Generally, the fuel tank is located close to the center  of gravity, so fuel burn does not affect the balance of  the aircraft. Some fuel tanks are clear for visual in - spection of the amount of fuel on board while others  are dark. Dark tanks or hidden tanks generally have a  sight tube to assist the pilot in determining the actual  amount of fuel. [Figure 3-14] Some powered para - chute manufacturers offer optional  fuel level probes  and instrument panel analog gauges or incorporate  this information into the EIS. As fuel is used by the  engine, air needs to enter the tank and take its place;  otherwise a vacuum will form inside the fuel tank  preventing the fuel pump from drawing fuel. This is  usually accomplished with a  fuel venting system. This  can be a vent in the fuel cap or some other means that  vents elsewhere, providing the ability for the fuel tank  to breathe. Any vent system must be free of debris or  it will cause fuel starvation in flight. This is especially  true when a small hole is in the fuel cap that can be  easily plugged. Check the fuel venting system during  each preflight inspection. operating handbook for specific engine specifica - tions). The typical powered parachute  engine can be two- or  four-stroke, liquid- or air-cooled, 50 to 100 horsepow- er. Some engines have electric starters and some have  pull starters. Most PPC engines have reduction drives  that, when attached, reduce the propeller RPM to half  to one quarter the engine RPM. [Figure 3-16] The en - gines are as varied as the powered parachutes they  power. Modern technology has allowed the powered  parachute engine to become lighter, more efficient  and, most importantly, dependable. Chapter 4 covers  the powerplant in more detail. The fuel shut-off valve can be located anywhere in the  fuel line. It is important to make sure the fuel valve  is open and stays open for normal operation. Most  designs have a fuel tank sump drain valve to remove  water and solid contaminants. Each design is differ- ent and the PPC POH will specify how to conduct  this check. Propellers are “power converters” that change the  engine horsepower into “thrust.” Thrust is the force  that propels the aircraft through the air by pushing  the powered parachute forward. Aerodynamically  speaking, a propeller is a rotating airfoil and the same  principles that apply to the wing will apply to the pro- peller. [Figure 3-17] Engine power is transferred to the  propeller through a rotating crankshaft that turns the  propeller through the air, producing thrust in the same  way as wings produce lift. The shape of the blade cre - ates thrust vectors because it is cambered like the air foil of a wing. Consequently, as the air flows past the  propeller, the pressure on one side is less than that on  the other. As in a wing, this produces a reaction force  in the direction of the lower pressure. In the case of  the propeller, which is mounted in a vertical plane, the  The throttle is the pilot’s hand control to regulate the  power provided by the engine. The configuration of  the throttle control varies from one cart manufacturer  to another. Refer to the POH of each individual PPC  for function reference. [Figure 3-15] The Propeller The Powerplant Figure 3-16. Reduction drives  reduce the propeller RPM from  the engine RPM by about half.  Figure 3-15. Powered  parachute throttle. Figure 3-14. Fuel tank with sight tube.  Throttle System 3-8