Thermal Surfing part 1

Thermal Surfing (Part One)

Learning to Soar

Soaring. It's quiet. Beautiful. And a unique challenge of your piloting skills. It's the challenge of flight using only the unseen forces of nature. Of successfully navigating the wind, finding and using rising currents of air to stay aloft, and avoiding sink (downward currents of air). It takes patience, skill and a well-designed sailplane. .

Have you ever been outside on a sunny day and suddenly noticed the wind become calm and the temperature rise several degrees? Then, after a few minutes, a strong gust of cool wind blows through, and the temperature and wind return to normal? Well, what you just witnessed was a strong thermal.

Thermals are rising currents of air that are generated as the sun unevenly heats the earth's surface. The warmer surface areas heat the air above them, and the heated air mass can sometimes rise several thousand feet into the air. Thermals can last from just a few minutes to several hours and vary greatly in size and strength.

The strongest thermal activity usually occurs between 10:00am and 4:00pm on warm sunny days that follow cool nights. On "great days", thousands of thermals typically move through a given area. And while thermals originate in areas where the ground heats the air above it, they usually break away and drift downwind, gaining strength when passing over moist warm areas like plowed fields, then eventually dissipating. Thermals are also produced on cloudy days, but they're usually weaker and fewer in number.

Finding and staying in a thermal to gain maximum altitude before your sailplane gets blown too far downwind, then racing back upwind to find the next thermal is a challenging skill that's fun and interesting to learn. Around here we've been chasing thermals for years and despite more than a few stiff necks from staring skyward, we think thermal soaring is one of the most dynamic forms of R/C.

Learn How to Hi-Start

Before you start hunting thermals it's a good idea to first learn how to get consistently safe, high launches. A Hi-Start launch system is much recommended (see Choosing a Launch System opposite).

Plan to launch directly into the wind, and for your first few launches it's a good idea to choose a day with very light (less than 5 mph) winds. You'll want to stretch the Hi-Start about 80% of full stretch length. That's 240 ft. from its resting position for a full-length version, or 120 ft. for a half-length version. It's easy to mark this distance. By using the rule-of-thumb that an average person's stride is about 3 ft., just walk about 80 paces (40 for the half length) down wind from where the Hi-Start's parachute rests, then place the reel at that position for reference on further launches..

If you're launching an Aspire remember that, unlike other sailplanes, it has an adjustable toe-hook that lets you optimize the launch. The fore/aft position of the toe-hook dictates stability/ launch height. For the first few launches, you'll want it in the far forward position. A far forward toe-hook position gives less launch height, but it will be a very stable, hands-off launch that will track straight up the line with very little rudder or elevator input. A far aft toe-hook position gives higher launches, but you're more likely to veer off course during launch, requiring rudder and elevator corrections.

With the sailplane facing into the wind and attached to the stretched Hi-Start, point the nose upward at about 30º, and keeping the wings level, gently toss the sailplane forward- you'll probably be surprised at the steep angle of climb. Using gentle rudder commands, if necessary, keep the sailplane headed into the wind. (Don't worry about the elevator for now.) At the top of the launch, the parachute will automatically fall off the toe-hook and you're free!

Practice this several times until you're comfortable, then begin optimizing your launches for increased altitude. Here's how to get maximum height:

1. Shortly after launch, start feeding some up elevator. It can make a significant difference in launch height, but holding too much up elevator will cause the sailplane to swerve uncontrollably. If this happens, release up elevator and steer back on course with rudder.

2. Move the toe-hook rearward 1/8" at a time. This will give you a higher initial climb angle. But remember, launch stability is reduced the farther back the toe hook is placed. If the sailplane is difficult to keep straight on launch and veers off course, the toe hook is too far aft.

3. Stretch the Hi-Start further. The maximum recommended stretch length is 300 ft. (100 paces) for the full length and 150 ft. (50 paces) for the half length. With light winds, a full-length stretch will greatly increase launch height.

The Hunt Begins

Once you've mastered Hi-Start launches and are comfortable with making right and left circles, it's time to start hunting thermals to extend your flight time. With some practice, you'll soon be able to double, then triple your current flight times. And with a little practice and a good day, an hour long flight is in your near future.

Timing is Everything

Thermal activity varies greatly from day to day. For first time soaring pilots, it's best to pick a calm day with lots of strong, easy-to-find thermals so you don't get blown downwind too quickly when you do hook a thermal. A sunny day with lots of puffy Cumulus clouds is ideal. Remember, the heat generated from the sun is the source for thermals, so the best time to try thermal soaring is on sunny days during the time the temperature is rising- usually mid-day.

Trimming the Sailplane

Elevator- Make a few launches and, using the elevator trim on the transmitter, add one or two clicks of up trim at a time while observing the sailplane. Continue adding up trim until the point just before the sailplane stalls. This is the minimum sink trim position and is used when in lift. Note this trim position on the transmitter as it will be frequently used.

When penetrating upwind between thermals, when in sink, or when searching for lift, an elevator trim setting of slightly more down trim will be used.

Rudder- It's very important that the sailplane fly perfectly straight, hands off the transmitter. When searching for thermals, a key indicator of the presence of a thermal is when the sailplane gently, on its own, turns off course. If you're constantly giving rudder corrections because your sailplane is improperly trimmed, there's a good chance that you'll miss this tell-tale "turn on its own" sign.

For proper trimming, at the top of a launch, fly the sailplane hands-off and trim the rudder so that it tracks perfectly straight for one minute or longer. On further flights, always check and adjust rudder trim if necessary. Many people miss thermals because they fail to do this, and as we explain how to find thermals in Part II of Thermal Surfing, you'll understand why it's so important.

Getting Good at Circling

Begin by trying a few circles- large diameter circles first then tighten them up, concentrating on keeping the fuselage level, losing as little altitude as possible. Remember to bank the sailplane using rudder to the desired bank angle, then release rudder and feed in up elevator. Most first time sailplaners are surprised at how much up elevator is used to achieve minimum sink in tight turns. The Aspire is particularly good in tight thermal turns as it maintains the established bank angle with very little rudder correction needed. Get good at circling with minimal altitude loss, because most of your time in lift will be spent circling.

Once you've mastered your launching and circling techniques, you'll be ready to take the next step in soaring- finding the thermals and surfing from one to the next...and the next...and the next. So watch for Part II in our next issue. We'll tell you how to search for thermals and how to "catch the wave."

Choosing a Hi-Start

Hi-Starts are available in different strengths and lengths, and it's important to choose the correct one for your sailplane and the area you fly in. Most, like G-Force SLS (Sailplane Launch System), are available in two strengths: a 2-meter and an Unlimited (sometimes called heavy-duty) version. The first, called 2-meter because they're designed to launch sailplanes with wing spans up to 2 meters (like the Aspire), use 1/4" diameter surgical latex tubing. This offers the proper amount of energy for a good launch but not so much as to over-stress the wing. Unlimited Hi-Starts usually have stronger 5/16" diameter surgical tubing that provides the extra needed strength to launch larger, heavier sailplanes with 100 in. spans and up.

You can also choose different Hi-Start lengths. A full length version will launch a sailplane up to 500ft. of altitude or more, but requires a large unobstructed launch area of 700ft. A half length Hi-Start only requires a 350ft. launch area, but the launch height is also reduced by half to about 250ft.

Available in four versions, the G-Force is top-of-the-line, featuring a well balanced, heavy duty reel, UV-resistant black rubber tubing, 100lb. test Dacron line, and a rip-stop nylon chute. Plus, it's fully-assembled and ready to use right out of the box.

If you're just learning to soar, we suggest you look for a larger, 700 ft. launch area and use a full length Hi-Start for maximum launch height. This will allow more time and distance to hunt for thermals, plus you're more likely to enter the thermal at a higher altitude where it's larger, stronger and easier to stay in.