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