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Variometers

BootBeeepbeepbeepbeep! Ah, that little voice of joy, the singing variometer. What it lacks in aesthetics it makes up for in the extended flight time. The views of grandeur it helps you attain soon make it an inseparable partner in xc flying. So you've finally got one strapped to your leg, but apart from the obvious, how do you interpret the beeps, bloops, squirgles and silent figures? To get that little bit higher, to fly that little further, I address two items - the averager function, and the first turn.

1.1 The Averager Function
Varios usually come with an analog display (the little needle or bar) and a digital one (little number like 1.4). The needle shows the immediate effect of lift and sink. The digital number can also show the same information, but it has an averager function which is very useful. When you buy your vario, the digital averager is usually set to 1 second. This renders the useful averager function useless. To check your vario, lift it by hand and watch the readout. If your digital number reads very close to what your needle shows, you have a delinquent vario, and it needs to be disciplined. ( If the vario sticks on 5m/s up, and doesn't stop squealing, kiss it, and go flying. But that's another story.) Your vario manual will tell you how to change the setting for 'averager time' used to calculate your average lift/sink. Its a setting that usually ranges between 1 .. 30 seconds. I use 15 seconds average. Why is this so usefull for flying xc?

As you are getting bumped around in the sky, cranking into scrappy bits of lift, falling out the badly shaped thermals, rocketting up in other bits, and then plummetting on the other side, or simply boating about in a light, inconsistent thermal, the Averager will tell you if it is worth staying where you are. It cuts out all the little ups and down caused by the glider moving around, and gives you a smoothed picture of what is going on. The needle will still give you the immediate lift/sink, and is unaffected by the Averager. In effect, you now have TWO varios (I'll call them Needle and Averager, from now on), one telling you when to tighten up your turn (needle reads a high climb rate) the other telling you whether you are, on average sinking, and need to move on.

1.2 The first turn
Because the vario has a minimum one-second delay (it needs a bit of time to work out what's happening) it is telling you what the air BEHIND you is doing. So if your needle is showing up - turn! - the thermal is around you and behind you.

In Natal the thermals are wide and gentle, due to the moist air, and mellow ground cover (grass, rivers). Pilots do well by turning in gentle, wide circles with little bank or body-steer. In the Cape we have tight, narrow thermal cores with heavy surrounding sink, due to the ever-present inversion, the dry air, and strong thermal sources (brown rocks, bare earth). Which means that if you wait until your vario shows the lift has slacked off, you will inevitably be turning in the sink immediately outside the thermal. You will experience a wide, frustrating turn - because you are turning, you lose more height than normal. Because of the sink, your turn is wider than normal. When you finally complete a circle and come back into the thermal, you may well be beneath the bubble, and never find it again. What's the solution? When you see lift on the vario, bank and turn. Which way? The thermal will try to push you out - If it rolls your glider to the left, resist the roll by leaning over in your harness to the right. Turn right, tight. You can always widen the turn once you are established in the thermal. But if you lose it, it's gone - ain't no crying gonna bring it back, no no.


A pilot, Mark Borzony, commented : How can you be sure that you are in the best part of the thermal (core) if you immediately turn on the up? I prefer to wait until the vario drops slightly and then I have a better understanding of the size or magnitude of the thermal.

Point taken Mark, but I am not turning immediately on the up. I am turning immediately on the vario's up, which is a second later. The skill to centre on the best part of the thermal core in the first turn is something which takes a lot of time and practice. The technique can be refined as you say, and I agree with you - I do that sometimes, cruising straight until I sense the slightest dropoff, but I turn when I feel the dropoff, 1 second before the vario begins to slacken off. Often the time between the vario slackening off (one second beyond when you have passed out of the core) and dropping out of the front of a thermal is very short. Especially in strong winds, the core is often toward the front edge of the collumn and the dropoff sharp. Also I have seen that most pilots beginning on thermalling and xc tend to turn in wide circles, slowly. It has nothing to do with the amount of brake input, it is the timing of the turn, and the lack of weightshift before the turn. If they start their turn with at least a part of their wing in the true core, then they'll have a chance for a better turn, remaining in lift for at worst 3/4 of a full circle, being able to straighten a bit on the second circle.

My advice in the dry Cape is to assume its a small thermal, hold on to it for the first turn, tight, then widen gradually until you have established the boundaries of the lift. That way you avoid the risk of dropping out the front, sinking in a wide turn, and losing the bubble completely. Your technique works too, but I feel it is more suited to Natal flying, and local days with very moist air masses and hence wide, big thermals.

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