1. Instrument Systems

2. Instrument Systems
Vacuum System
Pitot-static system
Magnetic System

3. Pitot-Static System
Types of Pressure
System components

4. Two types of Pressure Dynamic Air Pressure 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
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

5. Components of system Pitot Pressure Lines Static 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

6. Pitot-Static System

7. Pitot Static Flight Instruments

8. Pitot-Static Instruments
Airspeed Indicator
Altimeter
Vertical Speed Indicator

9. Airspeed Indicator

10. 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

11. 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

12. Inside airspeed indicator

13. 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

14. Airspeed Indicator

15. Airspeed Definitions Indicated Airspeed Value read from the indicator
indicated stall speeds remain constant
Uncorrected for installation(position) and instrument error

16. Airspeed Definitions Calibrated Airspeed True 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

17. Airspeed Definitions Ground Speed
Actual speed of the aircraft over the ground
True airspeed adjusted for the wind
Found using the E6B

18. Airspeed Definitions

19. Airspeed Indicator
White Arc
Green Arc
Yellow Arc
Red Line

20. Airspeed Errors Position Error Instrument 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

21. Altimeter

22. Altimeter
System Operation
Types of Altitude
Markings
Errors

23. 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 inches of mercury
Atmosphere declines 1 inch of mercury every thousand feet

25. 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

26. 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

27. Altimeter Operations

28. Altimeter Functions Air moves out Air moves in W afers expand
© UND Aerospace, 1994
Air moves out
Air moves in W
afers expand 1 2 3 4 5 9 8 7 6
afers contract

29. Types of Altitude Indicated Altitude Pressure Altitude
Read from Indicator
Pressure Altitude
Height above standard datum
Density Altitude
Pressure corrected for nonstandard temperatures

30. Types of Altitude True Altitude Absolute Altitude
True height above sea level
Airports and obstruction are based on
Absolute Altitude
Actual height above surface

31. © UND Aerospace, 1994

32. Altimeter

33. Altimeter Errors Pressure Error
High to Low-Look out below, low to high plenty of sky
Need to set in current altimeter setting

34. Vertical Speed Indicator

35. VSI
System Operation
Markings
Errors

36. 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

37. VSI Operations Expandable Capsule Calibrated Leak
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

38. 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

39. VSI Operations

40. 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

41. Markings

42. VSI Errors Abrupt changes cause errors
Rough control and turbulent air cause error

43. Vacuum System

44. 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

45. System Operation

46. 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

47. Gyroscopic Principals
Precession
When outside force is applied to gyro it will be felt 90 degrees in rotation of spinning
Includes friction

48. Gyroscopic Instruments
Heading Indicator
Attitude Indicator
Turn Cordinator

49. Heading Indicator

50. Heading Indicator
Operation
Markings and Use
Limitations and Errors

51. 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

52. Heading Indicator Operation

53. Markings & Use

54. Limitations Reset every 15 minutes Pitch - 55 degrees
Bank - 55 degrees

55. Heading Errors Precession Tumbling
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

56. Attitude Indicator
Operation
Markings and Use
Limitations and Errors

57. 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

58. Attitude Indicator Operations

59. Markings & Use

61. 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

62. Turn Indicators Two Types Turn and Slip Turn Coordinator Operation
Markings
Turn Coordinator

63. Turn & Slip Indicator

64. 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

65. Turn Coordinator

66. Turn Coordinator

67. Operation

68. Inclinometer Contains fluid and ball
Kerosene type fluid
Steel ball
Shows the quality of the turn (Coordination)
Shows forces acting ball in the turns

69. Quality of Turn
Skid
Turn Coordinator
Slip
Turn Coordinator

70. Magnetic Compass

71. Magnetic Compass Construction Diagram and function Markings and use
Compass Errors
Use of compass

72. Magnetic Compass Construction

73. The Earth’s Magnetic Field

75. Compass Errors Variation Deviation Magnetic Dip Oscillation Error
Northerly Turning Error
Acceleration/Deceleration Error
Oscillation Error

76. 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.

77. Variation

78. 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

79. Compass Card For N 30 60 E 120 150 Steer 357 023 050 080 111 145
For S W
Steer

80. Magnetic Dip
How it works
Errors it causes

81. 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

82. How it Works
Magnetic flux lines point downward at the poles, compass magnets dip to low side of turn

83. Magnetic Dip

84. Errors it Causes Acceleration error - ANDS Northerly turning error
North lags
SOS - south over shoot

85. Acceleration Error Accelerate Deceleration
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

86. Acceleration & Deceleration Errors ~ ANDS6 3 N
Constant Airspeed
Accleration
Deceleration E
01-185 S 12 15

87. Turning Errors Northerly Error Southerly Error
Initially indicate turn to opposite direction
Southerly Error
Heading will lead the turn

88. Questions?