In writing my book on Navy attack airplanes, Strike From the Sea, I didn't have much in the way of information on the Douglas Model 566 competitor for OS-106 except a three view and a mention that the proposal configuration was changed after initial submittal. Based on the drawing, I had guessed that the airplane had two P&W R-2800s and two small jet engines paired in the nacelles since there was clearly an exhaust at the end of the nacelle and no obvious jet exhaust from the fuselage. The protrusion on each side of the fuselage was possibly a barbarette for a defensive weapon (note that it doesn't appear in the front or side views). The change?: Perhaps from two jet engines to one in the fuselage like the winning North American design, with the available drawing being non representative of the final configuration. I therefore didn't include it in the book.
In trolling through the Spangenberg collection at the National Archives a couple of years later, I stumbled on what I wished I had when I wrote the book. It turned out that the exhaust at the end of the nacelle was for a turbosupercharger that maximized R-2800 power at altitude. The presumed barbarette was actually an intake for the I-40 jet engine, which exhausted out the bottom of the fuselage like the jet engine in the early Douglas D-558-2 Skyrocket. Since the I-40 was a centrifugal flow engine, the intake dumped the air into what is called a plenum chamber that surrounded the compressor section. Note that a more conventional alternative was provided with the intake located in the inboard leading edge of the wing in case the side inlet proved less efficient than predicted.
Other details in the Douglas proposal were that it was a two seater, pilot plus "bomber", and the bomb was to weigh 8,000 lbs, dropped from 35,000 feet 300 miles from takeoff.
In trolling through the Spangenberg collection at the National Archives a couple of years later, I stumbled on what I wished I had when I wrote the book. It turned out that the exhaust at the end of the nacelle was for a turbosupercharger that maximized R-2800 power at altitude. The presumed barbarette was actually an intake for the I-40 jet engine, which exhausted out the bottom of the fuselage like the jet engine in the early Douglas D-558-2 Skyrocket. Since the I-40 was a centrifugal flow engine, the intake dumped the air into what is called a plenum chamber that surrounded the compressor section. Note that a more conventional alternative was provided with the intake located in the inboard leading edge of the wing in case the side inlet proved less efficient than predicted.
Other details in the Douglas proposal were that it was a two seater, pilot plus "bomber", and the bomb was to weigh 8,000 lbs, dropped from 35,000 feet 300 miles from takeoff.
