Figure 25.—Master and link connecting rods. U.S. Navy test, 1931. (Smithsonian photo A48323A.) Figure 26.—Crankshaft with automatic-timing retarding device on rear end of pivoted- and spring-mounted counterweights. U.S. Navy test, 1931. (Smithsonian photo A48323B.)
Figure 27.—Propeller hub and vibration damper. U.S. Navy test, 1931. (Smithsonian photo A48325A.)

Crankshaft: Since this engine developed the high maximum cylinder pressure of 1500 psi, it was necessary to protect the crankshaft from the resulting heavy stresses. Without such protection the crankshaft would be too large and heavy for practical aeronautical applications. Although the maximum cylinder pressures were 10 times as great as the average ones, they were of short duration. The method of protecting the crankshaft took full advantage of this fact. It consisted of having the counterweights flexibly mounted instead of being rigidly bolted, as was common practice. The counterweights were pivoted on the crank cheeks. Powerful compression springs absorbed the maximum impulses by permitting the counterweights to lag slightly, yet forced them to travel precisely with the crank cheeks at all other times.

Propeller Hub: The propeller is, of course, subject to the same stresses as the crankshaft. Instead of being rigidly bolted to the shaft as was common practice, it was further protected from excessive acceleration forces by being mounted in a rubber-cushioned hub. This permitted the use of a lighter propeller and hub.

Valves: A further weight saving resulted from the use of a single valve for each cylinder instead of two as in the case of conventional gasoline aircraft engines. (A diesel engine designed in this manner loses less efficiency than a gasoline one because only air is drawn in during the intake stroke.) In addition to the weight saving brought about by having fewer parts in the valve mechanism, there was an additional advantage since the cylinder heads could be made considerably lighter.

Figure 28.—Cylinder disassembly, showing valve and fuel injector.
U.S. Navy test, 1931. (Smithsonian photo A48324D.)

Diesel Cycle Features

Although Woolson designed the ingenious weight-saving features, Dorner was responsible for the engine’s diesel cycle which employed the “solid” type of fuel injection. In order to understand Dorner’s contribution, a brief description of the type of diesel injection pioneered by Dr. Rudolf Diesel is necessary. His system injected the fuel into the cylinder head with a blast of air supplied by a special air reservoir at a pressure of 1000 psi or more. Known as the “air blast” type of injection it produced good turbulence, with the fuel and air thoroughly mixed before being ignited. Such mixing increases engine efficiency, but it involves the provision of bulky and costly air-compressing apparatus which can absorb more than 5 percent of the engine’s power. Naturally the compressor also adds considerably to the engine’s weight.