Blade deice operation with erosion strips installed may cause blade damage.
The rotor blade deice kit (Figure 2-15) consists of the following: deice control panel, deice test panel, system con-troller, power distributor, main and tail sliprings, main and tail blade heating elements, droop stop heaters, caution leg-ends, outside air temperature (OAT) sensor, a modi.ed am-bient temperature sense line and an icing rate meter sub-system. The blade deice system provides improved mission performance in icing conditions by applying controlled electrical power to integral heating elements in the main and tail rotor blades, causing the ice bond layer to melt, allowing symmetrical ice shedding. Droop stop heaters ap-ply heat to the droop stop hinge pins, to prevent icing and permit proper operation. The heaters are electrically pow-ered continuously whenever the blade deice system is op-erating, either with the power switch ON, or the system in the TEST mode. The blade deice system, excluding element-on-time (EOT) failure, may be ground checked us-ing the APU generator. To prevent generator overload when only the APU generator is operating, an interlock system is installed to inhibit blade deice test if the backup pump is operating. If the backup pump should go on during the test cycle, the MR DE-ICE FAIL caution legend will go on immediately, alerting the crew to an invalid test attempt. The test cycle must then be initiated again. The OAT sen-sor, installed below the windshield, provides a signal to the controller for heating EOT of the rotor blades. The lower the OAT, the longer EOT will be. To reduce power require-ments, the blades are deiced in cycles. Power to operate the blade deice is provided from the No. 1 and No. 2 ac pri-mary buses and No. 2 dc primary bus through circuit break-ers, marked ICE-DET, DE-ICE CNTRLR, and DE-ICE PWR TAIL ROTOR, on the mission readiness circuit breaker panel in the cabin. Main blade deice power is routed through current limiters in the deice junction box. When one main generator is inoperative, deice power can be supplied by the APU generator.
2.50.1 Blade Deice System Operation. The ice de-tector is operational anytime power is applied to the heli-copter. The ice detector senses ice accumulation on a vi-brating probe by a change in probe frequency. The frequency change is processed by the ice rate meter. The ice rate meter provides a visual display of icing intensity, T (trace), L (light) blue, M (moderate) yellow, and H (heavy) red. Also, the ice rate meter sends a signal to the ICE DETECTED caution legend when the BLADE DE-ICE POWER switch is off, informing the pilot of the require-ment to turn on the system. When the system has been turned on by placing the POWER switch ON, the ice de-tector aspirator heater is turned on, and the ICE DE-TECTED caution legend is turned off. If the MODE switch is at AUTO, the rate meter sends an ice rate signal to the controller. The controller processes the ice rate signal to produce heater element-off-time, and the OAT signal to produce the heater EOT. The controller sends command signals through the main rotor sliprings to the system dis-tributor which responds to controller signals by switching power in sequence to the main rotor blade heater zones. Tail rotor blade power is switched directly by the controller and sent through the tail rotor sliprings to the tail rotor blades. A tail blade distributor is not required since the power is applied to the four tail blades simultaneously. The deice control panel contains a rotary switch which allows automatic or manual control of blade heater element-off-time. In AUTO (automatic), the ice rate signal is passed on to the controller, which results in off-time variations pro-portional to the ice rate. In MANUAL, T, L,or M, .xed signals are transmitted to the controller, resulting in .xed element-off-time. Ice rate subsystem malfunctions are indi-cated by the appearance of a FAIL .ag on the rate meter face, requiring operation of the blade deice system in one of the three manual modes. MANUAL mode should also be used when the rate meter has no indicated malfunction, but any of these three conditions has occurred: 1. Pilot has determined by his judgment of ice intensity that the ice rate system is inaccurate. 2. Torque required has increased to an unacceptable level. 3. Helicopter vibration has increased to an unacceptable level. During a single main generator fail-ure, blade deice will be dropped until the APU is started and the APU generator switch is placed ON. Even though the APU generator switch is ON and providing power to the blade deice system, the APU GEN ON advisory legend will not be on because of one main generator operating.
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