Exam 2 Big Review Flashcards
What are the two types of constant RPM generators
CSD and IDG
output for constant rpm generators
voltage 115V AC
Frequency 400 Hz
What is the CSD
constant speed drive
installed between variable speed engine and constant speed generator
older aircraft
what is IDG
integrated drive generator
generator and speed control in one unit
IDG advantages
reduces weight and size
higher rpm and higher power output
higher alternator speed
improved cooling features
similarities of CSD and IDG
line replaceable units
both use oil / share oil with AC generator
(generator uses oil for cooling
CSD uses oil for operating the hydraulic transmission)
Variable RPM generator outputs
115 V AC
Hz may change
VSCF - 400 Hz
VSVF - changes
VSCF advantage
no CSD
smaller/lighter
more versatile installation
VSCF disadvantage
low power output
not as proven long term
VSVF advantage
no CSD or IDG
high power output
AC frequency made constant as needed during power distribution
parallel bus
electrical load shared equally by all working generators
connected by syncing bus
can be labor intensive for flight engineer
is apu operable on a parallel bus
not flight operable
ground only
split bus
generator powers one main AC bus
two generators can never power same bus
by closing breakers, one generator can power busses
are APUs operable in split bus
most are
split parallel power system
safer
parallel - normal operations
split - isolated during malfunction
split systems breaker closed during normal flight (connects left and right side busses/generators)
Split bus aircraft
A-320
A-310
B747
B777
B737
what is a RAT
ram air turbine
backup power source providing limited electrical if all engines are lost
Static inverter
most critical AC power source
changes DC to AC with battery power
must be checked each night
A/C with parallel bus
B727
early B747
purpose of nitrogen generator
removes oxygen from system to avoid potential fires or extinguish fire
B787 electric replacements
electric starters
cabin air conditioning
pressurization
motor driven hydraulic actuators
electro/hydraulic control surface actuators
nitrogen generation system
transformer rectifier
aircraft with split parallel
modern B747
What is fluid power
transmission and conversion of power using a fluid
Gas vs Liquid fluid power
Gas: compressible, low efficiency
Liquid: non compressible, high efficiency
Boyle’s Law
PV/T = PV/T
Pascal’s Law
when a force is exerted on a confined fluid, the resultant pressure is transmitted equally in all directions
force can be transmitted to remote units without significant energy loss
What is unit pressure
force on one unit of area (PSI)
stroke
distance piston moves in a cylinder (in)
volume
quantity of fluid contained (in^3)
Principle of fluid power
F=PA
force = pressure x area
V=AL
volume = area x length
Mechanical advantage
amount by which applied effort is multiplied in output of device
net gain in force by sacrificing movement
how does mechanical advantage work
F/A = F/A
the lifting force of a hydraulic jack is amplified directly by the ratio of the surface area of the two pistons
if two cylinders are connected by an incompressible fluid, and a given amount of pressure is applied to one cylinder, that same pressure is imparted to the second cylinder through the fluid connecting them. However, because pressure is equal to force per unit area, the cylinder that has a larger area will experience a force multiplication effect. Even though the pressure on both cylinders is the same, the force which is produced on the larger cylinder will be higher, proportionally higher based on the area of the cylinder.
Desired properties for hydraulic fluid
low viscosity
stable structure in all temperatures (don’t want different viscosity at different temperature(
high flash and fire point (don’t want vapors igniting)
High chemical stability (resist oxidation and deterioration)
Vegetable fluid
castor oil and alcohol
blue-blue green
extremely flammable
Mineral fluid
petroleum distillate
red
flammable
uses synthetic rubber seals
synthetic fluid
phosphate ester
(skydrol)
used for high pressure/temperature applications
anti-fire/low flammability
damaging to skin, wiring, paint, lungs….
rigid tubings
high pressure but non moveable components
flexible hose
medium pressures, deal with vibration/movement
aluminum fittings
low/medium pressure application
steel fittings
high pressure application
what seals used for synthetic fluid
Butyl seals
hydraulic filter purpose
remove particulate contamination
dirt is deadly :)
if a hydraulic filter is clogged….
typically bypass valve allows fluid to bypass if clogged
hydraulic reservoir purposes
primary: supply fluid to pumps and system components
secondary: thermal expansion, air purging, filtration and sediment, cooling
non pressurized reservoir
vented to atmosphere to let air dissipate
smaller aircraft
pressurized reservoir
higher altitude aircraft
minimizes foaming
hydraulic accumulator
stores hydraulic fluid under pressure
back up or intermittent loads
hydraulic pump
supplies fluid flow to actuating units
provides pressure to overcome system resistance
engine driven pump
active when engine is running
transport aircraft
good for large / constant need systems
electric pump
single use tasks
(landing gear)
lighter aircraft
big aircraft / airline hydraulic preflight checks
again I need to find this elsewhere
pressure relief valves
protect system from damage due to pressure build up
check valve
permits flow in only one direction
4 way selector valve
moves actuators in two directions
3 way selector valve
used if flow is required to move in one direction
2 way selector valve
controls flow on and off
actuating device purpose
convert fluid flow to mechanical motion
linear or rotary
trunnion
attaches landing gear assembly to airframe
pivots during extension and retraction
shock strut
vertical member that contains air-oleo shock absorber
truck / pivot fork and shaft
used when wheels are in tandem
tilts fore and aft with attitude
torque arm
connects shock strut to truck
restricts extension of shock strut during gear retraction
holds wheel and axle in alignment with shock strut
drag / side brace
stabilizes landing gear assembly
shock strut
supports weight of aircraft
absorbs / displaces landing loads
oleo strut
fluid acts to absorb shock of compression
slows strut collapse as fluid passes through
energy returning strut
spring steel landing gear
returns energy back to aircraft
aircraft wheel construction
split in 2 halves
halves held together by tie or through bolts
held on by single nut
tube type tire
needs inner seal
not seen with aircraft
tubeless type wheel
inflation valve into wheel half
o-ring seal between wheel halves
what safety feature due tubeless wheels have
fuse plugs to blow out and release tire pressure in event of overheat/temperature melts threads
important wheel preflight check
cotter pin retaining axle nut
what data is on the wheel data plate
part number
TSO number (approved AC part)
size tire accepted
manufacturer
torque value for tie bolts
brake purpose
employs hydraulic pressure
holds wheels locked for parking
independent brake system
individual master cylinders connected to reservoir or self contained
semi-rigid / flexible fluid lines
wheel cylinders to apply brake action
Integral power brake system
typically on transport aircraft
main system hydraulic pressure for braking
drum and shoe brake
older
drum rotates
shoes stationary
H. pressure presses shoe against drum
not great at dissipating heat
single disk brakes
small aircraft
better at dissipating heat than drum
multiple disk brakes
larger aircraft, heavy duty
more surface area = better friction = better braking
segmented rotor brakes
modern
better dissipating heat
what happens if air gets into hydraulic system
air compresses and energy input does not get transmitted to wheels
if air gets into hydraulic system -
can bleed the hydraulic system to get the air out
preventative maintenance
Cleveland type brake
piston actuates pucks on either side of disk brake to fixed disk
Goodyear type brake
disk is floating
how does the master cylinder work
has flexible hoses that run to caliper and sends hydraulic fluid
multiple disk issues
heat fires
heat build up prevents effective braking
indicator pin
how much material has been used - shows wear on brakes
