Stall Warning System GENERAL 27-31: STALL WARNING SYSTEM 1. General A. Stall Warning System - Serials w/o Ice Protection The airplane uses an electro-pneumatic stall warning system. As the angle of attack increases and the airplane approaches an aerodynamic stall, the stagnation point moves lower on the leading edge causing low pressure on the upper leading edge to increase. As low pressure passes over the stall warning port located on the leading edge of the right wing, negative pressure is sensed by a pressure switch which provides a signal to the avionics system to activate the aural stall warning and enables the Crew Alerting System (CAS) to display a STALL annunciation on the PFD. The pressure switch, located on the mid-console LH side panel, is a normally open, diaphragm-operated switch. The switch is powered by 28 VDC supplied through the 2-amp STALL WARNING circuit breaker on Essential Bus 2. B. Stall Warning System - Serials w/ Ice Protection The airplane uses an electro-mechanical lift transducer, mounted on the leading edge of the right wing. As the angle of attack increases, the stagnation point moves below the transducer, increasing the upward pressure on the spring loaded vane. The movement of the vane produces an electrical output that is sent to a stall warning computer located under cabin access panel CF3R. The stall warning computer provides a signal to the avionics system to activate the aural stall warning and enables the Crew Alerting System (CAS) to display a STALL annunciation on the PFD. The transducer is powered by exciter voltage supplied by the stall warning computer. The stall warning computer is powered by 28 VDC supplied through the 5-amp STALL WARNING circuit breaker on Essential Bus 2. 1
2. Maintenance Practices A. Stall Warning Pressure Switch - Serials w/o Ice Protection (See Figure 27-31-1) (1) Removal - Stall Warning Pressure Switch Set BAT 1, BAT 2, and AVIONICS switches to OFF positions. (b) Pull STALL WARNING circuit breaker. Remove LH mid console circuit breaker trim panel. (Refer to 25-10) Open circuit breaker panel. Disconnect pressure switch electrical connector. (f) Disconnect stall warning line from pressure switch. (g) Remove screws, washers, and nuts securing pressure switch to console. Remove pressure switch from airplane. (2) Installation - Stall Warning Pressure Switch Position pressure switch to console and secure with screws, washers, and nuts. (b) Connect stall warning line to pressure switch. Connect pressure switch electrical connector. Close circuit breaker panel. Install LH mid console circuit breaker trim panel. (Refer to 25-10) (f) Reset STALL WARNING circuit breaker. (g) Perform Operational Check - Stall Warning System - Ground. (Refer to 27-31) (h) Perform Operational Check - Stall Warning System - Flight. (Refer to 27-31) 2
(3) Operational Check - Stall Warning System - Ground Acquire necessary tools, equipment, and supplies. Description P/N or Spec. Supplier Purpose Suction Cup - Any Source Application of negative pressure. (b) (f) (g) (h) Set BAT 1 and AVIONICS switches to ON positions. Pull STARTER and FUEL PUMP circuit breakers. On RH wing leading edge, clean area surrounding stall warning port. Moisten suction cup and firmly press cup over stall warning port. Activate stall warning pressure switch by sharply pulling suction cup directly away from stall warning port. Verify horn sounds audible warning signal. Reset STARTER and FUEL PUMP circuit breakers. Set BAT 1 and AVIONICS switches to OFF positions. (4) Operational Check - Stall Warning System - Flight WARNING The following Operational Check must be performed by a Cirrus Design authorized test pilot. Remove access cap covering stall warning pressure switch located on lower portion of the left mid-console circuit breaker trim panel. (b) Perform Operational Check - Stall Warning System - Ground. (Refer to 27-31) In smooth air and at an altitude appropriate for stalls, place airplane in stall attitude. Record airplane speed that stall warning signal sounds. Record airplane speed that stall occurred. (f) Stall warning signal should sound 5 to 10 KIAS prior to stall. (g) If necessary, adjust stall warning pressure switch until stall warning signal sounds 5 to 10 KIAS prior to stall. 1 Rotating the adjustment screw 1 full turn clockwise will raise the speed at which the stall warning horn sounds by approximately 2 knots. 2 Rotating the adjustment screw 1 full turn counterclockwise will lower the speed at which the stall warning horn sounds by approximately 2 knots. 3 27 Dec 2017
Figure 27-31-1: Stall Warning System- Serials w/o Ice Protection FUSELAGE (REF) 4 3 2 6 7 5 12 4 10 7 8 8 9 13 8 CABIN FLOOR (REF) Serials w/o FIKI 1 11 4 10 8 LEGEND 1. O-Ring 2. Screw 3. Washer 4. Nut 5. Electrical Connector 6. Electro-Pneumatic Switch 7. Spring Clamp 8. Pneumatic Line 9. Tee Fitting 10. Tie Down 11. Olive 12. Plug 13. Grommet LEADING EDGE PANEL (REF) Serials w/o FIKI. DETAIL B SR22_MM27_4989 4 27 Dec 2017
B. Stall Warning Lift Transducer - Serials w/ Ice Protection (See Figure 27-31-2) (1) Removal - Stall Warning Lift Transducer (b) (f) Set BAT 1, BAT 2, and AVIONICS switches to OFF positions. Pull STALL WARNING circuit breaker. Pull STALL VANE HEAT circuit breaker. Remove screws securing lift transducer to wing. Disconnect wing wire harness connectors from lift transducer pigtail connectors. Remove lift transducer from wing. (2) Installation - Stall Warning Lift Transducer Acquire necessary tools, equipment, and supplies. Description P/N or Spec. Supplier Purpose Sealant (Refer to 51-30) (Refer to 51-30) Seal perimeter of lift transducer. (b) (f) (g) Connect wing wire harness connectors to lift transducer pigtail connectors. Position lift transducer to wing and secure with screws. Apply sealant to perimeter of lift transducer. Reset STALL VANE HEAT circuit breaker. Test lift transducer heat. 1 On bolster panel, set PITOT HEAT switch to ON. CAUTION The surfaces of the heated stall vane and plate are very hot. Do not touch or injury will occur. 2 Carefully feel for heat near lift transducer stall vane and plate. 3 Set PITOT HEAT switch to OFF. Reset STALL WARNING circuit breaker. 5
(h) Perform Operational Check - Stall Warning System - Ground. (Refer to 27-31) (i) Perform Operational Check - Stall Warning System - Flight. (Refer to 27-31) (3) Functional Test - Stall Warning Lift Transducer Acquire necessary tools, equipment, and supplies. Description P/N or Spec. Supplier Purpose Ohmmeter - Any Source Measure resistance. (b) Remove wing access panel RW9. (Refer to 6-00) Disconnect P442 connector from lift transducer. Using ohmmeter, measure resistance of lift transducer components. 1 Measure pins A and E to verify case heater resistance equals 39.0±5.8 ohms. 2 Measure pins B and C to verify mounting plate #1 resistance equals 9.2±1.4 ohms. 3 Measure pins D and G to verify mounting plate #2 resistance equals 9.2±1.4 ohms. 4 Measure pins F and G to verify vane heater resistance equals 37.2±5.6 ohms. Connect P442 connector to lift transducer. (f) Install wing access panel RW9. (Refer to 6-00) C. Stall Warning Computer - Serials w/ Ice Protection (See Figure 27-31-2) (1) Removal - Stall Warning Computer Set BAT 1, BAT 2, and AVIONICS switches to OFF positions. (b) Pull STALL WARNING circuit breaker. Remove access panel CF3R. (Refer to 6-00) 6
Disconnect electrical connector from stall warning computer. Remove screws securing stall warning computer to fuselage floor. Remove stall warning computer from airplane. (2) Installation - Stall Warning Computer If installing a new or different stall warning computer, perform Adjustment/Test - Stall Warning Computer Switch Settings. (Refer to 27-31) (b) Position stall warning computer to fuselage floor and secure with screws. Connect electrical connector to stall warning computer. Reset STALL WARNING circuit breaker. Perform Operational Check - Stall Warning System - Ground. (Refer to 27-31) (f) Install access panel CF3R. (Refer to 6-00) (3) Adjustment/Test - Stall Warning Computer Switch Settings (b) Loosen screws securing switch access covers to existing and new computers. Verify switch positions of existing computer match values entered in aircraft logbook. Adjust SW and VR rotary switch settings on new computer to match existing computer switch settings. Record switch settings in aircraft logbook. On stall warning computers, rotate switch access covers to closed positions and tighten screws. (4) Operational Check - Stall Warning System - Ground Acquire necessary tools, equipment, and supplies. Description P/N or Spec. Supplier Purpose Wooden Tongue Depressor - Any Source Fixture. (b) Remove access panel CF3R. (Refer to 6-00) 7
(f) (g) (h) (i) (j) (k) Loosen screws securing switch access cover to stall warning computer. NOTE Switch access cover is marked with relative location of SW and VR rotary switches and 4 LED indicators marked VAL (Valid), LTF (Lift Transducer Fault), AIR (Air Mode), and ICE (Ice Protection On). Set BAT 1 and AVIONICS switches to ON positions. On stall warning computer, verify red LTF LED is not on. Set FLAPS switch to 100% position. On stall warning computer, verify that VAL and AIR LEDs are on (green). CAUTION The surfaces of the heated stall vane and plate are very hot. Do not touch or injury will occur. On right wing, use wooden tongue depressor to gently apply upward pressure on tab of lift transducer and note stall warning horn sounds. Set FLAPS switch to UP position. Set BAT 1 and AVIONICS switches to OFF positions. On stall warning computer, rotate switch access cover to closed position and tighten screws. (l) Install access panel CF3R. (Refer to 6-00) (5) Operational Check - Stall Warning System - Flight WARNING The following Operational Check must be performed by a Cirrus Design authorized test pilot. Remove access panel CF3R. (Refer to 6-00) (b) Loosen screws securing switch access cover to stall warning computer. NOTE Switch access cover is marked with relative location of SW and VR rotary switches and 4 LED indicators marked VAL (Valid), LTF (Lift Transducer Fault), AIR (Air Mode), and ICE (Ice Protection On). In smooth air and at an altitude appropriate for stalls, place airplane in stall attitude. Record airplane speed that stall warning signal sounds. 8 27 Dec 2017
(f) (g) Record airplane speed that stall occurred. NOTE Stall warning signal should sound 5 to 10 KIAS prior to stall. If stall warning signal does not sound 5 to 10 KIAS prior to stall, adjust the SW 8-position rotary switch. 1 Rotate clockwise, one detent at a time, to decrease speed at which stall warning horn sounds. 2 Rotate counter-clockwise, one detent at a time, to increase speed at which stall warning horn sounds. On stall warning computer, rotate switch access cover to closed position and tighten screws. (h) Install access panel CF3R. (Refer to 6-00) 9
Figure 27-31-2: Stall Warning System- Serials w/ Ice Protection 2 AFT FLOOR (REF) CF3R (REF) 4 3 SWITCH ACCESS COVER (REF) RH OUTBOARD POROUS PANEL (REF) 2 1 LEGEND 1. Stall Transducer 2. Screw 3. Connector 4. Stall Computer SR22_MM27_4991 10