The whistle sound can be de-activated, simply by placing // marks in front of the Wind2-entry within the sound.cfg file, where then you will simply only hear the Merlin recordings. The inspiration for adding the authentic whistle, came from the high-spirited airshow displays in the UK, by pilots such as Peter Teichman, Rob Davies, and Alister Kay, at which times the whistle is very commonly heard. (Edit: Albert beat me.

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Research for this product began three years ago, and actual work going into the product began almost exactly two years ago. As a result of so much intensive detective work, using original engineering drawings, maintenance manuals, blueprint specifications, correspondance with the guys in-the-know, and what have you, you simply won't find a more accurately reproduced visual model of the P-51D, either inside or out, and I don't know if you ever will. It went far, far beyond simply looking at photos, and making a good recreation.
Jan Kees, personally I would rather fly a well-treated aircraft, lol, but the bit of weathering looks good. That, and the P-51D-30, as the restored "Happy Jack's Go Buggy" is, isn't really a WWII-type P-51D, as most all P-51D's that served in WWII were D-5's, D-10's, D-15's, and D-20's, which were very different aircraft. Most all D-30's were simply sent straight into storage, from production, in 1945, since there was already enough P-51D's in service. As a result, the RCAF got a lot of those D-30's - many of which now populate the warbird-P-51D inventory. There will be time to cover WWII-variants, I'm sure - and again, there has never been the real opportunity to fly a true D-5, D-10, or D-15 within flightsim.