18. Landing Gear Description

7/28/2019 18. Landing Gear Description

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Rev. A Sept. 18, 2007 18-1

Landing Gear

General Description: The S-64F landing gear is a non-retractable type with a right andleft main landing gear strut and a nose landing gear with a parking lock. Wheel brakesare mounted on the main gears for holding the aircraft still on uneven surfaces. Thelanding gear consists of the following subsystems

a. Main landing gear strut

b. Nose landing gear strut

c. Wheels and brakes Position and warning subsystem

d. Tail Skid

Main Landing Gear Strut Description: The main landing consists of two main gearstruts mounted to the side of the fuselage that support the helicopter while it is on theground. The main landing gear consists of the following components:

a. Strut and fork assembly

b. Torque arms

c. Schrader valve

Main Landing Gear Strut Component Description

Strut and Fork Assembly: The strut and fork assemblyconsists of the following parts:

a. a cylinder

b. a strut piston attached to

c. a fork,

d. a floating piston

e. a metering pin and orifice

f. a Schrader valve

g. a plug

h. and torque arms

The piston acts as a shock.

The fork houses the axle.

The floating piston separates the hydraulic fluid from the nitrogen charge.

The metering pin and orifice control the vertical movement of the piston.

The plug permits filling the strut with hydraulic fluid.

In normal flight the strut is held in the extended position by nitrogen pressure in

the strut and the weight of the wheel and brake assemblies.

As the wheels contact the ground, the hydraulic fluid moves up with the strutpiston, but must go through the orifice, slowing down the piston in its upward stroke. Asthe tapered metering moves down through the orifice, the hydraulic fluid is furtherslowed down, causing a slower upward movement of the piston.

Torque Arms: The torque arms are bolted to the cylinder and to the piston. Theseparate torque arms a bolted together to form a joint.


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The torque arm allows vertical movement, but prevents swiveling of the piston inthe cylinder. Three lubrication fittings are installed in each torque arm.

Schrader Valve: The Schrader valve is a high pressure charging valve located at thelower end of the main landing gear strut piston.

The Schrader valve permits charging the strut with nitrogen.Servicing instructions:

A/C on Jacks: Open Schrader valve and bleed all nitrogenfrom strut. Remove cover on top of strut. Remove filler porton top of strut.

Bottom the floating piston, using a hand pump, or along drift.

Remove pressure line to filler and fill with hydraulicfluid to level with the filler cap.

Replace servicing cap and cover.

Service with nitrogen to 270 psi.

Nose Gear Strut Description: The nose gear strut is a nonsteerable type oleo strut mounted to the front of thehelicopter to support the helicopter on the ground. The noselanding gear strut consists of the following components:

a. Strut housing

b. Strut assembly.

c. Torque arm

d. Schrader valve

e. Locking device housingf. Nose landing gear locking device

g. Spring Cylinder

h. Centering cylinder

i. Shimmy damper

Nose Gear Strut Component Description

Nose Landing Gear Strut Housing: The nose landing gear is attached to the fuselageby four bolts that pass through the housing structure. The cylinder, to which thecentering cylinder is connected, contains the lower bearing and spacer. This prevents

the orifice from bottoming on the bearing during full extension of the gear while in flight.The centering cylinder provides a positive trail position of the gear during flight.

Torque arms connect the strut with the cylinder. The nose wheel is locked in the trailingposition by a spring locking lever. The locking action is engaged or disengaged throughlinkage to the cockpit.


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Nose Landing Gear Strut Assembly: The strut and forkassembly consists of:

a. a cylinder,

b. a strut piston attached to

c. a fork,

d. a floating piston,

e. a metering pin, an orifice

f. a Schrader valve,

g. a plug, and

h. torque arms.

The piston acts as a shock.The fork houses the axle. Thefloating piston separates thehydraulic fluid from the nitrogen

charge. The metering pin andorifice control the verticalmovement of the piston. TheSchrader valve permits chargingthe strut with nitrogen and the plugpermits filling the strut withhydraulic fluid. As the wheelcontacts the ground, on landing, thehydraulic fluid moves up with thestrut piston, but must go throughthe orifice, slowing down the piston in its upward stroke. As the tapered meteringmoves down through the orifice, the hydraulic fluid is further slowed down, causing aslower upward movement of the piston.

Torque Arms: The torque arms are bolted to the cylinder and to the piston. Theseparate torque arms a bolted together to form a joint. The torque arms allow verticalmovement, but prevent swiveling of the piston in the cylinder. The torque arms arereached through the nose wheel door.

Schrader Valve: The Schrader valve is a high pressure charging valve located at thelower end of the nose strut piston. The Schrader valve permits charging the strut withnitrogen.

Locking Device Housing: A locking device housing is installed to provide support forthe shimmy damper and a connection point for the nose wheel centering cylinder.

It is keyed to the top of the strut cylinder.

The housing device contains mounting provisions for the roller and the bumperthat are parts of the nose landing gear parking lock.


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Nose Landing Gear Locking Device: The nose landing gear locking device consistsof:

a. a spring cylinder,

b. lever arm,

c. support arms,

d. cam spacers and

e. rollers.

The spring cylinder provides tension through cam action on the lever armattached through a linkage to the nose landing gear housing.

The lever arm engages the roller mounted on the locking housing, locking thestrut.

Cam and spring cylinder action absorb any shock on the locking mechanism ifthe nose wheel attempts to turn while locked.

A control handle on the right aft side of the center console, when pulled out,releases the locking lever this action locks the nose gear in the trail position.

The locking lever is disengaged by pressing the button on the handle andpushing the handle all the way in.

Spring Cylinder: The spring cylinder is a part of the nose gear parking lockmechanism and consists of:

a. an outer cylinder,

b. a cylinder base,

c. a link, and

d. a spring assembly.

The spring assembly contains:

a. an inner cylinder,

b. a series of spring washers,

c. two disks, and

d. a nut.

The spring cylinder dampens any violent movement of the locking mechanism when it isin the locked position, yet allows the locking mechanism to release during overload toprevent damage to the nose gear.


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Centering Cylinder: The nose wheel centering cylinder is a pneumatic unit andconsists of:

a. an outer cylinder

b. inner cylinder,

c. piston,

d. rod end, and

e. Schrader valve.

The cylinder is serviced to 125 psi and holds the nose landing wheel in trailingposition for flight and landing operations. The cylinder is reached through the nosegear door.

Shimmy Damper: The viscous shimmy damper controls nose landing gear wheelvibrations during take off, landing, and taxiing. The damper is an annular shaped unitinstalled at the top of the nose landing gear. It is reached through the nose landinggear door.

Energy Absorption Fuse: The energy absorption fuse is a safety device to prevent toomuch of a pressure surge in case of a hard landing.

A fuse is installed in the hydraulic line to each main landing gear and is mountedon the aft side of the landing gear support.

When a sudden pressure surge occurs due to hard landing, a piston in the fusebreaks the shear pin and moves forward to allow the fluid in the line to exhaust torelieve pressure.

Relief Valve: The relief valve is mounted on the hydraulic panel. The relief valverelieves excessive pressure caused by thermal expansion when the helicopter is

jacked.


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Landing Gear Wheels and Brakes Description The wheel brake system is a masterpower boost type system consisting of:

a. Master power boost cylinder

b. Parking brake valve

c. Shuttle valves

d. Brake assembly

e. Main Gear Wheel and Tire

f. Nose Gear Wheel and Tire

The brakes are actuated by the toe portion of the rudder pedals. The brakeshold the aircraft still on uneven surfaces

Landing Gear Wheels and Brakes Component Description

Master Power Boost Cylinder: The master power boost cylinders are connected toeach toe brake pedal by mechanical linkage. The cylinder increases braking pressureby acting as a primary mechanically operated hydraulic cylinder as initial brake action is

applied.

As foot pressure is increased, utility system pressure provides boost within thecylinder, increasing pressure to the main wheel brakes. The cylinders are locatedbelow the cockpit floor.

Parking Brake Valve: Theparking brake valve is a dualunit with internal sequencevalves. When actuated, thesequence valves trap pressureto the brakes.

They also providethermal compensation.

The parking brake valveis mechanically controlled bythe parking brake handle on thecenter console.

Shuttle Valves: The shuttlevalves are mounted on thecockpit floor structure next tothe left pilots master power

boost cylinders.They prevent

simultaneous brake applicationby both pilots.


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Brake Assembly: The wheel brake assembly is a single disc brake. The housing isbolted to the axle flange and the disc is keyed to the wheel in such a manner that it ispermitted to float laterally. Friction is produced when the linings on the face of thepistons are pressed against the disc

Main Gear Wheel and Tire: Four each. Two per axle. Each tire is a 8.5 x 10 tubeless,12 ply type 3 helicopter tire. Each wheel is a split rim type containing roller bearings, anSchrader valve, a hub cap and a retainer.

Nose Gear Wheel and Tire: The nose wheel consists of a tubeless tire and a bearingmounted aluminum split rim. The tire is an 8.5 x 10, 12 ply rating tubeless helicoptertire. The wheel is mounted to the nose landing gear axle.

Landing Gear Wheels and Brakes Theory of Operation When the pilot appliespressure to the toe portion of the tail rotor control pedals, mechanical linkage positionsthe master power boost cylinder directing metered utility system pressure to the brakeassembly on the main landing gear.

Initial pressure on the toe brake pedals supplies manually developed hydraulicpressure to the wheel brakes. Continuation of pressure on the pedals causes the utilityhydraulic system pressure to supplement the manually developed pressure through thepower boost cylinders.

The utility hydraulic system supplies 1500 psi pressure to operate thehydraulic power boost portion of the brake system.

To park, the brake pedals are held down and the parking brake valve handle ispulled up to the park position and the pedals released. The latching pins on the parkingbrake valve locks the valve and handle in the parked position.

The caution advisory panel light marked PARKING BRAKE ON will illuminate,indicating that the parking brake valves are in the parked position.

To release the brakes, (HOLD UP ON THE HANDLE), depress the brake pedalsand move the handle SLOWLY to the off position.

The brakes should always be parked with boosted pressure for the best brakingaction and proper thermal compensation.

Tail Skid Subsystem Description: The tail skid system is located at the base of thepylon and protects the aft empennage and pylon during abnormal landings. The tailskid system consists of the following components:

a. Strut and Knee

b. Brace

c. Fork.

The tube connects the male knee to the shock strut. The shock strut absorbsimpact loads that may occur on an abnormal landing.

The shock strut is a pneumatic-hydraulic cylinder containing a floating piston thatseparates the air from the hydraulic fluid, a damper that regulates the flow of hydraulicfluid during ground contact, and spacers in the piston and cylinder to limit the stroke ofthe strut.


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Brace: The brace consists of two tubes with end fittings. The brace is bolted to thebottom of the pylon and positions the bottom of the strut and knee.

Fork. The fork connects the strut and knee assembly to the fuselage at the bottom of

the pylon.

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18. Landing Gear Description