s 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.

[Illustration: 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.

In contrast to this, a "solid" type of fuel injection may be employed to
eliminate the complications of the "air blast" system. It consists of
injecting only fuel at a pressure of 1000 psi or more. Air is admitted
by intake stroke, as with a gasoline engine. Turbulence is induced by
designing the combustion chamber and piston so as to give a whirling
motion to the air during the intake stroke. The following quotation from
Dorner now becomes readily understandable. "Since 1922 my in