Variometers Types Explained

What is a Variometer

A fast response rate of climb instrument usually scaled to match typical glider rates of climb and descent (+/-10 knots). The variometer makes soaring possible by displaying the glider rate of climb to the pilot in near real time, enabling the pilot to manoeuvre the glider so as to remain in rising air. Variometers come in many types, some sense the airflow from a capacity bottle or flask (as the outside pressure increases or decreases due to altitude changes - air then flows in or out of the flask to equalise the pressure) either mechanically or electrically, others measure the air pressure directly using silicon pressure transducers and compute rate of climb electronically from the changes measured. Most instruments suffer from lag and vario’s can have around 1 to 3 seconds of lag. Modern electronics and computation in instruments such as LX Nav's Hawk software upgrade howvere, can all but eliminate this lag so the indication will match your 'seat of the pants' feel.

Mechanical Vario

Mechanical vario’s do not require electrical power to operate. Mechanical vario’s don’t have all of the fancy features that most electric versions do, but because they don’t rely on electricity to power them they are, at the very least, a good back up in case of a power failure.

Electric vario

As the name applies, an electric vario requires power to operate but in doing so gives the pilot some other features such as audio and averages.

Audio – To allow better lookout, electric vario’s can give out an audio tone that changes as the lift increases or decreases.

Averager – Some electric vario’s can give an average climb rate over a 20 or 30 second time period. This will give the pilot a more accurate actual climb rate as it is averaged over about one thermal turn. Some instruments will also give a bottom to top average (from when the glider starts turning to when it exits). Most basic electric vario’s will show the average climb rate on the dial when holding down a button while the audio remains as a standard TE (Total Energy) vario. Higher end vario’s will have a separate LCD screen showing the average climb rate.

Netto Vario

A Total Energy (standard) variometer as described above can be further improved as the standard vario will, in still air, not take into account the sink rate of glider at the speed being flown. As a glider increases airspeed, its sink rate also increases and this will show up on a standard vario as sink. A netto vario knows the polar curve (sink rate at various speeds) of the glider and is plumbed up to sense the airspeed. The end result is that the gliders sink rate is removed from the vario reading at all speeds. What this does is to help the pilot to pick the best path through the air in cruise (which is the path with the most and fastest rising air and OR the least and slowest sinking air). It also helps a pilot to decide whether or not to turn in lift while in a fast cruise as a standard TE vario won’t show the full strength of the lift. For example, 8 knots of lift may only show up as 3 knots due to the gliders sink rate at high speed.

Relative Netto Vario (or Super Netto)

There is one disadvantage with a netto vario and that is if we fly through our thermal rising at 8 knots we see 8 knots on the netto vario regardless of the airspeed we are flying at. This is fine until we begin to turn and thermal as a netto vario is only set for straight line flight and by turning, the gliders sink rate has increased for the same airspeed. A relative netto vario will compensate for the circling sink rate of the glider. What this means is that in “still air” while cruising, the vario will read about 2 knots down at all speeds. Not perfect for cruising but will still work fine if the pilot takes it into account The up side is that the vario will show what the climb rate will be if the pilot decides to turn in lift.

No TE Probe electronic variometers

The latest in variometer technology. Best explained here by Tim Bromhead in a couple of his Pure Glide videos.

And what it is like to fly with the Hawk.