| Ever wondered how that little motor on the front of | | | | which allows movement of the fuel/air mixture from |
| your model airplane delivers such amazing power? | | | | the crankcase to the combustion chamber are |
| Model airplane engines come in many shapes and | | | | always open or closed at the right time by the wall |
| sizes from many manufacturers. By far the most | | | | of the piston as it travels up and down the cylinder |
| common for the moment is the 2-stroke 'glow' | | | | bore. |
| engine though the modern electric motor is making | | | | The down stroke is created by the rapid expansion |
| rapid inroads. | | | | of the exhaust gases after the fuel/air mixture |
| The 2-stroke model airplane engine is an internal | | | | ignites. Both the exhaust port and the transfer port |
| combustion engine burning 'glow' or 'nitro' fuel | | | | are opened as the piston descends in the cylinder |
| consisting mostly of alcohol with nitromethane to help | | | | bore while the fuel/air inlet is closed. The downward |
| combustion and castor oil for lubrication of the metal | | | | movement of the piston now compresses the fuel |
| parts. There are also 4-stroke glow engines that | | | | air mixture drawn into the crankcase on the previous |
| work on the 4-stroke principle. While these two | | | | upstroke which now rushes up the transfer port into |
| types of model airplane engine produce the same | | | | the combustion chamber and helps force out the |
| result, and use the same fuel, they accomplish this | | | | exhaust gases from that space - and the cycle |
| goal in very different ways and have different | | | | begins again. |
| characteristics. For the moment we're just going to | | | | As the speed of this cycle increases, the power |
| consider the 2-stroke engine. | | | | output of your RC model airplane engine is increased. |
| RC model airplane engines working on a two stroke | | | | Due to it's simplicity the 2-stroke engine can operate |
| principle means that there is fuel ignition on every | | | | to high RPM and high power outputs. Unfortunately, |
| second stroke of the piston in the cylinder. When the | | | | this also means high noise levels. |
| piston is on its down stroke down the cylinder, fuel | | | | The 2-stroke engine in all it's forms is a very elegant |
| and air will enter the combustion chamber between | | | | engineering solution. The piston takes the place of 3 |
| the top of the piston and the cylinder head. When | | | | mechanical valves, a timing mechanism and a fuel |
| the piston reaches the bottom of its stroke and | | | | pump - thereby keeping the weight down and |
| starts to rise again it then compresses the fuel/air | | | | reliability up. In addition, the glow plug combustion |
| mixture in the rapidly shrinking volume of the | | | | method allows the battery to be removed after |
| combustion chamber. The fuel/air mixture is ignited | | | | starting thereby dramatically reducing the weight so it |
| by the glow plug just as the piston reaches the end | | | | is easy to see why the glow 2-stroke has been so |
| of it's upstroke. The glow plug is so called because it | | | | popular for so long. |
| contains a platinum wire that continues to glow from | | | | The 2-stroke glow engine is only one of a number of |
| the heat of the last fuel ignition. The new explosion | | | | choices you can make for your model airplane engine. |
| forces the piston back into the next down stroke. | | | | Where outright power and speed are the primary |
| This sounds very simple but the clever part is that | | | | requirement it has little competition and the simplicity |
| the upper, combustion chamber part of the cylinder | | | | and high volume production has led to highly reliable |
| above the piston and the lower crankcase below the | | | | and cost effective engines being developed. Noise is |
| piston are connected not only by the cylinder bore | | | | really the only negative consideration. |
| but also by a transfer port which enables gases to | | | | So for your next project balance the cost, |
| move from the crankcase to the combustion | | | | maintenance, exhaust noise level, and weight in order |
| chamber. By careful design, the inlet valve for taking | | | | to choose the right sort of model airplane engine for |
| in fresh fuel/air mixture, the exhaust valve for | | | | your project. |
| expulsion of exhaust gases and the transfer port | | | | |