Flight Instruments Flashcards
What instruments operate from the pitot/static system?
The pitot static system operates the altimeter, vertical speed indicator, and airspeed indicator
How does an altimeter work?
In an altimeter, aneroid wafers expand and contract as atmospheric pressure changes, and through a shaft and gear linkage, rotate pointers on the dial of the instrument.
What are the limitations that a pressure altimeter is subject to?
Nonstandard pressure and temperature.
a. Temperature variations expand or contract the atmosphere and raise or lower pressure levels that the altimeter senses
- On a warm day - the pressure level is higher than on a standard day. Altimeter indicates lower than actual.
- On a cold day - pressure level is lower than on standard. Indicates higher than actual.
b. Changes in surface pressure also affect pressure levels at altitude.
- higher than standard pressure - the pressure level is higher than on a standard day. The altimeter indicates lower than actual altitude.
- Lower than standard pressure - the pressure level is lower than standard. Indicates higher than actual.
* HIgh to low or hot to cold look out below*
What is the maximum allowable error for an altimeter IFR flight
off by more than 75 feet
Indicated altitude -
read of the face of altimeter
pressure altitude -
Indicated altitude with 29.92 set in the Kollsman window
True altitude -
heigh above sea level. Use the flight computer
Density altitude -
Pressure altitude corrected for nonstandard temperature
Absolute altitude -
Heigh above ground. Subtract the terrain elevation from true altitude
How does the airspeed indicator operate
The airspeed indicator measures the difference between ram pressure from the pitot head and atmospheric pressure form the static source
What are the limitations the airspeed indicator is subject to?
It must have proper flow of air int he pitot/static system
What are the errors that the airspeed indicator is subject to?
Position error - Static ports sense erroneous static pressure; slipstream flow disrupts. Varies with airspeed, altitude, configuration
- Density error - changes in altitude and temperature are not compensated for by instrument
- Compressibility error - caused by the packing of air into the pitot tube at high airspeeds, resulting in higher than normal indications. Usually above 180 KIAS
IAS
Indicated Airspeed - The speed of the airplane read off the airspeed indicator
CAS
Calibrated airspeed - the airspeed indicator reading corrected for position and instrument errors; equal to TAS at sea level in standard atmosphere. The color coding for various design speeds marked on the airspeed indicators may be IAS or CAS
EAS
Equivalent Airspeed - the AS reading corrected for position instrument error and for adiabatic compressible flow for the particular altitude; equal to CAS at sea level in standard atmosphere
TAS
True airspeed - the speed of the airplane in relation to the air mass in which it is flying
Aircraft speed pneumonic device?
ICET
White arc
Flap Operation range
Bottom of white arc
Flaps down stall speed
Top of white arc
Maximum airspeed for flaps down flight
Green arc
normal operating range
Bottom of green arc
Flaps up stall speed
Top of green arc
Maximum airspeed for rough air
Yellow arc
Structural warning area
Bottom of yellow arc
maximum airspeed for rough air
Top of yellow arc
NEver exceed airspeed
Red Radial line
Never exceed airspeed
How does the vertical speed indicator work?
In the VSI, changing pressures expand or contract a diaphragm connected to the indicating needle through gears and levers. The VSI is connected to the static pressure line through a calibrated leak’ it measures differential pressure
What are the limitations of the VSI?
It is not accurate until the aircraft is stabilized. Sudden or abrupt changes in the aircraft attitude will cause erroneous instrument readings as airflow fluctuates over the static port. These changes are not reflected immediately by the VSI due to the calibrated leak
What instruments are affected when the pitot tube ram air inlet and drain hole freeze?
Only the airspeed indicator will be affected. It acts like an altimeter - it reads lower than actual speed in level flight. Reads higher as aircraft climbs and lower as aircraft descents.
What instruments are affected when the static port freezes?
Airspeed indicator -
Altimeter - indicates the altitude at which system blocked
VSI - will indicate level flight
If the air temperature is +6 celcius at an airport elevation of 1,200 feet and standard temperature lapse rate, what will approximate freezing level be?
4,200 MSL; 6 divided by average temperature lapse rate of 2 results in a 3000 foot freezing level, add 1200
What corrective action is needed if the pitot tube freezes? Static?
Pitot - turn on pitot heat
Static - use alternate air if available or break the face of a static instrument (either VSI or A/S indicator)
What indications should you expect while suing alternate air?
If it is vented inside the aircraft
- Altimeter - will indicate higher than actual
- Airspeed - will indicate greater than actual airspeed
- VSI - will indicate a climb while in level flight
What instruments contain gyroscopes?
Attitude indicator, heading indicator, turn coordinator
Name several types of power sources commonly used to power the gyroscopic instruments in an aircraft.
Various power sources used are: electrical, pneumatic, Venturi tube, wet type vacuum pump, dry air pump systems. Aircraft and instrument manufactures have designed redundancy into the flight instruments so that any single failure will not deprive the pilot of his ability to safely conclude the flight. Gyroscopic instruments are crucial for instrument flight; therefore they are powered by separate electrical or pneumatic sources. Typically, the heading indicator and attitude indicator will be vacuum driven and the turn coordinator electrically.
** CONSULT POH
How does the vacuum system work?
The vacuum or pressure system spins the gyro by drawing a stream of air against the rotor vanes to spin the rotor at high speeds, essentially the same as a water wheel or turbine operates. Thea mount of vacuum or pressure required for instrument operation various but is usually between 4.5-5.5 in Hg. One sources of vacuum for gyros installed in light aircraft is the vane type engine driven pump, mounted on the accessory case of the engine.
Two important characteristics of gyroscopes?
Rigidity - the characteristic of a gyro that prevents its axis of rotation tilting as the Earth rotates’ attitude and heading instruments operate on this principle
Precession - causes applied force to be felt 90 degrees from that point int he direction of rotation. Rate instruments such as the turn coordinator use this principle
How does the turn coordinator operate?
The turn part of the instrument uses precession to indicate direction and approximate rate of turn. A gyro reacts by trying to move in reaction to the force applied thus moving the miniature aircraft in proportion to the rate of turn. The inclinometer measures the relative strength of the force of gravity and the force of inertia causes by a turn.
What information does the turn coordinator provide?
Rate of turn, rate of roll, and direction of turn. The inclinometer indicates quality of turn (slip and skid)
What is the source of power for the turn coordinator?
Either by air or electricity. Typically electrically powered
How does the heading indicator work?
The operation of the heading indicator works on the principle of rigidity in space. Rotor turns in a vertical plane, and fixed to the rotor is a compass card. Since the rotor remains right in space, the point on the card hold the same position in space relative to the vertical plane. As the instrument case and the airplane revolve around the vertical axis, the card provides clear and accurate heading information.
What are the limitations of the heading indicator?
They vary with the particular design and make of instrument: on some, limits are approximately 55 degrees pitch and 55 bank. When either of these attitude limits are exceeded, the instrument tumbles and no longer gives correct indication until reset. Many modern instruments used are designed in such a manner that they will not tumble.
What type of error is the heading indicator subject to?
Precession caused by friction. Heading will creep or drift. The amount is dependent upon condition of instrument. The earth’s rotation while in flight can also cause deviation.
What are the limitations of the heading indicator?
They vary with the particular design and make of instrument: on some, limits are approximately 55 degrees pitch and 55 bank. When either of these attitude limits are exceeded, the instrument tumbles and no longer gives correct indication until reset. Many modern instruments used are designed in such a manner that they will not tumble.
What type of error is the heading indicator subject to?
Precession caused by friction. Heading will creep or drift. The amount is dependent upon condition of instrument. The earth’s rotation while in flight can also cause deviation.
How does the attitude indicator work?
A gyro mounted on a horizontal plane. It operates upon rigidity in space.
What are the limitations of an attitude indicator?
Limits depend upon the make and mode. Instrument will tumble or spill and will give incorrect indications until restabilized.
Is that attitude indicator subject to errors?
are free from most errors, but there may be a slight nose up indications during a rapid acceleration and a nose down indication during a rapid deceleration.
How does that magnetic compass for?
Magnets mounted on the compass card align themselves parallel to the Earth’s lines of magnetic force
What limitations does the magnetic compass have?
The jewel and pivot type mounting gives the float freedom to rotate and tilt up to approximately 18 degrees angle of bank. At steeper bank angles, the compass indications are erratic and unpredictable.
Oscillation error?
Mag Compass error, erratic movement of the compass card caused by turbulence or rough control technique
Deviation error?
Mag Compass error, due to electrical and magnetic disturbances in the aircraft
Variation error?
Mag Compass error, angular differences between true and magnetic north, reference isogonic lines of variation
Dip errors?
Mag Compass error -
a. Acceleration errors
–ANDS on east or west heading- accelerate north, decelerate south
- -Northerly Turning Error - the compass leads in the south half of a turn, and lags in the north half of a turn – UNOS
- Undershoot North, overshoot south
