Radial Engines

Radial Engines

Nose Section

In general, it is either tapered or round in order to

place the metal under tension or compression instead

of shear stresses.

A tapered nose section is

used quite frequently on direct-drive, low-powered

engines, because extra space is not required to house

the propeller reduction gear.

The nose section on engines which develop from

1,000 to 2,500 hp. is usually rounded and sometimes

ribbed to get as much strength as possible.

Aluminum alloy is the most widely used material

because of its adaptability to forging processes and

its vibration-absorbing characteristics.

Since the nose section transmits many varied

forces to the main or power section, it must be

properly secured to transmit the loads efficiently.

It also must have intimate contact to give rapid and

uniform heat conduction, and be oiltight to prevent

leakage. This is usually accomplished by an offset

or ground joint, secured by studs or capscrews.

On some of the larger engines, a small chamber

is located on the bottom of the nose section to collect

the oil. This is called the nose section oil sump.

Power Section

On engines equipped with a two-piece master rod

and a solid-type crankshaft, the main or power

crankcase section may be solid, usually of aluminum

alloy.

This portion of the engine is often called the

power section, because it is here that the reciprocating

motion of the piston is converted to rotary

motion of the crankshaft.

Because of the tremendous loads and forces from

the crankshaft assembly and the tendency of the

cylinders to pull the crankcase apart, especially in

extreme conditions when a high-powered engine is

detonated, the main crankcase section must be very

well designed and constructed.

The machined surfaces on which the cylinders

are mounted are called cylinder pads. They are

provided with a suitable means of retaining or

fastening the cylinders to the crankcase.

The inner portion of the cylinder pads are sometimes

chamfered or tapered to permit the installation

of a large rubber O-ring around the cylinder

skirt, which effectively seals the joint between the

cylinder and the crankcase pads against oil leakage.

Diffuser Section

The diffuser or supercharger section generally is

cast of aluminum alloy, although, in a few cases,

the lighter magnesium alloy is used.

Because of the elongation and contraction of the

cylinders, the intake pipes which carry the mixture

from the diffuser chamber through the intake valve

ports are arranged to provide a slip joint which

must be leakproof. The atmospheric pressure on

the outside of the case of an unsupercharged engine

will be higher than on the inside, especially when

the engine is operating at idling speed. If the

engine is equipped with a supercharger and operated

at full throttle, the pressure will be considerably

higher on the inside than on the outside of the case.

If the slip joint connection has a slight leakage,

the engine may idle fast due to a slight leaning of

the mixture. If the leak is quite large, it may not

idle at all. At open throttle, a small leak probably

would not be noticeable in operation of the engine,

but the slight leaning of the fuel/air mixture might

cause detonation or damage to the valves and valve

seats.

Accessory Section

The accessory (rear) section usually is of cast

construction, and the material may be either aluminum

alloy, which is used most widely, or magnesium,

which has been used to some extent.

the

increased demands for electric current on large

aircraft and the requirements of higher starting

torque on powerful engines have resulted in an

increase in the size of starters and generators.

This means that a greater number of mounting bolts

must be provided and, in some cases, the entire

rear section strengthened.

In some cases there is a duplication of drives,

such as the tachometer drive, to connect instruments

located at separate stations.

The accessory section provides a mounting place

for the carburetor, or master control, fuel injection

pumps, engine-driven fuel pump, tachometer

generator, synchronizing generator for the engine

analyzer, oil filter, and oil pressure relief valve.