| Although today, the technological advancement of | | | | being by far the most popular. |
| airplane powerplant specially on the electric motors | | | | Engine sizes - and how they are specified. |
| which now uses Lithium Polymer batteries, we should | | | | Engine sizes are specified by displacement or the |
| also learn the internal combustion type since the | | | | interior volume swept by the piston in making its |
| development of those miniature airplanes and | | | | stroke up and down the cylinder (swept volume) In |
| helicopters owe so much. There are two main types | | | | the case of diesels, displacement is always quoted in |
| of model airplane engine - glow engines and diesels. | | | | cubic centimeters or cc (mainly because the model |
| Although the ignition type is popular on big birds (1/4 | | | | diesel originated in Continental Europe). In the case of |
| scale), we will concentrate on the 'standard' model | | | | glow engines, displacement is (nearly) always quoted |
| engines. Glow engine are by far the more numerous | | | | in cubic inches or cubic inches (because this type |
| and popular, faster revving and generally more | | | | originated in the United States) Manufacturer produce |
| powerful size for size. They are suitable for powering | | | | glow engine in a more or less standard range of |
| all types of model aircraft and are produced in three | | | | sizes, originally representing logical steps in power |
| general categories - standard engines for general use; | | | | output. These are 0.049 cubic inch (also known as 1 |
| racing engines for competition models; and RC | | | | 2A); 0.09 cubic inch (also known as Class A); 0.19 |
| engines for radio controlled aircraft. Standard engines | | | | cubic inch, 0.29cubic inch, 0.35cubic inch, 0.49 cubic |
| may also be used for radio controlled models fitted | | | | inch and 0.60 cubic inch Quite often the cubic inch is |
| with a throttle control or RC carburetor. This applies | | | | dropped and just the figures quoted 049, 09, 19, etc. |
| particularly to smaller engine sizes. Larger RC engines | | | | Some manufacturers produce additional sizes, e.g. |
| are generally specially designed to produce maximum | | | | smaller than- 0.049 cubic inch for powering tiny |
| power at more moderate revs than either standard | | | | models, and intermediate sizes to cater for a |
| or racing engines. | | | | particular size or type of model, such as 0.40 cubic |
| Glow engines have three particular disadvantages, | | | | inch for RC models. The need for intermediate sizes |
| although these are outweighed by the simplicity of | | | | is rather more commercial than realistic however. |
| operation and general flexibility of the type. First they | | | | Classification of porting nearly all present day model |
| need a special type of ignition plug, known as a glow | | | | airplane engine are of similar layout, the main |
| plug, which can burn out and need replacement. They | | | | differences being in the method of inducting the fuel |
| also need a battery connected to the plug for | | | | air mixture into the crankcase and then transferring it |
| starting (and if the battery is 'flat' the engine will not | | | | to the top of the cylinder. Induction is controlled by a |
| start!), and special alcohol-base fuels which are a little | | | | rotary valve, either a hole opening into a hollow |
| more costly than diesel fuels and also attack paints | | | | section of the crankshaft, or a disc with a hole, |
| and cellulose dope finishes. For this reason, model | | | | driven by the crankshaft. In either case, sheathe hole |
| aircraft powered by glow engines must be finished in | | | | in the crankshaft (or disc) comes opposite the end |
| fuel proof dopes, or given a final coat of special fuel | | | | of the carburetor tube the intake port is opened and |
| proof paint. | | | | then closed by subsequent rotation of the |
| Diesels are self-contained engines that they need only | | | | crankshaft. The circumferential length of this hole |
| a supply of suitable fuel to run. They are generally | | | | determines the intake timing. |
| heavier and more robust than glow engines, so they | | | | When induction takes place in front of the cylinder |
| are usually longer lasting. They vibrate more and are | | | | (through the crankshaft), the layout is known as |
| less responsive to throttle control than glow engines, | | | | front rotary (readily distinguished by the carburetor, |
| so are not generally recommended for powering | | | | or strictly speaking, the intake tube) coming in front |
| radio controlled models. They cannot rev as fast as a | | | | of the cylinder. With rear rotary engines the intake |
| racing glow engine, so are less competitive in this | | | | tube attaches directly to the back of the crankcase. |
| respect. On the other hand they can be excellent | | | | Transfer of fuel and air mixture drawn into the |
| power units for small and modest: size free fight | | | | crankcase to the top of the cylinder is controlled by |
| 'sports' models and certain types of control-line | | | | piston movement opening the top of a transfer port |
| models. Diesels are produced in a much more | | | | (or ports) formed in the side of the cylinder. This |
| restored range of sizes than glow engines. Very small | | | | porting may be conventional, or specially arranged to |
| diesels (smaller than 0.5cc) are difficult (and costly) to | | | | give a 'boost' to the charge to fill the cylinder head in |
| produce and can prove tricky to start and adjust. At | | | | the most effective manner. The latter is a relatively |
| the other end of the scale, diesels larger than about | | | | new development with model airplane engine and is |
| 3.5cc generally prove disappointing in performance. | | | | known as schnuerle porting. It is now a feature of |
| Thus diesel production is virtually limited to a size | | | | many high performance glow engines. |
| range from 0.5 to 3.5cc with the 1cc and 1.5cc sizes | | | | |