SD3-60 AIRCRAFT MAINTENANCE MANUAL SYSTEM - DESCRIPTION & OPERATION (PRE MOD A8005)

Transcription

1 SD3-60 AIRCRAFT MAINTENANCE MANUAL z AMM STALL WARNING SYSTEM - DESCRIPTION & OPERATION (PRE MOD A8005) 1. Description A. General Physical and aural warning of an incipient stall condition is respectively provided by the simultaneous operation of control column ('stick') shakers and a warning horn; the latter of which is equipped with a red light which comes on during horn operation. The system is twinned, left and right, and is operationally triggered by either of two electrically anti-iced, vane-type detector units, located one in each wing's leading edge at station 308. Horn operation is shared and each half-system additionally provides operational back-up for the opposite stick shaker so that capability for full warning is retained should one of the detector units become inoperative in flight. B. Equipment (1) Detector Units: The detector unit is essentially comprised of an 'angle of attack' vane operated microswitch and each is equipped with three anti-icing elements rated at 109 watts max. The unit plate is profiled to the undersurface of the wing leading edge. The exposed operating vanes are lightly biased rearwards (contacts broken). The warning system is operationally inactive with the aircraft on the ground (except for testrefer to para 2.C.). The left and right units are respectively circuit-idented 1WH11 and 2WH11. (2) Stick Shakers: A stick shaker unit is mounted on each control column; each is basically comprised of an alloy casing housing an out-of-balance rotor which is operationally rotated by a 28V dc permanent magnet motor. The left and right units are respectively circuit-idented 1WH2 and 2WH2. (3) Warning horn and light: This unit, circuit-idented WH12, is shared by the left and right twin systems and is located on the right side of the flight compartment roof at frame station 54. The centrally disposed red light comes on during horn operation. Page 1

2 z SD3-60 AIRCRAFT MAINTENANCE MANUAL (4) Relays: 2. Operation (a) Control Relays. Two double-pole relays, idented CU and CN are located on each of the left and right equipment panel (1C and 2C). A CU relay, when energized via the related half-systems detector unit or by combined use of the associated test and heater switches, will conect the operating supplies to the associated stick shaker and the horn. CN relays are similarly energized by their opposite half-systems such that an alternative feed is available to each stick shaker. (b) Current-sensing Relays: A. Warning function Two single-pole current sensing relays, one left and one right are located in the flight compartment roof; the relays, respectively idented 1WH14 and 2WH14 are employed to illuminate the STALL section of associated indicator modules located above the PITOT/STATIC/STALL anti-icing switches on roof panel 4P when a control switch is ON selection has been effective (related detector unit heater element functional). When the angle-of-attack approaches the stall condition, airflow from the stagnation point will deflect a detector unit vane forward to complete the energizing supplies to the related halfsystem's CU relay and the CN relay in the opposite half-system. The CU relays so energized will connect the operating supplies to that half-system's stick shaker and to the shared warning horn and light. The CN relay will avail the opposite stick shaker of its operating supply should its CU relay remain de-energized as a result of failure of its detector unit contacts to changeover. Warning will persist until effective pilot-action to combat the threatened stall is taken. The warning function is ground tested in conjunction with the detector unit anti-icing as detailed in para C. Page 2

3 SD3-60 AIRCRAFT MAINTENANCE MANUAL z Stall Warning - Control & Equipment Figure 1 Page 3

4 z SD3-60 AIRCRAFT MAINTENANCE MANUAL B. Detector unit anti-icing Except when on the ground (wieght switch inhibited), selection of the two PITOT/STATIC/ STALL control switches (panel 4P) to On will connect the operating supplies to the associated detector unit element via the related current sensing relay. Satisfactory function is confirmed by the continuous illumination of the STALL section of an indicator module located above each switch. For ground testing refer para C. C. Testing Simultaneous ground testing of each half-systems warning function and detector's heaters is afforded by holding the appropriate of two STALL WARNING test switches (panel 11P) at TEST in conjunction with an ON selection for the related detector units anti-icing control switch. The test switch thus held, will electrically bypass the open contacts of the detector unit and weight switch. 3. Power Supplies System operating supplies are derived from the 28V dc left and right Essential Services Busbars via C/B No. 28 (5 amp), 29 (5 amp) on distribution panel 1D, and C/B No. 181 (5 amp), 182 (5 amp) on distribution panel 2D. Page 4

5 SD3-60 AIRCRAFT MAINTENANCE MANUAL z AMM STALL WARNING SYSTEM - MAINTENANCE PRACTICES 1. Adjustment/Test A. Preparation NOTE: Tests are performed with the aircraft self-supported which isolates the detector unit heaters through the weight switch. (1) Set all avionic and electrical switches to the off or neutral position. (2) Energize the main busbars from an external supply. Refer to , pb301. (3) Select the ELECTRICAL MASTER switch on panel 4P to EXTERNAL POWER. B. Function check the left system. (1) Close circuit breaker No.29 on distribution panel 1D. (2) Open circuit breakers No.28 on distribution panel 1D, and 181 and 182 on panel 2D. (3) Select ANTI-ICING PITOT/STATIC/STALL switch (left) on panel 4P to ON. (4) Press and hold STALL WARNING LEFT TEST switch on panel 11P and check that:- (a) the left detector unit begins to heat (b) the indicator module (left) on panel 4P is illuminated and the warning horn sounds and its integral light (red) is illuminated. (5) Subsequent to the operation and checks detailed in (4), close circuit breaker No.28 on panel 1D and check that the left stick shaker operates. Close circuit breaker No.181 on panel 2D and check that the right stick shaker operates. (6) Release the STALL WARNING LEFT TEST switch and check that:- (a) both stick shakers cease to operate (b) the warning horn ceases and its integral light is extinguished. the indicator module (left) is extinguished and (d) the detector unit begins to cool, signifying that the unit is switched off. (7) Check that when the left detector vane is moved fully forward under a load of not more than 10 grams, the horn, its integral light and both stick shakers operate. Page 201

6 z SD3-60 AIRCRAFT MAINTENANCE MANUAL C. Function test the right system. (1) Close circuit breaker No.182 on distribution panel 2D. (2) Open circuit breakers Nos.181 on panel 2D and 28 and 29 on panel id. (3) Select ANTI-ICING PITOT/STATIC/STALL switch (right) on panel 4P to ON. (4) Press and hold STALL WARNING RIGHT TEST switch on panel 11P and check that:- (a) the right detector unit begins to heat (b) the indicator module (right) on panel 4P is illuminated and the warning horn sounds and its integral light (red) is illuminated. (5) Subsequent to the operation and checks detailed in (4), close circuit breaker No.181 on panel 2D and check that the right stick shaker operates. Close circuit breaker No.28 on panel 1D and check that the left stick shaker operates. (6) Release the STALL WARNING RIGHT TEST switch and check that:- (a) both stick shakers cease to operate (b) the warning horn ceases and its integral light is extinguished. the indicator module (right) is extinguished and (d) the detector unit begins to cool, signifying that the unit is switched off. (7) Check that when the right detector is moved fully forward under a load of not more than 10 grams, the horn, its integral light and both stick shakers operate. (8) Disconnect the external power supply if no longer required. Page 202