Saturday, May 14, 2011

Inside the Cockpit – Vertical Speed Indicator (VSI)



The vertical speed indictor (VSI), also called a vertical velocity indictor displays the rate of climb or descent in feet per minute.  Basically it how steep your climb to drop may be.  Instead of telling you the slope of the angle, it is telling every minute how many feet (in hundreds) you are going.  For example, it the needle was steady at 5 (above the zero) I would know that I could go from an altitude of 2,000 to 3,000 feet in two minutes (500 feet x 2 = 1,000 feet).


The VSI is capable of displaying two different types of information.
  • Trend Information shows you an immediate indication of an increase or decrease in the airplane’s rate of climb or decent.
  • Rate information shows you a stabilized rate of change.

One way this information is useful in a particle sense is that it helps the pilot predict better when they reach their desired altitude without over shooting.  When the pilot levels off the aircraft, depending on speed and other factors, it can take seconds before the aircraft climbing or descending.  This can mean hundreds of feet difference than desired.  So if I’m 200 feet away from my cruising altitude, and I’m descending at a rate of 500 f.p.m., then I know to start leveling off now since I’ll reach my altitude in just a few seconds.

The VSI uses the static port pressure to display its information.  The static port is usually flush-mounted on the side of the fuselage in an area of relativity undisturbed air flow.



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