Instrument Systems

7/28/2019 Instrument Systems

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Instrument Systems


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Instrument Systems

Vacuum System

Pitot-static system

Magnetic System


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Pitot-Static System

Types of Pressure

System components


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Two types of Pressure

Dynamic AirPressure Pitot or ram

pressure

Supplied by pitottube

Location varies

Needs to face

directly into therelative wind

Pressure causedby moving air

Only linked toairspeed indicator

Static Air Pressure

Also, ambientstatic air pressure

Supplied by static

port

Location varies

Needs to be inundisturbed air

Pressure justoutside of theairplane

Linked to all Pitot

Static instruments


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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


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Pitot-Static System


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Pitot Static Flight Instruments


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Pitot-Static Instruments

Airspeed Indicator

Altimeter

Vertical Speed Indicator


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Airspeed Indicator


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Airspeed Indicator

Displays the speedof the aircraftthrough the air

Only instrumentthat uses both typesof pressure

Measures thedifference betweenthe two pressures

Greater thedifference thegreater the airspeed


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Airspeed Indicator Operation

Instrument is contained withina sealed case

Pressure sensitive diaphragm

Ram pressure line is connecteddirectly to one side of thediaphragm

Diaphragm expands andcontracts due to ram pressure

Inside of the case is vented tothe static port


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Inside airspeed indicator


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Airspeed Indicator Operation

Diaphragm expands and contracts inproportion to the difference betweenthe two pressures

Measured by mechanical linkage

Linkage is displayed by the hands on theface of airspeed indicator


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Airspeed Indicator


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Airspeed Definitions

Indicated Airspeed

Value read from the indicator

indicated stall speeds remain constant

Uncorrected for installation(position)and instrument error


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Calibrated Airspeed

Indicated Airspeed corrected for installation andinstrument error

Determine from looking in the POH

True Airspeed

True speed of aircraft through the air

Calibrated corrected for altitude and nonstandardtemperature


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Ground Speed

Actual speed of the aircraft over theground

True airspeed adjusted for the wind

Found using the E6B


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Airspeed Indicator

White Arc

Green Arc

Yellow Arc Red Line


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Airspeed Errors

Position Error Occurs when the static port sense an

erroneous static pressure

Mainly caused by slipstream

Error may be determined by using theairspeed calibration chart

Instrument Error

Errors due to imperfections in theinstrument itself, imperfections withmanufacturing


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Altimeter


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Altimeter

System Operation

Types of Altitude Markings

Errors


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Altimeter

Simply a barometer that measuresstatic pressure of the air around theaircraft.

Uses only the static pressure

Operates by the changes in pressure

Standard pressure at Mean Sea Level in29.92 inches of mercury

Atmosphere declines 1 inch of mercury everythousand feet


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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 onwindow


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Altimeter Operation

Pressure Window

Kollsman window

Small adjustable

subscale that allowsthe current altimetersetting to be set in

Important to reset

with current Above 18,000

always set at 29.92

O


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Altimeter Operations


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Altimeter Functions

UND Aerospace, 1994

Air moves out

Air moves in

Wafers expand

01

2

3

45

9

8

7

6

W afers contract

01

2

34

5

9

8

76

01

2

3

45

9

8

7

6


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Types of Altitude

Indicated Altitude Read from Indicator

Pressure Altitude

Height above standard datum

Density Altitude

Pressure corrected for nonstandardtemperatures

T f Altit d


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Types of Altitude

True Altitude

True height abovesea level

Airports andobstruction arebased on

Absolute Altitude

Actual height abovesurface


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TrueAltitude AbsoluteAltitude PressureAltitude IndicatedAltitude

Pressure = 29.92" HgStandardDatum Plane

UND Aerospace, 1994


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Altimeter

Alti t E


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Altimeter Errors

Pressure Error

High to Low-Look out below, low to high plenty ofsky

Need to set in current altimeter setting


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VSI

System Operation

Markings

Errors

V ti l S d I di t


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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 O ti


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VSI Operations

Expandable Capsule

Directly connected to static port

Connected through mechanical linkage

Calibrated Leak

Instrument Cases connection to the staticport

Allows capsule to change pressure moregradually

VSI O ti


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VSI Operation

Pressure inside of capsule changes thesame as the outside air

Pressure in instrument case changesslower because of calibrated leak.

Gives us the rate

When pressure is equal straight and level

VSI Operations


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VSI Operations


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Types of Information Portrayed

Trend Information

Immediate indicationof an increase or

decrease First Indication

Rate Information

Shows the stabilizedrate of change

Take 6-9 seconds


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Markings

VSI Errors


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VSI Errors

Abrupt changes cause errors

Rough control and turbulent air cause

error


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Vacuum System


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System Operation

Vacuum System

Draws air through the filter system

Moves through Attitude and Headingindicator where it spins gyros

Spins at 18,000 RPM

Air continues into engine drivenvacuum pump


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System Operation


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Gyroscopic Principles

Rigidity in Space

Remains in a fixedplane when spinning

Gimbal instrumentaround gyro to allowit remain in planeable to showchanges in pitch andattitude


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Gyroscopic Principals

Precession

When outside forceis applied to gyro it

will be felt 90degrees in rotationof spinning

Includes friction


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Gyroscopic Instruments

Heading Indicator

Attitude Indicator

Turn Cordinator


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Heading Indicator


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Heading Indicator

Operation

Markings and Use

Limitations and Errors


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Heading Indicator Operation

Relies on Rigidity on Space

Primary source of Heading information

Senses rotation along the verticalaxis Gyro spins in the horizontal axis

Support gimbals drive the compass card

Works through gears and linkage Setting knob


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Heading Indicator Operation

M ki & U


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Markings & Use

Li it ti


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Limitations

Reset every 15 minutes

Pitch - 55 degrees

Bank - 55 degrees

H di E


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Heading Errors

Precession

Can be a negative in Headingindicator

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

Attit d I di t


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Attitude Indicator

Operation

Markings and Use

Limitations and Errors


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Attitude Indicator Operations

Mechanical Substitute for the naturalhorizon

Gives immediate and direct informationof planes pitch and bank

Gyro spins in the horizontal plane

Self erecting mechanisms Vacuum Driven, normally


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Attitude Indicator Operations

M ki & U


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Markings & Use


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Climb

Climb andLeft Bank

Level Flight

Glide

Glide andLeft Bank

Level Flightand Left Bank


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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 degreesof pitch

T I di t


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Turn Indicators

Two Types

Turn and Slip

Operation Markings

Turn Coordinator

Operation Markings

T rn & Slip Indicator


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Turn & Slip Indicator

L R L R

TURN2 MIN

BANK

Turn Coordinator


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Turn Coordinator

Operation

Like the Turn and Slip

But shows both rate of turn and rate ofroll

Gimbal is set at a 30 degree angle

Allows force to be felt

Allows gyro more movement

Turn Coordinator


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Turn Coordinator

Gyro gimble(mount not shown)

Cantedgyroaxis

Parallel tolongitudinalaxis of a/c

Gyroscoperotor

Indexmarks

Inclinometer

Aircraft

silhouette

Turn Coordinator


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Turn Coordinator

Operation


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Operation

Inclinometer


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Inclinometer

Contains fluid and ball

Kerosene type fluid

Steel ball

Shows the quality of the turn(Coordination)

Shows forces acting ball in the turns


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Quality of Turn

TurnCoordinator

Turn CoordinatorSkid

Slip


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Magnetic Compass

Magnetic Compass


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Magnetic Compass

Construction

Diagram and function

Markings and use Compass Errors

Use of compass

Magnetic Compass Construction


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Magnetic Compass Construction


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The Earths Magnetic Field

Magnetic Pole Geographic Pole

Magnetaligns itselfwith

magneticforce

Lines ofmagneticforce


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Compass Errors


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Compass Errors

Variation

Deviation

Magnetic Dip Northerly Turning Error

Acceleration/Deceleration Error

Oscillation Error

Variation


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Variation

Variation - Angulardifference between true

north and magnetic north.Agonic line - The line where

there is no angular

difference.Isogonic - Lines showing the

angular lines difference.


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Variation

13NorthMagneticPole

GeographicNorth Pole o

Isogonic linesAgonic

line

20

o

15o

10

o

5o

o

0

5o

10

o

15o

20

o

Compass Card


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Compass Card

Deviation

Error due tomagneticinterference withinthe aircraft

Compensatingmagnets in compasshelp to counteract

Called Swinging

Error on compasscorrection card

Compass Card


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Compass Card

For N 30 60 E 120 150

Steer 357 023 050 080 111 145

For S 210 240 W 300 330

Steer 178 213 246 278 307 333

Magnetic Dip


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Magnetic Dip

How it works

Errors it causes

Magnetic Dip


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Magnetic Dip

Most significanterror

Difficult to get

actual readings Magnet in compass

tries to point 3Ds topole

Causes errors inturns andacceleration

How it Works


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How it Works

Magnetic flux lines point downwardat the poles, compass magnets dipto low side of turn


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MagneticDip

AircraftFlight Path

Dip

North PoleNo Dip

Errors it Causes


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Errors it Causes

Acceleration error - ANDS

Northerly turning error

North lags

SOS - south over shoot

Acceleration Error


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Acceleration Error

Accelerate

Will show a turn tothe North

When speedstabilizes compassreturns to accurate

Error greatest onheadings of Westand East

Deceleration

Will show a turn tothe South

Use ANDS Accelerate NorthDecelerate South


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01-185

E6 3

N

N

N N

Constant Airspeed

Accleration

Deceleration

S

15

12

E

Acceleration & Deceleration Errors ~

ANDS

Turning Errors


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Turning Errors

Northerly Error

Initially indicate turn to opposite direction

Southerly Error

Heading will lead the turn


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Questions?

Instrument Systems

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