You might think that a vario altimeter is pretty simple. All it does is beep when you're going up and tell you how high you are, what more could you need to know? This article aims to reveal some of the hidden settings that most people don't understand and explain how to use the vario to best effect when flying XC.
1 - Sensitivity
Use your vario in HD mode
When you buy a new vario it comes set up and ready to use, but by who? The people who build varios certainly don't fly much in the UK! A new vario is set up perfectly if you're a profession competition pilot living in Switzerland. Figure 1 shows the typical response of a new vario.
The tone changes over it's full range from about +200 to +2000 feet per minute, perfect for flying in good, strong, spring alpine conditions. This isn't much use to a UK pilot who's trying to stay in the air in a weak, damp thermal coming off a peat bog. Firstly, the whole range below 200 feet per minute is silent because competition pilots in the Alps aren't interested in weak thermals. Secondly, the only way to get to +2000 feet per minute in the UK is to fly up a thunderstorm. The area highlighted is the typical range of thermals in the UK, on a good day. If you mostly fly in the UK, you can adjust the response to match. Figure 2 shows how I prefer to have my vario set up.
By moving the zero point down to zero, the vario will respond to any small patches of lift. I like to know if the air's going up, however slowly. By moving the saturation point down, the vario tone will 'max-out' sooner, so the change of tone for a given change of lift will be greater. This does mean that very strong thermals will all sound the same but this is offset by improved resolution at the bottom. I can find the core in a strong thermal by feel, it's the weak ones that I need most help with.
2 - Sink Alarm
Know when to speed up
The sink alarm tells you when you're going down. Many people turn it off, as though this somehow makes sinking air easier to fly through. If you set the sink alarm to just beyond the normal trim speed sink rate of your glider, (typically -250 feet per minute), it will only sound when you're flying through real sinking air. If the sink alarm is set to -300 feet per minute, it will sound whenever the air is going down at a rate that would require some speed above trim to achieve best glide, so the sink alarm becomes a 'speed up alarm' and the loss of the sink alarm becomes a 'return to trim' signal.
3 - Use the Integrator
Know when to leave a weak thermal
The integrator is also know as an 'averager', as it gives the average strength of the thermal over the last 'x' seconds, where the number of seconds, 'x', is adjustable between about 5 and 30. I suggest setting it to 10. Ten seconds is enough time to make one, lazy revolution in a large, weak thermal. Any less and you're not getting a complete picture of the thermal, any more is leaving it longer than necessary.
A common piece of advice for cross country flying is, "Never leave lift." This is most useful when the wind is strong, staying in weak lift when drifting downwind is an easy way to eat up XC kilometers. However, when the wind light, staying in weak thermals will often be counter-productive. You can waste time and height by trying to find a long gone thermal bubble while going nowhere slowly. The integrator, when used properly, will tell you if it's really worth persevering with the lift or if it's better to push on and look for something better.
4 - Use the 'Relative Altimeter'
Know where the clouds are
Most varios have at least two altimeters. One is always an 'absolute altimeter', which reads in either feet or meters above sea level. This is most useful for staying out of controlled airspace, which is always given as a height above sea level, in feet in the UK. Flight levels are heights above a theoretical sea level at 1013 mBar. Absolute altitude is also useful when discussing altitude on the radio, so that everyone is talking about the same altitude.
Knowing how high you are above the sea isn't very useful, most of the time. If you're flying alone and away from airspace, it's totally irrelevant. Most varios have a 'relative altimeter' that can be zeroed at any time and displays your height above or below that reference point. Many pilots use their relative altimeter when flying at the hill, to display height above take-off. Normally, the relative altimeter is zeroed when the vario is turned on, so it will display height above take-off by default. I find this very useful, for example, when planning a top-landing. It's also nice to see the relative altimeter tick over to 4 figures, I always try to get to 1000ft above take off before committing to an XC flight.
Knowing how high you are above take-off is next to useless once you've set off on a downwind XC flight, yet most people leave their relative altimeter displaying their height above a distant hill that they have no chance of returning to anytime soon. When I leave the hill and set off downwind, I give my relative altimeter a more relevant reference by zeroing it at cloudbase.
This has two uses.
Firstly, you can easily see, at a glance, how far you are below the cloud that you are climbing under. It's sometimes difficult to tell the difference between a small cloud, nearby and a large cloud, far away. They all look the same! Watching the negative value tick down to zero as you approach a cloud is a lot easier than trying to judge it by looking. On blue days cloudbase is still there, the thermals still stop at a constant height determined by the lapse rate but above the dew point. Knowing exactly where that point is will enable you to make better decisions and fly further.
Second, cloudbase usually rises during the day. Each time you reach cloudbase, before zeroing, it will normally read slightly positive, indicating the the cloud is higher than the last one was. This information doesn't actually help much, but it's better than knowing how high you are above a distant hill that you can't even see any more.