Sorry to disagree BUT there are Merlin engines that are run upon test beds for the public.There are Merlin engines that fly at air displays and i have seen several people with professional standard cameras and audio recording equipment.
If you wanted to hire out a Spitfire then yes i agree on costs BUT they are around and accessible if you want to make the effort.
There is no excuse for lawn mower sounds in 2011 and 6 years into the development of this sim.
Yes i know this isn't a Merlin LOL
but i managed to take this on amateur equipment years ago,there are better recordings around and available to use.