Rotor Blade Preservation and Storage Powerplant Helicopter Power Systems Reciprocating Engine When the piston moves away from the cylinder head on  the intake stroke, the intake valve opens and a mixture of  fuel and air is drawn into the combustion chamber. As the  cylinder moves back toward the cylinder head, the intake  valve closes, and the fuel/air mixture is compressed. When  compression is nearly complete, the spark plugs fire and the  compressed mixture is ignited to begin the power stroke.  The rapidly expanding gases from the controlled burning of  the fuel/air mixture drive the piston away from the cylinder  head, thus providing power to rotate the crankshaft. The  piston then moves back toward the cylinder head on the  exhaust stroke where the burned gases are expelled through  the opened exhaust valve. Even when the engine is operated  at a fairly low speed, the four-stroke cycle takes place several  hundred times each minute. In a four-cylinder engine, each  cylinder operates on a different stroke. Continuous rotation  of a crankshaft is maintained by the precise timing of the  power strokes in each cylinder. The two most common types of engines used in helicopters  are the reciprocating engine and the turbine engine.  Reciprocating engines, also called piston engines, are  generally used in smaller helicopters. Most training  helicopters use reciprocating engines because they are  relatively simple and inexpensive to operate. Turbine  engines are more powerful and are used in a wide variety of  helicopters. They produce a tremendous amount of power  for their size but are generally more expensive to operate. The reciprocating engine consists of a series of pistons  connected to a rotating crankshaft. As the pistons move up  and down, the crankshaft rotates. The reciprocating engine  gets its name from the back-and-forth movement of its  internal parts. The four-stroke engine is the most common  type, and refers to the four different cycles the engine  undergoes to produce power.  [Figure 2-56] Accomplish the following requirements for rotor blade  preservation and storage:  •  Condemn, demilitarize, and dispose of locally any  blade which has incurred nonrepairable damage.  •  Tape all holes in the blade, such as tree damage, or  foreign object damage (FOD) to protect the interior  of the blade from moisture and corrosion.  •  Thoroughly remove foreign matter from the entire  exterior surface of blade with mild soap and water.  •  Protect blade outboard eroded surfaces with a light  coating of corrosion preventive or primer coating.  •  Protect blade main bolt hole bushing, drag brace  retention bolt hole bushing, and any exposed bare  metal (i.e., grip and drag pads) with a light coating of  corrosion preventive.  •  Secure blade to shock-mounted support and secure  container lid.  •  Place copy of manufacturer’s blade records, containing  information required by Title 14 of the Code of Federal  Regulations (14 CFR) section 91.417(a)(2)(ii), and  any other blade records in a waterproof bag and insert  into container record tube.  •  Obliterate old markings from the container that  pertained to the original shipment or to the original  item it contained. Annotate the blade model, part  number (P/N) and serial number, as applicable, on  the outside of the container. Figure 2-56.  The arrows indicate the direction of motion of the  crankshaft and piston during the four-stroke cycle.  2-34 1. Intake 2. Compression 3. Power 4. Exhaust Intake valve Spark plug Exhaust valve Piston Crankshaft Connecting rod