04 Vertical Speed Indicator (VSI)

Question 1

What are the different names for a Vertical Speed Indicator?

Answer 1

• Rate of Climb and Descent Indicator (RCDI)
• Vario / Variometer
• Special Gauge

Question 2

What scale is used on a Vertical Speed Indicator and why?

Answer 2

• Logarithmic scale

- Give higher accuracy readings at lower readings

Question 3

What is vertical speed measured in on a Vertical Speed Indicator?

Answer 3

1000’s of feet per minute

Question 4

Describe how a Vertical Speed Indicator operates;

• What feeds it
• Components
• How it operates

Answer 4

• Feed by Static Pressure input
• Input feeds into a pressure capsule
• Which leads to a metering unit and the dial
• All of which is surrounded by a sealed case
• As outside static pressure drops, the pressure capsule contracts
• Turning the dial to indicate an increase in vertical velocity
• The metering unit slowly equalises the pressure in the capsule and the pressure in the case (4sec delay)
• The equalising of pressure causes the capsule to expand indicating a zero vertical velocity

Question 5

Name the two parts of the metering unit

Answer 5

• Knife edge: turbulent flow

- Capillary: laminar flow

Question 6

What errors does a Vertical Speed Indicator suffer from?

Answer 6

• Instrument
• Manoeuvre
• Position
• Lag

Question 7

What does an Instantaneous Vertical Speed Indicator (IVSI) do and how?

Answer 7

• Removes the lag error associated with a VSI
• With the addition of an accelerometer (aka Dash Pot)
• A weight attached between two springs which speeds up the expansion and contraction of the pressure capsule

Question 8

What additional errors are associated with a IVSI?

Answer 8

• Turning Error: the IVSI may indicate a slight climb when turning
• Turbulence Error: the IVIS may fluctuate up and down during turbulence

Question 9

What will happen if a VSI has a blockage in the Static Pressure feed?

Answer 9

Will not indicate any change in Vertical Speed as the case and the pressure capsule equalise in pressure (through the metering unit)

Question 10

What will happen if a VSI has a leak OUTSIDE the pressurised compartment?

Answer 10

It will continue to work but will be much less accurate

Question 11

What will happen if a VSI has a leak INSIDE the pressurised compartment?

Answer 11

VSI will initially show a decrease in vertical speed and will then equalise and no longer function

Question 12

How is temperature compensated for on the VSI?

Answer 12

It is compensated at the Metering unit by the means of the Capillary and Orifice