I did those detailed engineering drawings BY HAND. Computer skills are, unfortunately one area where I am a bit behind. However, the primary reason I made a working model instead of a computer model is that a computer does not prove that something works. I have seen a LOT of impossible animations, demonstrations, and simulations. A physical model show that either it works or it doesn't.
That being said, a good computer model would be a convincing and fantastic complement to a physical model. But time and money....