jp,  buzkill is right.  Ah download comes with generic sounds.
  the code looks first for folders in the sound directory for the 
particular plane.   if none exist, they refer to the default.
  For example, navigate to 
C:\Program Files\HTC\aces High\sounds and make a 
folder called 109f4.  Then in the 109f4 folder, you can 
make and store your files that you want to be specific to the 
109f4 plane.  You can do this for every plane and vehicle in the 
game, you just have to be certain you have the proper 
plane folder in the sounds file.  For example, 109f-4 wont 
work, it has to be 109f4.  Also, the file for engines is eng.wav.
  Just for practice, create your 109f4 folder,  then copy your favorite engine .wav file and save it as 
c:\program files\htc\aces high\sounds\109f4\eng.wav and then 
fly the 109f4.  You'll get the hang of it
For a list of the plane folder names, 
you can check your settings file in Aces high.
  Sound packs are available, but I prefer to make my own 
sounds to how I think the plane should sound as opposed to 
historical accuracey.
  MS combat flight simulator has sounds that are compatable 
to Aces High, if you dont want to get a edit/mix program, you 
can just copy a MS sound and paste it to the appropriate place 
with the approriate file name.
  It really does add a flavor to the game and making your own sounds is a bunch of fun.  
