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