You can figure it out mathematically, but the easiest way is with a program called "ThrustHP". It's a free download, but you'll need to do a search to find it as I don't have the link.

Thrust HP is ok for what you want, pitch/speed/rpm comparisons, but don't trust the thrust numbers it gives as they are inaccurate.

Whoops, I think I just found the link. Try this: http://freespace.virgin.net/barry.hobson/

Have fun,
AV8TOR