As a followup to the previous post regarding the use of a miniature helicopter, take a look at these two YouTube clips.
The first features a 1/72 scale model, combined with 3D elements and post-processed in a compositing program.
Visual Effects with Cheap 1/72 Model Kits
The second shows an impressive helicopter crash featuring a model helicopter with heavy post-processing to add rotors, atmosphere, and environment.
VFX Project - Helicopter Crash