AVIM 103D Landing GearAVIM 103D Landing Gear

Course Outline

• Landing gear

– Types

– Configurations

– Alignment

• Suspension systems

– Fixed gear

– Retractable

Course Outline• Retraction systems

• Steering systems

• Brakes– Dependent systems– Dependent systems

– Independent systems

– Anti-skid control

• Wheel assemblies

• Tires

Safety

• Shock strut servicing

• Gear retraction and extension

• Shimmy damper service• Shimmy damper service

• Tire servicing and dismounting

• Eye and skin protection

Safety

• Caustic fluids

–Burns skin

–Damages surfaces–Damages surfaces

• Flammable fluids

• Fluid contamination

– Leave containers closed

– Read labels, use proper handling equip.

Safety

• Retraction can crush you if you are in

the path of the gear

• Retraction without proper support can • Retraction without proper support can

destroy an aircraft as well

Landing Gear Purposes

• Supports the aircraft on the ground

• Absorbs landing shock (some)

• Absorbs taxi shock (some)

• Attachment point for:• Attachment point for:

–Brakes

–Steering

–Wheels and tires

Conventional Gear

Defn: Wheel Pants

• The tapered tail end of the pant provides the

major part of aerodynamic drag reduction

Defn: Cowlings & Fairings

• A shielded section that provides

aerodynamic smoothness to some area or

part of the aircraftpart of the aircraft

Defn: Wheel Base

The distance from the front

axle line to the rear axle lineaxle line to the rear axle line

Conventional Gear (Tail-Dragger)

Jodel d140c

C150 Tail Dragger Conversion

Older design – C.G. aft of main gear

• Steering:

– Rudder pedal cable connection to tail wheel

– Brake application and castering tail wheel

Conventional (Tail Wheel) Arrangement

– Differential braking to assist steering

• Tail wheel as far aft as possible to extend wheelbase and increase stability.

Advantages

• Prop clearance for low powered engines

• Sturdy design for unimproved runways

• Less drag in flight

Conventional (Tail Wheel) Arrangement

• Less drag in flight

• Greater ground maneuverability

• Tail wheel failure = minimal aircraft damage

Conventional (Tail Wheel) Arrangement

Disadvantages

• Ground loop and nose-over potential

• Crosswind control problems

• Restricted visibility during taxi• Restricted visibility during taxi

Tricycle Gear

• Nose gear as far forward as possible

– Longer wheelbase – more stable

– Lighter gear assembly due to longer lever arm

• Castering types use differential braking to steer

Tricycle (Nose Wheel) Arrangement

• Castering types use differential braking to steer

Tricycle (Nose Wheel) Arrangement

Main gear aft of C.G.

Advantages

• Difficult to nose over or ground loop

• More familiar ground maneuverability• More familiar ground maneuverability

• Better visibility during taxi

• Less vulnerable to cross wind landing

• Steering:

– Direct linkage with nose wheel bungee

– Hydraulic nose wheel steering

– Differential braking

Disadvantages

• Nose gear damage = major airframe damage

• Generally not suited for unimproved runways

• More expensive than conventional gear

Tricycle (Nose Wheel) Arrangement

• More expensive than conventional gear

• Much heavier aircraft

Nose Wheel Ski

Skis• Ski systems are usually pivot mounted to

the aircraft wheel axle

– incorporate travel limit straps or cables (front

and rear)and rear)

– usually have a bungee or spring to keep the

nose up, preventing pearling during landing

• May be retractable (skis retract higher then

bottom of wheel assemblies)

Skis• Auxiliary gear, nose or tail, may or may

not have a ski

• Are subject to corrosion damage and

hard landing damagehard landing damage

Floats

Floatplane Configurations

• Floats

• Amphibious floats – wheels and floats

• Hull floats – bottom of aircraft = boat

• Outrigger pontoons• Outrigger pontoons

– Hang from wing tips or struts

– Fold down from wing tips

Float/Hull/Pontoons

• Most common are dual float assemblies

• Usually are uniform shape

• May have retractable, and or steerable

N

• May have retractable, and or steerable

rudder assembly

• May require a vertical vane installed on

lower side of fuselage below vertical

stabilizer

Float/Hull/Pontoons• Almost all water aircraft use a float shape that

includes a chined V hull

• They usually have a stepped section that assists

the aircraft in planing across the water (reduces

N

the aircraft in planing across the water (reduces

water drag)

• Flying CG and floating CG may not be the same

– some hull planes have self flushing ballast sections

/ wheel well sections

Float/Hull/Pontoonsbasic shape

Step

Chine

Tandem Wheel ArrangementAircraft with narrow fuselage

• Gear positioned directly beneath fuselage

Tandem Wheel Arrangement

• Gliders

• U-2

• AV-8 Harrier

N

• AV-8 Harrier

• Usually has one main set of gears in center, one steerable nose gear, and outrigger gears on the wings

• Can be fixed or retractable

Tandem Wheel Arrangement

CG

CP

Tail Gear

Main Gear

Gear Types• Fixed Gear

– Popular on older and low speed aircraft

– Speed and fuel efficiency increase with pants

Efficiency increased by 4-5 knots

Fixed Gear

• Are not able to retract into some cavity

or aerodynamic shielding within the

aircraft

• May be fully rigid or able to absorb

landing / taxi loads

Fixed Gear• Are usually lighter and less complex

than retractable gear aircraft

• Have overall lower purchase and operating costs than retractable gearoperating costs than retractable gear

• The benefits from lighter weight can exceed the benefits of reduced drag from retractable gear

• Are subject to corrosion damage and hard landing damage

Retractable Gear

• Streamlines aircraft reducing drag

• More complex and heavier than fixed gear

• Retraction methods:

– Mechanical– Mechanical

– Electrical

– Hydraulic

Retractable Amphibious

Retractable Amphibious

Truck

Four wheel arrangement

Bogie

Two wheels or more

Anatov AN 225

Trailing Link landing Gear

B747-8 Landing Gear Ship Set

Skid Landing Gear

• Used on helicopters that do not ground taxi

• High skids and pop-out floats available

• May or may not have shock absorbing devices

• May or may not have skid pads (stellite faced)• May or may not have skid pads (stellite faced)

• Left skid / nose low wear pattern

• Loose skids may cause

– Vibration

– Ground resonance (fully articulated rotor)

Skid Landing Gear

• May have detachable wheel assemblies for ground

handling

• Are also found on early aircraft in place of the tail

wheel assemblywheel assembly

– Wooden skid with brass or steel plate for hard surface

or leather plate for grass

Pop Out Floats

Pop Out Floats

• Spring Steel Gear - Cessna Type

Load transfer only• Load transfer only

• Minimal rebound protection

• Generally not field repairable

• Serialized Cessna component

• Check Cessna maintenance manual table of

limits for alignment data

• Tubular Steel Nose Gear – Grumman TR2

• Load transfer only

• Minimal rebound protection

• Sometimes field repairable by welding

• Some have bungee shock cord

Wheel Alignment

• This is much more critical for tail draggers.

• The aircraft should be level and the wheels should be on some form of grease plates to eliminate gear binding.eliminate gear binding.

• The aircraft should be located inside where it is not subject to winds.

• Adequate measuring equipment should be available.

Toe in / out• Toe = the distance between the front of the

tires and the back of the tires.

• The best means to measure this is to project

lines out to a distance and calculate to the

specifications. specifications.

• Toe-in is front of tires in,

• Toe-out is front of tires out IN

OUTfront

back

front

back

Camber (- +)

• Camber = the distance between the top of

the tires and the bottom of the tires.

• This can be seen using a large square. • This can be seen using a large square.

• Positive is top of tires out.

• Negative is top of tires in.-

+top

bottom

top

bottom

Castor

• Castor = only really applies to a wheel

assembly that turns or steers.

• It is the measure of the angle that the

pivoting axis tilts front or back. pivoting axis tilts front or back.

• This is similar to the concept of rake used on

single strut assemblies such as nose

gears or motorcycles.

Inclination and Offset

• Steering inclination = is similar to castor but it is the measure of the angle between the pivot axis and the vertical axis of the wheel with no camber.the vertical axis of the wheel with no camber.

• Trail or offset = The amount of distance between the wheel axis and the steering axis.

Wheel Alignment Adjustment

• Some may be adjustable

by shimming the stub

axle at the mounting axle at the mounting

flange

Wheel Alignment Adjustment

• Some may be

adjustable by

shimming the shimming the

torque links at the

center pivot

Wheel Alignment

• The aircraft must be located on a flat smooth

surface, resting on grease plates, leveled as

per manufacturer's procedureper manufacturer's procedure

• First determine the landing gear are properly

mounted and not damaged or distorted

– Damage and conformity inspection, symmetry

checks, etc

Wheel Alignment

• Several methods for checking toe:

–Straight edge and a large square

–Scribe and a measuring tape or bar–Scribe and a measuring tape or bar

–Line of sight projection to a reference

Straight edge and a large square

Scribe and a measuring tape or bar

Line of sight projection to a reference

Note: Reference line

Ref. line

Note: Reference line

must be parallel to the

main wheel axle line

Axle line

Camber• Is checked using a ruler and a level

Undamaged

Cessna 182

nose wheel

assembly and

firewall

Damaged

landing gear

attachment

and buckled

firewall

Wheel alignment of an

oleo strut is adjusted by

adding or removing

shims from between shims from between

the arms of the torque

links.

Scissor Link Disconnected

END

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