Dawn Aircraft Motors Inc, in Los Angeles CA, built the "Duplex" engine in the USA in 1929. This was an air-cooled radial engine with 5 cylinders in two rows that gave 156 hp at 2,500 rpm, and was a copy of the French Gobron-Brillié (see) with two pistons in each cylinder.

-Based on the mechanism of the previous French Gobrón-Brillié engines, they used two opposite pistons in each cylinder.

-The inner pistons were connected directly to the crankshaft and the outer ones by long rods to the crankshaft.

“Dawn 5-cylinder radial”

-We see that the spark plugs are in the center of the cylinders, at whose height the combustion chamber is formed when the two pistons are in the center.

“Dawn G model”

-The G model is a small engine for motor gliders, giving 8 hp and a maximum of 15 hp at 8,000 rpm.

"Construction detail of the A model"

-In the engine A cutaway image we see the opposite pistons and their connection to the crankshaft. The A model had four cylinders and gave 125 hp.

From Appendix 6: Dawn Motors Ltd is the one that manufactured the engine designed by Bowman.

-With reverse operation, that is to say with the cylinder heads inside and the connecting rods pushing outwards and where some braces are connected to the crankshaft again at the center of the engine.

"Lee Bowman from Los Angeles with his engine" (PiP)

"Vibration tests with running engine" (PiP)

-The engine gave 100 HP. As it was suspected that the engine's complicated connecting rod system would cause many vibrations, tests were made like those of the photo above in which they placed some eggs in spoons attached to the engine, demonstrating that they did not fall.

-The 10 HP engine for gliders that in a chapter of UFE's appears as unidentified, also appears as designed by Bowman and built by Dawn.

"The little Bowman engine" (PiP)

-Presumably this smaller engine works with the same principle as the radial 5-cylinder.