Ultralight Soaring
by Ian Coristine

The Exhilaration Of Power-off Flight
COPA / Canadian Flight

A Primer On The Joys And Techniques Of Soaring An Ultralight

Ultralights. What wonderful inventions. They not only give us inexpensive flying, but so many new and wonderful ways to enjoy the skies. Their short takeoffs and landings let us go places that normal planes can't go, and their climb performance is thrilling. Floats are an adventure in themselves and so are skis that also take the boring out of winter.

If you've tried some or all of these things and think you already know all about the true essence of flying - wait until you try soaring. To spend the afternoon in almost total silence with the engine turned off, climbing to cloud base in one thermal, then drifting off to float up again in another is as close to being a bird as I've ever been. I guarantee that you'll love it.

What do you need to do it? Any good two seater ultralight flown solo will likely be capable of giving you a taste of soaring, and if its sink rate and stall speed are sufficiently low you may have just the ticket for a wonderfully satisfying new experience. With a little knowledge and practice, you'll be able to welcome the challenge of extended power-off flight, and the prospect of an engine failure that would strike terror in the hearts of most general aviation pilots will cause you little concern.

Most people think glide ratio is what makes a plane soarable, and they are largely wrong. There is a big difference between glide ratio and soarability. Believe it or not, jet airliners have a surprisingly good glide ratio but don't expect to do much soaring in one. Bob Pearson is an Air Canada captain (and a partner in my first 2 seat ultralight) who had both engines of his Boeing 767 flame out at 41,000 from fuel exhaustion. He glided his powerless 132 ton airliner with 69 people on board over a hundred miles of unlandable terrain to a successful landing on an abandoned airstrip in 1983. He was able to do that because of the plane's glide ratio, not its soaring capability. Obviously this is an extreme example, but airplanes with good glide ratios are not necessarily good at soaring.

Successful soaring comes first of all from being able to find and efficiently use thermals, the sometimes bumpy rising air that you encounter on sunny afternoons, often accompanied by puffy cumulus clouds. When the sink rate of the airplane is less than the rate of lift of the thermal, you will go up. It's as simple as that. There are other forms of lift too, like ridge lift and wave, but they both require special conditions and topography that are not available to everyone, so we'll stick with thermal soaring here.

If you want to soar, you need an aircraft with a low power off sink rate as well as a low power off stall speed. The lower, the better. If you can have glide ratio as well, so much the better, but without the first two items, don't expect to stay up with the motor turned off. The lower the sink rate, the less of a thermal you will need to keep you up, and the lower the stall speed, the smaller the diameter of the turn so you can keep in the small center core of the thermal where the lift is strongest. Low sink rates and stall speeds are enhanced by low empty weight and large wing area (light wing loading) and low drag. Ultralights are generally good at the first two items so if yours is also reasonable from a drag standpoint (preferably not wire braced or side by side) then you can probably expect it to soar.

I have found some people to be uncomfortable flying in thermals, finding the unpredictability of the lift and bumps disconcerting and unnerving. Understanding what's going on will make it a lot less intimidating and as you learn how to put the lift to work for you, it will become your friend and ally, to be sought out and used at every opportunity.

Even if you're not actually soaring, thermals can be very useful. They make a welcome source of lift on a hot summer day when you're heavily loaded or on floats and will help you get to altitude much more quickly. What goes up also comes down and that includes air. Remember the time you were at full throttle and not climbing worth a damn? That's the sink. Want to avoid it? A little understanding is all it takes.

Thermals are simply big bubbles of heated air that break loose from the sun-heated ground and float upwards. Often (but not always) the warm air reaches a height where the cooler temperatures condense the moisture in the warm air to form the round puffy cumulus clouds that you often see on summer afternoons. Have you ever noticed mornings that are calm and clear as a bell are often followed by breezy afternoons where the sky is littered with cotton balls, and then have the calm, clear (or clearing) conditions return in the late afternoon or early evening? That's because thermals need the warmth of the sun to form, and in the early morning and late afternoon the sun is at too shallow an angle to provide sufficient heating. For the same reason, the very best soaring conditions are generally found in the spring and early summer, when the days are longer and the sun higher, thus providing more effective daytime heating.

You may have thought that those cumulus clouds simply drifted there from somewhere else. That's not the way it works. While the wind may drift them somewhat, they are continually forming and dissipating. Picture the sun beating down and warming a plowed field. As the earth gets hotter, it will radiate heat that will warm the adjacent air and when this mass of air is buoyant enough (hot air rises), it will break loose and float upwards, making a tall column. If it is a particularly strong thermal, it may suck others loose that will converge with it to make the lift stronger and broader as it gets higher. If the air is moist enough, a cumulus cloud or Cu (pronounced quew in glider slang) will form marking the top of the thermal. When that thermal has cycled, and all of the warm air feeding it has risen, the lift will disappear and the cloud will begin to evaporate. This cycle repeats itself as long as the ground is sufficiently heated for the process to operate.

Often, you can identify likely thermal generators by looking at the terrain below. If there are mountains or rolling hills, the sides facing the sun will get warmed more efficiently than the flat land and are the best place to look for thermals early or late in the day. On the flat land, or when the sun is higher, look for surface terrain that is likely to collect the heat the most efficiently. Villages or built up areas with lots of asphalt and little vegetation are good prospects. Sandy or rocky areas are also good, as are plowed or freshly harvested fields. Young or low growing crops where plenty of soil is visible are a better prospect than those with higher growth or forests. Darker fields are more likely than lighter ones. You get the idea. All of these and more are capable of generating thermals. Some will develop thermals more rapidly than others, repeatedly popping them into the sky like an Indian's smoke signals. Perhaps you can remember seeing cloud streets, a series of Cu's all in a line drifting downwind from the source. These are a glider pilot's delight.

Ideally then, a thermal should be very easy to find. Simply look for a Cu in the sky, then look beneath it for the heat source and go fly between the two. In ideal circumstances that is exactly the way it works, but with 3 to 7 thousand feet between the cloud and the ground in my area (it may be well over 12 thousand feet if you are lucky enough to live on the prairies or south central U.S.), it's pretty difficult to be sure that this sand pit generated that particular cloud.

Some days the air is too dry for any marker Cu's to form, or a fresh thermal may not yet have risen high enough for the Cu to have developed. These last ones by the way, are usually the best of all. In any case, with a wind blowing, the thermal will not rise straight up, but at an angle with the top downwind from the source. How far downwind will depend on the strength of the wind. One way to get an idea is to look at what effect the wind is having on any smoke that you can see.

Picture a thermal from above as a 4 ring target. The bull's eye or center circle is the core of the thermal where the lift is strongest. This is what you want to find and where you want to spend your time. The next circle out, the second one from the center provides reasonable lift, but not as strong or as consistent. The 3rd circle is pretty jumbled, partly lift and partly sink. Something is going on, but it's not usable. The outer circle is sink, usually about as strong as the core's lift and to be avoided.

Because of the effects of the wind or perhaps even the terrain below, this ideal thermal is never a perfect circle. It is more than likely quite irregular, but the circle description is close enough to give you the idea.

Thermal strength and duration will vary greatly, largely due to weather conditions. An unstable air mass is best, often found following the passage of a cold front. Thermals are like fingerprints. No two are exactly alike. Some may last for a long time, providing an extended period of lift in the column between the generator and the cloud. Others may be cycling faster however, so that it is not at all inconceivable that you may be circling in the right spot, but the thermal may not have broken loose or reached you yet, or that it may have already passed you by, leaving a sucker Cu above but with no lift left at your altitude. Some may provide large diameter easy thermals where a gentle angle of bank will suffice, others may be small and sharp requiring a more aggressive angle of bank. I have seen thermal strengths from just enough to stay afloat, to 'boomers' of well over 1000 feet per minute. There's no shortage of variety.

Once at any height, I find clouds a more reliable indicator of lift than terrain, especially if you are close to them. Gliders have to earn their way up to the clouds, but we can cheat by using our own built in 'gasoline thermals' and that may be useful as you're learning. My experience is that as the thermal gains height, it usually gets more organized and easier to use, so I recommend that you power your way to within say, 1500 feet of cloud base and sniff around. Once you get a feel for it you can try it at lower levels or without the marking cloud.

The best Cu's are the ones in their growing stages with the thermal pumping them, not the ones that look tattered with ragged bottoms that are dissipating after the lift has cycled. I find the good ones have a healthy look to them and even seem to glow. A dark, concave bottom is a sure sign that this Cu is worth investigating. Look for the best lift where the cloud is darkest or the most concave. Don't always expect the lift to be right under the center of the cloud, however. If it's a big one, or if the wind is blowing, the lift may be feeding the Cu on the downwind side or elsewhere. Once you find where, look for it in the same place on other clouds that day.

So now that you've found the lift, how do you use it and get the best out of it? The best way is with the help of a variometer. To a certain extent, you can work the lift by feel, but you will miss all the subtle clues, only feeling the major transitions, and those only after you've become attuned to it. If you want to do well at this, I strongly recommend investing in a variometer. This wonderful instrument is actually an extremely sensitive rate of climb or Vertical Speed Indicator. Forget using your standard VSI. It's way too slow to be useful. By the time it registers that you're going up, you will probably have left the thermal and be in sink. You need a real variometer.

There are many fancy ones out there made by Winter, Ball, Cambridge and others with many varied and useful features. The best ones can get quite expensive. I get by very nicely with a hang glider type variometer made by Makiki in Hawaii. It cost about $100 and uses two little pellets that rise and fall in 2 parallel columns in a clear Lucite cube connected to a separate flask that measures the change in air pressure. When the green pellet rises I'm in lift, and when the red one rises I'm in sink. Very simple. Depending on how high the appropriate pellet rises, you can tell the rate of climb or sink accurately at that particular moment. Stay in the area which makes the green pellet rise while avoiding the area that makes the red pellet rise and you'll go up all day long and have a ball. In reality, it's impossible to stay in lift all the time, so what you want to do is maximize time in the best lift and minimize time spent in lesser lift and especially sink.

Here is where technique comes in, and practice makes perfect. My method is as follows. I fly in a straight line towards where I suspect there is lift. Often the lift is preceded by sink but as I get closer, the sink lessens followed by a bump and a hint of uncertain lift on the variometer. It feels almost like a jiggle. Remember the 2 outer rings of the bull's eye? Sink in the outer one followed by mixed up, uncertain air in the next. Then comes the lift. I keep the wings level but usually one wing will want to lift more than the other. That's the side the thermal is on. I watch my variometer as the lift builds and as soon as it peaks and starts to fall I turn to the side the wing rose and start a full 360 degree circle at a medium angle of bank.

Unless you're very lucky, this first turn will soon fly you out of the lift and back into the sink, but don't despair, keep going around until you're back in the lift. This time, when you hit the lift again, straighten out until it peaks, then go back into your turn. In short - increase bank in sink and decrease bank in lift. It may take several tries before you get it centered but you'll soon get the hang of it. In fact, you really need to keep correcting this way all the way up if you want to get the best out of the thermal. Don't however, make the mistake of making too many corrections in the same 360 degree turn or you'll soon correct yourself right out of the thermal.

Judging by how long you stay in the stronger lift during each circle, you will be able to tell how much bank you will need to keep in the core. That's where the ultralight's low stall speed helps a lot. The lower the stall speed, the smaller the diameter of the circle, and the easier it is to stay in the good stuff. I thermal my standard wing Challenger 2-seater about 5 miles an hour over stall which works out to about 29-30 mph. Even dedicated gliders can't fly that slowly and therein lies our advantage. We may not be able to go as far from on top, but we can core the thermal better, and make the ride up a lot easier.

Another useful rule to keep in mind when you're traveling between thermals. Slow down in lift and speed up in sink. The more time you spend in the lift, the more it will benefit you. Conversely, the less time you spend in sink, the less it will hinder you.

From a safety standpoint, never fly out of range of a suitable landing spot. With an ultralight, we need less room to land than any other aircraft but a helicopter, but don't let that lull you into bad habits. Maybe the engine won't want to start, or the battery is dead, or whatever. I have a personal rule that I always restart at 1000 feet unless I am in the process of making an engine off landing. Leaving it later than that not only gives you little time to set up an approach if it won't restart, but it doesn't give you the time to warm up the engine properly before giving it full power.

It is not difficult to imagine lots of ultralight pilots learning to soar their airplanes. We don't have to rely on, or pay for tow planes, or spend half the weekend waiting in line at the local club for a half hour flight. We have the instant ability to take advantage of good conditions whenever and to a certain extent, wherever they appear. That freedom is only a dream for most glider pilots. Just ask the next one you see on the ground when the sky is full of Cu's. Not only can we go up when we want but we can fly home when the lift dies. No midnight trailer retrieves for us. What's more, we can enjoy other types of flying when the soaring conditions aren't right, not to mention ski flying all winter long.

As more people discover this game, more will enjoy the competitiveness that informally goes with it. Trying to stay up longer than your last flight or the other guy, or climb higher, or even fly farther cross country. It's all part of the game. Just make sure that when the sky is full of thermaling ultralights, and you join another plane already using a thermal, to always keep your turns in the same direction, otherwise there is a greatly increased opportunity for collision as you repeatedly pass each other.

This reminds me of an interesting point. Not only do other circling aircraft mark thermals, but so do birds. Most birds of prey like hawks, falcons, eagles and even sea gulls are avid and skilled glider pilots. If you see them circling, join them. They know where the lift is. They won't mind you there if your engine is off, and in fact they will come to you immediately if they see you going up faster than they are. I can't begin to count the times that I thought I was completely alone in the sky, only to look over and see a hawk circling alongside me that wasn't there before.

I recently had the opportunity to learn another interesting fact about the birds' soaring skills. Low level soaring is not something that is practised very much by healthy glider pilots. However, with the power on, but set to idle, I have been able to safely do a bit of investigation in my ultralight at heights below 1000 feet. I recently saw a number of sea gulls circling together at about 600 feet in one spot - a guaranteed thermal. When I joined them there was no lift at all, but they persisted, so I did too. After about 2 or 3 minutes an absolutely booming thermal broke loose and took as all up like we were in an elevator. Obviously, the birds had some way of knowing it was coming. I wish I knew how.

The gliding world has a series of achievement awards that are much sought after and respected in the gliding community. I'm certain their silver award is fairly easily achievable by ultralight pilots. It calls for a series of flights that achieve goals including a minimum 3300 foot height gain, a 31 mile cross country and a flight of five hours duration. There are gold and diamond awards too, and while diamond seems a little far fetched (it requires a distance flight of 310 miles), the gold requirements of 186 miles and a height gain of about 9300 feet are probably within reach by a skilled pilot in the right conditions. To date, my best height gain is 7200 feet and I have had many power off flights of over an hour with a best of 2 hours and 36 minutes. I've never bothered to make note of how much ground I've covered, but by simply staying in the thermals while the wind drifts you would make the silver cross country requirement a relatively easy one.

If reading about soaring sounds intriguing to you, I can assure you that doing it is even better. It is such a wonderfully varied experience. There is the thrill of climbing like mad in a great booming thermal, the euphoria of sitting on top of the world near cloud base (a great time to listen to Beethoven's Ode to Joy on your Walkman), and the despair of sinking lower while desperately searching for more lift (try Beethoven's 5th - The Longest Day theme).

It is a sport that provides competitive challenges both with yourself and others. There is terrific satisfaction (not to mention economy), in using your skills and knowledge to gain altitude without an engine and stay airborne for extended periods. These skills will also make you a better, more knowledgeable and safer pilot.

Finally, the silence and peacefulness of soaring alone in the sky is something very special that few people ever experience. In my opinion it is quite simply, the very best of the many pleasures that a good ultralight can provide.

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