SD3-60 AIRCRAFT MAINTENANCE MANUAL ANGLE SECONDARY STOP & BLADE PITCH INDICATION DESCRIPTION & OPERATION

Transcription

1 AMM LOW BLADE ANGLE SECONDARY STOP & BLADE PITCH INDICATION DESCRIPTION & OPERATION 1. Description A. General NOTE: Nominal operational blade angles relative to the 42 in. blade checking station for 6- bladed and 5-bladed propeller installations are respectively presented in Tables 1 and 1 which follow: Table 1 OPERATIONAL BLADE ANGLES 6-BLADED PROPELLERS (PT6A-67R ENGINES) Flight Fine (FF) FF back-up Reverse Feather 8.5 deg 4.5 deg -16 deg* 75.5 deg Table 2 OPERATIONAL BLADE ANGLES 5-BLADED PROPELLERS (PT6A-65AR OR -65R ENGINES) Flight Fine (FF) FF back-up Reverse Feather 12.5 deg 8.5 deg -11 deg* 79 deg NOTE: The angles quoted thus* for reverse include overtravel set during propeller assembly. The actual full reverse blade angle is determined by the setting of the associated power levers reverse stop (when maintenance adjusted to provide required max reverse power). With the engines operating in the Propeller Governing Mode (POWER levers above FLIGHT IDLE) this system will, (in the event of failure of a normal flight fine pitch stop) - prevent a propeller from fining off blade angle by more than approximately a further 4 deg. Indication that a secondary stop has operated is provided by the illumination of the appropriate of two FINE PITCH indicator lamps (blue) on console panel 5P. NOTE: These lamps will also illuminate in normal circumstances ie. if associated engine is operating in the beta mode (POWER lever below FLIGHT IDLE). Two REVERSE PITCH indicator lamps (green), also mounted on panel 5P, illuminate when the blade angle of their associated propeller reaches full reverse pitch. Page 1

2 SD3-60 AIRCRAFT MAINTENANCE MANUAL B. Low blade angle (LBA) secondary stop With the engine operating at low power settings in the Propeller Governing Mode, the normal LBA hydraulic stop should not permit a blade angle below flight fine pitch. If for any reason, this stop fails to operate, the propeller blades may only fine off a further 4 deg (approx) at which point a solenoid valve on the propeller governor will be energied, causing it to close and prevent any further flow of oil to the propeller hub. Control of the left and right engine solenoid valves is by means of two proximity switch boxes, one each, respectively located in the left battery bay and the right equipment bay. Each of these 'two-card' boxes is activated by two proximity switch sensors, mounted on a plate which is support-bracket-attached to the propeller thrust bearing cover at the front of the reduction gearbox. These sense the proximity of a target plate which 'sweeps' the sensors in response to appropriate movement of the propeller low stop collar (below flight fine pitch). The target plate is integral with a camplate assembly which pivots on the sensor mounting plate and is driven by a carbon slipper block in the low stop collar channel. When due to the failure of the normal LBA hydraulic stop, the propeller blades begin to fine off, the low stop collar moves to rotate the target plate until, at the flight fine pitch back-up blade angle, the leading edge of the plate covers the first proximity switch sensor. This activates the LBA and FINE PITCH card of the associated proximity switch box, causing it to energie a relay which then connects 28V dc to the FINE PITCH warning lamp and to the solenoid valve. Operation of the solenoid valve will prevent the blades from fining off any further and illumination of the lamp will indicate that the secondary stop has come into operation. NOTE: Operationally, indication will be-cyclic, with fluctuating prpm; this is due to a continuous small leakage of propeller pressure oil to sump. C. Pitch Indication Test push switches are provided on panel 11P to enable the operation of the LBA secondary stops to be checked on the ground. With the exception of an LBA secondary stop operating contingency (para B), pitch indication is normally provided when the engine is operating in the Beta Mode i.e. POWER lever in the range below FLIGHT IDLE and ground/air lever set at 'ground'. NOTE: The LBA solenoid valves are inhibited by the operation of two microswitches when the ground/air lever is set at 'ground'. Indication that propeller blades are at or below the flight fine pitch back-up angle is provided by the illumination of the appropriate of two FINE PITCH lamps (blue) on console panel 5P. When full reverse blade angle is reached by either propeller the appropriate of two REVERSE PITCH lamps (green) will also illuminate. The indication circuit employs the sensors and proximity switch boxes referred to in para B. Page 2

3 2. Operation A. Low blade angle (LBA) secondary stop The LBA secondary stop will operate automatically as described in para B when the engine is operating with (a) the POWER lever set at or above FLIGHT IDLE and (b) the ground/air lever set at 'air'. The operation may be checked on the ground by (a) pressing and holding the appropriate LBA test switch (panel 11P) to override the lock pitch solenoid valve isolating microswitch (which is open-circuit when the ground/air lever is set to 'ground') and (b) selecting the POWER lever slowly into the ground range (approx. 1/2 in.) until the FINE PITCH lamp illuminates. Cycling of the lamp and fluctuating prpm will indicate that the stop is taking effect. NOTE: The POWER lever is returned to FLIGHT IDLE before the test switch is released. B. Pitch Indication When the engine is operating in the Beta Mode (POWER lever below FLIGHT IDLE and ground/air lever at 'ground') the first proximity switch sensor on the LBA secondary stop and pitch indicating mechanism on the engine will be covered by the target plate. This will have activated the associated proximity switch box to complete a supply via a relay to the appropriate FINE PITCH lamp on console panel 5P. As the POWER lever is retarded to the full REVERSE position, the target plate will rotate (as propeller pitch fines off) until it also covers the second proximity switch sensor. When this occurs the proximity switch box will also complete a supply via another relay to the REVERSE PITCH lamp on panel 5P. NOTE: As, in this condition, both sensors are covered by the target plate - both associated lamps will be lit. Page 3

4 AMM LOW BLADE ANGLE SECONDARY STOP AND BLADE PITCH INDICATION MAINTENANCE PRACTICES 1. Adjustment/Test A. Rig the mechanism Refer to Figure 201. NOTE: This procedure relates to Engine Model PT6A-67R which is equipped with a 6-bladed propeller. For Engine Models PT6A-65AR or -65R (which both have 5-bladed propellers installed) - refer to subsequent procedure B. Special tools and equipment:- - Beta Ring Puller: T (1) Remove spinner dome (2) Remove cowl panel 430AT and hinge down cowl panel 420BB. Refer to , pb1. (3) Locate the mechanism (front right of reduction gearbox). (4) Perform carbon slipper block wear check. Refer to , pb201. NOTE: (a) It is recommended that advantage of the work opportunity is taken to replace both slipper blocks (including that associated with beta control) to the as new condition referred therein. (b) Aeroshell 7 grease should be applied to slipper block spindles on installation. (5) With reference to view on arrow 'B', check that radial clearance between slipper block and low stop coller is as dimensioned. NOTE: Any necessary adjustment to bring within tolerance is achieved by placing shims under washer indicated (mechanism pivot attachments). (6) Remove propeller reversing lever to disengage its slipper block from the low stop collar as detailed in propeller removal. (7) Check that the distance between the respective rear and front faces of the low stop collar and the propeller mounting flange is in in. (datum position) as shown in detail C. (8) Fit beta ring puller to the support ring at the forward end of the low stop rods. (9) Check sweep clearance of target plate to fine pitch proximity switch face as follows:- (a) Use beta ring puller to move low stop collar forward until target plate lies over the switch. Page 201

5 SD3-60 AIRCRAFT MAINTENANCE MANUAL (b) Measure sweep clearance and establish the under-switch shimming requirement (if any) to achieve the nominal 0.27 in. dimension shown on view on arrow 'B'. (c) Return low stop collar to datum position (confirm full return by measurement). (d) If (b) indicated shimming requirement, remove both proximity switches and refit appropriately shimmed; leave attachments loose. (10) Set both proximity switches such that they lie at the installed forward ends of their mounting plate slots. NOTE: Attachments should only be tightened sufficiently to permit subsequent final adjustment of the switch positions by light 'finger-tapping' on their forward installed edges. (11) Refer to , pb301. Provide electrical power and close appropriate circuit breaker (No. 19 on panel 1D and No. 169 on panel 2D). (12) Employ beta ring puller to move the low stop collar forward 0.40 in. ie., to the fine pitch back-up position shown on detail C. Lightly tap the fine pitch proximity switch radially rearwards on mounting slots and arrest immediately the appropriate FINE PITCH lamp (blue) on panel 5P in the flight compartment comes on. Maintain switch position and tighten attachments. (13) Back off the low stop collar to a position 0.13 in. forward of datum (fine pitch position, detail C) and check that FINE PITCH lamp has gone out. (14) Move low stop collar forward 0.99 in. from position referred in (13) ie., total movement forward from datum of 1.12 in. (0.06 in. to the rear of full reverse position, detail C). Lightly tap the reverse pitch proximity switch radially reawards on its mounting slots and arrest immediately the appropriate REVERSE PITCH lamp (green) on panel 5P comes on. Maintain switch position and tighten attachments. (15) Return low stop collar to datum position and remove beta ring puller. (16) Select electrical power off. (17) Refit propeller reversing lever as detailed in propeller installation procedure. (18) Refit spinner dome and cowlings. Page 202

6 LBA Stop and Reverse Pitch Ind. Mech. - Rigging (PT6A-67R Engines) Figure 201 Page 203

7 SD3-60 AIRCRAFT MAINTENANCE MANUAL B. Rig the mechanism Refer to Figure 202. NOTE: This procedure relates to Engine Models PT6A-65AR or -65R which are both equipped with a 5-bladed propellers. For Engine Model PT6A-67R (which has a 6-bladed propeller installed) - refer to preceding para A. Special tools and equipment:- Beta Ring Puller: T (1) Remove spinner dome (2) Remove cowl panel 430AT and hinge down cowl panel 420BB (see ). (3) Locate the mechanism (approx 4 o'clock position at front of reduction gearbox). (4) Perform carbon slipper block wear check. Refer to , pb201. NOTE: (a) It is recommended that advantage of the work opportunity is taken to replace both slipper blocks (including that associated with beta control) to the as new condition referred therein. (b) Aeroshell 7 grease should be applied to slipper block spindles on installation. (5) With reference to view on arrow 'B', check that radial clearance between slipper block and low stop coller is as dimensioned. NOTE: Any necessary adjustment to bring within tolerance is achieved by placing shims under washer indicated (mechanism pivot attachments). (6) Remove propeller reversing lever to disengage its slipper block from the low stop collar as detailed in propeller removal. Refer to , pb201. (7) Check that the distance between the respective rear and front faces of the low stop collar and the propeller mounting flange is (datum positon) as shown in detail C. (8) Fit beta ring puller to the low stop rods support ring around propeller piston. (9) Check sweep clearance of target plate to fine pitch proximity switch face as follows:- (a) Use beta ring puller to move low stop collar forward until target plate lies over the switch. (b) Measure sweep clearance and establish the under-switch shimming requirement (if any) to achieve the nominal 0.27 in. dimension shown on view on arrow 'B'. (c) Return low stop collar to datum position (confirm full return by measurement). Page 204

8 LBA Stop and Reverse Pitch Ind. Mech - Rigging (PT6A-65AR or -65R Engines) Figure 202 Page 205

9 SD3-60 AIRCRAFT MAINTENANCE MANUAL (d) If (b) indicated shimming requirement, remove both proximity switches and refit appropriately shimmed; leave attachments loose. (10) Set both proximity switches such that they lie at the installed forward ends of their mounting plate slots. NOTE: Attachments should only be tightened sufficiently to permit subsequent final adjustment of the switch positions by light 'finger-tapping' on their forward installed edges. (11) Refer to , pb301. Provide electrical power and close appropriate circuit breaker (No. 19 on panel 1D and No. 169 on panel 2D). (12) Employ beta ring puller to move the low stop collar forward 0.26 in. ie., to the fine pitch back-up position shown on detail C. Lightly tap the fine pitch proximity switch radially rearwards on mounting slots and arrest immediately the appropriate FINE PITCH lamp (blue) on panel 5P in the flight compartment comes on. Maintain switch position and tighten attachments. (13) Back off the low stop collar to a position 0.13 in. forward of datum (fine pitch position, detail C) and check that FINE PITCH lamp has gone out. (14) Move low stop collar forward 0.48 in. from position referred in (13) ie., total movement forward from datum of 0.61 in. (0.06 in. to the rear of full reverse position, detail C). Lightly tap the reverse pitch proximity switch radially reawards on its mounting slots and arrest immediately the appropriate REVERSE PITCH lamp (green) on panel 5P comes on. Maintain switch position and tighten attachments. (15) Return low stop collar to datum position and remove beta ring puller. (16) Select electrical power off. (17) Refit propeller reversing lever as detailed in propeller installation procedure. Refer to , pb201. (18) Refit spinner dome and cowlings. Page 206