CITATION MUSTANG OPERATING MANUAL CHAPTER 14 LANDING GEAR AND BRAKES INTRODUCTION This chapter describes the landing gear, nosewheel steering, and brake system of the Citation Mustang. GENERAL The Citation Mustang has retractable tricycle In the event of hydraulic gear extension sys- landing gear that is electrically controlled and tem failure, an independent mechanical uplock hydraulically actuated. Each gear is retracted release and pneumatic system provide for by its own hydraulic actuator. When retracted, emergency gear extension. the nose gear and the struts of the main gear are enclosed by mechanically actuated doors Nosewheel steering is mechanically actuated connected to the gear struts. The trailing-link through linkage from the rudder pedals. A fric- main gear wheels remain uncovered in the tion shimmy damper is contained within the wheel wells. Gear position and warning are nose gear strut. A bungee allows tighter turns provided by colored indicator lights and an with differential power and braking. The aircraft aural warning. is towed by connections on the nosewheel strut. 510OM-00 14-1 CITATION MUSTANG OPERATING MANUAL Power braking (hydraulically actuated) is pro- vided with or without antiskid protection. A “touchdown protection” feature is provided to prevent landing with brakes locked. A spin- down feature stops tires from spinning before retracting into the wheel wells. In the event of a hydraulic brake system failure, an independ- ent pneumatic system provides for emergency braking. A parking brake system is available to temporarily lock the brakes on the ground. Crew alerting system (CAS) messages report the status of the braking and hydraulic systems and related systems. The rotary test switch tests all indications of the landing gear and brakes. LANDING GEAR Figure 14-1. Left Main Landing Gear and Door DESCRIPTION The main landing gear struts are trailing-link struts, supporting the wheels with a trunnion and air-oil (oleo) strut, connected by a trail- ing link (Figure 14-1). The nose landing gear strut is a conventional air-oil (oleo) strut ex- tending from the trunnion (Figure 14-2). Normally, the landing gear is hydraulically actuated, but if the normal gear actuation sys- tem fails, the gear can be mechanically and pneumatically released and extended. At air- speeds up to 250 KIAS, the gear can be ex- tended (VLO). The aircraft can be flown with the gear extended at airspeeds up to 250 KIAS (VLE). However, the gear cannot be retracted when the airspeed is above 185 KIAS. It takes 6 seconds to extend the landing gear. At airspeeds between 100 and 160 KIAS, it takes 11–14 seconds to retract the landing gear. At airspeeds between 160 and185 KIAS, retraction takes 18–20 seconds. Each inboard-retracting main gear uses two hy- draulic actuators (one for uplock release and one for gear actuation). Three more hydraulic actu- ators perform these duties for the forward-re- tracting nose gear. An electrically positioned Figure 14-2. Nose Landing Gear gear-control valve directs hydraulic pressure and Doors 14-2 510OM-00 CITATION MUSTANG OPERATING MANUAL for gear extension or retraction. If hydraulic free of the uplock roller, and the gear strut is extension fails, the emergency gear T-handle al- unlocked to start extension. lows the landing gear to mechanically release and free fall. A bottle of compressed nitrogen, Extension activated by the knob behind the T-handle, pro- vides pressure to ensure gear extension and When the uplock actuator is fully retracted, downlock (Figure 14-3). fluid passes through the uplock actuator to the gear-extend side of the gear actuator. Hydraulic pressure is then applied to the actuators, which extend until the gear is down- and-locked. To speed gear extension and improve free-fall ca- pability of the gear, a regenerative shuttle valve allows fluid to flow from the retract side of the actuators to the extend side. Abnormal Main Gear Extension System Two backup gear-extension systems are pro- vided in addition to normal gear extension: • The T-handle operates a cable system to mechanically release the uplock hooks from the struts. The gear should free-fall into position, aided by the pilot yawing the aircraft. NOTE It may require an acceleration above 150 KIAS to lock the nose landing gear into place. Figure 14-3. Emergency Gear Release Handle (Cover Removed) • The round knob behind the T-handle re- leases pneumatic pressure (high-pres- sure nitrogen) from a bottle in the nose Main Gear System compartment to pneumatically operate the uplock actuators and release the up- Main Gear Extension System lock hooks, then extend the gear actua- Figure 14-4 displays the landing gear actu- tors, which extend the gear. ation during gear extension. Figure 14-5 displays the landing gear actuation during abnormal/emergency extension. Once Uplocks the uplock hooks are released, the pneumatic The main landing gear struts are mechanically pressure is applied to ensure that the gear ac- locked in the retracted position by a spring- tuators properly extend and lock the gear. loaded, hydraulically released uplock hook. Without using the pneumatic gear-extension system, it is still possible to lock the gear down In normal operation, to release a strut from its by yawing the aircraft to force the gear into po- uplock, the gear-control solenoid valve routes sition. However, mechanical release and down- fluid to the uplock hook actuator, retracting the lock should always be followed by the piston into the actuator. When the piston re- pneumatic extension procedure to ensure com- tracts completely, it pulls the uplock hook plete and proper extension of the gear. 510OM-00 14-3 14-4 EMERGENCY GEAR EXTENSION HANDLE NOSE DOWNLOCK NOSE GEAR RELEASE ACTUATOR UPLOCK ACTUATOR UPLOCK HOOK NOSEGEAR ACTUATOR ACTUATOR EMERGENCY MUSTANG CITATION BLOWDOWN MAIN LANDING BOTTLE REGENERATIVE GEAR SHUTTLE ACTUATOR VALVE MAIN LANDING GEAR ACTUATOR TO BRAKE METERING VALVE MANUAL OPERATING UPLOCK RETRACT EXTEND UPLOCK ACTUATOR LINE LINE ACTUATOR ASSEMBLY ASSEMBLY SHUTTLE VALVE CABIN AIR NORMAL-PRESSURE SWITCH P GEAR RETRACT PRESSURE SWITCH P CONTROL HYDRAULIC LOW-PRESSURE SWITCH P MANIFOLD RESERVOIR PNEUMATIC DUMP VALVE GEAR CONTROL LEGEND SOLENOID VALVE SYSTEM PRESSURE FROM BRAKES RETURN ACCUMULATOR BLEED STATIC VALVE ACCUMULATOR NITROGEN 510OM-00 CABIN AIR TO BRAKES Figure 14-4. Landing Gear Schematic—Extension 510OM-00 EMERGENCY GEAR EXTENSION HANDLE NOSE DOWNLOCK NOSE GEAR RELEASE ACTUATOR UPLOCK ACTUATOR UPLOCK HOOK NOSEGEAR ACTUATOR ACTUATOR EMERGENCY MUSTANG CITATION BLOWDOWN MAIN LANDING BOTTLE REGENERATIVE GEAR SHUTTLE ACTUATOR VALVE MAIN LANDING GEAR ACTUATOR TO BRAKE METERING VALVE MANUAL OPERATING UPLOCK RETRACT EXTEND UPLOCK ACTUATOR LINE LINE ACTUATOR ASSEMBLY ASSEMBLY SHUTTLE VALVE CABIN AIR NORMAL-PRESSURE SWITCH P GEAR RETRACT PRESSURE SWITCH P CONTROL HYDRAULIC LOW-PRESSURE SWITCH P MANIFOLD RESERVOIR PNEUMATIC DUMP VALVE GEAR CONTROL SOLENOID VALVE LEGEND SYSTEM PRESSURE FROM BRAKES RETURN ACCUMULATOR BLEED STATIC VALVE ACCUMULATOR NITROGEN CABIN AIR TO BRAKES 14-5 Figure 14-5. Landing Gear Emergency Extension CITATION MUSTANG OPERATING MANUAL Main Gear Downlock Mechanism On takeoff, with weight off wheels, the nose- wheel steering remains engaged until retrac- Each main gear has a mechanical downlock tion. During retraction, nosegear steering is mechanism (integral to the gear actuator), disengaged and the nose gear is mechani- which locks the main landing gear in the down cally centered. In the wheel well, a spring- position. loaded mechanical uplock hook catches the uplock roller on the gear when it retracts. A Applying hydraulic pressure is the only way position-sensor switch in the uplock indi- to release the downlocks; therefore, no blocks cates up-and-locked. or external downlock pins are required. Main Gear Retraction System Nose Gear Door System Nose gear movement actuates two doors to com- Figure 14-6 shows landing gear actuation dur- pletely enclose the nose gear and wheel at re- ing retraction. The main gear retracts when hy- traction. The doors open during gear extension draulic pressure is applied to the retract side and remain open after the gear is extended. of the actuators. This first releases the down- locks, then forces the actuators to retract, pulling the gear into the wheel wells. Before COMPONENTS the wheels enter the wheel wells, an auto- matic braking feature (spindown) stops the Main Gear wheels from spinning to prevent loose wheel tread or debris from striking the interior of the Each main gear assembly includes (see wheel well. When the gear is fully retracted Figure 14-1): into the uplocks, a switch in each uplock de- • Trunnion tects that the main gear is up-and-locked. • Trailing link Nose Gear System • Oleo strut • Main gear actuators with integral Nose Gear Extension System downlocks Nose gear extension is similar to the main • Uplock assembly landing gear. In the wheel well, the uplock hook is hydraulically retracted, releasing the • Main wheel tire and brake assembly uplock roller on the gear. The nosewheel ro- • Squat switch tates down and aft from the nose wheel well. The nose gear is mechanically locked in the extended position by a spring-actuated down- Trunnion lock. A position switch on the drag brace in- A trunnion is the main support (leg) for each dicates down-and-locked. main gear. It connects to the wheel through the oleo strut and the trailing link and is extended Whenever the nosewheel is extended, nose- or retracted by the main gear actuator. During wheel steering is engaged, regardless of whether extension, the trunnion (with the main gear the aircraft is in flight or on the ground. components attached) rotates down-and-out- board on pivots attached to the forward and aft Nose Gear Retraction System wing spars. During nose gear retraction, a hydraulic actu- ator releases the nose gear downlock. The nose Trailing Link gear actuator extends, causing the nose gear to The trailing link connects the trunnion to the retract forward into the nosewheel well.