SMOKE RINGS
By 1931, Packard’s aero diesels were on sale and certified by the Aeronautics Branch of the Department of Commerce but slow sales and the Depression would force them to discontinue production. By the time Packard was done building radial aircraft engines in 1933, Guiberson had built two experimental radial diesels, the A-980 and the A-914, and was ramping up to do more.
The Numbers
Like Packard, Thaheld initially adopted a single valve cylinder head, where the engine inhaled and exhaled through the same valve. This simplified the valvetrain but limited power and efficiency. The first A-980 (980 ci) radial of 1931 made 185 horsepower from a 4.81 x 6 inch bore and stroke. It flew successfully in a Waco 10 biplane and was eventually given government certification. In 1934, Thahald completed the A-918 engine (918 ci, 4.75 x 5.75 inch bore and stroke) which made 240 hp at 2020 rpm. It went as far as getting the Navy 50-hour certification; but, by 1936, the Navy decided the engine was too heavy for the rated output.
Thahald determined the one valve per cylinder design wasn’t optimal and developed a two-valve engine. This led to the A-1020 engine, which was certified by the CAA (Civil Aeronautics Authority) in January 1940. The A-1020 was a 4-stroke engine with nine cylinders that displaced 1,020 cubic inches (5.12 x 5.5 inch bore and stroke) and was rated for a sustained 310 hp at 2150 rpm, with a maximum rating of 325 hp at 2275 rpm.
The A-1020 was tested extensively in a Stinson Reliant 4-seat aircraft against the original Wright Whirlwind R760 gas engine (320 hp @ 2200 rpm). Though the diesel engine itself was heavier than the gas, because of certain installation expediencies for the diesel, the overall aircraft was only six pounds heavier. Aircraft performance, was comparable between the engines but the diesel used at least a third less fuel. Plus, diesel fuel was only $.06/gallon in 1940 versus $.23/ gallon for aviation gas. Another notable plus for the diesel was a higher service ceiling. The Wright gasser was certified to 14,500 feet. The A-1020, with nearly double the compression ratio of the gasser, performed well at 20,000 feet, though it was finally certified for a conservative 18,500 feet.
WWII
The Guiberson was approved for U.S. military aircraft but fuel standardization worked against it. Except for certain narrow applications, the U.S. military air and ground forces were all gasoline, from motorcycles to aircraft. A glimmer of hope came when certain Lendlease countries receiving U.s.-built tanks requested diesels. All mainline American tanks of the era used aircooled radial aircraft gas engines. Guiberson adapted their A-1020 into the T-1020 (“T” for tank) and was soon building engines for Lend-lease tanks. Or rather Buda Engine Company was. Buda was contracted to build the Guiberson tank engine and thousands were manufactured. The T-1020 differed from the aircraft version in having a large cooling fan/flywheel and