Yes. An airplane on a treadmill-style runway takes off, because a plane's engines push against the air and not against the ground. The wheels just spin faster. The belt cannot hold the airplane back in any way that matters.
The question comes from a riddle that went around online: a plane sits on a long conveyor belt that runs backwards at the same speed the plane moves forward. Can it take off? Here is why it can, using the FAA's own explanation of how flight works.
The FAA's Pilot's Handbook of Aeronautical Knowledge explains thrust with Newton's third law: "For every action, there is an equal and opposite reaction." In an airplane, the propeller pushes air backward, and the air pushes the propeller, and so the airplane, forward. In a jet, the engine pushes a blast of hot gas backward and the equal and opposite reaction pushes the engine forward. Neither process involves the ground. The airplane is not a car, and its engines do not drive the wheels.
The wheels are free to spin. They are bearings that let the airplane roll, so they only add some rolling resistance. A belt moving backwards makes the wheels turn faster, because they now spin with the belt as well as the airplane's forward motion. It does not push the airplane back with any force that the engines cannot overcome. If the belt matches the airplane's speed, the wheels spin about twice as fast as they would on a still runway at the same airplane speed.
The handbook says lift "is produced by the dynamic effect of the air acting on the wing." A wing needs air moving across it, and that comes from the aircraft's forward speed through the air. The handbook adds that lift is proportional to the square of the aircraft's velocity: an airplane at 200 knots has four times the lift it has at 100 knots, if the angle of attack and other factors stay constant.
That velocity is airspeed. The handbook separates airspeed from groundspeed, which it defines as the actual speed of the airplane over the ground, adjusted for wind. A belt can change the ground under the tires, but the speed that makes lift is the speed through the air. That is why a headwind helps a takeoff: it adds to the airspeed without any extra ground speed.
The television show MythBusters tested the riddle in an episode first aired on January 30, 2008. It began with a model airplane on a treadmill, and the plane took off. For the large-scale test, the team used a 400 pound ultralight aircraft with a 2,000-foot tarp under it, pulled backwards to simulate a moving runway. According to the episode summary, the ultralight pilot had no trouble taking off, "because the thrust of the airplane engines acts on the air, not on the ground." The team rated the myth busted.
The belt is not completely harmless in theory. Faster wheels mean the tires and wheel bearings turn at a higher speed, and every tire has a rated limit. A belt that ran much faster than the airplane could push the wheels past that limit, though that is a property of the tires and not of flight. A real takeoff on any runway depends on the same factors: engine thrust, weight, wind, runway length and surface, and air density. Our guide on why planes struggle in hot weather covers density altitude, and the flaps guide shows how pilots change a wing's lift for takeoff and landing.
The trick is in the wording. Most people picture the airplane as a car, where wheel speed equals ground speed and a backwards belt cancels a forward drive. A plane is driven through the air, so the belt cancels only the wheel speed, and the engines keep accelerating the airplane relative to the air.
Yes. An airplane's engines push against the air and not the ground, so a belt moving backwards only makes the wheels spin faster. The airplane still gains airspeed and lifts off.
The belt acts on the wheels, which spin freely. It does not apply a force that the engines must overcome in the way a car's driven wheels would.
Airspeed is the speed through the air, and lift depends on it. The FAA defines groundspeed as the speed of the airplane over the ground, adjusted for wind.
Yes. In an episode first aired on January 30, 2008, they tested a model airplane on a treadmill and an ultralight aircraft over a tarp pulled backwards, and both took off.
Yes. A headwind adds to the airspeed over the wings at a given ground speed, so lift builds sooner.
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