Aircraft Hydraulics Unit 3 Test Study Guide

Bias Tire

Plies run at 30°–60° to direction of rotation

Radial Tire

Plies run at 90° to direction of rotation

Tube-Type Tire

Uses an inner tube to hold air

Tubeless Tire

Has inner liner to hold air; marked “tubeless”

Type III Tire

Low pressure tire used on GA aircraft under 160 mph; wide for cushioning

Type VII Tire

High pressure tire used on larger aircraft

Type VIII Tire

Very high pressure tire used on high-performance jets

Ribbed Tread

Most common tread on GA aircraft

Diamond Tread

Used on unpaved runways

Chine Tire

Deflects water away from engines on nose wheels

Overinflated Tire Wear

Wears in the center of the tire

Underinflated Tire Wear

Wears on the shoulders of the tire

Hydroplaning

Loss of traction on wet runway causing rubber reversion

Chevrons

Groove wear pattern; remove if extending across grooves

Chunking/Cutting

Tire damage; remove if deep enough to reach plies

Carcass Damage

Visible fabric; tire must be removed

Two/Three-Piece Wheel

Wheel made of multiple halves bolted together

Tubeless Wheel Feature

Seal between wheel halves

Fusible Plug

Melts at high temperature to release air and prevent explosion

Causes of Overheating (Fusible Plug)

Excess braking, low tire pressure, frozen bearings

Dye Penetrant Inspection

Used to detect cracks in wheel halves

Eddy Current Inspection

Used on bead seat area of wheel

Magnetic Particle Inspection

Used on wheel bolts

Wheel Bearings

Tapered roller bearings requiring cleaning and regreasing

Galling

Surfaces weld together due to friction

Spalling

Flaking of metal from impact

Brinelling

Indentations caused by high loads

Blue Discoloration

Indicates overheating

Black Discoloration

Indicates water damage

Tricycle Gear

Center of gravity forward of main wheels

Conventional Gear (Tailwheel)

Center of gravity aft of main wheels; prone to ground loops

Rigid Landing Gear

Does not absorb shock; transfers load to airframe

Shock Absorbing Gear

Uses shock struts to absorb landing forces

Shock Strut

Main component that absorbs landing and taxi shocks

Trunnion

Attaches landing gear to airframe and acts as pivot point

Torque Links

Prevent rotation and maintain alignment of wheel

Side Strut

Provides lateral support to landing gear

Drag Strut

Provides longitudinal support to landing gear

Toe

Inward or outward angle of wheels relative to centerline

Camber

Tilt of wheels inward or outward

Shim Adjustment

Used to correct alignment angles

Mechanical Steering

Uses rods or cables for steering (small aircraft)

Hydraulic Steering

Uses actuators for steering (large aircraft)

Shimmy Damper

Prevents nose wheel vibration

Oleo Shock Strut

Uses air/nitrogen and hydraulic fluid to absorb shock

Metering Pin & Orifice

Controls flow of hydraulic fluid during compression

Air/Nitrogen in Strut

Absorbs taxi shocks

Hydraulic Fluid in Strut

Absorbs landing shocks

Flat Strut

Loss of air; no extension

Hydraulic Leak Effect

Causes hard landings

Shock Strut Servicing Order

Hydraulic fluid first, then air/nitrogen

Electrical/Mechanical LG System

Motor drives actuators using rods or cables

Hydraulic LG System

Pump provides pressure to hydraulic actuators

Uplock

Holds landing gear in retracted position

Downlock

Holds landing gear in extended position

Overcenter Link

Mechanical lock preventing gear collapse

Hydraulic Emergency Extension

Manual pump, CO2 blowdown, or gravity drop

Electrical Emergency Extension

Hand crank or gravity drop

Green Light

Gear down and locked

Red/Yellow Light

Gear unsafe or in transit

Squat Switch

Prevents gear retraction on ground (weight-on-wheels)

Throttle Switch Warning

Warns pilot if landing with gear retracted

Microswitch

Provides position indication

Proximity Switch

Detects gear position without contact

Limit Switch

Controls sequence of gear operation

Safety Pins

Prevent accidental landing gear movement

Landing Gear Inspections

Include greasing, shock strut servicing, and visual checks

What happens if a shock strut loses air?

Flat strut and rough taxiing

What happens if hydraulic fluid is lost in a strut?

Hard landing

Why are fusible plugs used?

To prevent tire explosion by releasing pressure

Difference between bias and radial tires?

Angle of plies

What does a squat switch do?

Prevents landing gear retraction on ground

What causes hydroplaning?

Water causes loss of traction and rubber reversion

Difference between toe and camber?

Toe is direction, camber is tilt

What locks landing gear down?

Downlock or overcenter link