How do paper planes /cheap foam planes fly or maintain lift?


So in theory a plane can fly because the shape of the wing causes the air above it to have a lower pressure than the air below it making the plane fly. However paper planes and those cheap kids planes don’t have any curve to cause this. Both can still glide pretty well.

Is there something that makes these craft special that doesn’t apply to big jets? In the same vain how do fighter jets or stunt planes keep themselves in the air when they fly upside down?

In: Engineering

Basically they use the propulsion of you throwing it as energy to maintain lift, but of course after a while, the paper airplane falls due to nothing pushing it against the air to cause lift. Jets or really any planes on the other hand have engines that maintain that propulsion so they don’t depend the force of you throwing it to create lift, these planes in contrast to paper planes only depend on the engine or propeller running to maintain lift therefore planes being able to run for huge amounts of time.

Imagine an airplane that is traveling exactly horizontally forwards, i.e. the plane is perfectly level with the ground. If its wings are flat and also level (with the rest of the airplane and the ground), then air will move past the wings equally on both sides. The airplane does not generate any vertical force and will lose altitude under the pull of gravity.

Now imagine we tilt the airplane’s wings a little so that their leading edge (the edge nearest the nose of the plane) is higher than the trailing edge. The wings are still flat (not curved on either side), but as the plane travels forwards through the air, the now-diagonal bottom surface of the wings pushes against the air and deflects it downward. Pushing air downward creates an equal and opposite upward force: lift.

The curvature you referred to is called *camber* and is often present in airplane wings. It creates lift by different aerodynamic principles that I won’t go into (but you seem to be already familiar with). However, most airplane wings also have a positive angle of attack, contributing to the lift generated by the wings.

Paper planes usually have wings whose angle of attack is 0 in horizontal flight, as the wings are level with the body of the plane. However, if you launch a paper plane with its nose pointing slightly upwards, then the angle of attack of the plane as a whole, including its wings, will be increased, so that the thrust of your throw is converted partly into lift during the beginning of the plane’s flight. In addition, if you launch the plane along an upwards angle, that launch alone will also give the plane some additional height.

After climbing to its maximum height, though (and provided the plane doesn’t stall or otherwise loses stability) air drag will probably push the plane into a more level or slightly downward-facing orientation for the remainder of its flight. At this point, the angle of attack is going to be 0 again, or even slightly negative. However, as the plane starts falling, the wings start to act more like a parachute, slowing the plane’s descent simply by blocking the air. The resulting upward drag-force also creates lift. This lift is not enough to offset the plane’s weight, and so the plane loses altitude, but does so slower than if it was in free-fall (in other words, it is a glider – just not a very good one).

What this tells you is that you can improve your paper plane, by giving its wings a positive angle of attack, so that even in the gliding phase of its flight, the wings can convert forward motion into lift, rather than just act as a parachute-like barrier.