我 notice there's a hole on the nose of the d9,As far as I know, the d9 doesn't have a shaft gun, so what is this？
These truck mounted units were developed during WWI and known as Hucks starters.
First of all, I went to Greg's Aircraft YouTube and could not find an explanation about the hole in the 190's spinner. Hopefully Tommayer can point me to what Youtube and what minute mark.Go to Greg's Aircraft YouTube. View his 190 vids. The hole in the Jumo 190's spinner is explained in one of them.
I could not find any documents in German about aircraft that spoke to the hole. My modest research came to two separate conclusions about the hole. One, it could be a manufacturing artefact, meaning how the metal was mounted and spun to form a spinner, and provided a quick easy means to any cannon mounting if necessary. Two, Gordon Gollob's report on test flying the Fw190 spoke about windscreen fouling by oil. The hole could have created some dynamic pressure within the spinner to force any oil so it would not foul the windscreen. Just suppositions, but so far nothing else. The hole is small so it would not be useful for any maintenance type procedures.
Your top photo is of the D-13 Yellow 10. This has a 30mm cannon through the spinner. I think you are right with description of the pressed plates, top and bottom.Actually it is of a wrong shape in the pics you posted above. It was of more oval but not the round one. The pieces were the supports for the oil radiator sections. To make it lighter these were made of two plates pressed and welded. I'm not sure if these slots were the air intakes too though.
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the pic source: the net.