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Flashcards in VSI Deck (13):
1

What are the alternate names for a VSI?

RCDI - rate of climb and descent indicator
Variometer or vario
Or special gauge

2

What is a VSI measured in and what kind of display is used?

FPM and logarithmic scale.

3

What are the advantages of a logarithmic scale?

Greater accuracy at start of descent/ascent

4

What does the metering unit do?

It creates a (an approx 4 sec) time lag by ensuring the Ps in case lags behind the Ps in the capsule.

In either climb or descent, the ambient (present) px is measured against the case px.

5

The metering unit has 2 parts:

Knife edge: turbulent
Capillary: laminar

Together will give constant flow rate

6

In a climb, the capsule...

contracts

7

In a descent, the capsule....

Expands

When descending Ps increases thus the the Ps in the capsule is greater > then the px in case

8

What is used to combat the time lag in a VSI?

The dashpot or accelerometer unit.

Inertia will move the dashpot instantly causing a temporary fix until the px in the capsule equalises.

This unit is called the instantaneous VSI (IVSI)

9

When will the IVSI have disturbance erroneous errors?

IVSI will have a slight climb error during a turn and
Also in turbulence

10

If a VSI is blocked, what will it indicate?

Zero

11

What is the error when there is a px leak outside the px cabin?

Still works but a little less accurate.

12

What is the error of an VSI if there is a leak within the px cabin?

Only measures cabin altitude. Shows instantaneous descent.

13

Generally VSI only becomes useful in steady flight and particularly....

During an instrument approach.