Aviation Powerplants: Reciprocating-Engine Construction and Nomenclature

What type of bearing produces the least rolling friction?

Ball bearings

How may pistons be classified?

By the type of piston head used.

What is the function of a piston pin?

To attach the piston to the connecting rod.

List the basic components of the valve operating mechanism for an opposed engine

Cam- A device for actuating the valve lifting mechanism Valve lifter- A mechanism for transmitting the force of the cam to the valve pushrod Pushrod- A steel or aluminum alloy rod or tube, situated between the valve lifter and the rocker arm of the valve operating mechanism for transmitting the motion of the valve lifter Rocker Arm- A pivoted arm, mounted on bearings in the cylinder head, for opening and closing the valves. One end of the arm presses on the stem of the valve, and the other end receives motion from the pushrod

List the principal components in a cylinder assembly

Cylinder barrel with an integral skirt, cylinder head, value guides, valve rocker-arm supports, valve seats, spark plug bearings, and cooling fins.

Why are crankpins usually hollow?

1. It reduces the total weight of the crankshaft 2. It provides a passage for the lubricating oil 3. It serves as a chamber for collecting carbon deposits, sludge, and other foreign substances which are thrown by centrifugal force to the outside of the chamber where they will not reach the connecting rod bearing surface

What are the principal functions of piston rings?

1. To provide a seal to hold the pressures in the combustion chamber 2. To prevent excessive oil from entering the combustion chamber 3. To conduct the heat from the piston to the cylinder walls

What are pistons made of?

They are usually made of an aluminum alloy which may be either forged or cast.

What is the purpose of a Heli-Coil insert?

They make it possible to restore the thread by replacement of the inserts.

What are the purposes of propeller reduction gears?

To allow the propeller to rotate the most efficient speed to absorb the power of the engine while the engine turns at a much higher rpm in order to develop full power.

What are the angles of the intake and exhaust valve faces?

The face of the valve is usually ground to an angle of either 30 degrees or 45 degrees. In some engines, the intake valve face is ground to an angle of 30 degrees, and the exhaust valve face is ground to 45 degrees. The 30 degree angle provides better airflow, and the 45 degree angle allows increased heat flow form the valve to the valve seat.

Why are counterweights needed on many crankshafts?

To provide static balance for a crankshaft.

How is a piston cooled?

The heat in the piston is carried to the cylinder wall through the outside of the piston and is transmitted to the engine oil in the crankcase through ribs or other means on the inside of the piston head.

What is the purpose of dynamic dampers?

To relieve the whip and vibration caused by the rotation of the crankshaft.

What are the three principal types of connecting rod assemblies?

The plain type, the fork-and-blade type, the master and articulated type.

Describe the functions of a crankcase

The crankcase of an engine is the housing that encloses the various mechanisms surrounding the crankshaft; therefore it is the foundation of the engine. The functions of the crankcase are as follows: 1. It must support itself 2. It contains the bearings in which the crankshaft revolves 3. It provides a tight enclosure for the lubricating oil 4. It supports various internal and external mechanisms of the powerplant 5. It provides mountings for attachment to the airplane 6. It provides support for the attachment of the cylinders 7. By reason of its strength and rigidity, it prevents the misalignment of the crankshaft and its bearings

Why is the piston ring gap important?

The rings are split so that they can be slipped over the outside of the piston and into the ring grooves which are machined on the circumference of the piston.

How is the cylinder head attached to a cylinder barrel?

There are three methods used for joining the cylinder barrel to the cylinder head, in which are: -Threaded joint method -Shrink-fit method -Stud-and-nut joint method

Name the principal sections of the the crankcase for a radial engine

Front section- which is usually made of an aluminum alloy, its housing is approximately bells-shaped, and it is fastened to the power section by studs and nuts or cap screws Main Power section- Usually consists of two, or possibly three pieces of high strength heat treated aluminum alloy or steel forgings, bolted together if there is more than one piece Fuel Induction and Distribution section- Is normally located immediately behind the main section and may be of either one or two piece construction Accessory section- Provides mounting pads for the accessory units, such as the fuel pumps, vacuum pumps, lubricating oil pumps, tachometer generators, generators, magnetos, starters, two speed supercharger control valves, oil filtering screens, cuno filters, and other items of accessory equipment

What material is a cylinder barrel constructed of?

High-strength steel alloy

What is a full floating piston pin?

It is a pin that is free to run or slide in both the connecting rod and the piston and is the most widely used in modern aircraft engines.

What is the basic function of a piston?

It is a plunger that moves back and forth or up and down within the engine cylinder barrel. It transmits the force of the burning and expanding gases in the cylinder through the connecting rod to the engine crankshaft. As the piston moves down (toward the crankshaft) in the cylinder during the intake stroke, it draws in the fuel-air mixture. As it moves up (toward the cylinder head), it compresses the charge. Ignition takes place, and the expanding gases cause the piston to move toward the crankshaft. On the next stroke (toward the head), the piston forces the burned gases out of the combustion chamber.

What type of process is nitriding?

It is a process whereby the nitrogen from anhydrous ammonia gas is forced to penetrate the surface of the steel by exposing the barrel to the ammonia gas for 40 hrs or more while the barrel is at a temperature of about 975 degrees F.

What is meant by a chokebored cylinder?

It is a type of cylinder with a slight taper. The end of the bore nearest the head is made smaller than the skirt end to allow for the expansion caused by the greater temperatures near the head.

What is the function of a connecting rod?

It is the link which transmits forces between the piston and the crankshaft of an engine. It furnishes the means of converting the reciprocating motion of the piston to a rotating movement of the crankshaft in order to drive the propeller.

Name the accessories which are generally mounted on the accessory section

It provides mounting pads for fuel pressure pumps, fuel injector pumps, vacuum pumps, oil pumps, tachometer generators, electric generators, magnetos, starts, two-seed supercharger control valves, oil screens, hydraulic pump, and other units.

Of what materials is a crankcase usually made?

Most aircraft engine crankcases are mad of aluminum alloys because they are both light and strong.

What types of loads are normally applied to plain bearings? To ball bearings?

Plain bearings are designed to take radial loads. Ball bearings are designed to take thrust loads.

Describe two types of anti-friction bearings

Roller Bearings- These bearings are made in a variety of shapes and sizes and can be adapted to both radial and thrust loads. In a roller bearing, the roller is situated between an inner and an outer race, both which are made of case hardened steel. When a roller is tapered, it rolls on a cone shaped race inside an outer race. Roller bearings are use din high power aircraft engines as main bearings to support the crankshaft Ball Bearings- Consists of an inner race and an outer race, a set of polished steel balls, and a ball retainer. Some ball bearings are made with two rows of balls and two sets of races. The races are designed with grooves to fight the curvature of the balls in order to provide a large contact surface for carrying high radial loads. The balls are controlled and held in place by the ball retainer. This retainer is necessary to keep the balls properly spaced, thus preventing them from contacting one another. Ball bearings are commonly used for thrust bearings in large radial engines and gas turbine engines.

What engine requires a master and articulated connecting rod assembly?

They are primarily used for radial engines and on some V-type engines.