MIL-DTL-85670D
APPENDIX A
TEST METHOD
DIRECT EFFECTS - STRUCTURAL
A.1. SCOPE.
A.1.1 Scope. This appendix is a mandatory part of the specification. The information contained herein is intended
for compliance.
A.2. PURPOSE.
A.2.1 Purpose. This method is used to determine the direct affects which result from the interaction of lightning
currents with aerospace vehicles and hardware.
A.3. APPLICABILITY.
A.3.1 Applicability. This test method is applicable to aerospace vehicle structures and components which are
susceptible to lightning current attachment or transfer, which includes antennas.
A.4. APPARATUS.
A.4.1 Test apparatus. The test apparatus shall include:
a.
A high current generator(s) capable of producing the specified waveforms.
b.
High current measuring and recording instruments.
c.
Photographic equipment for recording strike points/damage areas.
A.4.2 Test setup. The test object should be a production hardware, a full-scale prototype, or an electrically
representative mockup of the production configuration. All conducting objects (within or on nonmetallic hardware)
that are normally connected to the vehicle when installed in the aircraft should be electrically connected to ground
(the return side of the lightning generator). Surrounding external metallic vehicle structure should be simulated and
attached to the test object. The test setup shall be such that the simulated lightning currents are delivered to and
conducted away from the test object in a manner representative of the aircraft being struck by lightning. Care must
be taken to assure that magnetic forces, and other interactions which are unrepresentative of the natural situation,
are minimized.
CAUTION
There may be interactions between the arc and the test conductors. Care must be taken to assure that these
interactions do not influence the test results.
A.4.2.1 Arc-entry tests.
a.
Test electrodes: The electrode material shall be a good electrical conductor capable of resisting the
erosion produced by the test currents involved.
b.
Test gap. The gap spacing shall be sufficient so that arc jet and blast pressure effects do not influence the
test results. This will require that the gap be at least 50 mm for component A or D and at least 10 mm for
multiple component tests. Alternatively, suitable jet-diverting techniques shall be incorporated in the design
of the electrode assembly. A fine wire such as No. 30 copper wire can be used as required in the gap to
assist in the current discharge of low-voltage-driven current generator(s).
c.
Electrode polarity. The electrode polarity of the waveform components A and D shall be either positive or
negative. The electrode polarity of the waveform components B and C shall be negative.
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