You’re sitting in a traffic jam, you’re late, and the exhaust is giving you a headache—suddenly your car sprouts wings, takes off, and flies away. If you’ve had this dream, you’re not alone. In fact, the U.S. military has been interested in making road vehicles fly since the 1930s when they tried to strap tanks to gliders. Similarly, the Defense Advances Research Projects Agency (DARPA) is now attempting to make Humvees fly. And for non-military personnel, Terrafugia is a company building a car with collapsible wings that can drive on the highway then takeoff from an airport.
To figure out if we could make your car fly, let’s start with the basics. An aircraft needs to thrust itself forward and lift itself upward—both after leaving the ground. To do this, airplanes use the air surrounding the airplane. According to Newton’s third law (for every action there is an equal and opposite reaction), your car needs to push enough air over the wings to lift up, and enough air backward to move go forward.
Unfortunately, just strapping a jet engine to the roof of your car probably isn’t practical. Jet engines require a lot of fuel, and unlike a car on the ground, a flying car will also need to lift its fuel when it takes off, requiring even more fuel. I’d recommend a propeller; it will use a lot less gas.
To generate lift, we use wings—large, specially contoured surfaces that are at a really small angle to the direction of flight. They need to be strong enough to hold the entire car, but they also need to be light otherwise they will have too much weight to carry. (Propellers, it’s worth noting, are just small, motorized vertical wings that spin really fast at a really small angle with respect to the oncoming air.)
In general, cars are not designed to fly, and airplanes are not made to fit within highway lanes (or get rear-ended). However, a vehicle that could do both well would certainly be useful to many people. — Thanks to Andrew March, Ph.D. candidate in the Department of Aeronautics and Astronautics, for his help with this answer.
Thanks to 16-year-old Sammi from West Boylston, MA, for this question.