Before you can understand how a flying Humvee works, you need to understand what a Humvee is. Humvee is the common spelling for off-road, armored, truck-based military vehicles, but the technical spelling is HMMWV, which stands for High Mobility Multi-purpose Wheeled Vehicle. The first Humvees were built in 1983 by American General. The military was looking for "a family of versatile, technologically advanced, cross-country vehicles capable of performing both combat and combat-support roles. The basic chassis was to be capable of being modified into a number of variants. It was also to be diesel-powered, consistent with the Army's desire to use diesel fuel throughout its tactical vehicle fleet, and it was to have an automatic transmission" [source: American General].
Today's Humvees don't stray far from those requirements. Compared to the first Humvees, today's Humvees have bigger engines, better towing and payload capacities and better reliability. There also more heavily armored. As improved as today's Humvees are, however, they can't live up to the requirements the Pentagon has for flying Humvees, namely that they be able to fly (for a start), drive on roads, carry personnel and cover 250 nautical miles (287.7 miles or 463 kilometers) in flight while carrying 1,000 pounds (453.6 kilograms) of payload with a maximum altitude of 10,000 feet (3,048 meters). DARPA also wants it to be "somewhat green" [source: Wired]. That will be tough for a vehicle that only gets about 14 miles per gallon (5.6 kilometers per liter). So, while we call these flying Humvees, the end product will have little in common with the ground-only Humvees the military uses today.