Engine Technique
FUEL SYSTEMS: The ideal fuel system isn't here yet, but a lot of work has been put into making engines run in optimum fashion. Let's begin by taking a look at some of the forces that affect the fuel delivered to your engine: gravity, centrifugal force, partial vacuum, turbulent and laminar flow. Starting with the fuel tank, there are many different types of tanks, but they all serve one basic purpose, to hold the engine's fuel supply. Tanks can be further broken into two basic categories: pressure and demand. Pressure tanks are the expanded bladder type, or hard tanks with an external pressure source-such as crank-case, muffler, or pipe pressure supplied to the tank. They supply fuel to the engine by forcing fuel to the carburetor. Demand tanks are unpressurized bladder or hard tanks that supply fuel to the engine as the result of the partial vacuum (fuel draw) created by the flow of air through the carburetor venturi.
Engine Technique
PROPS AND SPINNERS: The first props for model engines were like the one pictured with the Brown Jr. engine (courtesy of Dave Elias). They were quite large in diameter, rotated slowly (4-8000 rpm) and made of soft woods like bass and gum. They were not subjected to the high centrifugal forces and shock loads that modern engines produce. Second generation props were typically smaller in diameter, rotated faster (to 14,000 rpm) and made of harder woods like oak, walnut, and maple. Horsepower had increased from 1/4 to 1 in 60-size engines. The end of World War II brought a desire for many things, including hobbies.
