First in Flight

The Packard DR-980 Radial Aircraft Diesel

Dedicated to the late Robert J. Neal, who wrote the books on Packard.

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-valve-per-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 SM-1B 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 1,100-mile trip that used $8.50 of furnace oil. Packard advertised fuel consumption of 0.40 lbs/hp-hr (about 8.8 gph) for a cruising speed of about 90-100 mph. At full power the DR-980 used 0.46 lbs/hp-hr (about 14.8 gph). Packard stated the Wright J5 gasser delivered 0.60 lbs/hp-hr for (about 15 gph) at cruising.

Packard management was encouraged enough to invest $650,000 in a new aero engine plant, projecting 500 engines a month in production by the end of 1929. Well, the plant got built and tooled up, but it wasn’t cranking out 500 engines per month by the end of 1929. In mid-February 1930 Packard ran a standard 50-hour certification test on engine #100, the first production engine. It passed, and by March 6, 1930, the Department of Commerce issued an approved type certificate, the first ever issued for a diesel aero engine. Packard could begin to sell engines and announced this on April 5 at the Detroit Air Show.

The early production engines differed from the six hand-built prototype engines. The block was improved by adding ribbing and the cylinder head featured butterfly “chokes,” the intakes of each cylinder that activated to slow the engine when the throttle was brought to idle. After 10-15 engines were built that way late in 1930 a barrel valve appeared that restricted the valve port in a more elegant way. The barrel valve also signaled a drop in compression ratio from 16:1 to 14:1 and structural improvements to the head. This ratio drop was part of an effort to reduce vibration and so was a rubber-dampened propeller hub, but neither improvement completely solved the problem.

On May 28, 1931, a DR-980 powered Bellanca Pacemaker set the world’s non-refueling record for fixed-wing aircraft, 84 hours and 33 minutes. Walter Lees, one of the pilots, said they had at least four more hours of fuel in the tank but landed due to approaching stormy weather. For this milestone Packard would win the Collier Trophy, America’s highest aviation award, and the record would stand until 1986 and Dick Rutan’s record nine-day flight.

Packard installed DR-980s into five of its own aircraft: the original Stinson Detroiter, a Waco Taperwing biplane, Buhl Air Sedan, Bellanca Pacemaker and Bird Model F. Several aircraft companies tested Packard diesels. The biggest aircraft to use them was the 184-foot airship Defender, a Goodyear Model PA blimp on which a pair of DR-980s was tested from November 1931 to June 1932. Ford briefly offered them as an option on its Trimotor in 1930. The experimental Towle TA-3 amphibian used a pair of Packard diesels in 1930. Another experimental plane, the twin-engine Stewart M-2, briefly had Packards. The Verville Aircraft Company tested one in an Air Coach. The Army National Guard tested Packards in two planes, the XPT-8A trainer and the XPT-8 observation aircraft. A Packard-powered Bellanca Pacemaker on floats, owned by Transamerican Airlines, left Detroit in September of 1931 for the Shetland Islands off the coast of Scotland but disappeared. Weeks later, much of the plane was found afloat and it appeared to have landed intact. Engine failure was the prevailing theory.

Before long, the “whizbangness” of the engine soon faded in the cold light of reality. The DR-980 garnered a lot of negative comments from test pilots. In one instance, a cylinder hoop broke and the engine launched a jug, barely missing the pilot. Pilots universally complained about the exhaust fumes and more than a few refused to fly Packard diesel-powered aircraft for this reason. The vibration was reported as dastardly, in a few cases resulting in airframe damage. When the Navy took a late production engine, number 120, for a 50-hour durability test in early 1931, it failed three times and the test was terminated. It was not recommended for procurement.

The biggest downer was the fatal crash that killed Lionel Woolson and two others on April 23, 1930. The DR-980-powered Verville Air Coach on the way to the New York Air Show encountered a snowstorm trying to land near Attica, New York, and crashed into a hill. Though the crash was purely weather-related, it cast a dark cloud over the Packard diesel program—but the 1929 stock market crash had an even bigger impact.

The Great Depression soon rolled across the globe, and as a luxury carmaker Packard was especially vulnerable. It really wasn’t the time to have one’s corporate neck out with off-the-mark products. The light aircraft market slowed way down, putting the vulnerable low-production companies out of business and reducing the need for aero engines. Unfortunately, the DR-980 had also acquired a bit of a “reputation” in the aero engine market. The Packard “cavalry” had been ready to save the day as early as 1930, with a 300 hp, two-valves-per-cylinder engine designated the DR-980B. It was reputed to eliminate most of the issues under complaint, but unfortunately, just before his death, Woolson had chosen to continue with the single-valve design. Production officially ended in 1933, but the die was cast late in ’32. The exact number of engines produced is unknown but reported in some documents to have been 116 units total, including the prototypes.

Packard’s engineering prowess is legendary and there is little doubt the engine could have been perfected. Would that have ensured the success of a diesel in the aero engine market? Not likely. Gasoline aero engines were advancing very quickly. The introduction of high-octane gasoline in the early ’30s allowed higher compression ratios, greater power output and better high-altitude operation. Gassers never caught up to the diesel for fuel economy or fire safety, but in every other way they were a better product. The later Guiberson radial aero diesel (see Diesel World January 2018), very much superior to the Packard, also failed in the market in the late ’30s and early ’40s for largely the same reasons. Today there are some diesel aircraft engines being sold, none of them radials. They are very modern electronic engines and seem to be making sales headway due to the originally touted benefits: fuel economy and fire safety.

There are 12 Packard DR-980 engines known to survive, most in museums and none running. One is still mounted in a historic aircraft, Packard’s original Stinson SM-1DX test plane, repowered in 1930 with a production engine. The aircraft has not flown since the mid-1930s and likely never will again. The Smithsonian has the original prototype engine that powered it.

SOURCES

America’s Packard Museum
AmericasPackardMuseum.com
Engine 154

Franklin Institute
FI.edu
Unnumbered engine

Golden Wings Museum
GoldenWingsMuseum.com
Engine 135 in Stinson SM-1DX

Henry Ford Museum
TheHenryFord.org
Engine 144

Pioneer Village Museum
PioneerVillage.org
Engine 146

Museo Nacional de Aeronáutica de Argentina
GacetAeronautica.com/gaceta/wp-101/?p=1009
Engine 130

Smithsonian National Air and Space Museum
AirandSpace.si.edu
First prototype, unnumbered production engine

National Museum of the US Air Force
NationalMuseum.af.mil
Engine 116 and unnumbered engine

San Diego Air and Space Museum
SanDiegoAirandSpace.org/
Two engines, one early, unnumbered