What is this???

We found this on our air conditioning unit today. The picture doesn't really show how big this thing was. It was HUGE!!! It was probably a good 5-6 inches long with 6 legs, 2 antenna like things coming out from it's head, and 2 huge wings that are red underneath. It remained pracitcally still while Alex threw rocks at it and only barely moved when we sprayed it with water. And it made a strange mating-like call. WHAT ON EARTH IS IT???