"There is a utility that was posted a long time ago in the FSX Forums about this. It's called RADItor.exe. It allows you to open the mdl file and permanently correct the preview size of your aircraft. This is the Link:
Falcon has suggested a handy little utility to quickly adjust the size of the a/c in the preview (turntable) window of FS. It is simplicity itself, but after trying it on several a/c I get this message:
The MDL was not in the expected format!
Has anyone else gotten this? What is the problem?