The First Airplane Diesel Engine: Packard Model DR-980 of 1928 Part 4

Fire-Safe Fuel

_Furnaces in many a home burn similar oil_

_A lighted match cannot ignite or explode it_

_Saturated cloth can burn only like a wick_

_And the oil itself will quench this fire_

_But only when property atomized the spray may be ignited_

Graphic Proof of fuel safety in the Packard-Diesel Aircraft Engine

Figure 36.--Advertis.e.m.e.nt emphasizing the advantages of fire-safe fuel.

(Smithsonian photo A48848.)]

Due to the greater simplicity, it was more practical to build a large diesel than a large gasoline engine. Large airplanes would therefore need fewer engines if diesel powered. Smaller fuel tanks could be used because of the greater fuel economy of the diesel, and also because of the high specific gravity of fuel oil as compared to gasoline.

Furthermore, these smaller tanks could be placed in more convenient locations. Not having a carburetor the engine could not backfire, further reducing the fire hazard. The exhaust note was lower because of the diesel's higher expansion ratio. The absence of an ignition system permitted the diesel to operate in the heaviest types of precipitation.

Such conditions might cause the ignition system of a gasoline engine to malfunction. The Packard diesel was flown at times without exhaust stacks or manifolds; this was practical from a safety standpoint because of the diesel's lower exhaust temperature due to its higher expansion ratio. Elimination of these parts reduced the weight and cost of the engine installation. Finally, the engine was ideal for aerobatics, since the injectors, unlike carburetors, would work equally well whether right side up or upside down.

An advantage peculiar to the Packard among aeronautical diesels was its light weight. The English Beardmore "Tornado III" weighed 6.9 lb/hp, and the German Junkers SL-1 (FO-4) weighed 3.1 lb/hp, while the Packard weighed but 2.3 lb/hp. In fairness to the Beardmore, it was the only one of the three engines designed for airs.h.i.+p use, and part of its heaviness was due to the special requirements of lighter-than-air craft. A contemporary and comparable American gasoline engine, the Lycoming R-680, weighed 2.2 lb/hp. To have designed a diesel aircraft engine as light as a gasoline one was a remarkable achievement.

Disadvantages

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 cla.s.s is attempted." This latter statement probably refers to the 400-hp model.

A year had pa.s.sed 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 princ.i.p.al 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 pa.s.sengers' 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 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 ill.u.s.trated advertis.e.m.e.nt t.i.tled "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 advertis.e.m.e.nt was placed by Frank Hawks of the Texas Company largely as a gesture of friends.h.i.+p 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."

[Ill.u.s.tration: 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 fas.h.i.+on 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 Ha.s.sel 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 "h.e.l.lo, h.e.l.lo, h.e.l.lo" 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 gla.s.s 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 a.n.a.lysis 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 a.n.a.lyzed in this chapter, it could not meet this compet.i.tion, and therefore failed to survive.

Appendix

1. Agreement between Hermann I. A. Dorner and Packard Motor Car Company