Transcript Instrument Systems

Instrument Systems
Instrument Systems
• Vacuum System
• Pitot-static system
• Magnetic System
Pitot-Static System
• Types of Pressure
• System components
Two types of Pressure
• Dynamic Air
Pressure
• Pitot or ram
pressure
• Supplied by pitot
tube
• Location varies
• Needs to face
directly into the
relative wind
• Pressure caused
by moving air
• Only linked to
airspeed indicator
• Static Air Pressure
• Also, ambient
static air pressure
• Supplied by static
port
• Location varies
• Needs to be in
undisturbed air
• Pressure just
outside of the
airplane
• Linked to all Pitot
Static instruments
Components of system
• Pitot Pressure Lines
• Connects pitot tube to airspeed indicator
• Needs to run direct
• Sump in lowest point collects moisture
• Static Pressure Lines
• Connect to all three
• Has sump in lowest lines
Pitot-Static System
Pitot Static Flight Instruments
Pitot-Static Instruments
• Airspeed Indicator
• Altimeter
• Vertical Speed Indicator
Airspeed Indicator
Airspeed Indicator
• Displays the speed
of the aircraft
through the air
• Only instrument
that uses both types
of pressure
• Measures the
difference between
the two pressures
• Greater the
difference the
greater the airspeed
Airspeed Indicator Operation
• Instrument is contained within
a sealed case
• Pressure sensitive diaphragm
• Ram pressure line is connected
directly to one side of the
diaphragm
• Diaphragm expands and
contracts due to ram pressure
• Inside of the case is vented to
the static port
Inside airspeed indicator
Airspeed Indicator Operation
• Diaphragm expands and contracts in
proportion to the difference between
the two pressures
• Measured by mechanical linkage
• Linkage is displayed by the hands on the
face of airspeed indicator
Airspeed Indicator
Airspeed Definitions
• Indicated Airspeed
• Value read from the indicator
• indicated stall speeds remain constant
• Uncorrected for installation(position)
and instrument error
Airspeed Definitions
• Calibrated Airspeed
• Indicated Airspeed corrected for installation and
instrument error
• Determine from looking in the POH
• True Airspeed
• True speed of aircraft through the air
• Calibrated corrected for altitude and nonstandard
temperature
Airspeed Definitions
• Ground Speed
• Actual speed of the aircraft over the
ground
• True airspeed adjusted for the wind
• Found using the E6B
Airspeed Definitions
Airspeed Indicator
• White Arc
• Green Arc
• Yellow Arc
• Red Line
Airspeed Errors
• Position Error
• Occurs when the static port sense an
erroneous static pressure
• Mainly caused by slipstream
• Error may be determined by using the
airspeed calibration chart
• Instrument Error
• Errors due to imperfections in the
instrument itself, imperfections with
manufacturing
Altimeter
Altimeter
•
•
•
•
System Operation
Types of Altitude
Markings
Errors
Altimeter
• Simply a barometer that measures
static pressure of the air around the
aircraft.
• Uses only the static pressure
• Operates by the changes in pressure
• Standard pressure at Mean Sea Level in
29.92 inches of mercury
• Atmosphere declines 1 inch of mercury every
thousand feet
Altimeter Operation
• Aneroid wafer
• Stack of hollow, elastic metal wafers
• Expand and contract as pressure changes
• This is shown through mechanical linkage
• Each pressure setting is a definite size on
window
Altimeter Operation
• Pressure Window
• Kollsman window
• Small adjustable
subscale that allows
the current altimeter
setting to be set in
• Important to reset
with current
• Above 18,000’
always set at 29.92
Altimeter Operations
Altimeter Functions
Air moves out
9 0 1
8
7
6 5 4
2
3
Wafers expand
8
7
Air moves in
6 5 4
2
3
9 0 1
8
7
© UND Aerospace, 1994
9 0 1
6 5 4
2
3
Wafers contract
Types of Altitude
• Indicated Altitude
• Read from Indicator
• Pressure Altitude
• Height above standard datum
• Density Altitude
• Pressure corrected for nonstandard
temperatures
Types of Altitude
• True Altitude
• True height above
sea level
• Airports and
obstruction are
based on
• Absolute Altitude
• Actual height above
surface
True
Altitude
Standard
Datum Plane
© UND Aerospace, 1994
Absolute Pressure Indicated
Altitude Altitude Altitude
Pressure = 29.92" Hg
Altimeter
Altimeter Errors
• Pressure Error
• High to Low-Look out below, low to high plenty of
sky
• Need to set in current altimeter setting
Vertical Speed Indicator
VSI
• System Operation
• Markings
• Errors
Vertical Speed Indicator
• Provides reference to rate of change
• Will show trend away from level quickly
• Responds faster then the altimeter
• Shows both rate and trend
• Uses only static pressure
VSI Operations
• Expandable Capsule
• Directly connected to static port
• Connected through mechanical linkage
• Calibrated Leak
• Instrument Case’s connection to the static
port
• Allows capsule to change pressure more
gradually
VSI Operation
• Pressure inside of capsule changes the
same as the outside air
• Pressure in instrument case changes
slower because of calibrated leak.
• Gives us the rate
• When pressure is equal straight and level
VSI Operations
Types of Information Portrayed
• Trend Information
• Immediate indication
of an increase or
decrease
• First Indication
• Rate Information
• Shows the stabilized
rate of change
• Take 6-9 seconds
Markings
VSI Errors
• Abrupt changes cause errors
• Rough control and turbulent air cause
error
Vacuum System
System Operation
• Vacuum System
• Draws air through the filter system
• Moves through Attitude and Heading
indicator where it spins gyros
•Spins at 18,000 RPM
• Air continues into engine driven
vacuum pump
System Operation
Gyroscopic Principles
• Rigidity in Space
• Remains in a fixed
plane when spinning
• Gimbal instrument
around gyro to allow
it remain in plane
able to show
changes in pitch and
attitude
Gyroscopic Principals
• Precession
• When outside force
is applied to gyro it
will be felt 90
degrees in rotation
of spinning
• Includes friction
Gyroscopic Instruments
• Heading Indicator
• Attitude Indicator
• Turn Cordinator
Heading Indicator
Heading Indicator
• Operation
• Markings and Use
• Limitations and Errors
Heading Indicator Operation
• Relies on Rigidity on Space
• Primary source of Heading information
• Senses rotation along the vertical axis
• Gyro spins in the horizontal axis
• Support gimbals drive the compass card
• Works through gears and linkage
• Setting knob
Heading Indicator Operation
Markings & Use
Limitations
• Reset every 15 minutes
• Pitch - 55 degrees
• Bank - 55 degrees
Heading Errors
• Precession
• Can be a negative in Heading
indicator
• Causes the heading to drift
• Should check every 15 minutes
• Make sure you are in straight and level,
unaccelerated flight
• Tumbling
• Occurs after excessive pitch and roll
Attitude Indicator
• Operation
• Markings and Use
• Limitations and Errors
Attitude Indicator Operations
• Mechanical Substitute for the natural
horizon
• Gives immediate and direct information
of plane’s pitch and bank
• Gyro spins in the horizontal plane
• Self erecting mechanisms
• Vacuum Driven, normally
Attitude Indicator Operations
Markings & Use
Glide
Climb
Glide and
Left Bank
Climb and
Left Bank
Level Flight
Level Flight
and Left Bank
Attitude Indicator Errors
•
•
•
•
Usually very minor
Minor on acceleration and deceleration
Somewhat precesses on turns
Errors are maximum when rolling out of
a 180 degree or 360 degree turn
• Instrument Tumbling (older AI)
• Caging mechanism
• May take awhile for it to re-erect itself
• After 100 degrees of bank and 60 degrees
of pitch
Turn Indicators
• Two Types
• Turn and Slip
• Operation
• Markings
• Turn Coordinator
• Operation
• Markings
Turn & Slip Indicator
L
R
R
L
TURN
2 MIN
BANK
Turn Coordinator
• Operation
• Like the Turn and Slip
• But shows both rate of turn and rate of
roll
• Gimbal is set at a 30 degree angle
• Allows force to be felt
• Allows gyro more movement
Turn Coordinator
Gyro gimble
(mount not shown)
Gyroscope
rotor
Index
marks
Canted
gyro
axis
Parallel to
longitudinal
axis of a/c
Aircraft
silhouette
Inclinometer
Turn Coordinator
Operation
Inclinometer
• Contains fluid and ball
• Kerosene type fluid
• Steel ball
• Shows the quality of the turn
(Coordination)
• Shows forces acting ball in the turns
Quality of Turn
Skid
Turn Coordinator
Slip
Turn Coordinator
Magnetic Compass
Magnetic Compass
• Construction
• Diagram and function
• Markings and use
• Compass Errors
• Use of compass
Magnetic Compass Construction
The Earth’s
Magnetic
Field
The Earth's Magnetic Field
Magnetic Pole
Geographic Pole
Magnet
aligns itself
with
magnetic
force
Lines of
magnetic
force
Compass Errors
• Variation
• Deviation
• Magnetic Dip
• Northerly Turning Error
• Acceleration/Deceleration Error
• Oscillation Error
Variation
• Variation - Angular
difference between true
north and magnetic north.
• Agonic line - The line where
there is no angular
difference.
• Isogonic - Lines showing the
angular lines difference.
Variation
Geographic
North Pole
o
20
o
13
o
10
North
Magnetic
Pole
o
o
0
o
10 20
o
15
o
15
o
Isogonic lines
5
o
5
Agonic
line
Compass Card
• Deviation
• Error due to
magnetic
interference within
the aircraft
• Compensating
magnets in compass
help to counteract
• Called Swinging
• Error on compass
correction card
Compass Card
For
Steer
For
Steer
N
30
60 E
357 023 050 080
S 210 240 W
178 213 246 278
120 150
111 145
300 330
307 333
Magnetic Dip
• How it works
• Errors it causes
Magnetic Dip
• Most significant
error
• Difficult to get
actual readings
• Magnet in compass
tries to point 3Ds to
pole
• Causes errors in
turns and
acceleration
How it Works
Magnetic flux lines point downward
at the poles, compass magnets dip
to low side of turn
Dip
North Pole
No Dip
Aircraft
Flight Path
Magnetic
Dip
Errors it Causes
• Acceleration error - ANDS
• Northerly turning error
• North lags
• SOS - south over shoot
Acceleration Error
• Accelerate
• Will show a turn to
the North
• When speed
stabilizes compass
returns to accurate
• Error greatest on
headings of West and
East
• Deceleration
• Will show a turn to
the South
• Use ANDS
• Accelerate North
Decelerate South
Acceleration & Deceleration Errors ~
ANDS
N
N
N
E
• 01-185
S
E
6
3 N
Deceleration
Accleration
Constant Airspeed
15
12
Turning Errors
• Northerly Error
• Initially indicate turn to opposite direction
• Southerly Error
• Heading will lead the turn
Questions?