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5、 Effects on Hydraulic Transport Elements on Aircraft RATIONALE There is a need to address the effects of lightning on hydraulic systems in aircraft, especially where there is a significant use of composite materials in the aircraft structure. This is due to the potential structural damage and compon
6、ent failures that could occur. This document addresses this need. TABLE OF CONTENTS 1. SCOPE 3 1.1 Purpose . 3 2. REFERENCES 3 2.1 Applicable Documents 3 2.1.1 SAE Publications . 3 2.1.2 FAA Publications . 3 2.2 Related Publications . 3 2.2.1 SAE Publications . 3 2.2.2 FAA Publications . 4 2.2.3 Oth
7、er Publications . 4 3. INTRODUCTION . 4 4. ANALYSIS OF LIGHTNING EFFECTS ON HYDRAULIC TUBES AND COMPONENTS . 5 5. AIRCRAFT HYDRAULIC TRANSPORT ELEMENTS AS LIGHTNING CURRENT CONDUCTORS 5 5.1 High Voltage Breakdown through Insulating Materials Used in Hydraulic Transport Elements . 7 5.2 Electrical Ar
8、cing From Hydraulic Transport Elements to Adjacent Aircraft Structure or Parts . 9 5.3 Magnetic Deflection or Deformation Due to High Lightning Currents on Hydraulic Transport Elements . 10 5.4 Resistive Heating Due to High Lightning Currents on Hydraulic Transport Elements 12 6. HYDRAULIC SYSTEM LI
9、GHTNING PROTECTION VERIFICATION 14 7. MAINTENANCE AND REPAIR . 15 8. NOTES 15 8.1 Revision Indicator 15 Figure 1 Process flow for current and voltage effects analysis on hydraulic tubes and components . 5 Figure 2 Simplified architecture of aircraft single hydraulic system 6 Figure 3 Potential tube
10、puncture and pitting locations for swaged fitting 7 Figure 4 Areas of possible potential material erosion and deposit on typical swivel valve . 8 Figure 5 Possible hydraulic actuator internal damage caused by arcing 8 SAE INTERNATIONAL AIR6185 Page 2 of 15 Figure 6 Possible component damage caused b
11、y arcing between two conductive elements which are separated with air gap 9 Figure 7 Example of the parallel hydraulic tubes located in the nose landing gear bay with lightning induced currents flowing in the same direction . 11 Figure 8A Hydraulic tube temperature increase from ambient temperature
12、T1 = 68 F as a function of the peak pulse current . 12 Figure 8B Hydraulic tube temperature increase from ambient temperature T1 = 20 C as a function of the peak pulse current . 13 Figure 9 Areas of potential local heating caused by induced currents across different interfaces between hydraulic tube
13、 and hydraulic assembly . 14 SAE INTERNATIONAL AIR6185 Page 3 of 15 1. SCOPE This SAE Aerospace Information Report (AIR) describes hydraulic system design and installation to minimize the effects of lightning, especially when the aircraft structure is composite. Techniques for effective electrical b
14、onding, hydraulic system lightning protection, and lightning protection verification techniques are discussed. 1.1 Purpose The purpose of this document is to provide lightning effects consideration in design and installation of the hydraulic systems and components on aircraft. 2. REFERENCES The foll
15、owing publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this document and
16、references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1 Applicable Documents 2.1.1 SAE Publications Available from SAE International, 400 Commonwealth Drive,
17、Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or +1 724-776-4970 (outside USA), www.sae.org. ARP5415 Users Manual for Certification of Aircraft Electrical/Electronic Systems for the Indirect Effects of Lightning ARP5416 Aircraft Lightning Test Methods ARP5577 Aircraft Lightnin
18、g Direct Effects Certification 2.1.2 FAA Publications Available from Federal Aviation Administration, 800 Independence Avenue, SW, Washington, DC 20591, Tel: 866-835-5322, www.faa.gov. AC 20-136B FAA Advisory Circular, Protection of Aircraft Electrical/Electronic Systems against the Indirect Effects
19、 of Lightning 2.2 Related Publications The following publications are provided for information purposes only and are not a required part of this SAE Aerospace Technical Report. 2.2.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-73
20、23 (inside USA and Canada) or +1 724-776-4970 (outside USA), www.sae.org. ARP5412 Aircraft Lightning Environment and Related Test Waveforms ARP5414 Aircraft Lightning Zone SAE INTERNATIONAL AIR6185 Page 4 of 15 2.2.2 FAA Publications Available from Federal Aviation Administration, 800 Independence A
21、venue, SW, Washington, DC 20591, Tel: 866-835-5322, www.faa.gov. AC 20-53B FAA Advisory Circular, Protection of Aircraft Electrical/Electronic Systems against the Indirect Effects of Lightning 2.2.3 Other Publications Lightning Protection Guidelines for Aerospace Vehicles NASA/TM-1999-209734, C.C. G
22、oodloe, Marshall Space Flight Center, Marshall Space Flight Center, Alabama. The Aerospace Engineers Handbook of Lightning Protection, Bruce C. Gabrielson, 1988, by Interface Control Technologies, Inc., Route 625, Gainesville, VA 22065 U.S. Electrical Bonding for NASA Launch Vehicles, Spacecraft, Pa
23、yloads, and Flight Equipment, NASA-STD-P023, August 17, 2001. Lightning Protection of Aircraft, Franklin A. Fisher and J. Anderson Plumer, NASA Reference Publication 1008, Scientific and Technical Information Office 1977. 3. INTRODUCTION Aircraft are routinely struck by lightning, especially when ai
24、rcraft are flying in precipitation. Lightning attaches to two or more points on the aircraft, typically at extremities such as the nose, wingtips, engine inlets, stabilizer tips and blade antennas. When lightning strikes an aircraft, the aircraft structure and skin conduct the lightning current betw
25、een the lightning attachment points. Other equipment such as metal fuel and hydraulic tubes, control cables, pushrods, and wires within the aircraft can also conduct a portion of the lightning current. For aircraft that use aluminum for their skin and structure, most of the lightning current is cond
26、ucted through the skin and structure since aluminum is a very good electrical conductor. Much lower lightning currents are conducted on electrical conductors within the aircraft for aircraft with aluminum skin and structure. Other metals used for aircraft structure, such as titanium and steel, are a
27、n order of magnitude less electrically conductive than aluminum. Therefore, the lightning current conducted on metal tubes, cables and wires can be much higher in an aircraft with titanium or steel skin and structure. Carbon fiber composite aircraft skin and structure have electrical conductivity a
28、few orders of magnitude lower than aluminum, so the lightning current can be significantly higher on metal tubes, cables and wires in the aircraft. The lightning current conducted through the aircraft skin and structure will also create a voltage difference between points on the aircraft, due to the
29、 resistance of the material. As the resistance of the material increases, the voltage difference due to lightning currents will also increase. For example, when lightning current is conducted through an airplane wing with aluminum skin and structure, the lightning-induced voltage difference between
30、the wing tip and root can be on the order of tens of volts. A similar wing with carbon fiber composite skin and structure can have a lightning-induced voltage difference between the wing tip and root on the order of several thousand volts. Electrical conductors such as metal fuel and hydraulic tubes
31、, control cables, pushrods, and wires within the aircraft that are routed between these points on the aircraft can be exposed to high voltages. When hydraulic tubes or components bridge gear doors, control surfaces, or other moveable aircraft parts, high voltages can develop between these parts and
32、the aircraft structure, regardless of the structural materials used. These voltages can cause arcing at the hydraulic tubes or components and high currents through those hydraulic tubes and components resulting in damage and leakage. SAE INTERNATIONAL AIR6185 Page 5 of 15 4. ANALYSIS OF LIGHTNING EF
33、FECTS ON HYDRAULIC TUBES AND COMPONENTS The lightning environment in aircraft areas where the tubes and components are installed should be determined to evaluate lightning effects on hydraulic tubes and components. The aircraft geometry, structure and materials all affect the lightning currents and
34、voltages on hydraulic tubes and components. Electromagnetic simulation and analysis may be used to determine the lightning currents and voltages on the hydraulic tubes and components. For aircraft with conventional aluminum skin and structure, simple resistance calculations can be used to estimate t
35、he lightning current and voltage on hydraulic transport elements. Aircraft with unconventional configurations or aircraft that use significant carbon fiber composite skin and structure may require more detailed electromagnetic analysis to predict the lightning current and voltage on hydraulic transp
36、ort elements. A simplified process flow required for the current and voltage effects analysis on hydraulic tubes and components is shown in Figure 1. AIRCRAFT STRUCTURAL DESIGN LIGHTNING CHARACTERISTICSLIGHTNING CONDITIONS IN SPECIFIC AIRCRAFT SEGMENTS AND AREASELECTROMAGNETIC SIMULATION AND ANALYSI
37、SGEOMETRY AND SPATIAL INTEGRATION OF HYDRAULIC TRANSPORT ELEMENTS AND COMPONENTSMATERIAL AND ELECTRICAL PROPERTIES ENVIRONMENTAL CONDITIONS AND ALTITUDESYSTEM MODEL ANALYSISAIRCRAFT CONFIGURATIONLIGHTNING EFFECTS ON HYDRAULIC TUBES AND COMPONENTSFigure 1 - Process flow for current and voltage effect
38、s analysis on hydraulic tubes and components 5. AIRCRAFT HYDRAULIC TRANSPORT ELEMENTS AS LIGHTNING CURRENT CONDUCTORS Hydraulic transport elements are part of the aircraft flight control and landing gear systems. Hydraulic tubes and hydro-mechanical components can be located in the fuselage, on the
39、landing gear, in the horizontal and vertical stabilizers, in the engines and pylons, in electrical and electronic bays, in fuel tanks, in flammable areas, and throughout the wing, as shown in Figure 2. The hydraulic transport elements can go across moving parts of the aircraft, such as across the ho
40、rizontal stabilizer trim hinges and across the landing gear mechanisms. The hydraulic transport elements connect to hydraulic actuators that can be located near the extremities of the aircraft, where lightning attachment is the most likely. SAE INTERNATIONAL AIR6185 Page 6 of 15 Lightning attachment
41、pointsLightning attachmentpointsFigure 2 - Simplified architecture of aircraft single hydraulic system The hydraulic transport elements are typically made of electrically conducting aluminum, titanium, and corrosion resistant steel (CRES). Since the hydraulic transport elements are routed to the air
42、craft extremities, they can conduct significant lightning current and can be exposed to significant voltage along their span. The lightning current can create resistive heating, magnetic deformation, and high energy arcs. These lightning effects can result in high pressure hydraulic leaks and damage
43、 to hydraulic components. The lightning voltage can create arcs across air gaps and across insulating materials and coatings. Explanation of these effects are described in ARP5416, paragraph 3.1 Direct Effects. The hydraulic transport element and the installation design should consider the following
44、 issues related to lightning: a. High voltage breakdown through insulating materials used in hydraulic transport elements. b. Electrical flashover from hydraulic transport elements to adjacent aircraft structure or parts. c. Magnetic deflection or deformation due to high lightning currents on hydrau
45、lic transport elements. d. Resistive heating due to high lightning currents on hydraulic transport elements. SAE INTERNATIONAL AIR6185 Page 7 of 15 5.1 High Voltage Breakdown through Insulating Materials Used in Hydraulic Transport Elements Lightning can result in high voltage breakdown on hydraulic
46、 couplings with an electrically insulating coating. In many cases the fittings used to join hydraulic tubes use an anodized coating, particularly on aluminum fittings. The anodized coating is an electrical insulator but is typically not controlled to prevent high voltage puncture. The induced voltag
47、e along hydraulic tubes can break down and puncture the thin anodized coating. Once the anodized coating is punctured, the lightning current moving through the anodized fitting is concentrated at the puncture location. The resulting high-current arc can burn a hole in aluminum hydraulic tubes, or ca
48、n cause pitting across the fitting mating surfaces. Both of these can result in hydraulic leaks. The lightning voltage and current on hydraulic tubes installed in carbon fiber composite aircraft structure or across the joints of moveable structures can be much higher than on similar tubes installed
49、in an aluminum aircraft structure. Therefore it is more likely to have lightning puncture or pitting if anodized fittings are used in carbon fiber composite aircraft structure or across the joints of moveable structures. If hydraulic tubes or components, such as heat exchangers, are installed in fuel tanks, the design should prevent lightning-related sparks that could result in fuel ignition. Refer to AC 20-53B for further informati
