Section 2 EO M232.02 – IDENTIFY THE COMPONENTS OF PISTON-POWERED INTERNAL COMBUSTION ENGINES

Show the cadets a slide or handout of the piston-powered engine in Figure A-1.

Cylinder. In order to understand how an engine works, it is necessary to first know what parts make up an engine. The cylinder is the main component. This is where the combustion of a gasoline and air mixture takes place.

Piston. The piston is found in the cylinder and is driven up and down by the exploding air and fuel mixture.

Connecting Rod. The piston is attached by a connecting rod to the crankshaft. The connecting rod is joined to the piston and to the crankshaft with bearings which allow movement so that the reciprocating (up-and-down) motion of the piston can be transformed into rotary (spinning) motion of the crankshaft.

Crankshaft. As the piston drives up and down, the connecting rod rotates around the crankshaft, turning it. The crankshaft can rotate while the piston goes up and down.

Camshaft. The crankshaft often turns a second shaft called a camshaft. The cams are bumps on the camshaft that open and close the intake and exhaust valves at the correct time. Of course, the crankshaft also powers the aircraft’s propeller. Each cylinder has at least one set of valves operated by the cams on the camshaft. The intake valve opens to let the mixture of gasoline and air into the cylinder and then it closes. Once this is done and the mixture is burnt, the exhaust valve opens to release the exhaust and then closes.

Distributor. The gasoline and air mixture is ignited by a spark plug. Most aircraft have two spark plugs in every cylinder. The fuel takes time to burn completely. Because of this time delay, the spark must happen at just the right time; a fraction of a second before the piston has reached the top of its stroke. In a multi-cylinder engine such as aircraft use, an electrical signal must be sent to each cylinder’s spark plug at exactly the right time. The timing and distribution of spark sometimes relies on a central distributor, which is worked by gears from the crankshaft. Should this distributor fail, the engine will stop. A better, though more expensive method, is to equip each cylinder with its own spark timing and delivery system.

Show the cadets a slide or handout of a carburetor in Figure A-2.

Carburetor. Before fuel is delivered to the cylinder for detonation, it is mixed with air in exact proportion. A fuel injector or a carburetor does this. For effective detonation and clean burning, the fuel must be broken into tiny droplets and mixed with air.

Oil Sump. The moving parts of the engine all need to be coated with engine oil. Oil is provided under pressure to make sure that all moving parts are coated. A wet sump stores the oil supply in the crankcase with the crankshaft, while a dry sump stores the oil in a separate tank and delivers it to the engine via piping.

Show the cadets a slide or handout of a dry-sump lubrication system in Figure A-3.

The oil is circulated and re-used, serving other purposes in addition to lubrication. As the oil circulates, it cleans the engine by flushing dirt out of the engine. It also cools the engine by carrying heat away and it improves the pressure seal to keep the combustion chamber airtight.

Have the cadets label the parts of a piston-powered engine in Figure A-4.

Some early aircraft engines used rotary engines in which the cylinders themselves rotated around the stationary central crankshaft. These were different than the later radial engines in which the stationary cylinders were arranged around the rotating crankshaft.

Many larger older aircraft had radial engines. In this design the cylinders were arranged in a circle at the front of the engine with the cylinder tops pointed outwards. The crankshaft ran through the middle of the cylinders to the front of the aircraft. Radial engines had many cylinders; some aircraft from World War II had 13 cylinders.

Show the cadets a slide or handout of the radial engine located at Annex B.

Even older aircraft, before and during World War I, had rotary engines that were different but were often confused with the later radial types. In the rotary engine, the crankshaft was stationary and the cylinders rotated around the crankshaft. This is the opposite of the radial engine, which had stationary cylinders and rotating crankshaft. Rotary engine design was abandoned because the great weight of the spinning cylinders was found to interfere with turning the aircraft in flight.

Internal combustion engines come in a variety of styles that are described by how the cylinders are configured.

Show the cadets a slide or handout of the horizontally opposed engine located at Annex C.

The horizontally opposed engine is most commonly used in general aviation airplanes. This engine has two banks of cylinders lying flat, directly opposite each other and working on the same crankshaft. There may be four, six or eight cylinders. The advantage of this engine type is its flat shape that generates less form drag. Form drag is a force that opposes the aircraft’s movement through the air.

Show the cadets a slide or handout of an in-line engine located at Annex D.

Some older aircraft have in-line engines. This was the first type of aircraft engine used in great numbers. In an in-line engine, the cylinders are lined up in a row from the front of the engine to the back, with the tops pointed up. The crankshaft runs under the cylinders to the front of the aircraft.