground from the composite material airframe of an aircraft substantially reduces the threat of onboard fires caused by electrical shorts. Importantly, the system provides a mechanic, or an active resistance monitoring device, with the ability to detect circuits that are shorted to the airframe. In the system, a voltage source having a positive bus bar and a negative bus bar is mounted to the airframe. Further, an electronic device having a positive terminal and a negative terminal is mounted to the airframe. Accordingly, a power wire isolated from the airframe connects the positive terminal of the electronic device to the positive bus bar of the voltage source. Also, a circuit breaker is interconnected to the power wire. Further, a ground wire isolated from the airframe connects the negative terminal of the electronic device to the negative bus bar of the voltage source. As a result, a complete circuit that is isolated from the airframe is created.
Typically, the generators used by aircraft create electromagnetic interference. In order to eliminate electromagnetic interference on the circuit of the present invention, both the power wire and the ground wire may be connected to capacitors. Further, in order to reduce static electricity between the isolated circuit and the airframe, a pair of resistors may be interconnected between the wires and the airframe.
For purposes of the present invention, the aircraft includes an antenna that defines an antenna axis. In order to connect the antenna to the aircraft, while electrically isolating the antenna from the airframe, the airframe forms an aperture extending between its external and internal surfaces. Further, an external insulating gasket is positioned outside of the external surface to surround the aperture, and an internal insulating gasket is positioned inside of the internal surface to surround the aperture. Also, an antenna backing plate is positioned against the internal insulating gasket to fix the internal insulating gasket between the backing plate and the airframe. Mounted between the internal gasket and the airframe is a ground plane perpendicular to the antenna axis. Structurally, the ground plane is formed from a metallic wire mesh that surrounds the base of the antenna and is insulated from the airframe. The metallic mesh is contained in the outer layer of the composite airframe in the vicinity of the antenna. In order to ground the antenna, the ground plane mesh is electrically connected to the antenna.
For protection from lightning, the aircraft includes a second metallic mesh that is contained in the outer laminate of the composite airframe. Importantly, this lighting protective mesh is not applied in the vicinity of the antenna. Specifically, the ground plane mesh does not make electrical contact with the lightning protective mesh. Rather, the two distinct meshes are separated at the perimeter of the ground plane mesh by an insulating gap.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
Referring initially to
Referring to
As shown, the circuit 34 is equipped to eliminate radio interference and reduce noise by outside electromagnetic sources such as the onboard generators. Specifically, the ground wire 28 is connected to a groundside capacitor 36 that is coupled to the airframe 12. Also, the power wire 32 is connected to a powerside capacitor 38 that is coupled to the airframe 12. Additionally, a groundside and powerside resistor 40, 42, respectively, may be connected in parallel with the capacitor 36, 38 to bleed off static electricity between the circuit 34 and the airframe 12. As also shown in
Referring now to
In
As shown in
As noted above, due to the structure of the aircraft 10, a mechanic, or an active resistance monitoring device, may detect circuits that are shorted to the airframe 12. Specifically, a short is identified when the resistance between the wire 28 and the airframe 12 has a resistance value less than the resistor 42. Likewise, a short is identified when the resistance between the wire 32 and the airframe 12 has a resistance value less than the resistor 42. Thus, a short to the airframe 12 can occur without damage, then be identified and corrected.
While the particular Aircraft with Isolated Ground as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.
