Posted for Danny Creech <dannycreech@yahoo.com>:

Here is where having A/C is another advantage. If you have A/C you can
just do away with that flapper valve all together. I have flown several
IV-P and the first one I got into that made all that racket I almost
aborted the takeoff. That is really noisy! If you're still in the build
process you could even get rid of the nac. scoop on the vertical
stabilizer. This is if you are using the scoop style A/C.
Another noise complaint I have heard is from the air rushing into the
cabin from the four vent holes that pressurize the cabin. I know of a
builder that made this a LOT quieter by making baffling for the air to
go through.

Danny Creech
IV-P Instructor