Flashcards in VSI Deck (13):
What are the alternate names for a VSI?
RCDI - rate of climb and descent indicator
Variometer or vario
Or special gauge
What is a VSI measured in and what kind of display is used?
FPM and logarithmic scale.
What are the advantages of a logarithmic scale?
Greater accuracy at start of descent/ascent
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.
The metering unit has 2 parts:
Knife edge: turbulent
Together will give constant flow rate
In a climb, the capsule...
In a descent, the capsule....
When descending Ps increases thus the the Ps in the capsule is greater > then the px in case
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)
When will the IVSI have disturbance erroneous errors?
IVSI will have a slight climb error during a turn and
Also in turbulence
If a VSI is blocked, what will it indicate?
What is the error when there is a px leak outside the px cabin?
Still works but a little less accurate.
What is the error of an VSI if there is a leak within the px cabin?
Only measures cabin altitude. Shows instantaneous descent.