I wish I could get good performance in X-Plane. I tried it at MINIMAL settings on my brand new system, and it brought my system FPS down to a small 6 FPS!!!! D:
X-Plane will never go below 19fps. It introduces fog to lower the load and to maintain that 19fps.
I'm curious to know how "new" your system is. What are your computer specs? I know people running a single core CPU and 256MB graphics card and are able to get higher than 28 fps with all settings set to minimal.