Sailplanes and slopers
There is a silent beauty to being able to fly, sometimes for hours, without needing a motor. Sailplanes, also known as gliders, can also be simpler and less expensive than powered planes since you don't need the motor and its accessories. Powerless models present different and fascinating challenges to the pilot. In some ways, they are also easier to fly than powered models. As such, they are very good for learning to fly, which is why this installment of Primary Training is devoted to them.
There are many reasons to learn to glide, even if you don't start with gliders. A competent pilot should be able to fly almost any kind of RC model. Keep in mind that if the motor on your powered model quits, you have a glider landing coming up, whether you wanted to fly gliders or not. Glider pilots have to land on their first try: You can't turn on the motor and go around. Flying a glider on a slope sometimes gives you a few shots to set up an approach, but even then, once committed, you have to land. Because I have gotten ahead of myself, let me now introduce the two basic kinds of soaring of interest to the beginner: flat-field soaring and slope soaring.
FLAT-FIELD SOARING
In flat-field (or thermal) soaring, the model is launched, often with some force, into the air, and it is the pilot's job to get it back down safely. The goal of soaring can be put this way: The longer you take to bring the plane down from a given launch height, the better.
GETTING BACK DOWN
While sailplanes can fly aerobatics or at high velocities, the pilot-in-training's fastest learning will occur when he flies slowly and tries to keep the plane in the air for as long as possible. The secrets used include trimming the plane so that it flies efficiently without any control inputs, turning smoothly without ex-cessive loss of altitude, and smooth flying in general.
You learn to think way ahead of the plane when flying gliders. You think, "If I want to be there, later, I have to have the plane over there, now." With a glider, you are always planning for a landing: You are always coming down, whether it seems like it or not.
THERMALING
You are always coming down with respect to the air through which you are flying. If the air is moving up faster than the plane is coming down, you will gain altitude. One of the secrets of long-duration flying is to find air that is moving up. The highest form (both literally and figuratively) of flat-field soaring is thermal soaring, where bubbles of warm air known as thermals are moving upward. So will your plane, if you can find these invisible bubbles and stay in them. The art of thermaling is outside the scope of this article, but there are many books and articles on the topic. An experienced soaring in-structor is always a big help. Few accomplishments in RC flying are as gratifying as learning how to toss an unpowered model into the air and keep it up for an hour or more.
OUT TO LAUNCH
Many ways have been invented for getting the sail-plane aloft from a flat field. The simplest is to toss it like a paper airplane. Special "hand-launched" RC gliders are sold for this purpose. They are sturdy enough to take a very hard "overhand" type throw. Another form of hand-launched sailplanes are the "discus" style throw, whereby you fling the plane upwards, holding the plane by its wingtip. Discus-launched models are even more specialized structurally to withstand the high forces, but with the same energy, you can get a much higher launch than you would if you were just to throw a model forward. Discus launching is usable even by people whose shoulders will not permit them to do a forward throw.
All other launching methods involve towing the model on a string pulled by one method or another. The string can be pulled by a person running with a length of cord, making the plane rise like a kite. There is usually a ring on the end of the cord, which
is slipped over a backward-facing L-shaped metal hook on the plane. When the person stops pulling, the air drag on the line causes it to be pulled off the hook towards the back of the aircraft. A flag or parachute fitted to the line just below the hook further increases the drag and makes the release more positive. No special servo-operated release is necessary.
To avoid the work of running, an electric winch can be used to pull the line. Often, the winch is next to the person launching the plane and there is a pulley fastened to the ground at the far end of the field. Another less expensive alternative is to use a "high start," which is a length of rubber (often in the form of a hundred feet or so of latex tubing) attached to a longer length of kite cord. Otherwise, it works just like a human-towed launch.
These launches put a lot of strain on the hook assembly and on the wings. Commercial kits are designed to handle these loads. A high start launch begins with the plane nearly vertical, and it follows an arc around to the top where it flies over the ring, which comes off at the peak height. The speed with which the model ascends and the height it can reach often amaze first timers. In addition, the pull on the line can be surprisingly strong.
All launches start with the plane being towed into the wind. The student pilot's job is simply to keep the plane's wings level until release. Other ways of getting aloft include towing from a bicycle, a car, an RC car, or-just as is done with full-size gliders-with an aero tow. The latter is the most difficult to master, and requires a powered model to pull the sailplane. For safety, both models should have a servo-operated release. The sailplane has to have such a release. Aerotowing is not recommended as a beginner's launching method.
Many modelers use an electric motor just to get the model launched, and after that they turn off the motor and glide. Most of these models have folding propellers, where the blades fold back and lie against the sides of the fuselage, reducing drag. Glow engines can also be used to get up to altitude. On a few models, an engine/fuel tank module slides off after the model has reached altitude and the engine has stopped. A parachute brings the engine module back to the ground softly. This can be done with electrics, too.
SLOPE SOARING
Another place where air moves upward is at a hill, cliff, or slope. When the wind is blowing straight into the face of the rising land, the air must also rise, following the terrain. This upward moving air, like that of a thermal, can provide lift that lasts as long as the wind continues to blow from the right direction. Since the location of the lift is consistent, you can stay up for hours with far less skill than it takes to fly thermals. This makes slope soaring an excellent way to learn to fly.
Slope soaring models are usually tough. Many are made of EPP, a flexible plastic foam that enables the model to bounce upon impact. As with other sailplanes, not having a motor or heavy motor batteries makes slopers simpler, less expensive, and lighter than powered models-another advantage for the beginner. The big negative is that if you live in a place where the land and the wind don't cooperate, you can't slope soar at all.
Slope pilots usually fly from the top of the hill. It is best to start at a slope where others already fly. It is not easy for a novice to judge whether a slope is good or not. As always, a friendly instructor can be a great help. The basic flight pattern is an extended figure-8. Fly your model parallel to the slope, turn out (always outward!) into the wind and then fly back on a path parallel to the slope, turn outward again, and back toward where you started. Never turn with the wind into the hill. Your model will quickly be blown downwind toward the hill. Behind the lip of the hill you will often find a "rotor," a place where the wind is very turbulent. Stay out in front.
Landing at some slope sites can be very difficult. Many flights end with a solid smack into the earth. There are many techniques for safe slope landings-landing methods that have to be customized for each site. Watch others land (or crash). Copy the good ones and land into the wind. The challenges of slope landing account for the popularity of "bounceable" EPP models.
At a slope, you can fly in wind speeds that keep most other kinds of RC planes grounded. As you become more experienced, you can also fly very aerobatic models since slope lift can be very strong and consistent. I learned inverted flight while slope soaring. To launch on a windy day, try releasing the model just an inch or two above the ground at the edge of the slope. It won't have much energy to crash if it touches down quickly, and if it doesn't, you will soon have all the altitude you need in the rising air.
CONCLUSION
As you can see, soaring offers a lot for both pleasure and education. With a little experience, you will become a smoother pilot with all your planes and have a greater appreciation of how the wind affects your models in the air. You might even find that thermalling on a relaxing sunny afternoon, or zipping back and forth at the slope, is a welcome change of pace from flying powered models.
