7/30/2019 214 - Landing Gears

1/17

2.14 LANDING/DECELERATIONSYSTEM

CONTENTS

Description ........................................... 2.14-1Landing Gear ....................................... 2.14-1Drag Chute........................................... 2.14-4Main Landing Gear Brakes ................ 2.14-5Nose Wheel Steering........................... 2.14-9Operations ............................................ 2.14-10Landing/Deceleration System

Summary Data.............................. 2.14-17Landing/Deceleration System

Rules of Thumb ............................ 2.14-17

Description

The orbiter, unlike previous space vehicles, has

the capability of landing on a runway using aconventional type of landing system. Once theorbiter touches down, the crew deploys the dragchute, begins braking, and starts nose wheelsteering operations.

The orbiter drag chute, first used on the maidenflight of OV-105, improves the orbiter'sdeceleration and eases the loads on the landinggear and brakes.

Braking is accomplished by a sophisticatedsystem that uses electrohydraulic disk brakes

with an anti-skid system. Only the two maingear sets have braking capability, and each canbe operated separately.

Two primary steering options are available. Byapplying variable pressure to the brakes, thecrew can steer the vehicle by a method calleddifferential braking. Also, by selecting nosewheel steering, the crew can use the rudderpedal assembly to operate a hydraulic steeringactuator incorporated in the nose landing gear.The crew can also use the rudder to assiststeering while at higher ground speeds.

Landing Gear

The landing gear system on the orbiter is aconventional aircraft tricycle configuration con-sisting of a nose landing gear and a left andright main landing gear. The nose landing gearis located in the lower forward fuselage, and themain landing gear is located in the lower leftand right wing area adjacent to the midfuselage.

Each landing gear includes a shock strut withtwo wheel and tire assemblies. Each mainlanding gear wheel is equipped with a brakeassembly with anti-skid protection.

Landing Gear Doors

The nose landing gear has two doors, and eachmain gear has one door. When the crew com-mands gear deployment, the doors open auto-matically as the gear is dropped. This is accom-plished by the door extend/retract mechanism,which is actuated by the dropping gear. Thenose landing gear doors have two door hooksthat hold the doors closed, and the main geardoors have four door hooks.

In addition, the doors have door-assist bungeeassemblies. These assemblies exert additionalforce on the inside of the doors to assist in doordeployment to overcome the aerodynamic forcesacting against the doors and/or in case thepressure inside the wheel wells is less than theoutside pressure. The nose landing gear bungeeassist assemblies exert 2,000 pounds of force onthe doors; the main landing gear bungee assistassemblies exert approximately 5,000 pounds offorce on the doors over the first 2 inches of travel.

The nose landing gear also contains a pyro boostsystem to further assure nose gear door and gearextension in case high aerodynamic forces on thenose gear door are present. This pyro system isfired each time the landing gear is deployed.

Power and Control Signals

Nose Landing

Gear Steering

Actuator

Nose Landing

Gear Uplick and

Strut Actuators

System 3System 2System 1

Hydraulic System

Electrical

Power

System

Crew Controls

Main Landing

Gear Brakes

Main Landing

Gear Uplock and

Strut Actuators

Landing/Deceleration Interfaces

Each of the landing gear doors has high-temperature reusable surface insulation tiles onthe outer surface and a thermal barrier or doorseal to protect the landing gear from the hightemperatures encountered during reentry.

7/30/2019 214 - Landing Gears

2/17

Gear Retraction

During retraction, each gear is hydraulicallyrotated forward and up by ground supportequipment until it engages an uplock hook foreach gear in its respective wheel well. Theuplock hook locks onto a roller on each strut. Amechanical linkage driven by each landing gearmechanically closes each landing gear door.

The nose landing gear is retracted forward andup into the lower forward fuselage and isenclosed by two doors. The main landing gearis also retracted forward and up into the left andright lower wing area, and each is enclosed witha single door. The nose and main landing gearcan be retracted only during ground operations.

Nose Gear and Door Uplock Mechanism

Gear Deployment

When deployment of the landing gear iscommanded by the crew, the uplock hook foreach gear is unlocked by hydraulic system 1

pressure. (See Section 2.1 for more informationon orbiter hydraulic systems.) Once the hook isreleased from the roller on the strut, the gear isdriven down and aft by springs, hydraulicactuators, aerodynamic forces, and gravity. Amechanical linkage released by each gearactuates the doors to the open position. Thelanding gear reach the full-down and extendedposition within 10 seconds and are locked in the

down position by spring-loaded downlockbungees. If hydraulic system 1 pressure is notavailable to release the uplock hook, a pyrotech-nic initiator at each landing gear uplock hookautomatically releases the uplock hook on eachgear 1 second after the flight crew has com-

manded gear down.

The landing gear are deployed at 300 100 feetand a maximum of 312 knots equivalent air-speed (KEAS).

Nose Landing Gear Deployed

Main Landing Gear Deployed

7/30/2019 214 - Landing Gears

3/17

Shock Struts

The shock strut of each landing gear is theprimary source of impact attenuation at landing.The struts have air/oil shock absorbers tocontrol the rate of compression/extension andprevent damage to the vehicle by controllingload application rates and peak values.

Each landing gear shock strut assembly isconstructed of high-strength, stress- and corro-sion-resistant steel alloys, aluminum alloys,stainless steel, and aluminum bronze. Theshock strut is a pneumatic-hydraulic shockabsorber containing gaseous nitrogen andhydraulic fluid. Because the shock strut issubjected to zero-g conditions during spaceflight, a floating piston separates the gaseousnitrogen from the hydraulic fluid to maintain

absorption integrity.The nose landing gear shock strut has a 22-inchstroke. The maximum allowable derotation rateis approximately 9.4 per second or 11 feet persecond, vertical sink rate.

The main landing gear shock strut stroke is 16inches. The allowable main gear sink rate for a212,000-pound orbiter is 9.6 feet per second; fora 240,000-pound orbiter, it is 6 feet per second.

With a 20-knot crosswind, the maximumallowable gear sink rate for a 212,000-poundorbiter is 6 feet per second; for a 240,000-poundorbiter, it is approximately 5 feet per second.(Current maximum operational crosswind islimited to 15 knots.)

Wheels and Tires

Landing gear wheels are made in two halvesfrom forged aluminum. The nose landing geartires are 32 by 8.8 inches and have a normalnitrogen inflation pressure of 350 psi prior tolaunch. The maximum allowable load per noselanding gear tire is approximately 45,000pounds. Nose landing gear tires are rated for217 knots maximum landing speed. They may

be reused once.

The main landing gear tires are 44.5 by 21 inchesand have 16 cord layers in a bias-ply design.They are normally inflated with nitrogen to apressure of 370 psi. The maximum allowableload per main landing gear tire is 132,000pounds. With a 60/40 percent tire load distri-

bution, the maximum tire load on a strut is220,000 pounds. The main gear tires are rated at225 knots maximum ground speed and have alife of one landing.

Nose Landing Gear Stowed

7/30/2019 214 - Landing Gears

4/17

Drag Chute

The orbiter drag chute was designed to assistthe deceleration system in safely stopping thevehicle on the runway at end of mission (EOM)and abort weights. Design requirementsincluded the ability to stop a 248,000 lb TALabort orbiter in 8,000 feet with a 10 knot tail-

wind on a hot (103 F) day and maximumbraking at 140 knots ground speed or one halfrunway remaining. The drag chute, housed atthe base of the vertical stabilizer, is manuallydeployed by redundant commands from the

CDR or PLT at derotation. Drag chute deploy-ment may be done between main gear touch-down and derotation only for vehicle massmoments 1.53 million foot pounds. The dragchute is jettisoned at 60 (20) knots groundspeed to prevent damage to the main engine

bells. The drag chute will be used on lake bedand concrete runways except with crosswindsgreater than 15 knots or in the presence of mainengine bell repositioning problems. The dragchute may be deployed without engine bellrepositioning if landing/rollout controlproblems exist.

Drag Chute Configuration

Main Landing Gear Stowed

7/30/2019 214 - Landing Gears

5/17

Nominal Sequence of Drag Chute Deployment, Inflation, and Jettison

Pilot and Main Chutes

When drag chute deployment is initiated, thedoor is blown off of the chute compartment bypyros and a mortar fires deploying a nine footpilot chute. The pilot chute in turn extracts the

40 foot, partially reefed conical main chute. Themain chute is reefed to 40 percent of its totaldiameter for about 3.5 seconds to lessen theinitial loads on the vehicle. The main chutetrails the vehicle by 89.5 feet on a 41.5 foot riser.

Drag Chute Controls

The drag chute deployment and jettisonpushbuttons, ARM 1(2), DPY 1(2), and JETT 1(2)are installed on either side of both the CDR'sand PLT's HUDs. Activation of each lightedpushbutton initiates a signal through the

primary and redundant paths simultaneously.The deployment sequence requires that both theARM and DPY pushbuttons be activatedtogether. The JETT pushbutton signal will only

be effective if the ARM command haspreviously been initiated. (ARM and JETT may

be initiated simultaneously.) Circuit breakersfor the drag chute controls are located on panelsO15 and O16.

Main Landing Gear Brakes

Each of the orbiter's four main landing gearwheels has electrohydraulic disc brakes and anassociated anti-skid system. The disc brakeassembly consists of nine discs, five rotors, four

stators, a backplate, and a pressure plate. Thecarbon-lined rotors are splined to the inside ofthe wheel and rotate with the wheel. Thecarbon-lined stators are splined to the outside ofthe axle assembly and do not rotate with thewheel.

The brakes are controlled by the commander orpilot applying toe pressure to the upper portionof the rudder pedals; electrical signals produced

by rudder pedal toe pressure control hydraulicservovalves at each wheel and allow hydraulicsystem pressure to actuate braking. Brakes

cannot be applied until about 1.9 seconds afterweight on the main gear has been sensed. Theanti-skid system monitors wheel velocity andcontrols brake pressure to prevent wheel lockand tire skidding. The braking/anti-skid sys-tem is redundant in that it utilizes system 1 and2 hydraulic pressure as the active system withsystem 3 as standby, and it also utilizes all threemain dc electrical systems.

7/30/2019 214 - Landing Gears

6/17

Panels F2, F3

O PE N

CLO S E O PEN

CLO SE

O PEN

CLO SE

O PEN

CLO SE

Hyd sys 1

Hyd sys 2

Hyd sys 3

GPC

GPC

GPC

Lg arm& down

Main geardeploy

Brakes

Lg extendvalve 2

Lg extendvalve 1

NWSS/V NWS

Nose geardeploy

Brake isolvalve 3

Brake isolvalve 2

Brake isolvalve 1

Lg extendisol valve

FA1 Vrel = 800

FA1

FA2

FA3 WOW

WOW

WOW

R 4

R 4

R 4

R 4

Lg/NWS hyd sysAuto 1/2

Sys 2inhibitR 4

552.cvs

Landing Gear Hydraulics

Brake System Hydraulic Power

Each of the four main landing gear wheel brakeassemblies is supplied with pressure from twodifferent hydraulic systems. Each brakehydraulic piston housing has two separate brakesupply chambers. One chamber receiveshydraulic source pressure from hydraulic sys-tem 1 and the other from hydraulic system 2.There are eight hydraulic pistons in each brakeassembly. Four are manifolded together fromhydraulic system 1 in a brake chamber. Theremaining four pistons are manifolded togetherfrom hydraulic system 2. When the brakes are

applied, the eight hydraulic pistons press thediscs together, providing brake torque.

When hydraulic system 1 or 2 source pressure

drops below approximately 1,000 psi, switchingvalves provide automatic switching to hydraulicsystem 3. Loss of hydraulic system 1, 2, or bothwould have no effect on braking capability,

because standby system 3 would automaticallyreplace either system. Loss of hydraulic system3 and either 1 or 2 would cause the loss of halfof the braking power on each wheel, andadditional braking distance would be required.

7/30/2019 214 - Landing Gears

7/17

The brake valves in hydraulic systems 1, 2, and3 must be open to allow hydraulic pressure tothe brakes. All three valves are automaticallycommanded open after weight on the mainlanding gear is sensed. The 3,000 psi hydraulicpressure is reduced by a regulator in each of the

brake hydraulic systems to 2,000 psig.

Anti-Skid

The anti-skid portion of the brake systemprovides optimum braking by preventing tireskid or wheel lock and subsequent tire damage.

Each main landing gear wheel has two speedsensors that supply wheel rotational velocityinformation to the skid control circuits in the

brake/skid control boxes. The velocity of eachwheel is continuously compared to the average

wheel velocity of all four wheels. Whenever thewheel velocity of one wheel is 60 percent belowthe average velocity of the four wheels, skidcontrol removes brake pressure from the slowwheel until the velocity of that wheel increasesto an acceptable range.

The brake system contains eight brake/skidcontrol valves. Each valve controls the

hydraulic brake pressure to one of the brakechambers. The brake/skid control valvescontain a brake coil and a skid coil. The brakecoil allows hydraulic pressure to enter the brakechambers. The skid coil, when energized by theskid control circuit, provides reverse polarity to

the brake coil, preventing the brake coil fromallowing brake pressure to the brake chamber.

Anti-skid control is automatically disabledbelow approximately 10 to 15 knots to preventloss of braking for maneuvering and/or comingto a complete stop.

The anti-skid system control circuits containfault detection logic. The yellow ANTI SKIDFAIL caution and warning light on panel F3will be illuminated if the anti-skid faultdetection circuit detects an open circuit or short

in a wheel speed sensor or control valveservocoil, or a failure in an anti-skid controlcircuit. A failure of these items will onlydeactivate the failed circuit, not total anti-skidcontrol. If the BRAKES switches on panels O14,O15, and O16 are ON, and the ANTISKIDswitch on panel L2 is OFF, the ANTISKID FAILcaution and warning light will also beilluminated.

O F F

B R A K E S

MN B

O N

Panel 015

O F F

B R A K E S

MN C

O N

Panel 016

O F F

B R A K E S

MN A

O N

Panel 014

O F F

A N T I S K I D

O N

Panel L2

Commanderpedals

Pilot pedals

No-weight-on-main-gear

sensors

Brake/skid control boxesA and B

(4 circuits per box)

Transducers (8)

Power

To skid control

Transducers (8)

To skidcontrol

Hydraulicpower

A N T I S K I D

F A I L

Panel F3

Brake chambers (8)(2 per wheel)

Switch

valve

Switchvalve

Switchvalve

Switchvalve

Brake/skid controlvalves (8)

To skid

controlMain wheels (4)

Hydraulicpower

Wheel speedsensors (8)

(2 per wheel)

553.cvs

Brake/Skid Control System Overview

7/30/2019 214 - Landing Gears

8/17

ANTI SKID FAIL Caution and Warning Light on Panel F3

Pane l L2 Pane l 014 Pane l 015 Pane l 016

Panel F3

* Anti-skid fault detection circuits detect any of the ** Appl ies onl y if bra kefollowing failures: power swi tc hes M N B ,- Open or short in a wheel speed sensor circuit M N C o r bo th a re- Open or short in a skid control servovalve circuit a c t i v a t e d .- Fai lure in an ant i-sk id cont ro l c i rcu i t

Note: A fai lure wil l deact ivate only the f ai led circuit and not total ant i-skid control.

555.cvs

ANTISKID

ON

BRAKES

MN A

ON

BRAKES

MN B

ON

BRAKES

MN C

ON

OFF OFF OFF OFF

Anti-skidSwitch

Brake PowerSwitch

Anti-skidFailure*

Anti-skid**Fail Light

OFFON YES NO OFFON OFF ON

ANTISKID

FAIL

Anti-Skid Fail Light Status

Temperature Control

Insulation and electrical heaters are installed on

the portions of the hydraulic systems that arenot adequately thermally conditioned by theindividual hydraulic circulation pump system

because of stagnant hydraulic fluid areas.

Redundant electrical heaters are installed on themain landing hydraulic flexible lines located onthe back side of each main landing gear strut

between the brake module and brakes. These

heaters are required because the hydraulic fluidsystems are dead-ended, and fluid cannot becirculated with the circulation pumps. In

addition, on OV-103, OV-104, and -105, thehydraulic system 1 lines to the nose landing gearare located in a tunnel between the crewcompartment and forward fuselage. The passivethermal control systems on OV-103, OV-104, andOV-105 are attached to the crew compartment,which leaves the hydraulic system 1 lines to thenose landing gear exposed to environmentaltemperatures, thus requiring electrical heaters on

7/30/2019 214 - Landing Gears

9/17

the lines in the tunnel. Since the passive thermalcontrol system on OV-102 is attached to the innerportion of the forward fuselage rather than thecrew compartment, no heaters are required onthe hydraulic system 1 lines to the nose landinggear on OV-102.

TheHYDRAULICS BRAKE HEATER A, B, and Cswitches on panel R4 enable the heater circuits.On OV-103, OV-104 and -105, HYDRAULICSBRAKE HEATER switches A, B, and C provideelectrical power from the corresponding main

buses A, B, and C to the redundant heaters on themain landing gear flexible lines and the hydraulicsystem 1 lines in the tunnel between the crewcompartment and forward fuselage leading to thenose landing gear.

TheHYDRAULICS BRAKE HEATERA, B, and C

switches on panel R4 enable the heater circuitson only the main landing gear hydraulic flexiblelines on OV-102.

HYDRAULICS BRAKE HEATER Switches onPanel R4

Nose Wheel Steering

The nose landing gear contains a hydraulicsteering actuator that responds to electroniccommands from the commander's or pilot'srudder pedals. Two types of operation are

available, GPC and caster. The GPC mode issupported by hydraulic systems 1 and 2 throughthe selection of nose wheel steering (NWS)system 1 or 2 (NWS 1(2)). This providesredundant avionics modes regardless ofhydraulic system support. NWS 1 or 2 willwork with either hydraulic system 1 or 2.

In the GPC modes (NWS 1(2)), the flight controlsoftware uses accelerometer assembly feedback tomodify commands from the rudder pedaltransducer assemblies (RPTAs) to automaticallycounter hardovers or large lateral accelerations dueto gear or tire malfunctions. If GPC 1 or 2, or FF1or 2 is inoperative, steering downmodes to caster ifNWS 1 is selected. Similarly, the loss of GPC 3 or4, or FF3 or 4 will prevent the use of NWS 2 andcause a downmode. The loss of either NWSsystem will only cause a downmode to castor. Theother NWS system must be selected if required. Incaster, no positive control over the nose wheelposition is available, and differential braking andrudder are used for directional control.

A hydraulic servoactuator mounted on the nosestrut permits orbiter nose wheel steering up to9 left or right after system activation.Hydraulic systems 1 and 2 provide redundanthydraulic pressure to either NWS 1 or 2. If thepressure in one system is more than twice thatin the other, the higher pressure systemprovides hydraulic power for NWS. If NWS isnot activated, or if hydraulic systems 1 and 2fail, the NWS actuator acts as a nose wheelshimmy damper in the caster mode.

NWS can only be enabled after certainpreconditions are met. Among these preconditionsare two major milestones: weight-on-wheels(WOW) and weight-on-nose-gear (WONG). Thereare three sensors on each main gear designed tosense when main gear touchdown (MGTD) occursso that WOW can be set. One sensor is aproximity sensor and the other two are wheelspeed sensors (one per tire). Once WOW is set,the speed brake is commanded full open, flat turndiscrete is set, half gain RHC is enabled, and theHUD format downmodes. After WOW is set onone strut, brakes are also enabled.

7/30/2019 214 - Landing Gears

10/17

APU/HYD 1 APU/HYD 2

FF3

FF4

MN BO15

Note: Loss of any parameter within the dotted lines causes a loss of theassociated NWS mode.Loss of any paramenter within the dashed lines causes a loss of theassociated HYD system for NWS.

*Manual (switch) control is lost for this valve; GPC capability still exists.

MN BO15

LDG extisol valve

LDG extvalve #2

FA 1MNA AMC 1CNTL AB2*

MNA FPC 1CNTL CA1,CA3, AB3

NWS HYDswitching

valve

LDG extvalve #2

Brake isolvalve #2

FA2MNB ALC 2CNTL BC1*

MNB FPC 2CNTL AB1,BC1, BC2

Pilotsolenoid

B2

Pilotsolenoid

A2

Pilotsolenoid

A1

Pilotsolenoid

B1

NWS 1 NWS 2

FF1

MN AO14

FF2

MN AO14

557.cvs

OI-21 NWS Functional Drawing

WONG can be set by either of two proximitysensors located on the nose gear. Once WONGis set (presupposing WOW is already set andthe vehicle attitude (theta) is less than zero), the

ground speed enable "flag" is set. This enablesNWS and the I-loaded downward deflection ofthe elevons for tire load relief. As a backup tothe WOW and WONG discretes, the crewnominally selects

MANUAL ET or SRB SEP and presses theassociated pushbutton. This will manually

bypass the WOW/WONG discretes and set theground speed enable "flag."

Operations

Landing Gear

Landing gear deployment is initiated when thecommander (on panel F6) or pilot (on panel F8)depresses the guarded LANDING GEAR ARMpushbutton and then the guarded DNpushbutton at least 15 seconds before predictedtouchdown at a speed no greater than 312 KEASat 300 100 feet above ground level (AGL).

NOTE

Deploying the landing gear at equivalentairspeeds greater than 312 knots mayresult in high aerodynamic loads on thedoors and interference with the normalopening sequence.

Commanders LANDING GEAR Controlson Panel F6

Pilots LANDING GEAR Controls on Panel F8

Depressing the ARM pushbutton energizeslatching relays for the landing gear extendvalves 1 and 2 in preparation for gear deploy. Italso arms the nose and main landing gearpyrotechnic initiator controllers and illuminatesthe yellow light in the ARM pushbutton. This isnormally performed by the pilot atapproximately 2,000 feet AGL.

7/30/2019 214 - Landing Gears

11/17

The DN pushbutton is then depressed. Thisenergizes latching relays that open the hydraulicsystem 1 extend valve 1 and hydraulic system 2landing gear extend valve 2. Fluid in hydraulicsystem 1 flows to the landing gear uplock andstrut actuators and the nose wheel steering

switching valve. The green light in the DNpushbutton indicator is illuminated.

The proximity switches on the nose and mainlanding gear doors and struts provide electricalsignals to control the LANDING GEAR NOSE,LEFT, and RIGHT indicators on panels F6 andF8. The output signals of the landing gear anddoor uplock switches drive the landing gear UPposition indicators and the backup pyrotechnicrelease system. The output signals of thelanding gear downlock switches drive thelanding gear DN position indicators. The

landing gear indicators are barberpole when thegear is in transit.

The left and right main landing gear WOWswitches produce output signals to theguidance, navigation, and control software toreconfigure the flight control system for landingand rollout gains.

The two WONG signals, along with WOW andtheta (pitch angle) less than 0, allow the GNCsoftware to issue a nose wheel steering enablesignal. This signal is then sent to the steering

control box to enable nose wheel steering.

Six gear proximity switches are signal condi-tioned by the landing gear proximity sensorelectronics box 1, located in avionics bay 1. Sixadditional gear proximity switches are signalconditioned by the landing gear proximitysensor electronics box 2, located in avionics bay2. All WOW proximity switches are redundantthrough two signal conditioners.

Hydraulic system 1 source pressure is routed tothe nose and main landing gear uplock

actuators, which releases the nose and mainlanding gear and door uplock hooks. As theuplock hooks are released, the gear begins itsdeployment. During gear extension, a cammingaction opens the landing gear doors. Thelanding gear free falls into the extended posi-tion, assisted by the strut actuators and air-stream in the deployment. The hydraulic strutactuator incorporates a hydraulic fluid flow-

through orifice (snubber) to control the rate oflanding gear extension and thereby preventdamage to the gear's downlock linkages.

The BRAKE ISOL VLV 1, 2, and 3 switches onpanel R4 control the corresponding landing gear

isolation valve in hydraulic systems 1, 2, and 3.When the switch is positioned to CLOSE,hydraulic system 1 is isolated from the mainlanding gear brakes. The talkback indicatorabove the switch would indicate CL. Thelanding gear isolation valves cannot be openedor closed with hydraulic pressures less thanapproximately 100 psi. When the valve is open,hydraulic system 1 pressure is available to themain landing gear brake control valves. Thenormally closed landing gear extend valve 1,located downstream of the landing gearisolation valve, is not energized until a

LANDING GEAR DN command is initiated bythe commander or pilot on panel F6 or panel F8.

The BRAKE ISOL VLV 2 and 3 switches on panelR4 positioned to CLOSE isolate the correspond-ing hydraulic system from the main landinggear brake control valves. The adjacent talkbackindicator would indicate CL. When switches 2and 3 are positioned to OPEN, the correspond-ing hydraulic system source pressure isavailable to the main landing gear brake controlvalves. The corresponding talkback indicatorwould indicate OP. Landing gear extend valve

2 is located downstream of brake isolation valve2. This valve further isolates hydraulic system 2supply pressure from the nose wheel steeringand nose landing gear deploy actuators and isopened by a LANDING GEAR DNcommand.

When the nose and main LANDING GEAR DNcommand is initiated, hydraulic system 1pressure is directed to the nose and mainlanding gear uplock hook actuators and strutactuators (provided that the LG/NWS HYD SYSswitch is in the AUTO 1/2 position) to actuatethe mechanical uplock hook for each landinggear and allow the gear to be deployed and alsoprovide hydraulic system 1 pressure to the nosewheel steering actuator. The landing gear/nosewheel steering hydraulic system switching valvewill automatically select hydraulic system 2supply pressure if system 1 should fail, therebyproviding redundant hydraulics for NWSactuation and nose gear deploy.

7/30/2019 214 - Landing Gears

12/17

NOTE

Hydraulic system 1 is the only hydraulicsystem for deploy of the main landinggear.

The GPC position of the BRAKE ISOL VLV 1, 2,

and 3 switches on panel R4 permits the onboardcomputer to automatically control the valves inconjunction with computer control of thecorresponding hydraulic system circulationpump.

BRAKE ISOL VLV Switches and Talkbacks onPanel R4

Two series valves, landing gear retract controlvalve 1 and 2, prevent hydraulic pressure from

being directed to the retract side of the nose andmain landing gear uplock hook actuators andstrut actuators if the retract/circulation valvefails to open during nose and main landing geardeployment.

Prior to entry, the BRAKE ISOL VLV 1, 2, and 3switches are positioned to GPC. This allowsautomatic opening of the valves after weight on

main gear is sensed with GPC command viaMDM FA1, FA2, and FA3, respectively. At19,000 feet per second, the landing gear isolationvalve automatic opening sequence begins underGNC software control. If the landing gearisolation valve is not opened automatically, the

flight crew will be requested to manually openthe valve by positioning the applicable BRAKEISOL VLVswitch to OPEN.

If the hydraulic system fails to release thelanding gear within 1 second after the DNpushbutton is depressed, the nose and left andright main landing gear uplock sensors(proximity switches) will provide inputs to thepyro initiator controllers (PICs) for initiation ofthe redundant NASA standard initiators (pyrosystem 1 and 2). They release the same uplockhooks as the hydraulic system. As mentioned

earlier, the nose landing gear, in addition, has aPIC and redundant NASA standard initiatorsthat initiate a pyrotechnic power thruster 2seconds after the DNpushbutton is depressed toassist gear deployment. This "nose gear pyroassist" pyro fires every time the gear aredeployed.

The landing gear drag brace overcenter lock andspring-loaded bungee lock the nose and mainlanding gear in the down position.

Ground Reset

Landing gear reset is primarily a post landingfunction, which will be performed by the crew.

The LG ARM/DN RESET switch on panel A12positioned to RESET unlatches the relays thatwere latched during landing gear deployment

by the LANDING GEAR ARM and DNpushbutton indicators. The primary function ofthis procedure is to remove power to the PICcircuits that are still charged as a backuplanding gear deploy method. The RESETposition also will extinguish the yellow light in

the ARM pushbutton indicator and the greenlight in the DNpushbutton.

Drag Chute

During entry, as the vehicle decelerates from8000 to 3500 fps, the main engine bells arerepositioned 10 below the nominal to precludedamage during drag chute deployment. The

7/30/2019 214 - Landing Gears

13/17

crew cannot monitor the bell repositioning butcan determine that the system is enabled at item19 on the SPEC 51 OVERRIDE display. Thecrew can inhibit the repositioning while in MM

301-304 by toggling item 19 in SPEC 51.Nominal EOM drag chute deployment will beinitiated only if main engine bell repositioning isenabled.

LG ARM/DN RESET Switch on Panel A12

Although the drag chute may be deployed atspeeds up to 230 KEAS, current EOMprocedures call for its deployment at 190 KEAS(195 KEAS for heavyweight vehicles) with acrosswind component no greater than 15 knots.If the drag chute is deployed above 230 KEAS,the drag chute pivot pin is designed to fail,resulting in the chute being jettisoned.

Approximately one second after the CDR orPLT presses the ARM 1(2) and DPY 1(2)pushbuttons simultaneously, the pilot chutedeploys. Within one second, the pilot chuteextracts the main chute which deploys to its 40percent reefed diameter. After about 3.5seconds of reefed deployment, two cutterssever the reefing ribbon allowing the mainchute to inflate to its full 40 foot diameter.

WARNING

Deployment of the drag chute between 135and 40 ft AGL can cause loss of control ofthe vehicle. Drag chute jettison must beinitiated immediately to prevent loss of thevehicle and crew.

For pre-derotation deployment, anunreefed chute will produce a large nosepitch-up moment for a vehicle mass mo-ment 1.53 million foot pounds. The largepitch-up may produce handling difficultiesfor the crew that could lead to loss of thevehicle and crew.

7/30/2019 214 - Landing Gears

14/17

At 60 (20) KGS, the drag chute will bejettisoned. Below 40 KGS, if drag chutejettison has not been initiated, the chute willbe retained until the orbiter has stopped tominimize damage to the main engine bells.

Brake Controls

The BRAKES MN A, MN B, and MN Cswitches are located on panels O14, O15, andO16. These switches allow electrical power to

brake/anti-skid control boxes A and B. TheANTISKID switch located on panel L2provides electrical power for enabling theanti-skid portion of the braking system boxesA and B. The BRAKES MN A, MN B, andMN C switches are positioned to ON tosupply electrical power to brake boxes A andB, and to OFF to remove electrical power. The

ANTISKID switch is positioned to ON toenable the anti-skid system, and OFF todisable the system.

When weight is sensed on the main landinggear, the brake/anti-skid boxes A and B areenabled and brake isolation valves 1, 2, and 3are opened permitting the main landing gear

brakes to become operational.

BRAKES Switch on Panel O14

BRAKES Switch on Panel O16

BRAKES Switch on Panel O15

ANTISKID Switch on Panel L2

The main landing gear brakes controlled bythe commander's or pilot's brake pedals arelocated on the rudder pedal assemblies at thecommander's and pilot's stations. Pressure onthe toe of the adjustable brake/rudder pedalsresults in a command to the wheel brakingsystem.

Each brake pedal has four linear variabledifferential transducers. The left pedal trans-ducer unit outputs four separate brakingsignals through the brake/skid control boxes

7/30/2019 214 - Landing Gears

15/17

for braking control of the two left mainwheels. The right pedal transducer unit doeslikewise for the two right main wheels. Whenthe brake pedal is deflected, the transducerstransmit electrical signals of 0 to 5 volts dc tothe brake/anti-skid control boxes.

If both right pedals are moved, the pedal withthe greatest toe pressure becomes the control-ling pedal through electronic OR circuits. Theelectrical signal is proportional to the toe pres-sure. The electrical output energizes the mainlanding gear brake coils proportionately to

brake pedal deflection, allowing the desiredhydraulic pressure to be directed to the mainlanding gear brakes for braking action. The

brake system bungee at each brake pedalprovides the artificial braking feel to thecrewmember.

Nose Wheel Steering

GPC Mode

The NOSE WHEEL STEERING switch on panelL2 positioned to NWS 1(2) enables the corre-sponding NWS (avionics) system. In additionto the NWS mode selections of the switch, theFLIGHT CNTLR POWER switch on panel F8must be positioned to ON, and the flightcontrol system ROLL/YAW CSS pushbutton onpanel F2 or F4 must be depressed to enable the

GPC for nose wheel steering. When eitherpushbutton is depressed, a white lightilluminates the pushbutton.

NOSE WHEEL STEERING Switchon Panel L2

When the commander or pilot makes an inputto the rudder pedals in the NWS 1(2) mode,the rudder pedal command position isappropriately scaled within the GPC's soft-ware and transmitted to a summing network,along with lateral accelerometer inputs fromwithin the flight control system. The acceler-ometer inputs are utilized to prevent anysudden orbiter lateral deviation. From thissumming network, a nose wheel steering

command is sent to a comparison network, aswell as to the steering servo system.

ROLL/YAW CSS Pushbutton on Panel F2

NWS FAIL Light on Panel F3

7/30/2019 214 - Landing Gears

16/17

Steering position transducers on the nosewheel strut receive redundant electricalexcitation from the steering position amplifier,which receives redundant electrical powerfrom data display unit 2.

Each of the three transducers transmits nosewheel position feedback to a redundancymanagement mid-value-select software. Itthen transmits a nose wheel position signal tothe comparison network. The orbiter nosewheel commanded and actual positions arecompared for position error and for rates toreduce any error. Absence of an error

condition will allow nose wheel steering to beenabled after WOW, WONG, and theta lessthan 0 are sensed in the software. The enablesignal permits hydraulic system 1(2) pressureto be applied to the nose wheel steeringactuator via the NWS switching valve. If

hydraulic system 1 is lost, hydraulic system 2provides the pressure for nose wheel steering.If both systems' pressures drop belowapproximately 1,325 psi, the actuator remainsin the caster mode and a failure isannunciated to the NWS FAIL C/W yellowlight on panel F3.

7/30/2019 214 - Landing Gears

17/17

Landing/Deceleration System SummaryData

The orbiter has the capability of landing ona runway using a conventional type oflanding gear system. Once the orbiter

touches down, the crew begins braking andsteering operations.

The landing gear consists of a nose landinggear and a left and right main landing gear.Each landing gear includes a shock strutwith two wheel and tire assemblies.

The nose wheels are co-rotating through acommon axle, whereas the main gearwheels rotate independently.

Each of the four main landing gear wheels

has electrohydraulic brakes and an anti-skid system. Each gear wheel brakeassembly is supplied with pressure fromtwo different hydraulic systems. Systems 1and 2 are the primary hydraulic systemsfor brake pressure; system 3 can back upeither or both systems.

Redundant electrical heaters are installedon the main landing hydraulic flexible lineslocated on the back side of each mainlanding gear strut between the brakemodule and brakes.

The orbiter nose wheel is steerable afternose wheel touchdown at landing.

ANTI SKID FAIL and NWS FAIL cautionand warning lights are located on panel F3.

Landing/deceleration controls are locatedon panels F6, F8, R4, L2, F2, F4, A12, O14,O15, and O16.

Landing/Deceleration System Rules ofThumb

Landing gear should not be deployed atequivalent airspeeds greater than 312knots.

1 knot of touchdown speed correspondsto 90 feet of distance. This is oftenrounded up to 100 feet for convenience.