A method for airworthiness certification of lightning protection of a helicopter

Abstract

The present application relates to the technical field of aviation rescue, in particular to a kind of helicopter lightning protection airworthiness certification method, including microwave relay system is installed on the helicopter, obtain communication helicopter;Communication helicopter is directly and indirectly protected by lightning, and airworthiness verification is carried out, and verification is successful, and obtain protection helicopter;Lightning protection measures optimization is carried out to protection helicopter, and optimization result is obtained;Lightning protection and anti-static modification are carried out to protection helicopter based on optimization result, and airworthy helicopter is obtained, the safety of the airworthy helicopter obtained by the modification of helicopter based on the influence of direct and indirect effects of lightning on helicopter has been increased, the problem that the existing helicopter lightning protection method does not consider the influence of direct and indirect effects of lightning on helicopter, and the safety of helicopter flight is reduced.

Description

Technical Field

[0001] This invention relates to the field of aviation rescue technology, and in particular to an airworthiness certification method for helicopter lightning protection. Background Technology

[0002] Helicopters may be struck by lightning during flight. When a helicopter is struck by lightning, the lightning can have adverse effects, which can be categorized into direct and indirect effects depending on the form of the impact. Direct lightning effects include the burning, dissolving, exploding, and structural distortion caused by the attachment of the lightning arc and the accompanying high-voltage shock wave and magnetic force. Indirect lightning effects are the equipment damage or interference caused by overvoltage and overcurrent in electrical and electronic equipment due to lightning discharge.

[0003] One existing method for protecting helicopters from lightning strikes involves adding composite materials to the surface of the helicopter.

[0004] With the extensive use of composite materials in helicopter structures and the widespread application of microwave relay systems composed of large-scale integrated circuits, semiconductor technology, and computer technology in avionics systems, the transient induction of lightning within helicopters has become more complex, and the systems are more sensitive to it. Failing to consider the direct effects of lightning on external electronic and electrical equipment and the indirect effects of lightning on onboard electronic and electrical systems and equipment will reduce the safety of helicopter flight. Summary of the Invention

[0005] The purpose of this invention is to provide an airworthiness certification method for helicopter lightning protection, which aims to solve the problem that existing helicopter lightning protection methods do not consider the direct and indirect effects of lightning on helicopters, thus reducing the safety of helicopter flight.

[0006] To achieve the above objectives, the present invention provides an airworthiness certification method for helicopter lightning protection, comprising the following steps:

[0007] By installing a microwave relay system on a helicopter, a communication helicopter can be obtained;

[0008] The communication helicopter underwent direct and indirect lightning protection airworthiness verification, which was successful, resulting in a protected helicopter.

[0009] The lightning protection measures for the aforementioned protective helicopter were optimized, and the optimization results were obtained.

[0010] Based on the optimization results, the protective helicopter is modified to be protected against lightning strikes and static electricity, resulting in an airworthy helicopter.

[0011] The microwave relay system includes a microwave relay cabinet and 14 antennas.

[0012] The specific method for installing the microwave relay system on the helicopter to obtain a communication helicopter is as follows:

[0013] Remove the two front seats from the front seat rails inside the helicopter;

[0014] Remove either of the two rear seats inside the helicopter from the rear seat track, and install the remaining rear seat at the center of the rear seat track;

[0015] The microwave relay cabinet is installed on the front seat track, and the 14 antennas are installed on the outside of the helicopter to obtain a communication helicopter.

[0016] The specific method for conducting direct and indirect lightning protection airworthiness verification on the communication helicopter, and obtaining the protected helicopter upon successful verification, is as follows:

[0017] Determine the failure impact level of the microwave relay system;

[0018] The failure impact level was used to conduct a lightning indirect effect system-level test verification on the communication helicopter to obtain the equipment transient design level.

[0019] The failure impact level was used to conduct an aircraft-level test to verify the indirect lightning effect on the communication helicopter, and the actual transient level was obtained.

[0020] Compare the margin between the transient design level of the equipment and the actual transient level to see if it is greater than or equal to the safety margin. If the margin is greater than or equal to the safety margin, the verification is successful, and the indirect protection helicopter is obtained.

[0021] The external equipment of the indirect protection helicopter was tested for direct lightning effects, and the test was successful, thus obtaining the protection helicopter.

[0022] The lightning protection measures include basic protection measures and detailed protection measures;

[0023] The basic protective measures include flame spraying technology, rolled perforated metal mesh technology, woven metal mesh technology, interlayer hybrid composite material technology, and metal foil laying technology;

[0024] The detailed protective measures include grounding location, gaps between two adjacent parts, installation location of fasteners, and repair of damage to composite materials.

[0025] This invention discloses an airworthiness certification method for helicopter lightning protection, comprising: installing a microwave relay system on a helicopter to obtain a communication helicopter; performing direct and indirect lightning protection airworthiness verification on the communication helicopter, and obtaining a protected helicopter upon successful verification; optimizing the lightning protection measures of the protected helicopter to obtain optimization results; and modifying the protected helicopter for lightning strike protection and anti-static purposes based on the optimization results to obtain an airworthy helicopter. This invention increases the safety of the airworthy helicopter obtained by modifying the helicopter based on the direct and indirect effects of lightning, and solves the problem that existing helicopter lightning protection methods do not consider the direct and indirect effects of lightning on the helicopter, thus reducing the safety of helicopter flight. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart of an airworthiness certification method for helicopter lightning protection provided by the present invention.

[0028] Figure 2 This is a schematic diagram of the installation of 14 antennas.

[0029] Figure 3 This is a diagram showing the relationship between ATL, TCL, and ETDL.

[0030] Figure 4 This is the verification flowchart for a Level A system.

[0031] Figure 5 This is the test setup diagram for low-current pulses.

[0032] Figure 6 This is the pin injection test setup diagram.

[0033] Figure 7 This is a test layout diagram for cable bundles.

[0034] Figure 8 This is a diagram of a high-voltage discharge adhesion test setup.

[0035] Figure 9 It is a software simulation of the temperature distribution around the flash point. Detailed Implementation

[0036] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0037] Please see Figures 1 to 9 This invention provides an airworthiness certification method for helicopter lightning protection, comprising the following steps:

[0038] S1 installs a microwave relay system on a helicopter to create a communication helicopter;

[0039] Specifically, the microwave relay system includes a microwave relay cabinet and 14 antennas.

[0040] The specific method for installing a microwave relay system on a helicopter to obtain a communication helicopter is as follows:

[0041] S11 removed the two front seats from the front seat rails inside the helicopter;

[0042] Specifically, two pilots operate the helicopter, the front seats in the cabin are removed, and a microwave technician sits in the back of the cabin to operate the control cabinet.

[0043] S12 removes either of the two rear seats inside the helicopter from the rear seat track and installs the remaining rear seat at the center of the rear seat track;

[0044] Specifically, the microwave relay cabinet includes relay cabinet one and relay cabinet two, which are installed after the front seats in the passenger cabin are removed.

[0045] S13 Install the microwave relay cabinet on the front seat track and install 14 antennas on the outside of the helicopter to obtain a communication helicopter.

[0046] Specifically, both relay cabinet one and relay cabinet two are mounted on the front seat rails via quick-release locking seats. Both relay cabinet one and relay cabinet two integrate and install transmission and positioning equipment, down-converters, filters, intermediate frequency distributors, microwave receivers, monitors, 7GHz narrowband filters, communication systems, etc.

[0047] In relay mode, the helicopter has 14 antennas, such as Figure 2As shown, the two downlink transmitting antennas on the skid lifting arm have been replaced with EK-OA7 / 1H; one uplink transmitting antenna (GA-CHO2) is installed on the right side of the camera bracket at the top of the tail; four receiving antennas (GA-CHO2) are fixed to the footrests on both sides by trusses; one GPS antenna (GA-35) for the map system is installed above the sliding door on the right side of the fuselage; four communication system antennas are installed: two (MZ-400Z-3) are installed next to the side maintenance cover by brackets, one (HT400DXNK) is installed on the receiving antenna truss, and one (HT400DXNK) is installed behind the lower right viewing glass; and two VHF antennas (EK-GPS / 1, VHFRadio) for the map system are fixed on the tail reducer drive shaft fairing.

[0048] S2 conducted direct and indirect lightning protection airworthiness verification on the communication helicopter. The verification was successful, and the protected helicopter was obtained.

[0049] The specific method is as follows:

[0050] S21 determines the failure impact level of the microwave relay system;

[0051] Specifically, the prerequisite for verifying the protection against indirect lightning effects in a system is to conduct a lightning-specific risk analysis of the system and classify the system into an appropriate failure impact level:

[0052] a. System malfunction can affect or impede the safe continued flight and landing of an aircraft. The impact of such malfunction is catastrophic, and the malfunction impact level is A.

[0053] b. If a system failure would significantly reduce safety margins or functional capabilities, increase workload or cause physical fatigue to the point that the crew cannot be relied upon to perform tasks accurately or in full, or have an adverse effect on the crew, then the failure impact is dangerous and the failure impact level is B.

[0054] c. If a system malfunction significantly reduces safety margin or functional capability, significantly increases the unit's workload, conditionally weakens the unit's efficiency, or causes some discomfort to the crew, then the malfunction's impact is primary, and the malfunction impact level is C.

[0055] Based on the lightning-specific risk analysis results, and for Class A electronic and electrical systems, the lightning indirect effects protection verification process is as follows: Figure 4 As shown, lightning zones can be divided according to SAE.ARP5414, using methods such as scaled-down model tests.

[0056] S22 uses the failure impact level to conduct a lightning indirect effect system-level test verification on the communication helicopter to obtain the equipment transient design level;

[0057] Specifically, system-level testing can be conducted according to Chapter 22 of DO-160G, which covers lightning transient susceptibility testing. This includes pin injection testing and cable bundle testing. The test setup is detailed below. Figure 6 , Figure 7 Equipment Transient Design Level (ETDL): This is the test level for lightning transient sensitivity testing of electronic equipment. It represents the withstand voltage or current amplitude that the electronic and electrical system can maintain normal operation.

[0058] S23 uses the aforementioned failure impact level to conduct an aircraft-level test verification of the indirect lightning effect on the communication helicopter to obtain the actual transient level.

[0059] Specifically, Actual Transient Level (ATL): is the transient level actually generated at the port of the electronic device;

[0060] Transient control level (TCL): This is the maximum transient level allowed at the port of an electronic device. Design requirements dictate that TCL is slightly greater than or equal to ATL.

[0061] For Class A display systems, the ETDL should be determined according to Chapter 22 of DO-160G, based on the system installation location. For Class A control systems, aircraft-level verification can be performed using a low-current pulse test according to SAE.ARP5413 to determine the ATL. The test setup diagram is shown below. Figure 5 A simulated lightning current pulse is injected into the aircraft, with the current waveform referencing the current components A and H waves defined in SAEAR P5412B. Using a full-amplitude waveform may damage the aircraft or equipment; in engineering applications, the typical peak current range is between 1 and 20 kA, using the highest possible amplitude without damaging the aircraft or equipment. Open-circuit voltage and short-circuit current on individual conductors are measured and recorded using voltage and current probes and an oscilloscope; induced current on the interconnect cable bundle is measured and recorded using a current probe on the aircraft interconnect cable and an oscilloscope. The measured data are then linearly extrapolated to obtain the ATL (Average Current Tolerance) appearing on the interconnect conductors when the aircraft is subjected to a lightning current component A with a peak value of 200 kA and a lightning current component H with a peak value of 10 kA.

[0062] S24 compares whether the margin between the transient design level of the equipment and the actual transient level is greater than or equal to the safety margin. If the margin is greater than or equal to the safety margin, the verification is successful, and the indirect protection helicopter is obtained.

[0063] Specifically, the ETDL and ATL of the verified system are compared to determine the acceptable margin between them. Typically, a safety margin is defined as 6 dB. If the margin between ETDL and ATL is greater than or equal to the safety margin, it indicates that the system meets the requirements for protection against indirect lightning effects.

[0064] S25 conducted a direct lightning effect test on the external equipment of the indirect protection helicopter, and the test was successful, thus obtaining the protection helicopter.

[0065] Specifically, for electronic and electrical equipment that constitutes the system's functionality and is installed externally on the aircraft, lightning may directly damage the equipment and introduce lightning current into the aircraft's internal wiring through the equipment's conductors. Therefore, direct lightning effects testing is required to verify compliance. High-voltage discharge attachment tests and high-current physical damage tests are conducted according to the direct lightning effects testing requirements in Chapter 23 of DO-160G. High-voltage discharge attachment tests include initial leader attachment tests and swept-channel attachment tests, used to determine the possible lightning attachment locations on the tested equipment. If the possible lightning attachment points on the tested equipment can be determined, this test is not required for tested equipment without insulating coverings.

[0066] High-current physical destructive testing primarily involves arc introduction testing, used to evaluate the potential damage to the equipment under test when a lightning strike occurs near or adjacent to it. In cases of direct lightning strikes, transient voltages may be injected into the circuit; therefore, induced voltage measurement tests on external equipment are also necessary. The test setup is described in [link to test setup]. Figure 8 .

[0067] S3 optimizes the lightning protection measures for the aforementioned protective helicopter and obtains the optimization results;

[0068] Specifically, the flame spraying technology, rolled perforated metal mesh technology, woven metal mesh technology, interlayer hybrid composite material technology, and metal foil laying technology for protecting helicopters are optimized to increase the protective effect of helicopters. In addition, the grounding position, the gap between two adjacent parts, the installation position of fasteners, and the repair of damage to composite materials are optimized to increase the stability of helicopters. The optimized results are obtained. The lightning protection measures include basic protection measures and detailed protection measures.

[0069] The basic protective measures include flame spraying technology, rolled perforated metal mesh technology, woven metal mesh technology, interlayer hybrid composite material technology, and metal foil laying technology;

[0070] (1) Flame spraying technology:

[0071] Flame spraying of metal involves spraying a layer of metal (typically aluminum) onto the outer surface of a composite material skin to ensure good conductivity and continuity. This method offers advantages such as unrestricted surface shape and ease of repair. However, its disadvantages include a relatively heavy coating (area density approximately 0.49 kg / m²)⁴ and a loose structure, requiring additional sealing agents to ensure adhesion. The thickness and quality of commonly used flame-sprayed aluminum coatings are highly dependent on the operator's skill level, and the process stability is poor.

[0072] (2) Rolled perforated metal mesh technology:

[0073] The Boeing 787 aircraft uses a technique called rolling perforated metal mesh. This technique has advantages such as being less restricted by the aircraft's shape and having low repair and maintenance requirements; the disadvantages are that it is difficult to install on complex shaped surfaces and the width of a single metal mesh is limited.

[0074] (3) Weaving metal mesh technology:

[0075] The production cost of woven metal mesh is lower than that of rolled perforated metal mesh. In addition to the same application methods and advantages and disadvantages as rolled perforated metal mesh, there are also the following problems: 1) There is overlap resistance between the longitudinal and transverse metal wires, and theoretically its resistance value is higher than that of rolled perforated metal mesh of the same specifications; 2) Due to the overlapping of the metal wires, its flatness is lower than that of rolled perforated metal mesh.

[0076] (4) Interlayer hybrid composite material technology:

[0077] Hybrid composites, also known as super-hybrid composites, are hybrid laminates composed of alternating layers of thin metal sheets and fiber-reinforced composite materials. This type of composite material combines the performance advantages of fiber composites and metals, providing lightning protection while also exhibiting good fatigue performance, impact resistance, corrosion resistance, and fire resistance. However, due to high cost, low modulus, and susceptibility to electrochemical corrosion, its application in the field of composite material structure lightning protection is currently extremely limited.

[0078] (5) Metal foil application technology:

[0079] This protective measure has uniform conductivity, provides environmental sealing, and allows for complete replacement of the surface material; however, the added weight of the metal foil is relatively large, complex shapes are difficult to install, parts have poor workability, and the metal foil is easy to peel off and has poor repairability.

[0080] (6) Other protective technologies:

[0081] In the aerospace field, composite material structures for lightning protection have been studied, including technologies such as insulating varnish, conductive varnish, and nickel-plated carbon fiber. However, most of these technologies have not been widely adopted due to reasons such as excessive weight increase, unsatisfactory protection effect, or high cost.

[0082] The detailed protective measures include grounding location, gaps between two adjacent parts, installation location of fasteners, and repair of damage to composite materials.

[0083] (1) The impact of the "grounding" location on the protection effect (grounding location);

[0084] Lightning current is conducted along the conductive path within the machine towards the "grounding point" (i.e., the current emission point). Therefore, the "grounding" method of the conductive layer affects the direct effects of lightning. Software simulation analysis shows that when a C-wave lightning current is injected into the center of a geometrically symmetrical composite laminate with a lightning protection layer, and the quadrilateral component is grounded on only one side, the temperature distribution is as follows: Figure 9 As shown in the figure, the initial temperature is 273K. It can be clearly seen that the temperature cloud map, which should be symmetrically distributed, is significantly shifted towards the grounded side, and the temperature on the grounded side is generally higher than the temperature on the ungrounded side.

[0085] (2) Gap (the gap between two adjacent parts);

[0086] The structural form and maintenance requirements of aircraft dictate that a uniform conductive continuity cannot be formed on the aircraft surface. Numerous seams exist at the boundaries of parts and around openings on the aircraft surface. Appropriate electrical connections are required between adjacent parts to ensure the conductive continuity of the aircraft surface. This prevents localized burning or damage when lightning current flows through these seams due to the presence of air gaps and changes in connection resistance.

[0087] (3) Fasteners (the mounting points of fasteners);

[0088] Due to assembly processes, aircraft fuselage surfaces contain numerous metal fastener heads. Furthermore, the lightning protection layer around these fasteners is often damaged during installation, leaving gaps. If the lightning protection design for these heads is inadequate, lightning current may directly inject into the fasteners, creating eddy currents that melt them, or the fasteners may loosen under electromagnetic forces, endangering flight safety. On the other side of the fasteners, corona discharge and streaks may occur. If these occur in areas such as fuel tanks or flight control instruments, they could ignite fuel, damage the flight control system, and cause catastrophic consequences. Therefore, lightning protection treatment is necessary for metal fastener installation areas during or after aircraft assembly.

[0089] (4) Damage repair (damage repair of composite materials);

[0090] Since the lightning protection layer of composite airframe structures is typically located on the outer surface of the aircraft fuselage, corrosion, wear, and damage to the protective layer are inevitable during routine aircraft use. How to repair the protective layer promptly and effectively when these situations occur is one of the key issues considered in this study.

[0091] Based on the optimization results, S4 performs lightning protection and anti-static modifications on the protected helicopter to obtain an airworthy helicopter.

[0092] Specifically, all electrical equipment is connected to the helicopter fuselage to ensure the same electrical potential.

[0093] The above-disclosed embodiments are merely preferred embodiments of the airworthiness certification method for helicopter lightning protection according to the present invention. Of course, they should not be construed as limiting the scope of the present invention. Those skilled in the art can understand that implementing all or part of the above embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for airworthiness certification of helicopter lightning protection, characterized in that, Includes the following steps: By installing a microwave relay system on a helicopter, a communication helicopter can be obtained; The communication helicopter underwent direct and indirect lightning protection airworthiness verification, which was successful, resulting in a protected helicopter. The lightning protection measures for the aforementioned protective helicopter were optimized, and the optimization results were obtained. Based on the optimization results, the protective helicopter is modified for lightning protection and static electricity prevention to obtain an airworthy helicopter; the specific method of installing a microwave relay system on the helicopter to obtain a communication helicopter is as follows: Remove the two front seats from the front seat rails inside the helicopter; Remove either of the two rear seats inside the helicopter from the rear seat track, and install the remaining rear seat at the center of the rear seat track; A microwave relay cabinet is installed on the front seat rail, and 14 antennas are installed on the outside of the helicopter to obtain a communication helicopter. The specific method for conducting direct and indirect lightning protection airworthiness verification on the communication helicopter, which is successful, yields a protected helicopter: Determine the failure impact level of the microwave relay system; The failure impact level was used to conduct a lightning indirect effect system-level test verification on the communication helicopter to obtain the equipment transient design level. The failure impact level was used to conduct an aircraft-level test to verify the indirect lightning effect on the communication helicopter, and the actual transient level was obtained. Compare the margin between the transient design level of the equipment and the actual transient level to see if it is greater than or equal to the safety margin. If the margin is greater than or equal to the safety margin, the verification is successful, and the indirect protection helicopter is obtained. The external equipment of the indirect protection helicopter was tested for direct lightning effects, and the test was successful, thus obtaining the protection helicopter.

2. The airworthiness certification method for helicopter lightning protection as described in claim 1, characterized in that, The microwave relay system includes a microwave relay cabinet and 14 antennas.

3. The airworthiness certification method for helicopter lightning protection as described in claim 2, characterized in that, The lightning protection measures include basic protection measures and detailed protection measures; The basic protective measures include flame spraying technology, rolled perforated metal mesh technology, woven metal mesh technology, interlayer hybrid composite material technology, and metal foil laying technology; The detailed protective measures include grounding location, gaps between two adjacent parts, installation location of fasteners, and repair of damage to composite materials.

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