Motor glider

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

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.