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.

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."

Hangar 9 Aspire EP RTF Great Aspirations Hangar 9's Aspire™ EP has opened a whole new world of soaring excitement for modelers everywhere by giving them a beautifully crafted electric-powered sailplane that goes together in about three hours. With the introduction of the new ready-to-fly version of the Aspire EP, all that's left for a modeler to do now is install the transmitter batteries, bolt on the tail, slide together the wing halves, charge the included Ni-Cd battery, and fly! Click to enlarge The easy access battery tray allows packs to be swapped out in seconds. Same top-quality construction The only marked differences between the standard Aspire EP and the ready-to-fly version are the factory-installed radio and bolt-on tail. Everything else is identical, from the excellent balsa/ply structure to the artful use of transparent violet UltraCote® in the trim scheme on the wings. The use of UltraCote to cover the Aspire EP RTF will make repairs easy, not to mention practically invisible, by allowing modelers to match colors exactly with UltraCote from their local hobby shop. It's got the goods The Aspire EP RTF is, without a doubt, the most thoroughly equipped RTF electric sailplane ever. Complete assembly takes less than an hour. Control is provided by Hitec's reliable Focus 3 single-stick RC system. The same 550-type electric motor and folding prop combination that's found on the standard Aspire EP is included in the RTF. Regulating the power to the motor is E-Flite's sophisticated Maxx 25 proportional electronic speed controller. Hangar 9™ has even thrown in a 6-cell, 1500mAh sport battery pack and 30-minute fast charger. Everything is in place and ready to use. There is practically nothing left for the modeler to provide other than 8 "AA" batteries for the transmitter. Click to enlarge The Aspire EP RTF features a 3-channel Hi-Tec system that's completely installed. The Aspire EP RTF will easily offer 8- to 10-minute motor run times with the included 6-cell sport pack. The actual flight times will depend on just how good one is at fishing for thermals. Fortunately, if things are uncomfortably calm, the powerful 550 motor can prevent any impromptu safaris into the weeds. In calm conditions with the power on and a full charge, the Aspire EP RTF will climb at about a 20-degree angle. Cut the power, and the Aspire EP will settle into a nice gentle glide slope that can take the plane quite a ways with sufficient altitude. Stall behavior, even in turns, is very tame. The plane practically recovers itself. Turns are neutrally stable. Just feed in enough rudder to achieve the desired turn rate and then release the rudder and use elevator to maintain the circle. This will be nice for first timers since it will allow them to focus on hanging on to the lift rather than struggling to stay in the turn. There is no question that the Aspire EP RTF will bring a lot more people into the sport of R/C soaring, and we bet it brings in just as many first timers to R/C aviation in general. Its mild stall behavior and solid stability, coupled with its completely ready-to-fly simplicity, make it a fantastic trainer choice too. Whatever the reasons, those with great aspirations to fly will find Hangar 9's Aspire EP RTF a fantastic way to get started. View More Sailplanes Here