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BUGATTI U-16 ENGINE
ONE OF Ettore Bugatti’s more exuberant engine designs had logic, if not luck, in its favor. This engine was a U-16, a pair of Bugatti inline-8 designs aligned in two parallel banks, originally intended for powering World War I aircraft.
Famed engine manufacturers, Duesenberg in the U.S. and Breguet in France, took part in its engineering. Alas, the engine’s development involved the first U.S. casualty of WWI. At one point, Ettore Bugatti wrote to a business associate, “I really have no luck.”
In time, half of the U-16 design came to power the most famous of all Bugattis, the Type 41 Royale. Had Bugatti’s luck changed?
Bugatti’s first U-16, 24.4 liters, 500 hp, customer: Duesenberg, 1917. This and other images from Bugatti Magnum, by Hugh Conway with Maurice Sauzay, Motorbooks International, 1989. The book is listed at http://www.abebooks.com.
A U layout (or, alternatively, a V) increases power effectively by combining cylinders of existing designs. By contrast, merely increasing an engine’s bore can lead to a loss of efficiency because of an unfavorable ratio of cylinder surface to volume.
A V layout uses a common crankshaft for both banks and yields a lighter engine than a U. On the other hand, Bugatti’s U layout had a military benefit: Its twin crankshafts were geared to spin a central propeller shaft. This shaft and the engine’s aluminum alloy crankcase were bored to accept the barrel of a 37-mm cannon (the armament located aft of the engine).
Before its involvement in WWI, the U.S. set up a commission headed by Major R.C. Bolling charged with identifying European aero engines worth licensing for American production. The Bolling Commission, including automaker Howard Marmon, recommended a $100,000 licensing of the Bugatti U-16 to be produced by Duesenberg.
While the U-16 was undergoing French evaluations, an American serviceman witnessing the test was struck and killed by a failed propeller blade. He is considered the first U.S. casualty of WWI. Bolling also perished in the war. His staff car took a wrong turn and ran into German machine-gun fire.
A 1917 King-Bugatti U-16. Image from the Smithsonian National Air and Space Museum, www.airandspace.si.edu.
Once the engine was in Duesenberg hands, engineer Charles B. King made significant changes to its design, specifically in lubrication and production engineering. Ettore Bugatti was not amused.
Test data for the King-Bugatti. Image from http://goo.gl/hWjgrQ.
A 50-hour test was completed on October 4, 1918, in which the engine produced just over 500 hp. However, with the November 11 armistice, it was all for naught. Plans for 2000 American Bugatti engines were cancelled, and only 11 were delivered.
The Breguet works, with its updated version of the Bugatti U-16.
After WWI, the French aero manufacturer Breguet took a license to use the U-16 as a modular base for even more powerful aircraft engines. Banks of the U, Breguet reasoned, could be separately shut down for in-flight maintenance, a feature desirable to this aero specialist in its ultra-long-distance record-breaking. See “Flight of the ?,” http://wp.me/p2ETap-2Lg.
Breguet’s U.24 linked a pair of Bugatti U-16s, one behind the other and offset vertically. Its four crankshafts had separate clutches to achieve Breguet’s goal of selective maintenance. When it appeared in 1920, the U.24’s 1000 hp made it the world’s most powerful aircraft engine. This lengthy powerplant drove two counter-rotating propellers of the Breguet Leviathan.
1922 Breguet Leviathan and its pair of linked Bugatti U-16s. Image from http://goo.gl/PsuOci.
At the 1924 Paris Salon de l’Aéronautique, Breguet exhibited its Quadrimoteur Type B, a pair of Bugatti U-16s arranged one atop the other as an H-32.
The Breguet Quadrimoteur Type B. Image from http://goo.gl/hWjgrQ.
Displacing 46.9 liters, the Type B produced a maximum of 1015 hp. A large, heavy powerplant, it never powered an aircraft.
Not that Ettore Bugatti gave up on the U-16. In 1923, he designed the Type 34, a 34.3-liter counterpart to the earlier 24.4-liter version.
Bugatti Type 34.
It’s not certain whether any Type 34 engines were built. However, in 1927 when Bugatti designed his Type 41 luxury automobile, better known as the Royale, he envisioned it being powered by essentially half a U-16, a road-going straight-8 of nearly 15 liters displacement.
Bugatti saw the Type 41 as the choice of royalty, but again luck played a role. Along came the Great Depression; only six Royales were built. ds
© Dennis Simanaitis, SimanaitisSays.com, 2015
Simanaitis Says 
Dennis –
In the November, 2014, issue of Classic & Sports Car, there is an article about a Maserati U16 race car from the late 20’s, the V4. The layout is similar, with two crankshafts sharing a common crankcase, and a central gear taking power from both engines. The car’s success was limited by the lack of tires able to take the punishing power.
In December 1917 a “Bugatti Mission” sailed from Bordeaux for the US to supervise production of the engine at the Duesenberg Motor Corporation of Elizabeth, New Jersey, where the engines were planned to be made.