MIL-DTL-5421D
4.6.3 Endurance. Type I tubes shall be operated at 30 VDC and type 2 tubes shall be
operated at 120 VAC, 400 Hz, single phase continuously for five hours. There shall be no
damage of any kind except discoloration that will not affect corrosion resistance. This test may
be combined with the vibration test by extending the period of power application to five hours.
4.6.4 Heat conductivity. One liter (L) of tap water shall be placed in a glass beaker. The
heated part of the tube shall be supported vertically with the nose immersed in the water to a depth
of 1-1/2 inches. A thermometer shall be suspended in the water at a distance of approximately
1-1/4 inches from the surface of the tube. With the tube and water at approximately room
temperature, the temperature shall be recorded. With the water being gently stirred to assure
uniform temperature, the applicable rated voltage shall be applied to the tube. Fifteen minutes
after the voltage has been applied, the temperature of the water shall have risen not less than
8 °C (14.4 °F) from the temperature previously recorded.
4.6.5 Weight. The tube shall be weighed without the AN3115 electrical assembly,
NASM35207 screws or NASM35338 lock washers. The SAE AS5813 tubes shall be weighed
with the sleeve assembly installed. The weight shall not exceed 1.0 pound.
4.6.6 Magnetic property. The tube shall be held in various positions on an East-West line
and 5 lines from the center of a free magnet 1-1/2 inches long (an aircraft compass with the
compensating magnets removed may be used as the free magnet) in a magnetic field of
0.18 ± 0.01 gauss. The test shall be conducted first with no voltage applied to the tube and then
repeated with the applicable rated voltage applied. The deflection of the free magnet (compass)
shall not be greater than 5 degrees.
4.6.7 Error at zero angle of attack. The tube shall be mounted in a wind tunnel in line
with the air flow and tested separately for impact pressures at speeds of 50 knots to 600 knots in
increments of 50 knots. This test shall be made by comparison with the results obtained under
similar conditions with a standard tube (a standard tube is a pitot tube with a known accuracy and
calibration). The error in indicated airspeed obtained shall not exceed 1.0 knot.
4.6.7.1 Error at various angles of attack. The tube shall be tested at 150 knots for impact
pressure at angles of attack varying by 2-degree increments from +14 degrees to -10 degrees.
The indicated airspeed at any test interval shall not differ from the indicated airspeed, at zero
pitch, by more than 1.0 knot.
4.6.8 Corrosion due to salt spray. The tube, complete with sleeve (SAE AS5813 only)
and electrical receptacle attached, shall be exposed to salt spray in accordance with ASTM B 117
for a period of 50 hours. No excessive corrosion or damage to any part of the tube shall result
from this test.
4.6.9 Deicing. The tube shall be tested in an icing wind tunnel at an indicated tunnel
speed of 100 knots and a temperature of -15 °C ± 5 °C (5 °F ± 9 °F). The nose of the tube shall
be coated with an ice cap approximately 1/4 inch thick and then the type I tubes shall be operated
at 22 VDC and type 2 tubes shall be operated at 105 VAC, 400 Hz, single phase. The time
required to clear the ice cap after the applicable voltage is applied shall not exceed two minutes.
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