There are four main reasons why the Packard diesel was not successful.
First the Packard Motor Car Company put the engine into production a
brief three years after it was created. The only successful airplane
diesel, the German Junkers "Jumo," was in development more than three
times as long (1912-1929). The following tests indicate that the
Packard diesel was not ready for production, and hence was unreliable.
Packard Motor Car Company 50-Hour Test (Feb. 15-18, 1930): This test was
identical to the standard Army 50-hour test which was used for the
granting of the Approved Type Certificate. The engine tested was
numbered 100, and was the first to be made with production tools
(approximately half a dozen engines had been handmade previously). It
had to be stopped three times, twice due to failure of the fuel pump
plunger springs and once due to the loosening of the oil connection
ring. These failures were attributed to manufacturing discrepancies. In
addition, 4 out of a total of 103 valve springs broke.[29]
U.S. Navy 50-Hour Test (Jan. 22, 1931, to March 15, 1931): The engine
used in the Navy test was numbered 120. (Apparently only 20 production
engines had been built during the preceding 12 months; Dorner in a
letter of March 3, 1962, states that the total number of Packard diesels
produced was approximately 25.) The engine had to be stopped three
times, twice due to valve-spring collar failures and once due to a valve
head breaking. Because of these failures this test was not completed.
The following significant quotations have been extracted from the test:
"The engine is not recommended for service use.... Flight tests, until
the durability of the engine is improved, be limited to a determination
of the critical engine speeds, and to short hops in seaplanes.... It is
believed that this size engine should be made suitable for service use
before this type in a larger class is attempted." This latter statement
probably refers to the 400-hp model.
A year had passed between the making of engine 100 and 120, yet the
reliability had not improved. Although unreliability was the immediate
cause of failure, there were two design defects which would have doomed
the engine even if it had been reliable. All the Packard diesels were of
the 4-stroke cycle unblown type, yet the most successful airplane
diesels were of the 2-stroke cycle blown type.[30] The advantages of the
latter type for aeronautical use are that it is of a more compact
engine, of lower weight and greater efficiency.[31] The engine was
therefore built around the wrong cycle.
The Packard diesel of 1928 was designed to compete with the Wright J-5
"Whirlwind" which powered Lindbergh's "Spirit of St. Louis" in 1927.[32]
The specifications were within two percent of each other. The diesel
engine's fuel consumption was far less although its price was
considerably higher.
_Packard Diesel_ _Wright J-5_
_DR-980_ _"Whirlwind"_
Diameter (in.) 45-11/16 45
Horsepower 225 225
Weight (lb) 510 510
Weight-horsepower ratio 2.26 2.26
Fuel consumption (lb per hp/hr at 0.40 0.60
cruising).
Cost $4025 $3000
The advantages of lower fuel cost and greater cruising range offered by
the diesel engine would be relatively unimportant to a private pilot
flying for pleasure, but would be vital to the commercial operator using
airplanes powered by engines having several times the horsepower of the
Packard diesel. Its size, moreover, was too small for the technology of
fuel injectors.[33] The Packard Company realized that the production
engine was too small.[34] In 1930 a 400-hp version was built but was not
put into production, probably because of the unreliability of the 225-hp
model.
The fourth principal reason why the engine failed is explained by the
following quotation from _The Propulsion of Aircraft_, by M. J. B. Davy
(published in 1936 by His Majesty's Stationery Office, London):
Although the development and adoption for transport purposes of the
relatively high-speed compression ignition engine has been rapid
during the last few years, there has been no corresponding advance
in its adoption for aircraft propulsion. A reason for this is the
recent great advance in "take-off" power in the petrol (gasoline)
engine due to the introduction of 87 octane fuel (which permits
higher compression ratios) and the strong probability of 100 octane
fuels in the near future, still further increasing this power. The
need for increased take-off power results from the higher wing
loading necessitated by the modern demand for commercial aircraft
with higher cruising speeds with reasonable power expenditure.
Production of the Packard diesel ceased in 1933. During that same year
the Pratt & Whitney Aircraft Company and the Wright Aeronautical
Corporation specified 87-octane fuel for certain of their engines. Less
than 10 years later octane ratings had increased to over 100, putting
the diesel at a further disadvantage.[35]
Although the above disadvantages sealed the Packard diesel's fate, there
were other minor reasons for its failure. The Packard diesel had the
highest maximum cylinder pressure (up to 1500 psi at peak rpm) of any
proven contemporary aircraft diesel engine. Leigh M. Griffith, vice
president and general manager, Emsco Aero Engine Company, had this to
say about the Packard diesel's high maximum cylinder pressure in the
September 1930 _S.A.E. Journal_:
The designers considered it necessary to adopt unusual but
admittedly clever expedients to counteract the great torque
irregularity caused by the excessive maximum pressure. The adoption
of the lower pressure of 800 lbs. would have eliminated the
necessity for the pivoted spring-mounted counterweights and the
shock-absorbing rubber propeller-drive.... The use of such high
pressures is in reality the quick and easy way to secure high-speed
operation and can be justified only from this standpoint, although
the resulting increased difficulty in keeping the engine light
enough was a strong offsetting factor.[36]
Insofar as the engine life was concerned it is true that 1,500-psi
peak pressures 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 Packard's
reduced structural safety factor. It is significant that as the Packard
developed, it became heavier.[40]
Like other diesels, the Packard cost more to build than a comparable
gasoline engine, because of the type of construction required for the
diesel's higher maximum cylinder pressures and the difficulty of
machining the fuel injectors. Having fuel injectors, the engine was more
sensitive to dirt in the fuel system than a carburetor-equipped
gasoline engine.[41] The fuel injectors were "a crude and deficient
mechanism" subject to rapid wear, and often these injectors caused
smoking exhausts and high fuel consumptions.[42] In the event of battery
or starter failure, a comparable gasoline engine could be started by
swinging the propeller. Because of the engine's high compression, it
would have been impossible to have hand-started a Packard diesel this
way.
In a letter to the Air Museum, January 15, 1962, Dorner commented:
"During my first demonstration (of high-speed diesel engines) in 1926 in
California and later in Detroit I learned from Capt. Woolson that the
large transport airlines were controlled by oil companies which were not
interested in (supplying) two different kinds of aircraft fuel, and in
savings of fuel." The May issue of _Aero Digest_ had a full-page
illustrated advertisement titled "Announcing National Distribution for
Texaco Aerodiesel Fuel." Although distribution was limited, the American
oil industry did not prevent the airplane diesel from becoming a success
in the civil market. However, it is significant that the advertisement
was placed by Frank Hawks of the Texas Company largely as a gesture of
friendship to Woolson.[43]
The situation in the military market was different, however, as
testified by this quotation from the same letter. "The military
administration, having paid all of the expenses for the testing period
to that date (1931), came after the tests to the conclusion that the
advantages of the diesel as compared to its disadvantages did not
justify the great risk to procure and distribute two different kinds of
fuel in case of war."
Two accidents, which received wide publicity and no doubt did
considerable harm to the entire project, occurred to Packard
diesel-powered airplanes. The following quotation is from the _Herald
Tribune_ for April 23, 1930: "Attica, New York--Losing their bearings in
a blinding snowstorm and mistaking the side of a snow-covered hill for a
suitable landing place, three men, one of them Capt. Lionel M. Woolson,
aeronautical engineer for the Packard Motor Company and adapter of the
diesel engine to airplanes, were killed here today."
[Illustration: Figure 37.--Interior of Bellanca, showing Parker D.
Cramer, pilot (left), and Oliver L. Paquette, radio operator, just
before taking off from Detroit, Michigan, on July 28, 1931. (Smithsonian
photo A202.)]
The second of these accidents is described in the September 1931 issue
of _U.S. Air Services_:
Columbus wanted to sail west beyond the limits set by the learned
navigators of his time, and in much the same consuming fashion
Parker D. Cramer wanted to show his generation and posterity that
a subarctic air route to Europe via Canada, Greenland, Iceland,
Norway, and Denmark was feasible.... On July 27, without any
preliminary announcement, Cramer left Detroit in a Diesel-engined
Bellanca, and following the course he took with Bert Hassel three
years ago, he flew first to Cochrane, on Hudson Bay. His next stop
was Great Whales and then Wakeham Bay. From there he flew to
Pangnirtum, Baffin Land, and across the Hudson Straits to
Holsteinborg, Greenland. He crossed the icecap at a point farther
north than the routes that have been discussed heretofore, but
almost on the most direct or Great Circle route from Detroit to
Copenhagen. He was accompanied by Oliver Paquette, radio operator.
They were on their way more than a week before they were
discovered. To Iceland, to the Faroe Islands, to the Shetlands.
They were taxiing across the little harbor of Lerwick, Shetland
Islands, when a messenger from the bank waved a yellow paper. It
was a warning of gales on the coast east to Copenhagen. Cramer
apparently thought it was an enthusiastic bon voyage, and, after
circling the town, flew away. A Swedish radio station reported a
faint "Hello, Hello, Hello" in English, but the plane was not seen
again.
As the result of a personal conversation with his brother, William A.
Cramer, in 1964, the author learned that the fuselage and floats of the
airplane were found six weeks later. Since there was no indication of a
heavy impact (not a single glass dial on the instrument panel was
broken), a successful landing must have been made. Several weeks later,
a package was found wrapped in a torn oilskin containing instruments,
maps, and a personal letter, all substantiating the evidence that the
landing was successful. It can only be surmised that there was engine
failure, probably due to a clogged oil filter.[44]
Once before during the trip a forced landing had been made due to engine
malfunctioning, and a successful takeoff was accomplished in spite of a
moderately rough sea. This time, however, storm conditions probably made
the takeoff impossible.
As a final summary of the author's analysis of the Packard diesel
engine, it must be emphasized that although the engine burned a much
cheaper and safer fuel more efficiently than any of its gasoline rivals,
it was too unreliable to compete with them. Even if it had been
reliable, it was too small to be useful to the large transport
operators, to whom its fuel economy would have appealed. In addition,
this mechanism operated on the wrong cycle: 4-stroke, rather than the
lighter, more compact, and more efficient blown 2-stroke cycle. Lastly,
it was doomed by the advent of high octane gasolines, first used while
it was still in the development stage. These new fuels reduced the
diesel's advantage resulting from low fuel consumption, and, in
addition, gave the gasoline engine a definite advantage from the
standpoint of performance. The Packard diesel was a daring design but,
for the reasons analyzed in this chapter, it could not meet this
competition, and therefore failed to survive.