Gyroscopes and boomerangs

Just weights and stretching yesterday. Upper body only to give the battered legs a rest. But I do have something else odd to write about instead.

I think I mentioned it in the 100 things about me page that I can make and throw a boomerang. And an email conversation with Jank a while back made me think of this again.

My Dad used to make and throw boomerangs as a hobby since us kids were very little. He did it so much that he would give little talks on it to groups like Cub Scouts and 4H and stuff like that. He was even on the news a few times.

One important thing about boomerangs is that the real ones really do go out and come right back to you. I have one called the Hurricane Hook which has a throwing distance of 45 yards (thrower to maximum distance away). Its remarkably easy to throw and has a beautiful flight pattern. Not sure its still available anymore.

So how do they work? OK, here’s the best explanation that I can remember. If anyone out there has better info, just let me know.

The boomerang has a cross-section like an airplane wing, with a flat side and an airfoil side. It has a leading edge and a trailing edge. So that as it spins, the leading edge is always heading into the direction of spin. When you have an airplane wing and you move it quickly through the air, you find that the air moves slightly faster on the bottom (flat) top (airfoil side) than over the top (airfoil side) bottom (flat side) , which gives you get a pressure differential.** With more pressure on the bottom, you get lift!

So, when you throw the boomerang, there is “lift” pushing against the flat side. Since the boomerang is perpendicular to the ground when you throw, it moves across the field to the left (in the case of a right-handed boomerang).

Now the turning part. A spinning boomerang acts like a gyroscope. Have you ever taken your front bike tire off and spun it while you held the axle, and then tried to turn it? Its hard to do, right? Well, that’s because the gyroscope doesn’t react to an external force the way you would expect. Rather, it will move in an axis perpendicular to the axis of the applied force (I think I have that right).

Think of the boomerang spinning around. There are two “arms” to the boomerang, and when it spins, one is going faster than the other. That is, the one moving in the direction the boomerang is traveling is moving faster than the one moving backwards. Force from the airfoil (that we talked about above) is going to be higher on the one moving faster. When that airfoil force is applied to it, the gyroscopic boomerang responds not by tilting (like if you pushed the top edge of a plate that was balancing on its side), but by rotating. Imagine it rotating counter-clockwise if you are looking down from above.

So now you have a spinning gyroscopic boomerang that is both being pushed across the field from right to left, but also rotating the same time. But remember that as the boomerang rotates, the direction that it is being moved “across” the field changes with the rotation, so that it moves in a circle (or more accurately a tear drop shape).

As I mentioned above, and as you would guess, there are left handed boomerangs and right handed boomerangs because the airfoil has to be going in the proper direction when you throw it. I have tried turning a left-handed booomerang around and thowing it “backwards” with my right hand, but the natural tilt of your throw is hard to conteract and it always ends up going off in a funny direction.

If you want a better explanation and nice images of how this all works, I found a nice demo at howstuffworks.

Gosh, the wierd stuff you learn when you aren’t out running. :)

**Thanks, Brenden, for the correction. :)

This entry was posted on Tuesday, May 17th, 2005 at 12:03 pm and is filed under Mindless musings. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.