VSI Question

chewsta · Post by **chewsta** » Wed Apr 14, 2004 5:58 pm

Can anyone explain why the VSI has an opposite indication when a climb/descent is started abruptly?

sakism · Post by **sakism** » Wed Apr 14, 2004 6:04 pm

Very simple.

Needle is mounted horizontally. With an abrupt movement of the aircraft, inertia causes the needle to resist the movement of the aircraft momentarily.

If you've ever done the 'floating pencil' trick - same principal.

shitdisturber · Post by **shitdisturber** » Wed Apr 14, 2004 8:00 pm

The floating pencil is nowhere near as much fun as playing "float the student"!

snapped · Post by **snapped** » Wed Apr 14, 2004 11:42 pm

MAke sure a coffee cups are empty

imfsub12 · Post by **imfsub12** » Thu Apr 15, 2004 7:47 am

we did the floating book trick, and took a movie of it and then watched it when we landed. and it was ok till we started to laugh so hard that we looked in he back of the plane and all the book and stuff was floating in the storage bin... now i know why there are nets there...

oldtimer · Post by **oldtimer** » Thu Apr 15, 2004 9:09 pm

Turbine twins all have or should have IVSI's just to cure that problem. An IVSI has an accelerometer that will get the thing going right direction instantly. That the "I" in IVSI.

ahramin · Post by **ahramin** » Thu Apr 15, 2004 9:45 pm

Our IVSI actually stands for Intermittent. But we don't really have a problem with the VSI reading the wrong way as we do very little wrenching around the sky anyway.

But the best systems are the electronic variometers we have in the competition gliders. A total energy probe sticks out of the tail and measures both forward and vertical speed. If you pull back on the stick in smooth air, the vario shows no change, as you are trading off kinetic energy for potential. When you hit a thermal it shows you how much energy you are gaining. In addition you can get your climb rate integrated over the last sixty seconds at the push of a button. As well as an audible tone so that you do not have to look at the vario as you are soaring (very important when you are climbing in a gaggle with 20 other gliders).