Main Rotor Drive Indicating
The main rotor drive indicating system monitors the temperature, pressure, and level of contamination of the lubrication oil in the transmission and freewheel assemblies and provides signals as to the value of these measurements at a point in time or if a pre-set value has been reached. These signals are used by the power control system and the general computers system to monitor transmission running conditions. The transmission is equipped with a sight glass so that lubrication levels may be checked visually by people on the ground.
The indicating system has the systems that follow:
Transmission indicating
The transmission indicating system has the components that follow:
Oil temperature bulb
The oil temperature bulb is a Resistive Temperature Detector (RTD) that provides continuous temperature measurement readings of pressurized unfiltered uncooled oil. As the oil temperature changes, the resistance of the bulb changes. The oil temperature bulb is installed on the oil filter housing and manifold assembly of the transmission assembly.
Oil temperature switch
The oil temperature switch is a normal-open switch that closes at a predefined value of pressurized unfiltered uncooled oil temperature of 230°F (110°C). It is installed on the oil filter housing and manifold assembly of the transmission assembly.
Oil pressure transmitter
The oil pressure transmitter provides continuous readings of the oil pressure that is being supplied to the lubricated parts. It is a strain gauge pressure transducer sensor. As the oil pressure changes, the output voltage from the strain gauge bridge changes. The oil pressure transmitter is installed on the oil manifold in the lower main rotor drive compartment.
Oil pressure switch
The oil pressure switch is installed on the oil manifold, in the lower main rotor drive compartment. It is a vented gauge switch that is usually in the closed position and controls the CAS indication when the discharge pressure of the oil pressure regulating valve is too low.
Chip detector, upper
The upper chip detector has a metallic outer electrode, a permanent ceramic magnet, and a metallic inner electrode. The ceramic magnet attracts and retains ferrous metal particles. When a sufficient amount of ferrous metal particles collect between the outer and inner electrodes, the circuit closes.
The upper chip detector is installed on the top case of the transmission assembly. It is a two-pole, two-wire type of chip detector that controls the CAS indications through the detection of ferrous metal (steel) particles collected in the oil pan, below the mast bearing.
Chip detector, lower
The lower chip detector has a metallic outer electrode, a permanent ceramic magnet, and a metallic inner electrode. The ceramic magnet attracts and retains ferrous metal particles. When a sufficient amount of ferrous metal particles collect between the outer and inner electrodes, the circuit closes.
The lower chip detector uses a bayonet-type mount for attachment to its self-closing valve. The valve is spring loaded and closes to prevent an oil leakage when the chip detector is removed. It is also used as a drain port for the transmission assembly.
The lower chip detector is installed on the main case of the transmission assembly. It is a two-pole, single-wire type of chip detector that includes a self-closing valve. The chip detector controls the CAS indications through the detection of ferrous metal (steel) particles in the oil sump, upstream of the oil pump.
Oil filter bypass indicator
The oil filter bypass indicator is installed on the transmission assembly. It senses the differential pressure across the oil filter and gives an indication on ground when the filter is bypassed.
Freewheel indicating
The freewheel indicating system monitors the quantity of ferrous metal particles in the lubrication oil of the freewheel assembly and gives indications to the aircrew.
The freewheel indicating system has the component that follows:
Freewheel chip detector
The freewheel chip detector housing is
The freewheel chip detector is installed on the housing of the freewheel assembly. The chip detector controls the Crew Alerting System (CAS) indications through the detection of ferrous metal (steel) particles free in the oil of the freewheel assembly. It is a two-pole, two-wire type of chip detector.
The freewheel chip detector is equipped with a bayonet-type mount for attachment to its self-closing valve. The valve is spring loaded and closes to prevent an oil leakage when the chip detector is removed. It is also used as a drain port for the freewheel assembly.
The freewheel chip detector has a metallic outer electrode, a permanent ceramic magnet, and a metallic inner electrode. The magnetic field from the magnet causes steel particles to collect between the outer and inner electrodes. When there is a sufficient quantity of particles to bridge the gap between the electrodes, the circuit closes.
Operation
Transmission indicating
The oil temperature bulb sets its resistance to a given value in relation to the temperature of the oil. This resistance is measured between two inputs of the engine and airframe interface unit (GEA). This is then converted to a digital signal for the integrated avionics unit (GIA) and the central display systems to give the indication of transmission oil temperature.
When the temperature of the oil is at 230°F (110°C), contacts in the oil temperature switch close and apply a ground to the XOT hot relay and a ground to the integrated avionics unit (GIA). This causes the XMSN OIL TEMP warning message to come on.
The strain gauge bridge of the oil pressure transmitter receives an excitation voltage of 10 volts DC from the engine and airframe interface unit (GEA). When the pressure of the oil changes, the force that is applied onto the diaphragm changes the strain gauge bridge and then the output voltage is returned to the GEA. This is then converted to a digital signal for the integrated avionics unit (GIA) and the central display systems to give the indication of transmission oil pressure.
When the pressure of the oil decreases to between 28 and 32 PSIG (193 and 221 kPa), contacts in the oil pressure switch close and apply a ground to the XOP Low relay and a ground to the integrated avionics unit (GIA). This causes the XMSN OIL PRESS warning message to come on. The warning message goes off when the pressure of the oil increases to 38 PSIG (262 kPa).
When a sufficient quantity of particles collects to close the circuit, the upper chip detector applies a ground to the integrated avionics unit (GIA) and a ground to the engine and airframe interface unit (GEA). This causes the XMSN CHIP caution message and the XMSN CHIP 1 advisory message to come on. The GIA applies a ground through a diode to do a check of the wiring. If the wiring is defective, the fault will cause the DRIVE CD INOP caution message and the XMSN CD 1 INOP advisory message to come on.
When a sufficient quantity of particles collects to close the circuit, the lower chip detector applies a ground to the integrated avionics unit (GIA). This causes the XMSN CHIP caution message and the XMSN CHIP 2 advisory message to come on. The GIA applies a ground through a diode to do a check of the wiring. If the wiring is defective, the fault will cause the DRIVE CD INOP caution message and the XMSN CD 2 INOP advisory message to come on.
When the differential pressure upstream and downstream of the oil filter is between 30 and 34 PSI (207 and 234 kPa) as a result of a clogged filter or very cold temperatures, the magnet of the oil filter bypass indicator moves in the opposite direction of the red indicator button. Thus the magnetic force that holds the button in position decreases until the force of the button spring is strong enough to push the red indicator button to the extended position.
Freewheel indicating
When a sufficient quantity of particles collects to close the circuit, the freewheel chip detector applies a ground to the integrated avionics unit (GIA) and a ground to the engine and airframe interface unit (GEA). This causes the XMSN CHIP caution message and the F/W CHIP advisory message to come on. The GIA applies a ground through a diode to do a check of the wiring. If the wiring is defective, the fault will cause the DRIVE CD INOP caution message and the F/W CD INOP advisory message to come on.
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