# The 50 Cent Toy Hovercraft / Helicopter- Demonstrate the Magnus Effect

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## Introduction: 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!

The 50 cent Hovercraft:

The 5 cent Hovercraft:

## 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.

## Step 2: Gather Supplies

Real simple.  You need:

2, 4, 6, 8, or however many styrofoam cups
20" of thin dowel
Tape (scotch, masking, duct tape, whatever!)
Rubber Band

Hot glue Gun
Something to cut the dowel with
Pencil or other sorta sharp object

## Step 3: Build!

Build the cylinders.  You will need to repeat this step once, leaving you with two sets of cylinders.

Start by taping two cups together at the top as shown in Picture 1.

Using your pencil or other sharp object, poke a small hole in the bottoms of the cup right in the center, as show in Pictures 2 and 3.

Slide the dowel through the holes so that about an inch is sticking out one side as shown in Picture 4.  Using the hot glue gun, Glue the dowel to the cup as shown in Picture 5

Poke another hole in the bottom of the next cup as shown in Picture 6.

Slide the 3rd cup over the part of dowel that sticks out as shown in Picture 7.  Hot glue helps, but it isn't necessary because this cup also gets taped to the other two.

Viola!  Half done.  Repeat the above steps for the other side, but make sure to LEAVE ABOUT 3 INCHES between the two sets as shown in Picture 8.

## Step 4: Flying Tips and Tricks

I've found the best way to launch this thingamabob is to wrap the rubber band only about 4 times around the dowel, starting on the top and wrapping away from you and underneath.  This way, when you launch, it is spinning away from you.  I tried to show this in the video also.

Once you have the rubber band wrapped, hold it down low, let go of the stick, and yank up all at the same time.  Takes some practice but you should be able to get a good launch after about 5 tries or so.

Thats it!

The video is not real great quality, but I think it's pretty good considering it was shot by my 8 year old son!

I'd love to hear about anyone else experimenting with this, I've found a couple of videos on youtube of different versions of this and even an r/c airplane base on this concept.  You can look at the picture below to see a few of the things I tried and experimented with. Thanks again to Hoopajoo for the idea to begin with!

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## Questions

Really cool
they also use the magnus effect on ships as a sail

Hey, nice! If I ever find some styrofoam cups, this is the first thing I will do with them.

Win Guy

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.

2 replies

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.