Two questions, David603:
Were you trying to do a minimum-radius turn, or a best-rate turn? The results would be different. In combat, rate is usually more important than radius.
Are these sustained turn rates? Unless you can maintain speed, altitude and turn rate continuously, the results may be misleading. Even a loss of height of a few meters can make a noticable difference to results.
EDIT ---
I've been doing a bit of experimenting, using my prototype autopilot application (see
http://forums.ubi.com/eve/forums/a/t...097#4121016097), and though I need to investigate further, I find it very difficult to believe a Fw 190 A5 will do a 360 degree sustained turn in 18.7 seconds, regardless of throttle settings. IL-2 compare suggests the best turn time will be around 24s, which is much more consistent with the results I'm getting at full throttle, and trying to turn at that sort of rate at 80 % throttle results in a rapid decay in airspeed. My autopilot is struggling to hold a smooth turn in these conditions (it was never designed to do this), but I'd be surprised if a human pilot could do much better - the plane is right on the edge of the stall.
As Ernst says, we need to see a track.