VI Scan the text to fill in the gaps with correct prepositions.
1 Because __the fixed number __poles, the only means __fine-tuning the output frequency is controlling rotor rpm, often done __ using CSDs. 2 CSDs receive drive power __ hydraulic power, pneumatic power, or the accessory drive section __ an engine. 3 It is __ this reason that __ most aircraft a CSD unit is located __ the aircraft engine and the ac generator. 4 __ helicopters, the main generators are mounted __ an accessory gearbox that is driven __ the main transmission. 5 The purpose __the CSD is __transfer and convert aircraft engine variable-speed rotation __ a constant-speed rotation, which drives the generator. 6 The CSD consists __ a variable-displacement hydraulic pump, constant- displacement hydraulic motor, and a governing system. 7 The governing system controls the rate __flow __ the pump, thereby controlling the speed __ the motor. 8 There are several other components __ the CSD that are necessary __ self- regulating constant-speed operation. 9 A gear __ the CSD output shaft drives these pumps, the limit governor, and basic governor. 10 The inner race is separated __ the wobbler shell__ bearing rollers. 11 It is free __ turn __ the pump pistons, which are always __ contact __ the race during operation. 12 The CSD functions __ three different phases __operation: overdrive phase, straight- __ phase, and __drive phase. 13 When the engine input rpm is less than the rpm required __the generator, the CSD makes __ the difference __ rpm. 14 The CSD does this __ causing the pump wobbler system __respond __ governor signals. 15 This response causes the pump __ supply more oil __the motor. 16 The difference __ the input and output rpm depends __ the quantity __ oil pumped __ regulating the wobbler pump. 17 The pump wobbler would, theoretically, be positioned __ the action __ the governor to be concentric __ the cylinder block assembly. 18 __ this condition, the pump neither sends oil __ the motor nor accepts oil __the motor. 19 Since the drive starts__ underdrive and operates normally __ overdrive, this straight-__condition is only temporary. 20 When engine input rpm exceeds the output rpm requirements __ the generator, the CSD acts to subtract __ the input rotation. 21 The wobbler pump accomplishes this __ response __ the governor signal. 22 The pump-motor action __underdrive is the reverse __the action required __ overdrive. 23 __ the underdrive phase, the pump performs __ a negative pumping action. 24 Excess input torque is dissipated __ the reverse pumping action __the charged oil system. 25 When the engine overspeeds or if the basic governor fails, the CSD goes __ underdrive __protect the generator __ overspeed. 26 __ some CSDs, aircraft engine oil __ the engine lubricating system is the hydraulic medium. 27 __ this case, the CSD also functions as a pump __supplying the generator __ engine oil __ cooling. 28 Due __ cooling capabilities, oil-cooled generators are __ smaller construction than air-cooled generators having a similar rating. VII Are these sentences true or false? Discuss with a partner. 1 Because of the fixed number of poles, the only means of fine-tuning the output frequency is controlling rotor rpm, often done by using CSDs. 2 CSD unit is located on the aircraft engine and the ac generator. 3 The purpose of the CSD is to transfer and convert aircraft generetorvariable-speed rotation to a high-speed rotation, which drives the generator. 4 The CSD consists of a variable-displacement hydraulic pumponly. 5 Three control pistons in the CSD housing move the wobbler sideways to vary the output of the pump. 6 The CSD functions in five different phases of operation: overdrive phase, straight-through phase, and underdrive phase. 7 The difference between the input and output rpm doesn`t dependon the quantity of oilpumped by regulating the wobbler pump. 8 When the engine overspeeds or if the basic governor fails, the CSD goes into overdrive to protect the generator from underspeed. 9 The overspeed pressure switch in the governor oil line functions to break the electrical circuit of the ac control system. 10 The system is protected during an underspeed condition.
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