VINTAGE SMOKE
THE PACKARD D390 AIRCRAFT ENGINE
Packard is best known for high-performance luxury cars and lasted into the late 1950s. The company is less known for excellent marine and aircraft engines. One of Packard’s most proficient engineers, Jesse Vincent, collaborated to design the World War I era Liberty V12 and did it in just five days. For World War II, Packard built the V-1650 Packard-merlin that powered the legendary P-51 Mustang and other aircraft. On the marine engine front, Packard is most famous for the 1,500 hp 4M-2500 engines that powered WWII American PT boats. Hardly anyone knows Packard built the first aircraft diesel to make it into the Wild Blue Yonder.
It started in 1927, when Captain Lionel Woolson, Packard’s chief aeronautical engineer, noticed a new patent for a diesel injection system by German engineer Hermann Dorner, and Packard
eventually licensed the Dorner system. Woolson and the Packard engineering team then designed a nine-cylinder diesel radial aircraft engine that weighed only 500 pounds. It was sized to physically replace the very popular Wright Whirlwind J5 radial gasser. The magnesium alloy crankcase was only 34 pounds and high-end alloys were used to make the crankshaft and master rod strong and light, with spring-dampened counterweights. Probably the most interesting feature of the crankcase was the way the cylinders were attached. Instead of bolts, they used two hoops of a high-end alloy that clamped the cylinders to the block.
The Dorner injection system used what we would now call a unit injector driven by an eccentric ring on the crankshaft. The injectors sprayed from the side into a contoured chamber in the piston. A very unique feature was the one-valveper-cylinder design. Yep, this four-stroke engine inhaled and exhaled through the same valve, making for some very odd valve timing events. Woolson knew it wasn’t optimal but it saved a lot of weight and development time. Initially the compression ratio was 16:1. The prototype engine used a Heywood compressed air starter.
Once the first engine was built, dyno tested and ready for operational tests, Packard purchased a 1928 Stinson SM1B Detroiter monoplane. After baseline tests they removed the Wright gasser and installed the prototype Packard diesel. It “officially” flew the first time on September 19, 1928, though test pilot Walter Lees had taken it up the day before as a check. Good thing he did because they discovered a design flaw. The engine was doing fine but Lees discovered he couldn’t power the engine back to idle rpm for landing. Being a diesel with no throttle, it had less compression braking than a throttled gas engine. The aircraft in motion windmilled the propeller and engine at 1,500 rpm, so landing speeds were too high. To get the plane on the ground, Lees had to cut the fuel off completely and land “dead-stick.” This flaw was cured overnight in a temporary fashion by adding a pilot-controlled device that cut off the air to several cylinders… kind of an airborne Jake brake. With the diesel swap, the Stinson became a new model, the SM-1DX, the “X” for experimental.
The official first-flight hoopla was positive but behind the scenes there were many technical issues. On the upside, the engine delivered exceptional fuel economy and the diesel did well at high altitudes. There was no ignition system to create interference, so the diesel was particularly suited for use with two-way radios. On paper, the diesel had virtually the same power ratings as the Wright J5. The major downsides included excessive vibration, difficult cold starting, excessive smoke and fumes in the cabin and slow response to the throttle.
After the Packard-powered Stinson underwent further tests and tweaking, Packard became confident enough to try a long-distance trip. On May 13, 1929, Lees and Woolson flew 700 miles from Detroit to Langley Field in Virginia for an aeronautics conference. The furnace oil for the trip cost $4.68. In March of 1930 they took the same plane and engine to Miami, Florida, an