There are two types of model airplanes, a static non-flying model, or a flying model. This is very important to choose right from the beginning, as construction for each type will vary greatly. Of course though, it is possible to turn a static airplane later on into a flying model, you would just need to do a major overhaul and add the necessities to get it into the air.
Model airplanes that fly can usually be placed into one of the three different groups. The first group is free flight, which basically means that the aircraft is built and designed to fly without any attachment to the ground (not even a remote control).
The second group is control line flying, and this method has a cable or two leading from the wing to the pilot. So of course it is not as realistic as a wireless one is, but it ensures your airplane will not just fly away.
The last group is radio-controlled model airplanes, which are the most intriguing and fun to fly, since you have complete freedom of movement and YOU get to control it.
There are some rc airplanes that resemble real aircraft, just like static models, but are harder considering that since they actually fly you have to continuously keep it looking nice and the engine running smoothly.
R / C aircraft though do come in many different types, as there are even remote control birds, dinosaurs, and flying lawn mowers! The various forms that can be accomplished are endless, and make for some pretty interesting looking aircraft.
For free flight model airplanes, an elastic motor is usually used to power them. An elastic motor is simply a rubber band that is wound up very tight before flying, and then released to make the propeller turn. The elastic motor is actually the most widely used engine for model airplanes, and can be found in children's toys, all the way to professional model aircraft.
The reason the elastic motor is so popular of course, is because of its simplicity and the ability to have a long lifetime. Also, there is no waiting for the battery to charge or having to buy fuel for the engine. Of course the major drawback is that fact that it can only run for a certain amount of time, which depends on how long your rubber band is.
Another simple propulsion method is mounting compressed gas, CO2 to be more specific, and having it come out the back to push it along. You could even get real complicated, and have the CO2 power a piston expansion engine. CO2 engines, like elastic motors, are considered cold power, because the engines become cold when running, not hot like fuel powered engines and batteries.
For most hobbyists though, the standard glow engine is the engine they use. A glow engine runs on the same principal as an internal combustion engine that is in your car, but it is a very small version of it.
Most commonly used by rc model airplane enthusiasts, are two stroke cycle engines, which use a glow plug to ignite fuel. The fuel is just a mix of slow burning methanol, nitro methane and some kind of oil lubricant. Company's who make model airplane glow engines, rate their size in terms of engine displacement. The most common sizes range from 0.01 cubic inch to over 1.0 cubic inch.
The simplest, and most beginner friendly models are electric powered model airplanes, which use a battery to power the engine. The speed is controlled through an electronic speed control, which will regulate the output of the motor. Of course the best model airplanes to put an electric motor in, is small and lightweight ones.
If you want a big, heavy airplane, then a glow engine fuel powered airplane is what you want. If you just want a simple small model airplane, then you want an electric rc airplane.