Instructables

The 50 cent Toy Hovercraft / Helicopter- Demonstrate the Magnus Effect

This is an expansion on a cool instructable called the $.05 Toy Hovercraft / Helicopter made by Hoopajoo.
I really liked how simple the original project was, but I got to thinkin... bigger is better, right!?  Hoopajoo's is quick and easy, mine requires a little more time but it is still very simple to build and it will stay in the air a bit longer too!



Ready to build?  Me too, but lets talk a little first about this "Magnus Effect".

The 50 cent Hovercraft:



The 5 cent Hovercraft:



 
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Step 1: What the heck is the Magnus Effect?!

So what the heck is the Magnus Effect?  According to Wikipedia:

The Magnus effect is the phenomenon whereby a spinning object flying in a fluid creates a whirlpool of fluid around itself, and experiences a force perpendicular to the line of motion. The overall behaviour is similar to that around an airfoil (see lift force) with a circulation which is generated by the mechanical rotation, rather than by aerofoil action.

See the complete article here:  http://en.wikipedia.org/wiki/Magnus_effect

Turns out, the Magnus Effect is what is usually responsible for curve balls in just about all types of sports-  you now have something to blame for that nasty slice in your golf game!

To be totally honest, until I saw this project, I'd never heard of it...  but lets see if I can enlighten y'all

Bernoulli discovered that fluids moving fast create low pressures, and fluids moving slowly create high pressures.  Air flowing over the top of the wing moves faster than the air flowing underneath, so you have a high pressure underneath and a low pressure above causing the wing to rise.

A SPINNING object- a ball, or our little hovercraft thingamabob here- causes air to move.  When the spinning object moves, the spinning air around the object speeds up in the direction the object is moving and slows down behind it, creating a low pressure in front and a high pressure behind.  Clear as mud?!?  Took me a few tries to understand it too!  Check out the picture below for a little more help.

Okay.  Lets get to it.
Starsword79 months ago
Really cool
they also use the magnus effect on ships as a sail
Win Guy2 years ago
Hey, nice! If I ever find some styrofoam cups, this is the first thing I will do with them.

Win Guy
rimar20002 years ago
Good work.

I think the image in step 1 is wrong: if the wind direction and rotation are so, the faster windspeed is at the lower side of the device.
dorkpunch (author)  rimar20002 years ago
I'm about the furthest thing from an expert so I could be wrong. I've looked at a few different images and from everything I can find, it is correct. Intuitively, I would think that the air speed would be HIGHER on the BOTTOM of the image- because the wind going around the spinning object is going against the oncoming wind. Apparently, the opposite is true- the wind from the spinning object is fighting the oncoming wind, slowing it down and giving and overall SLOWER velocity. Low speed = High pressure. The opposite is true on the top, relative wind joins with the wind from the spinning object making the speed INCREASE, causing a LOW pressure. Seems to make sense, but like I said, I could be wrong! I've attached a second image that supports the first one.
True, if you want the ball is raised, you have to give that effect to turn back. I am not an expert in aerodynamics, and to remember this situation I guess the ball obeys the force that causes the turbulence of its wake. That is: if it turns back, rises; if forward, go down.

In short, I recant that I said before.