Model Engines: And Their Essentials
FIRST THINGS FIRST. This is an article on engines, not on motors. I had a thermodynamics professor many years ago who was quite insistent that his students should understand that engines are not motors. Since I have always tried to learn my lessons well, my foremost pet peeve has remained when engines are called motors. An engine is a prime mover. That is, an engine is a primary converter of energy to mechanical motion. Motors normally are secondary energy converters. Actually, some model airplanes do use motors, but the power source is an electric motor, rubber strands, or CO-2 motor. This article is about engines.
Model Engines: And Their Essentials - Part 2
TUNED PIPES refer to an exhaust system that is tuned to a particular engine and operating range. There are many ways to tune the exhaust on a two-cycle engine, and most have been used successfully on model engines. To my recollection, Bill Wisniewski was the originator of the modern tuned pipe expansion chamber for model engines. At least he made them popular, circa 1966. Bill's system used an expansion chamber that amounted to an inlet pipe, a diverging nozzle or taper from the inlet pipe connected to a converging taper, then a very small outlet pipe. All dimensions of these systems are carefully calculated and tested to provide maximum power.
Model Engines: And Their Essentials
GLOW PLUGS. The "fire" or ignition process in a glow engine is a combination of the compression of the fuel-air mixture near TDC and the heat generated by the glow plug. The parts of a typical glow plug include the body (or outer shell) that threads into the engine, the post (or protrusion) that one leg of the battery is connected to, the insulation and seal composed of a dielectric between the post and the body that withstands the compression pressures, and the element (or heating coil) that is welded to the post on one end and the body on the other. Assuming that the glow plug has a good seal, and most of the name brands now do, the critical part is the element. This is a coil of fine (.006 to .008 in. dia.) wire
