DarkShade:
I'm not sure if this will help, but the old Steve Jackson Games RPG
CAR WARS--and its successor,
AUTODUEL, had a vehicle called a "Grasshopper".
There were several designs, all built upon what the game series referred to as the "Sedan" body style--a basic four-door platform that was larger than a Coupe (2-door) , but smaller than a Luxury (4-door--essentially a short-wheelbase limousine).
Grasshoppers used Small Helicopter powerplants, and followed the Acceleration/Maneuver rules for Sedans while on the ground; when airborne, they used the rules applicable to Small Helicopters.
They could be fitted with any armor or weaponry suited for autos or helicopters--except top-mounted turrets/weapons (no room because the rotors were in the way), and any underbody-mounted weapons for use while airborne had to be retractable in order for the vehicle to be driven on the ground.
It was possible to build a Grasshopper with retractable rotors and tail surfaces, but most of the models listed in the rulebooks weren't designed that way due to interior space limitations. Also, there were rules for amphibious vehicles (car/boat or truck/boat hybrids) or "triphibious" vehicles--grasshoppers capable of operating in water as either an amphibious helicopter or a speedboat (the latter looked like a World War II amphibious Jeep with rotors and tail surfaces).
I know that this isn't much help, but I hope that it'll at least give you or someone else ideas.

--Foreigner