tyres wheels and braking Flashcards
tyre parts
-casing (Rubberized fabric plies) carcass
-outer covering(abrasion resistant rubber tread)
-tubeless or tubed (creep marks to show if tyre is moving)
two types of tyre
cross ply, bias: (hash marked, traditionally in aviation)
most are suitable for retreading many radials are not
radial (Getting more popular) plies go in one direction
less plies and thinner sidewall
radial loads transferred to the wheel by pressure rather than through the sidewall
claim to provide more landing per tyre
structural components
tread: the wearing surface to provide traction
bead: embedded wire to anchor carcass and provide firm mounting on a wheel
flippers/turn ups; layers of rubber and fabric around beads to insulate the carcass from the bead wire to prolong tire life.
apex strips: Rubber streamline shape strips around beads
carcass: rubber bonded cord structure of tyre integral with the bead which provides the requisite strength to carry the load
chafers: wrap around the end of carcass plies and beads prevents fitment damage
breakers: fabric plies under the tread to reduce shocks by spreading forces and prevent carcass from direct damage
belts: circumferential plies between the carcass and the tread reinforcement to add strength to tread area
sidewall: rubber covering area extended from the tread down to the bead area to protect carcass
retreading
most can be re treaded up to 10 times
inflation pressures
under 40 psi: unimproved low strength soil surface and rough terrain
40 to 75 psi: suitable for improved airfields
75 to 125 psi: suitable for unlimited operation from improved surface runways such as asphalt and concrete for larger A/C
over 125 psi: unsuitable for high A/C in relation to runway surface damage, tyre life, safety during inflation
wheel material
magnesium alloys: low weight and stiffness
aluminum alloys (current type): higher strength and size reduction around rim, allows bigger air gap between brake and wheel
higher corrosion resistance
heat dissipation not a problem in light aircraft.
main wheel structure
-tapered roller bearings press fit into housings
-grease seals held by snap rings
-fusible plugs installed in jet aircraft main wheels for releasing high pressure produced by heat from heaving braking
-bearing seals felt or rubber stop dust getting in and grease escaping
basic brake designs
drum brakes: first type used
circular shoes and inflatable tube pushes many shoes into back plate springs retract shoes
or pistons push two shoes into back plate springs retract
disc brakes: most common now
non rotating friction pads are forced against rotating steel discs (sometimes ceramic or carbon friction pads)
disc rotates with wheel (keyed moves in and out caliper stuck, bolted is stuck caliper moves)
way to operate brakes
mechanically
pneumatically
hydraulically (most common)
electric
disc brake advantages
better performance with less weight
better heat dissipation
visual inspection possible
less maintenance
easier to repair
self cleaning
unaffected by water
three brake systems (all hydraulic)
independent: most light AC
self contained hydraulic system
hydraulic pressure directly proportional to force applied by pilot by depressing piston inside a master cylinder
boosted: adds extra hydraulic pressure in addition to pilot force. works similar to independent
power: brakes actuated from main hydraulic system. strength calculated from pilot pressure but not proportional.
