CHECK THOSE THRUST ANGLES: Many R/C designs call for a small amount of downthrust and/or sidethrust in the engine mounting. Often times this offset thrust is built right into the structure and you don't have to worry about it. Simply double check the installation after the model is done to confirm that the offset called for is present. Since it is very difficult to make a precise measurement of thrust angles, an "eyeball" check is adequate. Installing the propeller will make it easier to sight the model from the side-view and top-view to verify that the installation is close to correct. Slight variations in thrust offset are not super critical, it takes several degrees of sidethrust or downthrust to make a difference in the way the airplane flies.

A portion of the Kadet Senior plans is shown here to illustrate the meaning of "downthrust". The thrust line slopes downward 6° from horizontal. The downthrust is automatically built into the model, but it's still a good idea to check it visually after the engine is installed.

MUFFLERS

KEEP 'EM QUIET: Unless you are one of the lucky few who has a flying site miles away from any sort of civilization, you should use an effective muffler on your engine. The sound of an unmuffled R/C engine can be annoying to anyone within earshot. The last thing you want to do is turn potentially friendly neighbors into enemies that could in the worst case, go so far as to have all flying activity at your field shut down.

Most manufacturers supply good mufflers with their engines. If for some reason you have an engine without a muffler, or the supplied muffler doesn't fit your airplane, you can use one of the many aftermarket mufflers that are available. Several companies make mufflers with special shapes to fit popular engine and airplane combinations (especially scale models). If your engine/muffler installation comes very close to fitting, but the muffler bumps into part of the model structure in one or two places, don't be afraid to modify the model slightly to make room. It is common procedure to make small cutouts in the cowling/engine compartment area to make room for the muffler.

FUEL TANK SELECTION

Standard practice for almost all R/C airplanes is to use a "clunk-type" plastic fuel tank. This type of tank will continue to feed fuel regardless of the attitude of the model in flight. A weighted pickup on the end of a flexible fuel feed line inside the tank follows the movement of the fuel throughout the flight. There are several different brands, shapes, and sizes of plastic clunk tanks from which to choose.

HOW BIG SHOULD THE TANK BE? Most kits specify the exact size and shape of fuel tank that will work best in the model. Their recommendation is determined by the amount of space available inside the model. Round, rectangular, or slant shaped tanks perform equally well in flight, but the structure of the airplane may make one shape more desirable than the other for installation. The following list gives a general indication of the appropriate tank capacity to use with certain size engines. Note: Since four-stroke engines are more fuel efficient than two-stroke engines, the tank size can be reduced about 25% for equal running time.

TANK ASSEMBLY
When you buy a fuel tank of any brand, the final assembly of the tank is left to the modeler, who must first decide whether he wants to use a "single-vent" or "double-vent" set-up.

SINGLE-VENT: This is the simplest and best fuel tank set-up for most R/C sport models. There are two brass tubes installed through the rubber stopper going into the tank - one for fuel feed to the carburetor and one for an overflow vent (see photo). Inside the tank, the vent tube should curve up to the top of the tank. The brass fuel feed tube stops just inside the rubber stopper and has a piece of flexible rubber tubing attached to it. The flexible tubing is just long enough to reach the back of the tank and has a heavy metal "clunk" on its back end. The clunk will stay submerged in the fuel no matter what the attitude of the aircraft. During assembly, be sure that the fuel feed line swings freely without hitting the back of the tank. To fuel an airplane with this tank set-up, simply remove the fuel feed tubing from the carburetor and pump the fuel into that line. When fuel runs out of the vent line, the tank is full. Reconnect the feed line to the carburetor and you are ready to fly. This simple single-vent tank set-up is recommended for any R/C model that has the engine exposed enough for you to take the fuel feed line on/off of the carburetor.

SINGLE-VENT FUEL TANK	DOUBLE-VENT FUEL TANK