Exam 2 Flashcards
advantages of split bus system
one entire bus can fail with other systems operating normally
starter generator
one unit
direct drive (saves weight, less complex)
parallel generators advantages
safer
more power
generators carry load equally
parallel generator disadvantage
unable to maintain full output at low rpm
type 1 and type 2 ac generators
type 1 - constant RPM
type 2 - variable RPM
Parallel bus systems
older aircraft
load shared equally by all working generators
split bus
each generator powers only one main AC bus
two generators can’t power the same bus simultaneously
most apps are operational
split parallel power
safer
parallel - normal
split - isolated during malfuciton
constant speed drive
installed between variable speed engine and constant speed generator
integrated drive generators
generator and speed control to one unit
integrated drive advantages
weight / size reduction
higher RPM and power output
improved cooling
similarities CSD and IDG
hydraulic units
share oil with AC generator
oil cooling
variable rpm generators
type two
115V AC
frequency may change with engine rpm
variable speed constant frequency
400 hz output
solid-state circuitry
no need for CSD - more reliable
variable speed constant frequency advantages
no CSD
smaller / lighter
more versatile installation
variable speed constant frequency disadvantages
relatively lower power output
not as proven through one term operating
variable speed variable frequency AC generator
newer
output frequency changes with engine rpm
frequency made constant as needed during power distribution
high power output
RAT
provides limited electrical power if all engines are lost
static inverter
most critical AC power source
must be checked every night during routing maintenance
line replaceable unit
what is fluid power
transmission and conversion of power using a fluid
what is the application of fluid power
transmission of force and power through a distance
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 and undiminished in all directions
gas vs liquid compressibility
liquids - non compressible
high % output achieved (low loss, high efficiency)
gas - highly compressible
loss in efficiency
stroke
distance piston moves in a cylinder
inches
volume
quantity of fluid contained in a reservoir, displaced by a pump, or displaced by an actuating cylinde
in cubic inches
hydraulic fluid
medium by which power is transferred within an aircraft
hydraulic equations
F=PA
V=AL
f=force, p=pressure, a=area, L=length, V=volume
what is mechanical advantage
amount by which the applied effort is multiplied in the output of the device
less distance = more forceq
what is flow rate measured in
gallons per minute
where do hydraulics have loss
friction within line
component loss in motors and filters
better hydraulic fluids have _____ viscosity
low
what thermal characteristics do we want for hydraulic fluid
stable structure in all temperatures
what flammability for hydraulic fluid
high flash and fire point
what is flash point
lowest temperature at which a combustible liquid produces sufficient vapor to generate an ignitable mixture
What chemical stability for hydraulic fluid
high chemical stability
vegetable base fluid
blue
older and not used much
extremely flammable
mineral base fluid
red
common in modern aircraft
what is blue hydraulic fluid made of
castor oil and alcohol mixture
what is red hydraulic fluid made of
petroleum distillate
what is purple hydraulic fluid made of
synthetic
phosphate ester based fluid
synthetic base fluid
purple
butyl seals
used in high pressure / temperature applications
low flammability
very damaging to wiring, paint, insulation
what is the SDS
safety data sheet
how to handle chemicals and what not
what should we use when messing with Skydrol
chemical safe resistant gloves
rubber boot
avoid all contact
rigid tubings advantage
can handle high pressure
rigid tubing disadvantages
cannot be used to connect vibration or movable components
flexible hose
low
medium
high pressure
hoses specific to fluids
what hose type works for all fluids
teflon
1500-3000psi
fitting types
aluminum - low / medium pressure
steel - high pressure
seal type
O ring
(cross section is an O shape)
purpose of hydraulic filters
dirt is deadly, want it not there
primary purpose of reservoirs
supply fluid to pumps and system components
secondary purpose of hydraulic reservoirs
thermal expansion
air purging
filtration and sediment
cooling
non-pressurized reservoir
vented to atmosphere to allow air to dissipate from system
hydraulic accumulator
stores hydraulic fluid under pressure
back up or intermittent loads
hydraulic pumps
supply fluid flow to actuating units
provide pressure to overcome system resistance
engine driven hydraulic pump
activated any time engine is running
large systems
electric hydraulic pumps
single, short use tasks
very efficient
lighter aircraft
vane pumps
move more fluid than gear pumps
need more maintenance
best type of hydraulic pump
piston pump
what do pressure relief valves do
protect system from damage due to excessive pressure buildup
what do flow control devices do
control direction of fluid flow
control rate movement takes place
determines sequence of movement
what is a check valve
allows fluid to flow in one direction only
4 way selector valve
moves actuators in two directions
(flap movement)
3 way selector valve
moves flow in one direction
2 way selector valve
controls flow on and off
What is an actuating device
converts fluid flow to mechanical motion
linear or rotary
purpose of landing gear
supports aircraft during ground operations
dampens vibrations when taxiing
cushions landing impact
retractable landing gear
more aerodynamic - saves fuel
more complex
more expensive
what is the trunnion
attaches landing gear assembly to airframe
what is the shock strut
vertical member of the landing gear
pivot fork and shaft
used when wheels are in tandem
torque arm
connects shock strut to truck
drag brace and side brace
stabilizes landing gear assembly longitudinally and laterally
shock strut purpose
supports weight of aircraft
absorbs and displaces shock loads during landing
oleo struts
fluid passing through orifice acts to absorb shock of compression
fluid is not compressible so it slows the strut collapse
energy returning struts
spring steel landing gear absorbs shock of landing
(high wing Cessna type)
why do tubeless wheels have fuse plugs
allows plug to blow out and release tire pressure before wheel blows up
how are aircraft wheels retained
on the axle by a single axle nut in the center of the wheel
cotter pin retains axle nut
what type of bearings do wheels have
roller bearings
segmented rotor disk brakes
more modern design
better dissipate heat
advantage of disc brake over drum brake
better at dissipating heat
downside of disc brakes
single disk limits amount of friction obtained
heavy aircraft may not have enough surface area to stop aircraft
what’s a way to get air out of the brakes
bleed the brakes
how does the master cylinder work
master cylinder has flexible hoses that run to the caliper and sends hydraulic fluid
Cleveland type brake
piston actuates pucks on either side of disk to brake
fixed disk
good year type brake
disk is floating
multiple disc problems
heat fires
heat build up prevents effective braking
what indicator pin
how much material has been used
mechanical gear retraction
older and lighter aircraft
powered by pilot operating lever or crank
electrical landing gear retraction
small and light enough hydraulics are not needed
hydraulic gear
all size of aircraft
landing gear is large and not economically operated
Fuel strainer and filter purpose
remove foreign matters from fuel system
