SD3-60 AIRCRAFT MAINTENANCE MANUAL INDICATION - DESCRIPTION & OPERATION

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Joan Carr
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1 AMM ENGINE TORQUE INDICATION - DESCRIPTION & OPERATION 1. Description A. General The torquemeter built into the engines power section reduction gearbox provides the input reference for the Edison torque indication system. The torquemeter comprises a floating gear, piston and metering valve plunger all of which are axially displaced rearward or forward in response to respective increases or decreases in propeller absorbed torque. The positional displacement for a given torque is limited when metered oil pressure within the torquemeter chamber at the rear of the piston exactly balances the displacement load. The difference between the torquemeter oil pressure and datum air pressure within the gearcase thus provides an accurate indication of the torque being produced. Tappings from both sources are located on the left side of the reduction gearbox case; these are piped to a transmitter, which in response to the sensed pressure differential, will appropriately signal the associated indicator on panel 1P which displays the pressure differential in terms of torque. B. Transmitters, Edison Pt.No Both transmitters are circuit-idented EB2 and each is located on a torquemeter pressure switch manifold attached to the right side of the engine mounting frame (aft of rear fireshield). The transmitter is essentially a diaphragm operated electrical signalling device which takes torquemeter oil pressure reference from the manifold and is equipped at the aft installed end with (a) an electrical connector and (b) an adapter which receives the reduction gearcase air pressure datum line. NOTE: The manifold also provides essential torquemeter oil pressure references for the control and operation of: - the autofeather system. Refer to , pb1. - the reserve power system. Refer to , pb1. C. Indicators, Edison Pt.No These are centrally located on panel 1P; each is a single pointer instrument which in response to the associated transmitters signal will indicate developed torque on a dial graduated in 100 lb.ft. divisions over the range lb.ft. NOTE: For explanation and details of the dial presentation limit markings. Refer to , pb Page 1

2 SD3-60 AIRCRAFT MAINTENANCE MANUAL 2. Operation With the 26V AC 400 H system operating supplies available, movement of the transmitter diaphragm in response to sensed changes in torquemeter pressure will cause axial movement of an attached armature between two fixed coils, which in conjunction with fixed coils in the indicator, form a galvanometer circuit. Resultant unbalancing of the bridge circuit will cause a moving coil (and attached pointer) within the indicator to assume a position relative to that of the armature, thus indicating torque appropriate to the torquemeter pressure. 3. Power supplies The 26V AC 400 H operating supplies for the left and right systems are respectively taken from panels 1D and 2D via 1 amp C/B Nos. 303 and Page 2

3 AMM ENGINE TORQUE INDICATION - MAINTENANCE PRACTICES 1. Adjustment/Test A. Calibrate torque indicating system Special tools and equipment:- Portable mini tester - Barnet Instruments Ltd (Pt.No.4490/7) or other equivalent Dead Weight Tester capable of supplying accurate pressure of dry air in the range 0-80 psi. NOTE: Ensure that system piping disconnected during calibration is blanked; conversely, ensure blank removal before reconnection. (1) Refer to , pb301. Provide electrical power and close C/B Nos. 303 and 353 on respective distribution panels 1D and 2D. (2) For the left and right engines in turn, perform the following:- (a) Lower the intake cowl and remove cowl panel 410AR to locate the torque transmitter (circuit-idented EB2). (b) Disconnect torquemeter oil pressure pipe (Pt.No.SD ) from elbow on pressure switch manifold and connect test piping with suitable end fittings between the elbow and the dead weight tester air delivery connector. (c) Disconnect gearcase datum pressure pipe (Pt.No.SD ) from transmitter to allow unit to vent to atmosphere. (d) Close air valve on tester. (e) Check associated torque indicator (panel 1P) readings on progressive rising and falling pressures of 10, 20, 30, 40, 45 and 50 psi are within tolerances quoted in the subsequently presented table. The procedure is as follows:- 1 Place weight or combination of weights representative of required pressure on the tester weight pan. 2 Raise tester air pressure slowly and arrest immediately the weight pan rises. Check indicator reads the corresponding torque within tolerance. 3 Further raise air pressure above test pressure (weight pan raised) and then reduce slowly and arrest immediately weight pan falls. Check that indicated torque has remained within tolerance. (f) Reduce air pressure to ero Page 201

4 SD3-60 AIRCRAFT MAINTENANCE MANUAL (g) Disconnect test equipment and restore system piping. (h) Replace cowling. Test Pressure (psi) Torquemeter Indication (lb ft) Indication Tolerance (lb ft) 0 0 ± ± ± ± ± ± ± Page 202

5 AMM GAS GENERATOR SPEED INDICATION - DESCRIPTION & OPERATION 1. Description A. General This is a self contained system which provides continuous indication of gas generator speed as a percentage. It also provides a controlling signal for the engine starting system. The equipment is supplied by General Electric. B. Tachometer generators Each of the tachometer generators is mounted on the rear face of the engine, in one 1, near the bottom of the accessory gearbox. A generator consists of a three-phase stator coil with a two-pole rotor which turns at 4200 RPM for 100% gas generator speed. The three-phase outputs from the generators are connected directly to the indicators. A connection is taken from one phase on each generator to provide a signal which, when the gas generator reaches a pre-determined speed, terminates the engine starting sequence. Refer to , pb1. C. RPM indicators 2. Operation The indicators are mounted on the pilots instrument panel 1P. Each instrument consists of a three-phase synchronous motor whose rotor turns in synchronism with the tachometer generator. Two pointers on the indicator are driven by the rotor via a magnetic drag cup assembly. The large pointer indicates from 0 to 100% of engine RPM on the main dial and the small pointer indicates from 0 to 10% on the sub dial. The system is permanently operational and will indicate immediately the gas generator begins to turn. The main dial is calibrated from 0 to 100% in 10% increments for coarse readings and the sub dial from 0 to 10% in 1% increments for fine readings Page 1

6 AMM ENGINE CONDITION TREND MONITORING PT6A-65R ENGINES DESCRIPTION AND OPERATION 1. General Operators are advised to set up and maintain a trend monitoring system based on the turbine engine characteristic of repeatedly reproducing its output at, or very close to, predicted gas generator parameter values for known operating conditions. Trend monitoring will provide forewarning of developing mechanical deterioration affecting engine performance; this will enable early planning of required rectifications, so reducing unscheduled engine removals and operating costs. It is recommended that systems be modelled on that outlined in Pratt & Whitney publication 'Aircraft Gas Turbine Operation Information Letter (AGTOIL) No.20'. NOTE: Trend monitoring is best introduced when engines are new or newly overhauled; this ensures complete recording of gas generator parameter deviations and trends throughout the life of the engine Page 1

7 AMM INTERTURBINE TEMPERATURE INDICATION - DESCRIPTION AND OPERATION 1. Description A. General The interturbine temperature (ITT) sensing system provides indication of engine operating temperature at a point between the compressor turbine and the first-stage power turbine. Essentially, the e.m.f. output of a thermocouple assembly (in response to an equivalent temperature) is amplified by an associated electronics unit and applied to the related millivoltmeter type indicator on panel 1P. B. Sensing For each engine, sensing is by means of eight parallel-connected chromel-alumel thermocouples, the probes of which project into the compressor turbine discharge airstream. The thermocouple harness exits through a sealed exhaust duct to appropriately connect to two terminal posts (one chromel, one alumel) on a T 5 terminal block located on the gas generator case at the 2 o'clock position. The block provides attachment for (a) the indicator circuit and (b) the engine-furnished externally mounted trim thermocouple. NOTE: The trim thermocouple is selected by P & W Ltd on final checks so that all engines have the same initial power/indicated temperature relationship; consequently, the trim harness must only be replaced in the field by one of an identical class (dash number). C. Indication The two indicators are mounted on panel 1P; each displays the amplified e.m.f. output of the associated thermocouple assembly in terms of centigrade degrees over the range 200 to 1200 C in 100 C increments. The scale is expanded between 650 and 900 C and is further graduated in sub-divisions of 10 C. NOTE: For explanation and details of the dial presentation limit markings. Refer to , pb1. D. Electronic units For the left and right systems, these are correspondingly located in the flight compartment sidewall between frames 22 and The units (circuit-idented 1ED2 - left, 2ED2 - right) provide cold-junction compensated amplification of the probe generated signals. E. Power supplies Operating supplies are taken from the left and right 28V dc Essential Services busbars via respective 5 amp C/B Nos. 56 and 202 on distribution panels 1D and 2D Page 1

8 SD3-60 AIRCRAFT MAINTENANCE MANUAL 2. Operation Each system essentially functions as detailed in the preceeding paragraphs, requiring only the availability of the relevant 28V dc supply. NOTE: An open-circuit fault in a thermocouple assembly or its wiring will be immediately apparent; in this condition the indicator will read slightly higher than top of range Page 2

9 AMM INTERTURBINE TEMPERATURE INDICATION - MAINTENANCE PRACTICES 1. Adjustment/Test A. Check calibration of indicator. Special Tools and Equipment:- Calibration Tester: Type BH153-3 (Howell Instruments Inc.) or equivalent. 115V A.C. 400 H Tester supply. (1) Remove engine cowl panel 430AT to gain access to T 5 terminal block (located at 2 o'clock position on gas generator case). (2) Disconnect airframe and engine leads from terminal block. (3) Using suitable alumel and chromel leads connect calibration tester together with airframe leads to the T 5 terminal block. NOTE: Leave thermocouple and trim thermocouple leads unconnected. (4) Refer to , pb301. As appropriate to engine, energise the left or right 28V dc essential services busbar and open relevant circuit breaker as undernoted:- (a) left engine : C/B No. 56 on Panel 1D. (b) right engine : C/B No.202 on Panel 2D. (5) Connect 115V A.C. power source to Calibration Tester. (6) Check that pointer on relevant ITT indicator on Panel 1P displays below 200 C (off scale). Close C/B referred at (4). (7) Select the undernoted temperature readings on test set and check that flight compartment indicator concurs within tolerance quoted:- Test setting C Indicator tolerance ± C (Panel 1P) (8) Remove 115V A.C. power source and disconnect test set from T 5 terminal block Page 201

10 SD3-60 AIRCRAFT MAINTENANCE MANUAL (9) Identify and reconnect thermocouple, trim thermocouple and airframe leads to the terminal block. (10) Refit cowling panel Page 202

SD3-60 AIRCRAFT MAINTENANCE MANUAL

SD3-60 AIRCRAFT MAINTENANCE MANUAL AMM 11.0.0.0AUTO-FEATHERING SYSTEM - DESCRIPTION & OPERATION 1. Description A. General This system is employed to speedily reduce propeller drag by automatically feathering the propeller on an engine which