In order to use any sounds for a certain air craft you must first put the sounds you want into that planes sound folder then make a sound cfg file to use them.
Just putting sound files in a sound folder is not going to do anythning but take up space. 8)
Or you can edit the existing sound cfg file to use the files you want by swapping one sound for another,
as an example say your start sound uses a file called CSSTART, simplay remove that and put in the one you want it to use say MYSTART, this might work but I do not know about the other parameters the orignal file used and what effecet if any it might have on your sound.