Ground lesson 14, (2) - Flight instrument systems

• Flight instrument systems
• FAA instrument requirements 
• FAR 91.205
• VFR instruments + IFR instruments 
• IFR - GRABCARD
• Generator/alternator
• Radio
• Altimeter
• Ball
• Clock
• Attitude indicator
• Rate of turn coordinator 
• Directional gyro
  
  
• Pilot's Operating Handbook (POH)

Gyroscopic flight instruments

• Gyroscope principals
• Gyroscopic precession 

• A force applied to a gyro will react 90º later in the direction of rotation
• Used by turn coordinator/indicator
  
  
• Rigidity in space
• Means that once the gyro is spinning, it tends to remain in a fixed position
• Resists external forces applied to it
  
  
• Used by DG and AI
• Attitude indicator 
• How it works
• Mounted on a double gimbal to sense pitch and roll
• Horizontal gyro, vertical axis 
• Vacuum or electrical
  
  
• Errors
• Instrument tumbling/caging 
• Exceeding pitch(60º) /roll (100º) limit, the gyro housing will contact the gimbals
  
  
• Maneuver errors 
• Might get slight nose up/down when rapid acceleration/deceleration
  
  
• Heading indicator/ Directional gyro
• How it works
• Uses rigidity in space
• Mounted in a double gimbal 
• Spin axis horizontal, gyro vertical
• No compass errors 
• Vacuum or electrical
  
  
  
• Errors
• Friction - earth rotates 15º every hour 
• Must be set to agree with magnetic compass
• If fluxgate present 
• Slave mode
• Aligns constantly to magnetic north 
• Electric coils sense the direction by strength of current through them
• Does not need to be set manually every 15 minutes
   
• Turn indicator/coordinator 
• How they work
• Usually electrical 
• Uses precession 
• Mounted in a single gimbal
• Horizontal axis, vertical gyro
  
  
• Turn indicator provides you with rate of turn
• Turn coordinator provides you with rate of turn and rate of roll
• Tilted 30º
  
  
  

Magnetic compass

• Function 
• Self contained
• Helicopter rotates around the compass card
  
  
• Magnetic fields of the earth
• The earth is a huge magnet surrounded by a magnetic field made up of lines of flux
• These lines leave magnetic north pole and reenter the south pole
  
  
• Variation 
• Angle between magnetic north and true north
  
  
  
• Deviation 
• Compass errors caused by magnetic disturbances from electrical and metal components in the aircraft 
• Magnets installed in housing to compensate for the error
• Correction is placarded on the compass
  
  
• Oscillation 
• Erratic movements of the compass card
• Turbulence , control inputs
• Magnetic dip
• Tendency of the north seeking needle to deflect downward as it approaches the north pole
• Flux is Perpendicular at the magnetic north pole
• Strong deflection
  
  
• Flux is parallel at the equator
• No dip error
• Dip compensating weight at the “south end
  
  

            

• Dip errors
• Acceleration / deceleration errors 
• Because of the weight that compensates for magnetic dip
• Most noticeable on easterly or westerly headings 
• Non at north or south headings
• ANDS 
• accelerate north/ decelerate south
  
  
• Turn errors 
• Most noticeable when turning to/from a north or south heading, none at east/west
• UNOS
• Undershoot north, overshoot south
• When on a south heading and turning north, needle leads
  
  

Pitot-static instruments

• Pitot static system
• Pitot tube
• Dynamic pressure enters (ram air)
• Drain hole
• Some aircraft's have pitot heat 
• Used by airspeed indicator
  
  
• Static port
• Measures static pressure
• Used by ASI, VSI, and ALT
  
  
  
• Airspeed indicator 
• Function 
• Indicates the speed of the aircraft through the air
• Compares dynamic pressure with static pressure
• The greater the difference, the greater the speed
  
  
• Altimeter- +/-75 error permitted 
• Function 
• Measures the difference between static pressure and altimeter setting
• Static port connected to the housing
• Wafer has set pressure
  
  
• Vertical speed indicator 
• Function 
• Displays rate of climb/ descent
• Measures how fast the static pressure increases and decreases 
• Static pressure enters diaphragm which instantly compresses/ decompresses 
• Static pressure also enters VSI housing through calibrated leak
  
  
• ICING
• Pitot tube ice
• Only affects the airspeed indicator 
• Pitot + drain clogged = ASI works as altimeter 
• Higher altitude = higher airspeed
  
  
• Pitot tube ice, drain cleared
• Drain hole lets the pressure out, airspeed drops to zero
  
  
• Static port ice 
• Affects ASI, ALT, VSI
• ASI
• Works normal at altitude it froze at
• Higher airspeed at lower altitude, lower airspeed at higher altitude
  
  
• ALT
• Freezes at current altitude
  
  
• VSI
• Shows zero, senses no difference in pressure
  
  
• Alternate static source
• Break the VSI glass
• ASI and ALT will show higher than normal
  
  
  
  
  
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