AVIM 103D Landing Gear

AVIM 103D Landing Gear
Course Outline
• Landing gear
– Types
– Configurations
– Alignment
• Suspension systems
– Fixed gear
– Retractable
Course Outline
• Retraction systems
• Steering systems
• Brakes
– Dependent systems
– Independent systems
– Anti-skid control
• Wheel assemblies
• Tires
Safety
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Shock strut servicing
Gear retraction and extension
Shimmy damper service
Tire servicing and dismounting
Eye and skin protection
Safety
• Caustic fluids
–Burns skin
–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
destroy an aircraft as well
Landing Gear Purposes
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Supports the aircraft on the ground
Absorbs landing shock (some)
Absorbs taxi shock (some)
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 aircraft
Defn: Wheel Base
The distance from the front
axle line to the rear axle line
Conventional Gear (Tail-Dragger)
Jodel d140c
C150 Tail Dragger Conversion
Conventional (Tail Wheel) Arrangement
Older design – C.G. aft of main gear
• Steering:
– Rudder pedal cable connection to tail wheel
– Brake application and castering tail wheel
– Differential braking to assist steering
• Tail wheel as far aft as possible to extend
wheelbase and increase stability.
Conventional (Tail Wheel) Arrangement
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Advantages
Prop clearance for low powered engines
Sturdy design for unimproved runways
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
Tricycle Gear
Tricycle (Nose Wheel) Arrangement
• 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
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Main gear aft of C.G.
Advantages
Difficult to nose over or ground loop
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
Tricycle (Nose Wheel) Arrangement
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Disadvantages
Nose gear damage = major airframe damage
Generally not suited for unimproved runways
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)
– 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 damage
Floats
Floatplane Configurations
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Floats
Amphibious floats – wheels and floats
Hull floats – bottom of aircraft = boat
Outrigger pontoons
– Hang from wing tips or struts
– Fold down from wing tips
N
Float/Hull/Pontoons
• Most common are dual float assemblies
• Usually are uniform shape
• May have retractable, and or steerable
rudder assembly
• May require a vertical vane installed on
lower side of fuselage below vertical
stabilizer
N
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
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/Pontoons
basic shape
Chine
Step
Tandem Wheel Arrangement
Aircraft with narrow fuselage
• Gear positioned directly beneath fuselage
N
Tandem Wheel Arrangement
Gliders
U-2
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
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Tandem Wheel Arrangement
CG
CP
Main Gear
Tail 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 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
– 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
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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)
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 assembly
– Wooden skid with brass or steel plate for hard surface
or leather plate for grass
Pop Out Floats
Pop Out Floats
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Spring Steel Gear - Cessna Type
Load transfer only
Minimal rebound protection
Generally not field repairable
Serialized Cessna component
Check Cessna maintenance manual table of
limits for alignment data
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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.
• 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.
front
• Toe-in is front of tires in,
IN
• Toe-out is front of tires out back
front
back
OUT
Camber (- +)
• Camber = the distance between the top of
the tires and the bottom of the tires.
• This can be seen using a large square.
• Positive is top of tires out.
top
• Negative is top of tires in.
top
bottom
+
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.
• 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.
• 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
flange
Wheel Alignment Adjustment
• Some may be
adjustable by
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 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
–Line of sight projection to a reference
Straight edge and a large square
Scribe and a measuring tape or bar
Ref. line
Line of sight projection to a reference
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
the arms of the torque
links.
Scissor Link Disconnected
END
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