Fuel/Oil Mixing Procedure Description of Systems Cooling System Opposed Light-Sport, Experimental, and  Certified Engines  Rotax 912/914  Fuel System The following describes the process for fuel/oil mixing. Use a  clean approved container of known volume. To help predilute the oil, pour a small amount of fuel into the container. Fill  known amount of oil (two-stroke oil ASTM/Coordinating  European Council (CEC) standards, API-TC classification  (e.g., Castrol TTS) mixing ratio 1:50 (2 percent)), into  container. Oil must be approved for air-cooled engines at  50:1 mixing ratio. Agitate slightly to dilute oil with gasoline.  Add gasoline to obtain desired mixture ratio; use fine mesh  screen. Replace the container cap and shake the container  thoroughly. Then, using a funnel with a fine mesh screen  to prevent the entry of water and foreign particles, transfer  mixture from container into the fuel tank.  WARNING: To avoid electrostatic charging at refueling, use  only metal containers and ground the aircraft in accordance  with the grounding specifications. Many certified engines are used with light-sport and  experimental aircraft. Generally, cost is a big factor when  considering this type of powerplant. The certified engines  tend to be much more costly than the non-certified engines,  and are not ASTM approved.  Figure 11-6  shows a typical four cylinder, four-stroke Rotax  horizontally opposed engine. The opposed-type engine has  two banks of cylinders directly opposite each other with a  crankshaft in the center. The pistons of both cylinder banks  are connected to the single crankshaft. The engine cylinder  heads are both liquid cooled and air cooled; the aircooling  is mostly used on the cylinder. It is generally mounted with  the cylinders in a horizontal position. The opposed-type  engine has a low weight to horsepower ratio, and its narrow  silhouette makes it ideal for horizontal installation on the  aircraft wings (twin-engine applications). Another advantage  is its low vibration characteristics. It is an ideal replacement  for the Rotax 582 two-cylinder, two-stroke engine, which  powers many of the existing light aircraft, as it is the same  weight as the Rotax 582. These engines are ASTM approved  for installation into light-sport category aircraft, with some  models being FAA certified engines.  The cooling system of the Rotax 914, shown in  Figure 11-7 ,  is designed for liquid cooling of the cylinder heads and  ram-air cooling of the cylinders. The cooling system of the  cylinder heads is a closed circuit with an expansion tank.  [Figure 11-8]  The coolant flow is forced by a water pump  driven from the camshaft, from the radiator, to the cylinder  heads. From the top of the cylinder heads, the coolant passes  on to the expansion tank (1). Since the standard location of  the radiator (2) is below engine level, the expansion tank  located on top of the engine allows for coolant expansion.  The expansion tank is closed by a pressure cap (3) (with  excess pressure valve and return valve). As the temperature  of the coolant rises, the excess pressure valve opens and  the coolant flows via a hose at atmospheric pressure to the  transparent overflow bottle (4). When cooling down, the  coolant is sucked back into the cooling circuit. Coolant  temperatures are measured by means of temperature probes  installed in the cylinder heads 2 and 3. The readings are taken  on measuring the hottest point of cylinder head depending  on engine installation.  [Figure 11-7] The fuel flows from the tank (1) via a coarse filter/water trap  (2) to the two electric fuel pumps (3) connected in series.  [Figure 11-9]  From the pumps, fuel passes on via the fuel  pressure control (4) to the two carburetors (5). Parallel to  each fuel pump is a separate check valve (6) installed via  the return line (7) that allows surplus fuel to flow back to the  fuel tank. Inspection for possible constriction of diameter or  obstruction must be accomplished to avoid overflowing of  fuel from the carburetors. The return line must not have any  resistance to flow. The fuel pressure control ensures that the  fuel pressure is always maintained approximately 0.25 bar  (3.63 pounds per square inch (psi)) above the variable boost  pressure in the airbox and thus, ensures proper operation of  the carburetors. Figure 11-6.  Typical four cylinder, four-stroke horizontally  opposed engine.  11-7