aviation during World War One
WW1 aero engines

Anzani 10 Radial
Salmson Z-9 Radial

Radial Engines

Air-cooled engines offered tempting advantages. They dispensed with radiators that leaked, hoses that burst, cooling jackets that corroded, and water pumps that failed. The disadvantages of the rotary engine  prompted the development of the radial engine. They offered reliability along with light weight.

This type of air-cooled engine arranged its cylinders to extend radially outward from its hub, like spokes of a wheel.

You can see in the illustration that this is a five-cylinder engine -- radial engines typically have anywhere from three to nine cylinders. The radial engine has the same sort of pistons, valves and spark plugs that any four-stroke engine has. The big difference is in the crankshaft.

Instead of the long shaft that's used in a multi-cylinder car engine, there is a single hub -- all of the piston's connecting rods connect to this hub. One rod is fixed, and it is generally known as the master rod. The others are called articulating rods. They mount on pins that allow them to rotate as the crankshaft and the pistons move.

Master-and-articulating-rod Assembly

The master-and-articulating-rod assembly is used on X-type engines, radial-type engines, and on some V-type engines. The master rod is similar to any other connecting rod except that it is constructed to provide for the attachment of the articulated rods on the big end.

The articulated rods are fastened by knuckle pins to a flange around the master rod. Each articulated connecting rod has a bushing of nonferrous metal, usually bronze, pressed or shrunk into place to serve as a knuckle-pin bearing. The knuckle pins may be held tightly in the master-rod holes by press fit and lock plates or they may be of the full-floating type.

If the big end of the master rod is made of two pieces, the cap and the rod, the crankshaft is made of one solid piece. on the other hand, if the rod is made of one piece, then the crankshaft may be of either two-piece or three-piece construction. Regardless of the type of construction, the usual bearing surfaces must be supplied.

It should be understood that the type of connecting rod used in an engine depends largely on the cylinder arrangement. If the cylinders are arranged in a line parallel to the crankshaft, the connecting rod is similar to that used in most automobile engines. However, certain types of aircraft engines have a system of connecting rods connected to the same crankshaft bearing, called an articulating connecting-rod assembly. The main rod or master rod joins one of the pistons with the crankshaft, and the other rods, called articulating rods or link rods, connect the other pistons to this same master connecting rod.