March 1, 2003

Different lift types
By Mike Miller

After an extensive search of the internet and of the available literature, I found that there has been little in the way of classifying lift types encountered in flying sites. There are many clues that can be used to determine which type of lift you are in, and how to fly that lift. Those clues are more than just the sound of a vario. They involve looking at the time of day, the landscape, the wind cycles, the brake pressure, the accelerations you feel and most importantly, talking to the local pilots.

We have available in Canada many flying sites which presents us with different lift types. I’ve found there are sites, which will have different types or kinds of lift at different times of the day.

I think that when pilots first learn to fly, they get used to a particular style of lift in their area, and tend to be wisely wary of anything different. It is during those one or two days of different lift when the experienced pilots sky out, while the others sit on the ground looking up at the fun wishing to be up there too.

The three types of lift mentioned in the literature I have come across are well known and many of you have perhaps experienced them: thermalling, ridge lift and magic lift... We have all hit the "classic " thermal, with a "bubble" of rising warmed air.

Then there is ridge lift. That’s when the wind strikes a ridge, and it is forced upwards. A ‘band of lift’ is generated by the diverted air as it moves over the ridge (or any object).

Finally, we see "magic, or restitution lift." This occurs when at the end of the day, warm valley air rises en-mass due to the cooling of the air above it.

As we fly, we are subjected to two accelerations; vertical and lateral. If you tune into these feelings through the brakes you can use it to centre yourself into a thermal, or to tell if it is a thermal and not some other type of lift.

Below is a list of all the lift that I could think about.

• Basic Thermal
• Dynamic (ridge) lift
• Magic Lift (Restitution Air)
• Convergence lift
• Converging thermals
• Wave lift
• Frontal Wave lift
• Ridge thermal convergence
• Leeside thermal
• Ground Effect
• Dynamic lift with thermals
• Pant thermal
  

I plan to give a brief description and location of occurrence, to outline how it might look, describe how it feels in the air then list some possible indicators of this particular type of lift.
So, to begin:

1. Basic Thermal

The cause is air heated from the ground rising, like it does from an electric heater or wood stove, or car hood or hot pavement in the summer.

The common view of this is a mass of warm air is rising in either an isolated bubble or as a column. It does rotate, but not with any regular direction. Sometimes it even rotates horizontally. This model works for most, but can be disputed by the physics experts. But what is important is what a thermal does and where to find it.

In the morning of sunny days you will feel and see short duration increases of wind on the east and south facing inland launches. These are the short, young thermals rising from the sun-heated ground. As the day progresses, the south and south-west sites will experience these wind gusts with increasing frequency and force until it may become a constant breeze around 1:00-3:00 in the afternoon.

How does it feel in the air? As you approach the thermal, the wing will speed up slightly. If the thermal is large, you may encounter some turbulence. When the wing enters the thermal, you will feel the brake pressure suddenly increase. If only one side of the wing enters, that side’s brake will tighten and then the wing will lift on that side and the thermal will try to ‘spit’ you out by turning the wing away from the thermal. If you enter the thermal straight on, the wing will pitch backwards. The pitching is caused by the front of the wing being forced upwards and backwards. The best thing to do is to keep the wing flying fast until it is level, then slow down and begin turning. Turn either into the lifted side, or the direction you think the thermal is. If you can feel it, turn towards the lateral acceleration or ‘push.’ As you circle, adjust your circle to keep the brake pressure constant. Take the wind drift into account and watch you don’t get spit out the back of the thermal into turbulence, or toward solid objects.

There are tactile, visual, auditory, and olfactory clues to a thermal.

You can feel temperature differences, although often I’ve smelt it from pollen, moisture, or ground sources i.e.: cow shit.

Look for bugs, as they don’t like to go high so if you see one, it is most likely caught in a thermal. Also, look for seeds like Cottonwood, Dandelion, Fireweed, etc.. Birds can be an indicator, as can the local newspapers front page.

Finally, listen to the wind. The loudness and pitch may vary as you approach, then it gets quieter as you enter the edge of the thermal. In the thermal the wind noise picks up to slightly louder as you accelerate vertically.

From the air you will see indications on the ground. This could be a swath of trees waving while those around it are still, cats-paws of riffles across bodies of water, windsocks in front and below you picking up and blowing in one direction, then the wind indicators beside you stand out.

Feel the wind on your face, constant and steady in direction and speed.

2. Dynamic (Ridge) Lift

The wind is blowing, and you are sipping your first Margarita at the beach when you see behind you a bare ridge top.

You’ve fallen out of your beach chair, you scramble up to the top of this 20-2000 m hill to find the wind fresh, but less than 30kph. It is near midday, and your wing is laid out with plenty of room if you get dragged backward. You can see a place to safely land below you and you won’t die if you go up and backwards. You can also see the ocean in front of you to keep an eye on wind speed by watching for consistent whitecaps on the waves.

As you reverse launch, you fly the wing and don’t worry that your feet are off the ground but you are still facing backwards.

Note: Good reverse launching technique is a must.

You begin to crab to the end of the ridge, your brakes are pulling smoothly, without any jerks or increase in pressure regardless of ascending or descending.

You slowly find the sweet spot, above and in front of launch, within the compression zone of the lift band. As you climb higher the lift band becomes broader but weaker. You can now soar above, in front and behind launch. But, you find that the further back you go, the stronger the wind gets and the less lift you find. Welcome to venturi-land.

Venturi-land: the lift back here is now converted to a compressed, horizontal, higher velocity air flow that will see you either going backwards or straight down.

First, use the speed bar.

Second, try to find variation in the terrain that will give some lift. Or, find a place along the ridge where you can turn crosswind or downwind and land in a rotor and tree-free zone.

Ridge soaring involves using slightly more brake while watching carefully for increasing winds, or changing wind directions that will leave you sinking out where you might not want to.

Ridge Soaring is easy once you’ve mastered the high wind reverse. So much so that after a while you might know it by it’s other names; Ridge Boring.

3. Magic Lift (Restitution Air)

Ahhhhh!

Here is the favourite lift type for newbies and for old hands. It has been named Magic; Restitution; Idiot air....

But it is smooth and effortless lift that seems to span the whole area you are flying.

This lift occurs at the end of a warm day in spring and early to mid-summer. It is usually in a valley system, with a general east-west orientation.

The launch will show a moderate to strong, steady wind. There may be a few end of day thermals making the windsocks pick up a bit more... remember this for later.

Reverse technique is suggested.

After take-off, the wind speed will decrease but you will notice light lift, everywhere.

The brakes will give smooth, even pull and there should be very little feeling of acceleration, either lateral or vertical. But regardless of where you go, up you go.

What is said to happen is that as the sun lowers the upper air cools and the warm air trapped in the valley begins to expand? The south or west facing slopes also benefit from this by cool air sinking (catabatic) on north or east and forcing the valley air up on the S. and W. aspects.

I’ve had magic air be set off from an incoming valley wind pushing off the warm air.

You can tell it is magic air by the time of day, sunset, and by the history of the site you are at.

Keep an eye on your landing site; the wind just above the ground can be 180° from what you are in due to surface catabatic flows.

4. Convergence lift

Convergence is the coming together of two air masses. They can either collide, or meet at angles from 120° to 180° . Less and they just make turbulent wind.

It can be large scale covering kilometers or a local effect over a particular ridge.

Finding it is usually a matter of timing, luck, and/or experience.

It feels like a rough ride! Ever sit on the beach and watch an outgoing wave hit an incoming one? It can feel about as bad as that looks.

You begin to experience turbulence, with slacking and tightening brake lines lots of lateral accelerations and quite a bit of wind noise that varies in volume and pitch. Active flying is a must do.

The air is mixing, so there will be times when you are going down, although with all the bumping about, on average, you do climb. Sometimes to the point where you have to fight to get down.

So not only are you in holy-shit air, you are also in it for a very long time.

Now, this isn’t as strong as full-on rotor. The wing moves around a lot but there are few collapses. It is full-on flying.

Most of the times I’ve encountered this have been at inland sites, overlooking a broad, flat valley. In these cases, you look for dust or smoke to change direction on the valley floor. Or a light haze will appear on the horizon and make its way towards you. You may see it by an increase in dust devils.

The best way to tell is by the constant turbulence, by which time it is too late to do anything but fly it.

Flying the wing fast, without speed bar, and actively works best in this air. You may find that nearer to the ground you suddenly find smooth air, so take the time to relax and get your mind wrapped around either landing or finding lift again.

Continued in next issue