MIL-PRF-38135C(USAF)
change no more than 0.01 inch of Hg. This procedure shall be repeated with a pressure of 10
inches Hg. The mercury level shall change no more than 0.01 inch of Hg per minute.
4.6.11 Static pressure test. With the static connection open to the atmosphere, a pressure
sufficient to produce full scale deflection of the pointer shall be applied to the pitot connection of
the indicator. The pointer shall not proceed past 358° of rotation. All external connections shall
then be sealed. The pointer shall change its position by no more than 1 knot per minute.
4.6.12 Dielectric strength. A potential of 500Vac shall be applied simultaneously between each
terminal and the case for 5 seconds. There shall be no insulation breakdown or permanent
damage to the indicator. The indicator shall then be subjected to the individual tests.
4.6.13 Pointer oscillation. The indicator shall be subjected to the vibration error and vibration
tolerance tests. There shall be no change in excess of ±5 knots in the pointer indication due to
vibration.
4.6.14 Lighting. The indicator shall be subjected to the lighting tests specified by the
procuring activity (see 6.2).
4.6.15 Damping. Pressure shall be applied to the pitot connector to produce full-scale deflection
of the airspeed pointer. The pressure shall be released. The time required for the airspeed pointer
to reach the 120-knot graduation shall be between 0.8 and 2.0 seconds
4.6.16 Low temperature. The indicator shall be subjected to -65° ± 3°F for 48 hours. At the end
of 48 hours and while still at -65° ± 3°F, the indicator shall be subjected to the scale error test.
The error at the test points shall be no more than ±5 knots in addition to the scale error in table II.
4.6.17 High temperature. The indicator shall be subjected to 160° ± 3°F for 24 hours. At the
end of 24 hours and while still at 160° ± 3°F, the indicator shall be subjected to the scale error
test. The errors at the test points shall be no more than ±5 knots in addition to the scale error in
table II.
4.6.18 Vibration error. Pressure shall be applied to produce a deflection of 200 knots. The
indicator shall be mounted to the vibration stand in its normal operating position. The indicator
shall be subjected to vibration with an amplitude between 0.003 and 0.005 inch at frequencies
from 500 to 3,000 Hz. The path of vibration shall be in a circle inclined at a 45° angle. All
resonant frequencies of the airspeed indicator shall occur outside of this range. While the
indicator is being vibrated, the pointer error shall be no more than ±5 knots.
4.6.19 Vibration tolerance. Increasing pressure shall be applied to produce a deflection of 200
knots. The indicator shall be vibrated at 1,000 Hz for 1 hour, followed by 1 hour at 2,000 Hz,
and then by 1 hour at 3,000 Hz. The vibration shall be in a circle with a diameter between 0.018
and 0.020 inch. At the end of the vibration period, pressure shall be released. The same
increasing differential pressure shall be reapplied. The difference between this indication and that
determined prior to the vibration shall be less than ±5 knots.
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