Re: Why were inverted V12s popular with the Germans?
The packaging is better with the sump/crank upwards (the widest part of the engine is towards the widest part of the fuselage. It's a reason why flat-12 and wide V were used in formula 1 - easy to build aero around.
The reason you don't get hydro lock and a very expensive set of flying piston rods is the DB engine was a dry sump design - car engines are wet sump, invert one while it's running and expensive things happen quite quickly.
Specific to the 109 it also allowed a 20/30mm motorcannon to fire through the hollow crank and for two 151 to be placed above the flat deck of the "sump". The toasty motor kept the guns warm (its - 30c at 35,000ft) & the narrow mounting of most of the weapons (compared to a spit for example) made it much easier to put shells through a target in a nice tight pattern. Win-win unless you were the other guy.
However it wasn't all sweetness and light. The canopy opened to the side, so forget about getting out in a hurry, the undercarriage had all the design flair of an Austin Allegro (although it's understandable why it was done that way, to save weight) - and the wing tabs turned the thing into basically a giant 1700hp vibrator on fast sharp turns (to the point that some pilots wired them shut). A good pilot was roughly on parity until about late 43, an inexperienced one would be dug out of the permafrost after about a week.
The engine had mechanical fuel injection so it could be bunted when a Merlin would half stall in a cloud of black smoke (partly solved by miss shillings orifice). But being early FI and being 6 litres larger than the Merlin it drank fuel and gave only a 20 minute combat radius over the UK.
Being higher compression than the Merlin - they didn't like artificial petrol either and there are many unexplained accidents were aces just disappeared or had engine failure possibly attributable to fuel that would make 2** cut with Guinness seem like a good idea.
Incidentally if anyone ever tries to sell you purple petrol I'd not bother - they used to use it in racing cars post war but don't leave it overnight - it dissolves the fuel tank.