The PAL-V sounds great to the average person (It's a car! It can fly! You don't need a pilot's license to drive it!), but building a flying car presents unique engineering challenges that aren't easily overcome. Take the amount of force a car's suspension — the system that maintains the contact between the tires and the road during driving — needs to take. A car's suspension maximizes the car's handling abilities and absorbs bumps and imperfections in the road. Most car suspensions are engineered to absorb about 2 Gs worth of bumps [source: Brown].
Now, you're probably thinking that planes don't need strong suspensions because there aren't a lot of bumpy roads up in the skies. You're forgetting, however, that planes need to land at some point, and those landings can be harsh. Plane suspensions need to be able to take up to 4 Gs of force. No problem, just beef up the suspension and boom, flying car, right? Nope. While a car can take some added weight with no big problems, plane design is all about keeping weight to a minimum. Every ounce matters. So if you add weight for the suspension system, you're going to have to take it away from somewhere else — say, the sound-deadening material, frame reinforcements or seats.
Then there's the issue of the wings. If a car has wings like an airplane, it's not going to fit on the road. Parking will also be a nightmare. Folding wings are an option for when the car is on the ground, but wings that fold are weaker than wings that don't, making them not the best choice for flying. Then there's the issue of power delivery. To save weight, you'd only want one engine on a flying car. On a car, the engine sends power through the transmission to the wheels. On a plane, the engine powers a propeller. For a flying car, how would the engine's power be switched between the wheels and the propeller?
When you take all of those challenges into consideration, it's a wonder anyone has ever tried to build a flying car, let alone do it successfully. But the PAL-V company did.