The Variometer

[Squawk7777]

I was furtunate enough to be invited to take a ride in glider. One instrument that caught my attention in the Grob G103 was the variometer. It looks like a VSI however, the vertical rate is not measured in ft/min but in knots. I was told that the variometer measures true lift.

None of my old ATPL notes or any other book I found even mentions this instrument. Since it is obviously very much gliding related I wonder if there are (ex) glider pilots on pprune that wouldn't mind sharing the principle of this instrument.

[Volume]

I think this will answer all your questions :
Gene Moore (http://www.betsybyars.com/guy/soaring_symposia/69-vario.html)
Part II (http://www.betsybyars.com/guy/soaring_symposia/70-vario.html)

[cwatters]

Did you turn the vario sound up?

The audio pitch is proportional to rate of climb so you either get a wonderfully exciting shreek or a depressing low pitch growl. The sound the vario makes always seems extreemly appropriate to me.

[Circuit Basher]

Of course, there are about 3 types of variometers:-

The ancient one, which consists of (IIRC) 2 fluid-filled tubes, one with a red floating level indicator and one with a green floating level indicator. As you hit rising / sinking air masses, either the green or the red float rises up the tube, according to whether you're in lift / sink.

The 2nd type is more or less a VSI (with the same construction and working on the same principle) but with a much more sensistive indication of lift / sink. This is purely mechanical.

The 3rd type (which is what cwatters refers to) is electronic and has a variable audio tone according to the rate of lift / sink. This is particularly useful when trying to centre on patchy thermals as you can stay 'heads up' rather than trying to scan your vario whilst trying to dodge all the other pilots who are trying to get in on 'your' thermal ;) It's a very quick reacting instrument and can be really irritating during normal flight or when well established in a thermal. It does have its uses and IMHO is a good flight safety feature for gliders.

[ft]

Only three? :) VSI, IVSI, TEC VSI... all can be electronic or various kinds of mechanical devices (vane, twisted glass ribbon, diaphragm...).

Then you have VSIs and altimeters which connect to your GPS and handheld computer. You can get graphs of the lift around the circle while trying to center a thermal live on-screen. The gadgetry has advanced far!

I recently heard a description of how to prepare a real gadgeteer for flying in mountainwaves. "Place pilot in cockpit. Fill cockpit to rim with electronics. Put helmet on head of pilot. Send off". :D

Cheers,
Fred

Edited to add some highlighting ;)

[Mike Cross]

Wot about the difference between a total energy variometer and a VSI?

The VSI measures how fast you are going up or down. The total energy vario compensates for speed changes.

For example you are gliding in still air. If you pull the stick back you will reduce your rate of descent and a VSI would show it. However you are trading speed for height. Although your VSI may show that you are climbing you are not actually gaining any energy, as you would in rising air, all you are doing is converting kinetic energy into potential energy (height).

This is not much use for the glider pilot so the total energy vario takes inputs from pitot as well as static to give the pilot an indication of total energy rather than rate of climb/descent.

In a typical scenario the pilot is flying through sinking air and has increased his speed so as to spend as little time in it as possible. He hits a thermal and immediately slows down and circles to take advantage of it. During the slowing down he will be converting speed to height. Without compensation a simple VSI would show the thermal as being much stronger than it actually is. It wouldn't show the true position until he had settled at a constant speed, at which point he might find that the lift was not as strong as he thought and not worth staying in. Total energy compensation works to eliminate this effect.

Mike