were observed but the engine was so developed to
withstand these pressures.... One of the most severe problems
connected with the development of this engine was the piston ring
sealing. Special compression rings were made with no gaps and
further work in this respect could have been used to advantage had
the engine been kept in production.[37]

It is significant that in 1930 the Packard diesel had a compression
ratio of 16:1, whereas in 1931 it has been reduced to 14:1. This was
probably done to reduce vibration and the problem of piston-ring
sealing.[38] The exhaust products had an unpleasant odor which was
particularly objectionable during taxiing. Professor C. Fayette Taylor,
writing in the January 1931 issue of _Aviation_, remarked about this
fault: "One is inclined to question whether the disagreeable escaping of
exhaust gas from the intake ports can be overcome, while still retaining
the obvious advantages in weight and simplicity of the single valve."
The engine exhaust deposited a black oily film. In fact some airplanes
fitted with the Packard diesel engine were painted black, so that soot
deposits from the exhaust would not be noticed.[39] Since the
passengers' and pilots' compartments were generally located behind the
engines, and were not airtight, damage to clothing resulted. This fault
could have been eliminated by the use of separate valves for the intake
and exhaust systems.

It was not possible to start the engine when the temperature dropped
much below 32 deg. F unless glow plugs were used. These spark-plug-like
devices, which were only used for starting, had resistance windings
which glowed continuously when turned on. The additional heat glow plugs
provided made starting an easy matter in the coldest weather; however,
they complicated the design of an engine noted for its simplicity, and
they used so much electricity that only a long flight would allow the
generator to fully recharge the battery.

H. R. Ricardo, writing in the June 4, 1930, issue of _The Aeroplane_
said: "Referring to the very fine achievement of the Packard Company of
America in producing a small radial air-cooled heavy-oil engine, a
petrol engine of similar design and with the same margin of safety would
weigh less than 1-1/2 lbs. per hp." The important point made is that a
gasoline engine designed along the same lines as the Packard diesel
would weigh considerably less, but would then suffer from the Pac