V-Type Engines Radial Engines Reciprocating Engines  Design and Construction Crankcase Sections 1-5 Figure 1-2. Radial engine. Figure 1-3. Double row radials. In V-type engines, the cylinders are arranged in two in-line  banks generally set 60° apart. Most of the engines have 12  cylinders, which are either liquid cooled or air cooled. The  engines are designated by a V followed by a dash and the  piston displacement in cubic inches. For example, V-1710.  This type of engine was used mostly during the second World  War and its use is mostly limited to older aircraft. The radial engine consists of a row, or rows, of cylinders  arranged radially about a central crankcase.  [Figure 1-2]  This  type of engine has proven to be very rugged and dependable.  The number of cylinders which make up a row may be  three, five, seven, or nine. Some radial engines have two  rows of seven or nine cylinders arranged radially about the  crankcase, one in front of the other. These are called double-  row radials.  [Figure 1-3]  One type of radial engine has four  rows of cylinders with seven cylinders in each row for a total  of 28 cylinders. Radial engines are still used in some older  cargo planes, war birds, and crop spray planes. Although  many of these engines still exist, their use is limited. The  single-row, nine-cylinder radial engine is of relatively simple  construction, having a one-piece nose and a two-section  main crankcase. The larger twin-row engines are of slightly  more complex construction than the single row engines.  For example, the crankcase of the Wright R-3350 engine  is composed of the crankcase front section, four crankcase  main sections (front main, front center, rear center, and  rear main), rear cam and tappet housing, supercharger front  housing, supercharger rear housing, and supercharger rear  housing cover. Pratt and Whitney engines of comparable size  incorporate the same basic sections, although the construction  and the nomenclature differ considerably. The basic major components of a reciprocating engine are  the crankcase, cylinders, pistons, connecting rods, valves,  valve-operating mechanism, and crankshaft. In the head  of each cylinder are the valves and spark plugs. One of the  valves is in a passage leading from the induction system; the  other is in a passage leading to the exhaust system. Inside  each cylinder is a movable piston connected to a crankshaft  by a connecting rod.  Figure 1-4  illustrates the basic parts of  a reciprocating engine. The foundation of an engine is the crankcase. It contains  the bearings and bearing supports in which the crankshaft  revolves. Besides supporting itself, the crankcase must  provide a tight enclosure for the lubricating oil and must  support various external and internal mechanisms of the  engine. It also provides support for attachment of the  cylinder assemblies, and the powerplant to the aircraft. It  must be sufficiently rigid and strong to prevent misalignment  of the crankshaft and its bearings. Cast or forged aluminum  alloy is generally used for crankcase construction because  it is light and strong. The crankcase is subjected to many  variations of mechanical loads and other forces. Since the  cylinders are fastened to the crankcase, the tremendous  forces placed on the cylinder tend to pull the cylinder  off the crankcase. The unbalanced centrifugal and inertia  forces of the crankshaft acting through the main bearings  subject the crankcase to bending moments which change  continuously in direction and magnitude. The crankcase 