Overview:
The Packard DR-980 diesel engine, showcased in the Smithsonian National Air Museum, marked a significant milestone in aviation history. It was the first compression-ignition engine to power an airplane, achieving a remarkable 225 horsepower at 1950 revolutions per minute. Developed under the guidance of L.M. Woolson, the engine’s success was rapid and noteworthy, with production examples powering airplanes to impressive feats like a record-breaking 84-hour non-refueled duration flight.
However, despite its pioneering status, the Packard diesel was ultimately destined for failure. While it boasted exceptional fuel economy and safety advantages, its design flaws, particularly the use of a single valve for both intake and exhaust and the absence of a supercharger, proved to be its Achilles’ heel. Furthermore, the rapid emergence of high-octane gasolines offered gasoline engines an edge in performance, further eclipsing the diesel’s appeal.
Key Findings:
- The Packard DR-980 was the first successful diesel engine to power an airplane.
- It was innovative for its time, employing features like magnesium construction and a dynamically balanced crankshaft.
- The engine’s fuel economy and safety were significant advantages over gasoline engines.
- The engine’s design flaws, primarily the single valve system and lack of a supercharger, ultimately led to its failure.
- The rise of high-octane gasolines contributed to the decline of the Packard diesel.
Learning:
- Diesel Engine Operation: The text explains the fundamental differences between gasoline and diesel engines. Diesel engines ignite fuel through compression heat, achieving greater fuel efficiency and safety due to the absence of an electric spark ignition system.
- Weight-Saving Techniques: The Packard DR-980 exemplified innovative weight-saving techniques like the use of magnesium alloys, single-valve design, and a flexibly mounted crankshaft, paving the way for lighter and more efficient aircraft engines.
- Diesel Cycle Features: The text delves into the “solid” type of fuel injection pioneered by Hermann Dorner, highlighting its advantages over the traditional “air blast” system. It also explains how the unique design of the engine’s valve ports and fuel injector pumps contributed to its efficiency and fuel versatility.
- Engine Development Challenges: The document illustrates the complexities of engine development, showcasing the evolution of the Packard diesel from its early prototypes to production models. The text highlights the various modifications and improvements made to address issues like idling speed, oil cooling, and cylinder fastening.
Historical Context:
The Packard DR-980’s development and rise to prominence occurred in the late 1920s, a period of significant growth in aviation technology. During this time, the industry was witnessing the emergence of commercial airlines, the dawn of transatlantic flights, and the allure of airship travel. The search for more efficient and reliable engines was paramount, with the Packard diesel representing a promising alternative to gasoline-powered engines.
Facts:
- The Packard DR-980 developed 225 horsepower at 1950 revolutions per minute.
- It was designed under the direction of L.M. Woolson.
- In 1931, a production Packard DR-980 powered a Bellanca airplane to a record-breaking 84-hour non-refueled duration flight.
- The engine had a weight-power ratio of 2.26 pounds per horsepower.
- The first Packard diesel-powered flight took place on September 19, 1928.
- The engine utilized distillate or “furnace oil” as fuel.
- The engine featured 9 cylinders in a static radial configuration.
- The engine’s compression ratio was 16:1, with a maximum combustion pressure of 1500 psi.
- The engine’s displacement was 982 cubic inches.
- The engine’s fuel consumption was 0.46 pounds per horsepower-hour at full power.
- The engine’s weight was 510 pounds without the propeller hub.
- The engine featured a direct fuel injection system with a pressure of 6000 psi.
- The engine’s outside diameter was 45 11/16 inches.
- The engine’s overall length was 36 3/4 inches.
- The engine used poppet valves, one per cylinder.
- The engine’s starting system utilized glow plugs for ignition and air compression at 500 psi and 1000° F.
- The engine’s optional accessories included an Eclipse electric inertia starter, a type G-1 generator, and a fuel circulating pump.
- The Packard DR-980 was the only airplane diesel engine designed and built in the United States.
- The engine’s production ceased in 1933.
Statistics:
- The Packard DR-980’s weight-power ratio was 2.26 pounds per horsepower.
- The engine consumed 0.46 pounds of fuel per horsepower-hour at full power and 0.40 pounds per horsepower-hour at cruising.
- A 1930 test of the engine by the Packard company involved 1500 hours of operation, totaling 338,000 horsepower hours.
- The engine was designed to be 2.5 pounds per horsepower, significantly lighter than contemporary gasoline engines.
- The engine was capable of operating on a wide variety of fuels, from gasoline to melted butter.
- The engine’s fuel consumption was claimed to be 20 percent lower than gasoline engines.
- The engine’s cooling fin area was 35 percent smaller than comparable gasoline engines.
- The engine could run without exhaust stacks or manifolds.
- The engine’s maximum cylinder pressure reached 1500 psi.
- The engine’s compression ratio was reduced from 16:1 to 14:1 in 1931.
- The Packard DR-980 cost more to build than a comparable gasoline engine.
- The engine’s fuel consumption at cruising was 0.40 pounds per horsepower-hour, compared to 0.60 pounds per horsepower-hour for the Wright J-5 “Whirlwind”.
Terms:
- Diesel Cycle: A type of internal combustion engine cycle that uses compression ignition rather than spark ignition.
- Compression Ignition: A method of igniting fuel in an engine by compressing air to a high temperature.
- Compression Ratio: The ratio of the volume of the combustion chamber before compression to the volume after compression.
- Fuel Injection: A method of delivering fuel directly into the combustion chamber of an engine.
- Supercharger: A mechanical device that forces more air into the combustion chamber of an engine, boosting power output.
- Octane Rating: A measure of a gasoline’s resistance to knocking (premature detonation) in an engine.
- Glow Plugs: Heating elements used in diesel engines to assist with starting in cold weather.
- Poppet Valve: A type of valve used in engines that opens and closes by a cam-driven mechanism.
- Static Radial Configuration: An engine design where the cylinders are arranged in a radial pattern, but the crankshaft is stationary.
Examples:
- The first Packard DR-980 powered a Stinson SM-1DX “Detroiter,” which made the first diesel-powered flight on September 19, 1928.
- The world record for non-refueled, heavier-than-air aircraft duration flight was set by a Bellanca “Pacemaker” powered by a Packard DR-980 in 1931.
- The Packard DR-980 was used to power a variety of airplanes, including the Ford 11-AT-1 Trimotor, the Towle TA-3 Flying Boat, and the Stewart M-2 Monoplane.
- The engine was used in the Goodyear nonrigid airship “Defender” in 1932.
- The engine was also used in a Lockheed “Vega” owned by Clarence Chamberlin, who later made an official altitude record with the aircraft.
- The Packard DR-980 powered a Verville “Air Sedan” in which L.M. Woolson was killed in a crash in 1930.
- The engine was flown by Parker D. Cramer in a Bellanca “Pacemaker” on a flight from Detroit to Lerwick, Shetland Islands in 1931.
- During a 1930 test by the Packard company, the engine had to be stopped three times due to fuel pump plunger spring failures and a loosening oil connection ring.
- In a 1931 test by the U.S. Navy, the engine experienced valve-spring collar failures and a broken valve head, leading to the test’s termination.
Conclusion:
The Packard DR-980 diesel engine, while a groundbreaking achievement in airplane design, ultimately fell short due to its design limitations and the rapid advancement of gasoline engine technology. While its fuel efficiency and safety were undeniable advantages, its inability to compete in terms of power, weight, and performance doomed its success. The engine’s story serves as a reminder of the constant evolution of technology and the challenges of staying ahead of the curve, even in the face of significant innovation.