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Pressure Instruments Flashcards

1
Q

Dynamic Pressure Formula

A

KE (dynamic pressure) = 0.5pV ²
P = local air density
V = true airspeed

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2
Q

Altimeter

A

Equilibrium created by the pressure of the atmosphere and the tension of a spring
Closed capsule mounted in a case fed by the static source

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3
Q

Altimeter instrument Error

A

Due to capsule movements small irregularities are impossible to avoid
Error increases with altitude

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4
Q

Altimeter Pressure Error

A

Atmospheric pressure not accurately transmitted to the instrument due false static pressure created in the vicinity of the pressure head due airflow over it
Negligible at low altitudes and speeds
Correction applied at indicated height

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5
Q

Altimeter Time Lag

A

Response not instantaneous therefore a lag causing an under-read on the climb and over-read on descent
Proportional to rate of descent

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6
Q

Altimeter Hysteresis Error

A

Capsule under stress exhibits an imperfect elastic response
Non-linear response of bellows
Noticeable after sharp climbs and descents

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7
Q

Altimeter Barometric Error

A

Actual sea level barometric pressure differs from that assumed and calibrated by the standard atmosphere set on the sub scale
High to low pressure = overreads

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8
Q

Altimeter Temperature Error

A

Atmospheric conditions differ to standard atmosphere
Cold air = decreased pressure and altimeter will read high
ISA +, the altimeter will underread

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9
Q

Altimeter Static Vent Blockage

A

No change to altimeter readout

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10
Q

Calculate Aircraft True Altitude Using Wiz Wheel

A
  1. Calculate pressure height
  2. Determine OAT at aircraft pressure height
  3. Using flight computer set Pressure height against OAT
  4. Find calibrated altitude and across will be the true altitude
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11
Q

Calculate Aircraft True Altitude

A

4% of indicated height AGL (local QNH) per 10 degrees of ISA variation
4% of indicated altitude AMSL (area QNH) per 10 degrees of ISA variation

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12
Q

Pressure Height

A

Elevation + 30(1013 - QNH)

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13
Q

Airspeed Indiactor

A

Measures dynamic pressure in a capsule enclosed by static pressure

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14
Q

TAS

A

Is equal to IAS at ISA conditions
If conditions vary a correction is required

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15
Q

Airspeed Instrument Error

A

Manufacturing tolerances in the construction
Determined using calibration and any correction is combined with that for pressure error

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16
Q

Airspeed Pressure Error

A

Disturbances in static pressure around the aircraft due to movement through air

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17
Q

Pressure Error Correction (PEC)

A

Tabulated with Instrument Error Correction (IEC) on a correction card and applied to IAS to obtain CAS or rectified air speed (RAS)

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18
Q

Airspeed Compressibility Error

A

The compressibility of air is significant at higher speeds if different at all from ISA
At higher altitudes, less dense air is more easily compressed resulting in greater dynamic pressure and causing the ASI to overread
Compressibility increases with speed

19
Q

Equivalent Air Speed (EAS)

A

Application of compressibility error by the flight computer (f factor) to CASA
Above 250-300kts

20
Q

Airspeed Density Error

A

Dynamic pressure varies with airspeed and density
As altitude increases, density decreases so IAS and EAS will progressively become lower than TAS
For the same capsule deflection as that at MSL the aircraft must be travelling faster
Correction calculated by flight computer

21
Q

Blockages (PUDSUC)

A

Pitot blocked: no changes in level flight
Static blocked: overread at lower altitudes and underread at higher altitudes than that at which the blockage occurred.

22
Q

Mach Meter (IMN)

A

ASI with altitude sensing capsule to compensate for pressure height

23
Q

Mach Meter Errors

A

Instrument and pressure errors
True Mach Number (TMN) accounts for these errors

24
Q

Vertical Speed Indicator

A

Records rate of change of atmospheric pressure
As the aircraft climbs, pressure escapes the capsule faster and contracts causing the pointer to indicate a rate of climb and vice versa.

25
Q

VSI Metering Unit

A

Provides a definite pressure difference for any ROC or ROD
Uses an orifice and capillary to allow readings to remain correct over a wide range of temperatures

26
Q

Pressure Compensation (Height)

A

The pressure difference across an orifice for a given ROC decreases with increasing height.
The pressure difference across a capillary type metering unit at a constant rate of climb increases with increasing height.
Therefore a combination compensates for both issues.

27
Q

VSI Lag

A

There is a delay before the pointer settles on the correct ROC/ROD due to the pressure difference developing however a trend is immediately indicated

28
Q

VSI Pressure Error

A

Due to the movement of air around the pitot/static heads it may incorrectly indicate during a considerable change in airspeed

29
Q

Static Line Blockage VSI

A

Becomes unserviceable
If breaking VSI glass, due to the metering device the VSI will work in reverse and the altimeter will lag

30
Q

VSI Instrument Error

A

Small errors can be taken out with the zero adjustment screw

31
Q

Instantaneous VSI

A

Minimises lag by using a Dash Pot
Works to pressurise the system when a climb or descent is initiated causing the correct Trent to show instantly

32
Q

Dash Pot

A

Consists of an inertial operated air pump reacting to pitch and accelerations

33
Q

IVSI Errors

A

Same as VSI except lag

34
Q

Direct Reading Compass

A

Magnetic compass which aligns itself with Earth’s magnetic field and may not sit horizontal
This is called compass dip which increases as latitude increases
Causes compass centre of gravity to move away from the compass pivot point

35
Q

Compass Errors

A

SAND (Max on E/W headings)
ONUS (Max on N/S headings)

36
Q

DG Rigidity

A

Rigidity of the gyroscope causes the heading indicating to change whilst the card remains still
Axis reference will gradually shift due to real and apparent precession

37
Q

Apparent drift

A

Movement across the Earth’s surface and the Earth’s rotation

38
Q

Real Drift

A

Gyro imperfections and bearing drag

39
Q

Remote Magnetic Indicator (RMI)

A

A DG which maintains its ow alignment with the aircraft heading
An electric heading reference signal from a flux valve and a motor on the instrument card to realign the card to the correct heading

40
Q

Flux Valve

A

Remotely located to decrease the effect of magnetic deviation
Consists of 3 electrical coils generating electrical signals when passed through the Earth’s magnetic field
Signals are then fed to the control unit

41
Q

Main Error of a Flux Valve

A

Is still deviation! Just to a smaller degree

42
Q

Flux Valve Control Unit

A

Where flux signals are compared to a reference
If signals are synchronised gyro is aligned
Minimises turning and acceleration errors

43
Q

Bootstrapping

A

Left flux valve supplies heading reference for the left RMI and right HSI

44
Q

Horizontal Situation Indicator (HSI)

A

An RMI with a full VOR/ILS display

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