SYSTEM DESCRIPTION (cont)
c. Flight Instruments.
Flight instruments measure and display helicopter performance and provide visual
displays of attitude and flight conditions. Pilots indicator edgelighting is controlled by the pilot EXT LT/INTR LT
panel. CPGs indicator edgelighting is controlled by CPG INTR LT panel.
(2) System of Operation.
(a) The airspeed indicator (fig. 814) is connected to the static port for air pressure reference. As the
helicopter moves forward, the Pitot tube provides ram air into an airtight diaphragm. The expanding diaphragm
triggers the mechanical multiplier. The mechanical multiplier drives the instrument pointer to display airspeed on
the calibrated indicator dial.
Airspeed Indicator Functional Block Diagram
(b) The VSI (fig. 815) is connected to the static port for air pressure reference. The VSI has a capillary
tube for air pressure. Air pressure inside and outside is equal when the helicopter remains at the same altitude.
Pressure changes are sensed by the airtight diaphragm when the helicopter moves up or down. The airtight
diaphragm moves the mechanical multiplier. The mechanical multiplier proportionally moves the indicator dial
clockwise for upward movement and counterclockwise for downward movement.