1、AST 473 Cessna Citation II Landing Gear and Brakes,Dr. R. Kurt Barnhart,Landing Gear and Brakes,Electrically controlled- Hydraulically activated Mechanically actuated doors cover nose gear and struts of main gear when retracted- main gear wheels uncovered in flight Nosewheel steering- via mechanical
2、ly linked rudder pedals- shimmy damp. Included- on top of nose strut Braking- W/ or W/O anti-skid & pneumatic emerg. Braking Indication- colored indicator lights & warn. horn,Landing Gear and Brakes,Overview: Each gear retracts inboard utilizing 2 hyd. Actuators ea.- one for uplock release and one f
3、or gear actuation Nose gear- 2 identical actuators- retracts forward Elec. Cntl valve directs hyd. Press. For gear actuation,Landing Gear and Brakes,Indication: One red and three green down/locked position indicator lights plus warning horn when Throttle or flap settings indicate lndg. But gear not
4、down & locked,Landing Gear and Brakes,Nose wheel- steering via a cable linkage enabled when gear extended Centering during retraction accomplished automatically via a centering cam,Landing Gear and Brakes,Brakes- separate hyd. system powered by an electric pump Each main gear- multiple disk brake- a
5、ctuated by press. From Electric pump Master cylinder Air Pressure (emergency),Landing Gear and Brakes,Struts: conventional oleo struts (air/oil) Floating piston- air/hyd. Fluid- data plate on strut tells amt. Of strut to be showing on preflight Gear normally hydraulic pneumatic for emerg. Ext.,Landi
6、ng Gear and Brakes,Main Gear: Strut 2 ea. Actuators Torque links Landing light Wheel Multiple disk brake Squat switch- left main (and on nose if Thrust Rev.),Landing Gear and Brakes,Main gear- locked in retract by spring loaded/hydraulic uplock actuator In sequence with main actuator such that it mu
7、st reach full travel (release) prior to main actuation Lock ring within main actuator locks gear down Released with hyd. Press. To the retract side of actuator thus no downlock pins required,Landing Gear and Brakes,Main Gear: Gear door covers strut upon retraction- wheel not covered Each main wheel
8、has fusible plug- melts & diffuses tire pressure after overheat (such as heavy braking),Landing Gear and Brakes,Nose Gear: Strut 2 hyd. Actuators Torque links Single wheel Self-contained shimmy damper,Landing Gear and Brakes,Nose Gear- held retracted by hyd. Uplock mechanism- same as main gear 3 doo
9、rs fully enclose nose gear upon retraction 2 fwd. Doors only open during extension & retraction (transit)- aft remains upon during extension,Landing Gear and Brakes,Nosewheel Spin-up System (optional): Reduces gravel spray at touchdown- uses bleed air Prior to touchdown place Bleed air switch to LOW
10、 or HI Winshield Bleed AIR valve to OFF Nosewheel spin up control to ON,Landing Gear and Brakes,Nose wheel spin up system (above 60% N2)- Nosewheel RPM indicator illuminates green as speed incr. Into 1,600 2,400 RPM range. Maintain speed with NOSE WHEEL SPIN-UP control- overspeed changes indicator c
11、hanges to red Use of windshield bleed (ice or rain) reduces wheel acceleration rate Position Spin-up control of OFF at nose touchdown,Landing Gear and Brakes,Controls- gear handle completes circuits to extend or retract solenoid of gear cntl valve On gnd. Spring-loaded plunger in handle mechanism pr
12、events inadvertent retraction. DC power to: lights, horn, lock solenoids via LDG GEAR CB on left panel (warning section),Landing Gear and Brakes,Operation- with squat switch in flight pos. Lock solenoid energizes to retract plunger (if pwr. Fails- no retract possible) Gear handle actuated by pulling
13、 it out of detent position to either UP or DOWN Indication- as each gear locks down the respective light should illuminate. Red light indicates gear unsafe (illuminates when handle moved out from up position until all 3 are down and locked & at retraction when any down lock released until all 3 gear
14、 are up and locked) Lights & horn can be tested by rotary test switch,Landing Gear and Brakes,Warning Horn- sounds when: One or more gear not down & locked AND one or both throttles less than 70% N2 (later SNs also have an airspeed below 150 rqmt)- Horn can be silenced by HORN SILENCE PUSH button on
15、 gear control panel Flaps beyond 15 deg. And one or more gear not down & locked- Warning horn cannot be silenced,Landing Gear and Brakes,Movement of gear handle: Energizes gear control valve Closes hyd. System bypass valve to create hyd. Press. (HYD PRESS ON light illuminates) When cycle complete va
16、lve opens & light goes outDC for lndg. Gear control circuit via GEAR CONTROL CB (in systems section) on left panel,Landing Gear and Brakes,Retraction- moving gear handle to UP: Energizes retract solenoid (gear cntl valve) & positions to direct press. To retract side of each gear actuator & preloads
17、uplocks Down lock in ea. Actuator releases Retraction begins,Landing Gear and Brakes,Retraction- As each gear fully retracts Spring loaded uplock engages Uplock switch actuated When all 3 actuated gear cntl valve circuit is interrupted Valve returns to neutral All position indicator light on panel g
18、o out,Landing Gear and Brakes,Extension- Placing handle in ext. pos.: Energizes extend solenoid (gear cntl valve) Valve positioned to direct press. To uplocks releasing them then: Press. Continues to actuators to extend then: Downlock switch is actuated- when all 3 actuated: Cntl valve circuit inter
19、rupted- valve returns to neutral position With no pressure on gear actuator- internal lock mechanism engages; verified by visual indicator pins & 3 green lights.,Landing Gear and Brakes,Emergency Extension- during hydraulic or electrical failure Manually release uplocks Blow down with 2,00 psi pneum
20、atic bottle (in rt. Nose baggage compt.,Landing Gear and Brakes,Emergency Extension: Pull AUX GEAR CONTOL T-handle & rotate clockwise (releases uplocks for gear free fall- 150 kts.) Use rudder to yaw aircraft (aids full extension- flaps 0) Pull round know behind T-handle to blow gear down and ensure
21、 extension (also opens a hyd. Fluid dump valve & provides for fluid return to reservoir Maintained in locked position by actuators (internal lock). Hyd. Ext. inop. After bottle - Mx. Required.,Landing Gear and Brakes,Nosewheel steering- mechanically linked through nosewheel. Travel limited by rudder
22、 pedal stops to 20 deg. Application of diff. thrust actuates spring loaded bungee in nose gear providing additional swivel,Landing Gear and Brakes,For towing- ensure flight control lock disengaged- dont exceed 95 deg. Nosewheel deflection or damage will occur- Indicated by loss of nosewheel steering
23、- DO NOT FLY! Center nosewheel just prior to touchdown during crosswind lndg. Since nosewheel deflects anytime its extended,Landing Gear and Brakes,Brakes- multi-disk powered by separate hyd. System Constant press. Maintained for braking Use with or w/o anti-skid feature Emer. Pneumatic braking avai
24、lable if brake hyd. Pressure lost. Braking initiated by rudder pedal master cylinders- pilot & co-pilot in series- whoever pushes harder (most scared) has braking control,Landing Gear and Brakes,Brake System components: Hydraulic accumulator- stores pressure Reservoir- pressurized by cabin air- flui
25、d level and pressure- pre-flight items,Landing Gear and Brakes,Anti-skid system- permits max. braking w/o skidding under all conditions Speed transducer in ea. Wheel sends speed signal to control box (detects sudden decel.- impending skid) Causes anti-skid valve to relieve hyd. Brake pressure- self-
26、restoring system,Landing Gear and Brakes,Touchdown protection available on later models (prevents touchdown w/ locked wheels) otherwise allow wheels spin up after lndg. To prevent blowout; Also- do not pump brakes- HOLD. W/O touchdown protection taxi w. anti-skid OFF Deploy speedbrakes after touchdo
27、wn to aid braking (increases effectiveness by putting more wt. on wheels).,Landing Gear and Brakes,Anti-skid System Operation- W/ gear handle down a separate DC hyd. Pump maintains 900 1,300 psi for brake system Accumulator- dampens pressure surges Reservoir supplies fluid to master cylinders Depres
28、sing brake pedals applies master cylinder press. To actuate the PBV (power brake valve which meters pump pr. To brakes w.r.t. pedal pressure),Landing Gear and Brakes,Anti-Skid operation ctn.: Fwd. speed of 12 kts. Required for operation- disengages below 12 kts. Differential braking available If ANT
29、I-SKID INOP annunciator comes on- a system fault has been detected- switch system off. Pressure below 750 psi causes this plus the PWR BRK PRESS LO annunciator to come on,Landing Gear and Brakes,Anti-Skid Test- On ground place rotary test switch in ANTISKID- ANTISKID INOP light comes on then Goes ou
30、t 3 sec after test switch moved System self-tests airborne each time gear handle is selected down- result same as gnd. test,Landing Gear and Brakes,Parking Brakes Apply brakes as normal and pull park brake handle on left lower side of pilots instr. Panel Mechanically actuates parking brake valve- tr
31、aps fluid Release brakes by pushing on PARK BRAKE handle NOTE: Do not apply park brake after a hard stop- heat x-fer to wheel may melt fuse plug,Landing Gear and Brakes,Emergency Brakes- uses same pneumatic system as for emerg. Gear ext. Bottle press. Adequate for stopping even if gear has been blow
32、n down. On SNs 2 460 if pump fails manual braking still avail using accumulator press.- be ready with emerg. Brakes.,Landing Gear and Brakes,Emerg. Brake Operation: Pull EMER BRAKE PULL aft- mechanically actuates emerg. Brake valve- meters air press. Via shuttle valves to brakes- proportional to amt
33、. of movement Air supplied to both brakes simultaneously- no diff. braking Return lever to orig. position to vent trapped brake press. Overboard- releases brakes,Landing Gear and Brakes,EMER. BRAKE NOTES: Do not actuate brake pedals during emerg. Braking as shuttle valve may be disrupted allowing air press. Into hyd. Line rupturing brake reservoir. No anti-skid avail. During emerg. Braking Do not attempt taxi after Emer. Brake application- mx. Required.,The End,
