B - The VSI (17-05-18) Flashcards
How does a VSI work?
It senses rate of change of static pressure by a static tube feeding directly to the capsule with a metering unit/choke valve feeding static pressure into the casing but in a delayed manner.
So the static pressure is reached in the capsule before the casing.
What errors are associated with a VSI?
Lag
Instrument error
Maneouvre error
Position/pressure error
LIMP
What is the lag in a VSI and what is it caused by?
Approx 4 seconds and cause by the static pressure taking time to be reached in the casing.
How does an Instantaneous/Inertial lead VSI work?
An accelerometer/dashpot damper/dynamic vein causes air to immediately draw in or out of the capsule causing a pressure differential to occur immediately so the 4 second delay is eliminated.
A bypass restrictor directs the air in and out of the capsule instead of going elsewhere
By the time the accelerometer returns to neutral the pressure difference between capsule and case has been achieved.
What errors are associated with an IVSI?
Instrument error
Maneouvre error
Position/pressure error
Turbulence error
Turning error
IMP TT
What kind of error do VSIs and IVSIs experience worse than others and why?
Maneouvre error due to the principle movement during their operation being pitch.
How does a blockage of a static port affect a VSI?
It will cause the needle to remain at or return to 0 due to the pressure in the casing eventually equalising with that in the capsule and it not being able to change.
How would a leek in the static port affect a VSI in a pressurised aircraft?
It would initially show a rapid descent followed by it measuring any change in cabin pressure
How would a leek in the static port affect a VSI in an unpressurised aircraft?
It would show a small blip initially but then continue to work normally
What kind of display is on a VSI?
logarithmic
What glide slope do you assume for approach unless stated otherwise and what is your required rate of descent?
3 deg and 5 x GS
What is the 1/60 rule regarding rate of descent and nm miles to destination?
For every 1 deg of glide slope, your rate of descent is 100 x the number of nm to destination.
