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