How on earth to rotational spinning wings keep an airplane in flight?
The Magnus effect is an incredible thing - and it has kept aerospace engineers wondering whether they can use it to build a plane for at least a century.
Check out this video I made about my first Magnus Effect experimental aircraft.
To understand the Magnus force (or Magnus effect), let’s step back in time for a moment. In 1672, after observing tennis players in a Cambridge college, Isaac Newton correctly identified and described the force that made the tennis balls take a curved trajectory when spun. This was many years before the effect's namesake, German physicist Gustav Magnus, developed a full theory through his studies in 1852.
The knowledge of the force at this time was helpful for military applications as ballistics experts understood what made projectiles, such as artillery shells, follow various trajectories when spun. Later the idea was used to make a cylindrical bomb bounce when spun in the Dambuster raids in 1943. You can read all about this here.
How It Works
Right, here's a super simple explanation (without getting into the nitty-gritty of boundary layers, flow separation and all of that) we can imagine the Magnus effect in terms of Bernoulli's Therum and Newton's Third Law. With a ball spinning through the air, the rotating ball drags some of the air around with it. Viewed from the position of the ball, the air is rushing by on all sides.
"The drag of the side of the ball turning into the air (into the direction the ball is traveling) slows the airflow, whereas on the other side the drag increases the airflow speed. Greater pressure on the side where the airflow is slowed down forces the ball in the direction of the low-pressure region on the opposite side, where a relative increase in airflow occurs." - Britannica.com
So, the airflow behind the ball is pushed downward because of the speed difference in the air around the ball. According to Newton's law, this downward push on the air creates an equal and opposite upward force on the ball, giving it lift. This is similar to how a rotating cylindrical wing on a plane can help the plane stay in the air, just like a traditional wing - isn't that cool!
The idea of using the Magnus effect to lift an aircraft isn't a new one. This plane was the earliest attempt to use a Magnus effect for a heavier-than-air aircraft. It was tested in 1930 with less than promising results. You can read more about this experiment here.
If you'd like to see another Project Air video experiment using the magnus effect, check out this Magnus Effect RC Boat I made! Maybe I should revisit this one...