Whatever type of motor you are using the amount of power being fed to the electric motor needs to be regulated.  This is done by the Electronic Speed Controller or ‘ESC’.  The ESC is located between the power supply battery and the motor and is wired to your throttle channel. When you want to go faster and increase the power through your radio transmitter, the ESC allows more power from the battery to the motor, increasing its RPM and making your model go faster. ESC will usually only work with either brushed or brushless motors but there are some available that will work with either.

This brings us to the gearbox. Electric motors are most efficient at high rpm. But there are some occasions when you need to lower the rpm to make the propeller more efficient or to fit a larger prop.  Whether it is a boat or plane or vehicle, there is always a trade off between ultimate power from high RPM or torque.

Finally the batteries. There are many types of electric model battery to list here.  Among the most common types are Nickel Cadmium (Nicad), Nickel Metal Hydride (NiMH), and Lithium Polymer (Li-Po). Again, cost is usually the great divider.  The two nickel based batteries are often used where cost is the most important issue. The power output from these batteries is not constant. They start off strong and slowly give out less power till finally the model runs out of power.

Alternatively, Li-Po batteries have a very constant power output. They are just as strong at the end of a flight as they were at the beginning. Powering your model with a Li-Po battery is the best way of achieving consistent performance.  However, they are not so tolerant of mis-use and abuse and care needs to be taken when charging and discharging.  Incorrectly charging or discharging a Li-Po battery has been known to cause toxic smoke, fire and explosions.

Electric motors are rapidly overtaking the 2-stroke engine for most modeling activities.  They are clean and quiet and more environmentally friendly, especially for your near neighbours as they make little or no noise! 

A model with an electric motor is likely to contain several specific components; the electric motor, an electronic speed controller (ESC), high powered batteries and possibly a gearbox make up the power train.  Understanding how they work together can be helpful in getting the most from your hobby.
First, electric motors come in two forms; ‘brushed’ or ‘brushless’.  Brushless motors are constructed without ‘brushes’ and are therefore simpler.  As simple usually means more efficient in any machine so they operate more efficiently than brushed and deliver more power and/or more operating time.  However, brushless motors can cost substantially more.

Brushed motors are sometimes called canned motors.  These can be much cheaper but deliver less power. Most pre-packaged electric powered models are delivered with a brushed motor.  If you want to improve or upgrade your model then you can upgrade to brushless if you wish to do so. With the popularity of brushless powered electric models rising, more brushless packages are available and may soon be the standard electric model power plant.

Until recently, the most common internal combustion engine found on model airplanes was the ‘2-stroke’ although this is rapidly being overtaken by the quiet electric motor.  A 2-stroke engine is an internal combustion engine burning ‘glow’ or ‘nitro’ fuel consisting mostly of alcohol with nitromethane to help combustion and castor oil to provide lubrication.

The 2-stroke principle means that there is fuel ignition on every second stroke of the piston in the cylinder. When the piston is on its down stroke down the cylinder, fuel and air will enter the cylinder between the top of the piston and the cylinder head. When the piston starts to rise again after reaching the bottom of its stroke, it then compresses the fuel/air mixture in the reducing volume of the combustion chamber. The glow plug ignites the fuel/air mixture just as the piston reaches the end of it’s upstroke. The glow plug is a plug similar to a spark plug but containing just a platinum wire with no electrics.  The platinum wire continues to glow both from a catalytic reaction with the fuel mixture and from the heat of the last fuel ignition. The new expansion of gases drives the piston back into the next down stroke.

The upper part of the cylinder and the lower crankcase are connected by a transfer port  as well as by the cylinder bore.  This allows gases to move between the crankcase and the combustion chamber. According to their location, the inlet valve for taking in fresh fuel/air mixture, the exhaust valve for expulsion of exhaust gases and the transfer port which allows movement of the fuel/air mixture from the crankcase to the combustion chamber are always open or closed at the right time by the wall of the piston as it travels up and down the cylinder bore. 

The down stroke is created by the rapid expansion of the exhaust gases after the fuel/air mixture ignites. Both the exhaust port and the transfer port are opened as the piston descends in the cylinder bore while the fuel/air inlet is closed. The downward movement of the piston now compresses the new fuel/air mixture in the crankcase which rushes up the transfer port into the combustion chamber and helps force out the exhaust gases from that space. 
The piston will close off the exhaust port and the transfer port on it’s way back up the cylinder and create the enclosed space of the combustion chamber ready for the next ignition.  At the same time it will open the inlet valve and draw fresh fuel/air mixture into the crankcase below the piston.  It will then reach the top of its stroke, ignition occurs and the cycle begins again.

The power output of a 2-stroke engine increases with RPM and modern standards of construction have led to high reliability.  It isa very simple design. The piston carries out the functions of fuel valves, timing and compression.  Using a glow plug allows the battery to be removed after starting to reduce the weight. 
It is easy to see why the 2-stroke engine was so dominant in modelling for so long.

There are also some mechanical aids to launching.  The model is attached to a line connected to elastic tubing that is secured to the ground, or to a winch. Pull the plane back to stretch the elastic and then release.  If you are on your own you will need to be quick to lay your hands on your RC transmitter to establish control of your model so it is easier to have a friend help with this type of launch. This is known as bungee or hi-start.

More friendly cooperation is also required with a towed launch where your sailplane is towed into the air by a second powered model airplane.  This is more complicated as you obviously need a helpful friend with a powered model as well as another actuator to release the towline when you have gained enough altitude.

More expensive still are those models that incorporate an electric motor for the first launch and for regaining altitude when required.  These are more complex as the propeller blades are sprung loaded to fold back out of the airflow when the motor is not running.  Otherwise they would be a major source of drag.

Competition is always going to creep in no matter how much you start out looking for quiet solitude and slope and thermal soaring have a whole range of competitions specific to their niche.

To fly your sailplane using slope lift then you need a prevailing wind and a hill. A suitably shaped hill forces the prevailing wind upwards in a consistent upward air stream.  Good sites for slope soaring are usually found where there is a long ridge to create a smooth and constant upward wave of air – and a prevailing wind.  Of course, they also need to be reasonably accessible.

Using radio control with your sailplane will allow you to guide your model to find lift, to fly from point to point if you are competing and to bring your model sailplane back to you when you eventually run out of either time or altitude.

Without an engine, launching a model sailplane is rather different to just lining it up and opening the throttle as with most models. You need some altitude and fast.  From ground level the most basic method is to simply throw the model using what is called either a discus or javelin launch. The plane gains about 50 feet of altitude from the momentum of the throw – then you have to work hard to find some lift before gravity takes over again. Slope soaring is much easier in this respect because you can launch your model sailplane horizontally off the slope when you know there is lift available from the prevailing wind.