A motor glider is actually a sailplane equipped with a ‘means of propulsion’. Depending on the type of the motor, motor gliders can be classified in some categories. Although this ‘unusual’ addition, motor gliders are capable of soaring like any other sailplane, but with a loss in performance. Despite this backdrop, motor gliders have their own advantages like the possibility to fly over longer distances and a better chance in avoiding out-landings which can be dangerous and costly.
Main categories of motor gliders
- Touring motor gliders are quite common and are often mistaken as planes. Indeed there is a striking similarity, but the differences consist in mass and soaring performances of the TMGs. They are equipped with a front fixed propeller powered by a motor of 80 to 100 horsepower. Touring motor gliders aren’t equipped with a towing hook and their performances are considered to be ‘moderate’ in comparison with classic gliders. The surplus of drag created by the propeller and the twin landing gear prevents them from participating in competitions. The real gain with touring motor gliders is the overall boost in efficiency compared to other light aircrafts.
- Retractable propeller gliders are considered to be the modern solution. The fuselage contains bay doors similar to those of the landing gear from which the motor – propeller block rises. In newer models the motor remains in the fuselage in order to reduce noise and mainly to reduce drag. Most retractable propeller gliders have hooks for towing like normal gliders and are equipped with a single retractable main wheel and that`s way they require assistance during ground operations.
- Sustainer motor gliders have a retractable propeller but they are not capable of self-launching. Their motors are not powerful enough so they must be launched like classic gliders. Once in the air, they can use their motor in order to extend the time of flight by slowly gaining altitude. In general they are not equipped with an alternator or a starter motor like any another powered aircraft and so the engine is started with the help of the wind which turns the propeller. Sustainer motor gliders are lighter and easier to operate than typical motor gliders. Their engines have normally around 15 to 30 hp and do not require a throttle, but instead they use a simple mechanism to allow the engine to start and to stop.
- Self launching motor gliders dispose of an engine powerful enough in order to take of by their own. While having a tow-hook like normal gliders, the preferred launching method is by starting the motor on the ground. This is possible because of the battery, starter motor and alternator with which the motor glider is equipped. They also benefit from a throttle which enables pilots to better control ground operations. Self-launching motor gliders dispose of a 50 to 60 horsepower engine which is more than enough.
- Other not so common types of motor gliders include cross-overs between touring motor gliders and retractable propeller motor gliders. A good example is the Stemme S10 which folding into the nose cone propellers powered by an engine located in the rear part of the glider. This motor glider has a double retractable landing gear enabling it to taxi without assistance and to soar without extra drag. Some versions of this motor gliders are equipped with a tubocharged engine and propeller with a variable pitch wich allow the sailplane to reach altitudes of over 30000 feet or 9000 meters. Although most motor gliders have gasoline engines, electric powered self launching sailplanes were developped. Their main advantage is that they are lighter than common motor gliders. Another oddity in sailplane developing is jet engine propulsion. In general, the jet engine is mounted inside the fuselage and behind the wings. Such radical solutions are used in aerobatic shows or in research.
Why Fly a Powered motor glider?
Motor gliders provide opportunities
One of the most interesting things is how people that aren’t powered sailplane pilots have a very limited concept of what a powered sailplane can provide.Everyone understands what “towplane avoidance” is. The ability to self-launch gives you the freedom to launch when you are ready, avoiding the wait for the towplane and the delay caused by all those other people in front of you. This part everybody envies.
Secondly, everyone easily grasps the idea of “retrieve avoidance”, using the motor to avoid landing out. Most people like this idea, though some don’t, believing the chance of landing out iswhat defines the sport of soaring.
Indeed, self-launch and self-retrieve are important, but these abilities don’t really allow a change in the way you soar, but just allow you to do it more conveniently or more often. After all, a weekend flyer at the typical gliderport has little trouble getting a tow, avoiding a landout, or getting a friend or towplane to retrieve them once or twice a year. “Opportunity” is the key word.
Not so obvious is that a powered sailplane allows you the opportunity to enhance your soaring. This is what is really important. Most glider pilots don’t realize how much their selfimposed constraints limit their soaring. The biggest constraint is probably the desire to soar home. Once you realize you no longer have to soar home, your soaring opportunities increase immensely. Here are some examples:
1) You can stay hours longer in the great soaring in the mountains, while the unpowered gliders scoot for home before the thermals die on the flat lands.
2) You can fly in low cloudbase, marginal, but exhilarating conditions when no one else will bother launching, because the lift is too unpredictable.
3) Sometimes I fly like it’s a record attempt, speed ring way up and ruthlessly rejecting all but the very best thermals. Great practice, and the palms still get sweaty!
4) If the soaring is dying between home and your position, you can keep going towards the still good air knowing you can motor home if needed.
5) If you miss the wave on the first try, instead of dashing back to the airport to get back in the line for tows,you can try another place, and another, until it`s the right one.
6)One can fly to another place on one day, fly back on the next, and never worry about finding a towplane there or a long retrieve. Great for people that still have to work during the week!
7) Safaris (flying holiday) with or without a ground crew: an expansion of (6), just keep going towards the good soaring, day after day, until it’s time to head back home.
Sometimes I do have to use the motor to get home. Most of the time, I discover there is more lift out there than we realize. Because a retrieve or landout is so inconvenient, most glider pilots play it safe by heading back early, or by not going there in the first place. We take pride in getting back, and don’t think of all the soaring we missed. Why else is the first question a motor glider pilot is often asked after the flight is “Did you use the motor?”, instead of “How was the soaring?”.
It astounds me that many glider pilots, even some motor glider pilots, consider it a “failure” if the motor is used after the launch. A record attempt will fail if the motor is used, but not the flight itself. If it was good soaring, it was good soaring, even if the end wasn’t a landing! Most of my post-launch motor use is anticipated hours before it happens: I frequently, consciously, make soaring decisions that will almost surely require the motor to return home. Why? So I can do more and better soaring.
Motor gliders add responsibilities
The motor that gives the self-launching sailplane its opportunities also exacts additional responsibilities. The towpilot is no longer responsible for the safe operation of the launch vehicle: you, the motor glider pilot, are now responsible. Even flying a sustainer-equipped gilder still adds much responsibility.
These extras include the:
- Maintenance of the engine and its systems
- Preflight of the engine and extension mechanism
- Fuel and oil addition and checking
- Ground operation (starting and taxiing)
- Entire launch operation
- Converting back to a glider
- Perhaps restarting the motor in flight
The life of a motor glider is more difficult due to the extra complexity, weight and vibration. The powered glider should not be treated as casually as the unpowered gliders often are. If you are not an experienced airplane pilot, you will have a lot to learn. Don’t rush the learning.
Soaring – also called “gliding” by some people – dates from the 1800s. The two terms, however, are quite different. Both are practiced by individuals who either fly for the sheer personal enjoyment of powerless flight (gliding), or who compete as either individuals or members of teams in local, regional, national, and international glider competition (soaring). Many pilots do both.
In 1848 Sir George Cayley, an eminent British scientist, is credited with having designed and built the first successful heavier-than-air device, a glider said to have carried a 10-year-old boy several yards after its launching from a hill. From the 1890s onward, research and development of gliders, flying techniques, and similar subjects were being notably pursued in Germany, England, and the United States.
World War I halted glider development, but when the Treaty of Versailles prohibited powered flight in Germany, one result was enormous progress in the development of soaring flight. The first world championships were held at Wasserkuppe, Germany, in 1937. Progress continued,but was slowed again during World War II when military applications of gliding forced sport flying into the background.
From then until now, the sport has flourished, and several countries boast aggressive,healthy soaring programs. At least 5,500 pilots throughout the world have earned diamond badges and over 150 have now flown flights farther than 1,000 kilometers (620 miles).
Rules and Play
Air flows over the wings of a glider in much the same way as it flows over the wings of a powered airplane, which is propelled through the air by the force of its engine. Glider flight can be achieved only by descending the glider, speeding it up, and causing air to flow around its wings and tail surfaces. In gliding flight, therefore, a glider (or sailplane, as it is often called) is always descending, usually at a rate of between 45 and 90 meters (150 and 300 feet) per minute in still air. The acceleration of air over the wings of the glider produces a lifting force that counterbalances the weight of the glider and actually slows down its rate of descent. Were it not for the force of “lift,” gliders would go straight down. Instead, they follow predictable “glide ratios.” Glide ratio is a measure of how far a sailplane will travel forward (horizontal distance) for each foot of altitude it loses (vertical distance).
What makes soaring a sport is the challenge to the pilot of finding and using ascending air currents to keep the glider aloft—to cause it to climb faster than it is descending (which it always is)—and so achieve height, distance, or flight durations impossible in “still air”. Updrafts are the fuel of gliders. Pilots who excel at finding and using the invisible ascending currents are the champions and record holders, and the ones who reap the full enjoyment of solitary soaring flight.
Three classes of gliders are generally recognized in world competition: Open, 15-meter, and Standard. A fourth type of glider, the so-called “World Class” glider, has been internationally classified but it has yet to be built or compete on any widespread basis. Except for motorgliders, which have engines that enable them to take off under their own power,other types of gliders require some outside force to create airflow over the wings. This gets the glider moving at sufficient speed so adequate airflow passes around the wings to overcome the force of gravity and cause it to fly. Many different methods have been used to provide this speed: pushing gliders down the slopes of hills until airflow over the wings is sufficient to produce flight; dropping heavy weights on the ends of ropes to pull them into the air; pulling them with elastic-like ropes and “slingshotting” them to flying speed; pulling them into the air on long cables reeled in by engine-driven mechanical winches; pulling them into the air on ropes behind automobiles; and hooking them behind airplanes that take off and pull the glider to an altitude from which gliding flight can begin.Most gliding in the United States today starts with the glider being towed by a rope attached to a powered airplane. The technique is called “aerotow.”
Types of Gliding
Glider pilots aim to soar, not glide. Soaring involves finding parcels of air going up at a greater rate than the glider is going down. The several methods of remaining aloft all involve pilot skill and knowledge in finding these air currents. They are generally categorized as thermaling, ridge flying, mountain wave flying, and land and sea breeze flying. An additional source of lift can be obtained by flying under or near newly developing cumulus clouds that owe their formation and sustenance to the updrafts found directly underneath them.
The International Gliding Commission (IGC) is the sport’s governing body. The first world championship of soaring was conducted in 1937 at Wasserkuppe, Germany. Recently, during every odd calendar year, the FAI sanctions a World Gliding Championship for each of the three classes of gliders (Open, 15-meter, and Standard). The world contest is usually held over a three-week period, with the first week devoted to official practice and the last two weeks to actual competition. Individual phases of soaring competition are called “tasks.” Each day at the world championship competition, pilots fly around a specifically assigned course composed of carefully selected and clearly defined turn points on the ground.These turn points are the ends of airfield runways, prominent road intersections, or other distinctly identifiable geographical landmarks over which competition pilots must precisely fly.Win or lose, soaring pilots still score a victory: the triumph, however temporary, of a nonmechanized craft over the force of gravity.