The Magnus Effect: How to Fly (Or Sail!) With Spinning Cylinders

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Everybody knows that airplanes fly because the shape of their wings causes air to move over the top faster than it does under the bottom. Faster moving air has lower pressure, and thus the difference in pressure between the air under the wing and on top of it pushes the wing upwards.

However, there's more than one way to achieve a pressure differential in air substantial enough to use for an aircraft. Enter: The Magnus Effect. When you have something round that spins, whether it's a sphere or cylinder, providing it's spinning at the correct orientation and direction relative to its path of motion, it can generate lift.

This is because the spinning surface exerts traction on the air. If it's spinning against the airflow under it, then the air moving under it will be slowed down. It will then also necessarily be spinning such that it accelerates air moving over the top, which decreases the pressure of that air.

Perhaps you've seen this widely circulated video demonstration of what happens if you put a spin on a basketball opposite the direction you throw it:

There's also a neat toy "Magnus Glider" you can make out of a pair of cups and a rubber band (used to achieve the spin):

However, the Magnus effect has also been used for radio controlled airplanes:

That RC plane uses a variation on the usual design called a "fan wing", also seen here:

However, it's good for more than just aircraft. The same effect can be used as a sail to propel boats:

In fact, Jacques Cousteau had a marine research vessel built that was propelled mainly by three Magnus sails, and finally this design is catching on in the maritime world:

Another example:

Of course it costs energy to spin the cylinders, but you get dramatically stronger thrust from the wind as a result. The spinning cylinders could be powered by solar panels on the top deck without much trouble.

The advantages for aircraft applications are also numerous. Because Magnus wings generate lift even at a standstill, such craft could take off from a very short runway, they won't stall at slow speeds, and if power is lost they can perform an auto-rotational landing similar to helicopters.

So, what do you think of this technology? Had you heard about it already before reading this, or is my article your first exposure to this principle?

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^{Stay Cozy!}