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
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