I posted recently a riddle about an airplane on a conveyor belt. Originally, I thought of the riddle this way, if the conveyor is moving at exactly the same speed as the plane, but in the opposite direction, how can the plane lift off from being in the same spot? I couldn’t picture this in real life so I thought that the plane could not take off.

To further strenghten my thought process, I considered how a plane is able to fly. A plane generates lift by using Bernoulli’s principle; or in simpler terms, air passes faster beneath the wing than above which results in a pressure difference. So if the plane is stationary, then the air around the wing would also be stationary.

But that is where we make an incorrect assumption and our argument ends up falling apart. See, we assume that because the conveyor is moving exactly opposite the plane, then the entire system is stationary. However, the wheels of the plane have nothing to do with the plane taking off. If say, the plane has jet engines on its wings, then they will pull air underneath the wing faster than the air passing over the wing, and the plane will indeed be able to lift off!

So while it would be a weird sight (someone post a video!) to see a “stationary” plane life up into the air like a helicopter, it can actually happen.

Different explanations: 1, 2

Posted by Kevin in Blogs